Basic Ophthalmology (4th Edition) PDF - R Jogi

 Basic Ophthalmology  Basic Ophthalmology FOURTH EDITION Renu Jogi MBBS MS Ex Associate Professor MGM Medical College, Indore (MP) Pt. Jawahar Lal Nehru Memorial Medical College...

 Basic Ophthalmology  Basic Ophthalmology FOURTH EDITION Renu Jogi MBBS MS Ex Associate Professor MGM Medical College, Indore (MP) Pt. Jawahar Lal Nehru Memorial Medical College Raipur, Chhattisgarh, India ® JAYPEE BROTHERS MEDICAL PUBLISHERS (P) LTD. New Delhi Ahmedabad Bengaluru Chennai Hyderabad Kochi Kolkata Lucknow Mumbai Nagpur Published by Jitendar P Vij Jaypee Brothers Medical Publishers (P) Ltd Corporate Office 4838/24 Ansari Road, Daryaganj, New Delhi - 110002, India, Phone: +91-11-43574357 Registered Office B-3 EMCA House, 23/23B Ansari Road, Daryaganj, New Delhi - 110 002, India Phones: +91-11-23272143, +91-11-23272703, +91-11-23282021, +91-11-23245672 Rel: +91-11-32558559, Fax: +91-11-23276490, +91-11-23245683 e-mail: [email protected], Website: www.jaypeebrothers.com Branches  2/B, Akruti Society, Jodhpur Gam Road Satellite Ahmedabad 380 015, Phones: +91-79-26926233, Rel: +91-79-32988717 Fax: +91-79-26927094, e-mail: [email protected]  202 Batavia Chambers, 8 Kumara Krupa Road, Kumara Park East Bengaluru 560 001, Phones: +91-80-22285971, +91-80-22382956, 91-80-22372664 Rel: +91-80-32714073, Fax: +91-80-22281761, e-mail: [email protected]  282 IIIrd Floor, Khaleel Shirazi Estate, Fountain Plaza, Pantheon Road Chennai 600 008 Phones: +91-44-28193265, +91-44-28194897, Rel: +91-44-32972089 Fax: +91-44-28193231, e-mail: [email protected]  4-2-1067/1-3, 1st Floor, Balaji Building, Ramkote Cross Road Hyderabad 500 095, Phones: +91-40-66610020, +91-40-24758498, Rel: +91-40-32940929 Fax:+91-40-24758499, e-mail: [email protected]  No. 41/3098, B and B1, Kuruvi Building, St. Vincent Road Kochi 682 018, Kerala, Phones: +91-484-4036109, +91-484-2395739, +91-484-2395740 e-mail: [email protected]  1-A Indian Mirror Street, Wellington Square Kolkata 700 013, Phones: +91-33-22651926, +91-33-22276404, +91-33-22276415 Rel: +91-33-32901926, Fax: +91-33-22656075, e-mail: [email protected]  Lekhraj Market III, B-2, Sector-4, Faizabad Road, Indira Nagar Lucknow 226 016, Phones: +91-522-3040553, +91-522-3040554, e-mail: [email protected]  106 Amit Industrial Estate, 61 Dr SS Rao Road, Near MGM Hospital, Parel Mumbai 400 012, Phones: +91-22-24124863, +91-22-24104532, Rel: +91-22-32926896 Fax: +91-22-24160828, e-mail: [email protected]  “KAMALPUSHPA” 38, Reshimbag, Opp. Mohota Science College, Umred Road Nagpur 440 009 (MS), Phone: Rel: +91-712-3245220, Fax: +91-712-2704275, e-mail: [email protected] USA Office 1745, Pheasant Run Drive, Maryland Heights (Missouri), MO 63043, USA, Ph: 001-636-6279734 e-mail: [email protected], [email protected] Basic Ophthalmology © 2009, Renu Jogi All rights reserved. No part of this publication should be reproduced, stored in a retrieval system, or transmitted in any form or by any means: electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the author and the publisher. This book has been published in good faith that the material provided by author is original. Every effort is made to ensure accuracy of material, but the publisher, printer and author will not be held responsible for any inadvertent error(s). In case of any dispute, all legal matters are to be settled under Delhi jurisdiction only. First Edition: 1994 Second Edition: 1999 Third Edition: 2003 Fourth Edition: 2009 ISBN 978-81-8448-451-9 Typeset at JPBMP typesetting unit Printed at Ajanta Offset and Packagins Ltd., New Delhi Dedicated to our beloved Anusha  Preface to the Fourth Edition The eye is the lamp of the body. If your eyes are good, your whole body will be full of light. The Bible The need for a textbook for undergraduate medical students in ophthalmology dealing with the basic concepts and recent advances has been felt for a long-time. Keeping in mind the changed curriculum this book is intended primarily as a first step in commencing and continuing the study for the fundamentals of ophthalmology which like all other branches of medical sciences, has taken giant strides in the recent past. While teaching the subject I have been struck by the avalanche of queries from the ever inquisitive students and my effort therefore has been to let them find the answers to all their interrogatories. It is said that revision is the best testimony to the success of a book. In the competitive market of medical text publishing, only successful books survive. Any textbook, more so, a medical one such as this, needs to be updated and revised from time to time. Yet the very task of revising Basic Ophthalmology presents a dilemma: how does one preserve the fundamental simplicity of the work while incorporating crucial but complex material lucubrated from recent research, investigations and inquiries in this ever expanding field. In essence, Basic Ophthalmology is both a ‘textbook’ and a ‘notebook’ that might as well have been written in the student’s own hand. The idea is for the student to relate to the material; and not merely to memorize it mechanically for reproducing it during an examination. It is something I wish was available to me when I was an undergraduate student not too long ago. The past few years have witnessed not only an alarming multiplication of information in the field of ophthalmology, but more significantly, a definite paradigmatic shift in the focus and direction of ophthalmic research and study. The dominant causes of visual disabilities are no longer pathological or even genetic in nature, but instead a direct derivative and manifestation of contemporary changes in predominantly modern urban lifestyles. The student will thus find a new section devoted to a discussion on Visual Display Terminal Syndrome (VDTS) that is an outcome of excessive exposure of the eyes to the computer monitor as well as the use of contact lenses. Two additional sections deal with the Early Treatment for Diabetic Retinopathy Study (ETDRS) classification and Scheie’s classification for hypertensive retinopathy that replaces the pre-existent taxonomy prevalent for little less than seven decades. With posterior chamber intraocular lenses establishing themselves as the primary modality in the optical rehabilitation of patients undergoing cataract surgery, the emphasis has shifted from just visual rehabilitation to an early, perfect optical, occupational and psychological rehabilitation. When I initiated this project I scarcely realized that it only had toil, sweat and hard work to offer. Whenever anyone reminded me that I was working hard, my answer always was; I am trying to create something very enduring. viii Basic Ophthalmology To conclude, for me, this has really been a trabalho do coracao a phrase which does not have a correct synonym in English but when literally translated from Portuguese would mean “a work of the heart”. In truth, it is a vivid reflection of my long lasting concern and affection for my students. All books are collaborative efforts and I would like to take this opportunity to thank all the people who have advised and encouraged me in this project: specially my husband Shri Ajit Jogi, my son Aishwarya, Amit and Dr Nidhi Pandey. I offer special thanks to my publisher Shri JP Vij, Chairman and Managing Director of M/s Jaypee Brothers Medical Publishers (P) Ltd., Mr Tarun Duneja, Director (Publishing) and his staff namely Mrs Yashu Kapoor, Mr Manoj Pahuja, Mr Arun Sharma, Mr Akhilesh Kumar Dubey and Mrs Seema Dogra. By the grace of the Almighty God and with the continuing support of the teachers, I am happy to present the fourth updated edition of my book. xzkáa p :iL; eq[kL; “kksHkk] çR;{kcks/kL; p gsrq Hkwre~! rfeL=-fnd-deZlq ekxZnf”kZ] us=a ç/kkua ldysfUnz;k.kke~A An eye can perceive forms, it adorns the face; it is a source of direct knowledge; it is a guide to avoid wrong deeds; hence the eye is most important of all the sense organs. Renu Jogi  Contents 1. Embryology and Anatomy................................................................................................ 1 2. Physiology of Vision.......................................................................................................... 9 3. Neurology of Vision.......................................................................................................... 15 4. Examination of the Eye.................................................................................................... 22 5. Errors of Refraction.......................................................................................................... 47 6. The Conjunctiva................................................................................................................ 71 7. The Cornea....................................................................................................................... 107 8. The Sclera......................................................................................................................... 153 9. The Uveal Tract............................................................................................................... 161 10. The Lens........................................................................................................................... 205 11. The Vitreous..................................................................................................................... 246 12. Glaucoma........................................................................................................................... 258 13. The Retina......................................................................................................................... 300 14. The Optic Nerve.............................................................................................................. 341 15. Injuries to the Eye........................................................................................................... 361 16. The Ocular Motility and Squint (Strabismus).............................................................. 375 17. The Lids............................................................................................................................ 403 18. The Lacrimal Apparatus................................................................................................. 424 19. The Orbit........................................................................................................................... 437 20. General Therapeutics...................................................................................................... 448 21. The Causes and Prevention of Blindness.................................................................... 458 22. Ophthalmic Instruments................................................................................................. 469 Index................................................................................................................................... 489  EMBRYOLOGY The central nervous system develops from the neural tube. A thickening appears on either side of the neural tube in its anterior part, known as the optic plate. The optic plate grows towards the surface to form the optic vesicle. The two eyes develop from these optic vesicles and the ectoderm and mesoderm coming in contact with the optic vesicles. The optic vesicle invaginates from in front and below to form the optic cup. The line of invagination remains open for sometime as the embryonic fissure. The hyaloid artery enters through the fissure to provide nutrition to the developing structures. Later it atrophies and disappears. The inner layer of the optic cup forms the inner nine layers of the main retina and the outer layer develops into the pigment epithelium. The neural ectoderm secretes jelly-like structure, the vitreous which fills the cavity. The ciliary body and iris are formed by the anterior portion of the optic cup and mesoderm. The mesoderm around the cup differentiates to form the coats of eye, orbital structures, angle of anterior chamber and main structure of cornea. Meanwhile the surface ectoderm invaginates and later separates to form the lens. The surface ectoderm remains as the corneal and conjunctival epithelium. The mesoderm in front of the cornea grows in folds, unites and separates to form the lids. 2 Basic Ophthalmology PRIMORDIA OF OCULAR STRUCTURES The eye originates from neural ectoderm, surface ectoderm and mesoderm. SURFACE ECTODERM MESODERM NEURAL ECTODERM 1. Conjunctival epithelium 1. Corneal stroma 1. Sensory retina 2. Corneal epithelium 2. Corneal endothelium and 2. Retinal pigment epithelium Descemet’s membrane 3. Crystalline lens 3. Iris stroma 3. Pigment epithelium of iris 4. Eyelash 4. Choroid 4. Ciliary body epithelium 5. Epithelium of 5. Sclera 5. Sphincter pupillae — meibomian glands 6. Vitreous 6. Dilator pupillae — glands of Moll 7. Extraocular muscles 7. Melanocytes — lacrimal gland 8. Ciliary muscles 8. Neural part of optic nerve — accessory lacrimal glands 9. Bony orbit 1. Eyelids—They develop from both surface ectoderm and mesoderm Derivation of various ocular structures 2. Zonules (tertiary vitreous)—They develop from surface ectoderm and mesoderm 3. Bruch’s membrane—It develops from neural ectoderm and mesoderm The Eye at Birth 1. Orbit is more divergent (50°) as compared to an adult (45°). 2. Eyeball is about 70% of adult length. It is fully developed at the age of 8 years. 3. The newborn is hypermetropic by +2.5 D. 4. Cornea is approximately 80% of its adult size, being fully grown at the age of 3 years. 5. Anterior chamber is shallow and the angle is narrow.  Embryology and Anatomy 3 ANATOMY The eye is the organ of sight situated in the orbital cavity. It is almost spherical in shape and is about 2.5 cm in diameter. The volume of an eyeball is approximately 7 cc. The space between the eye and the orbital cavity is occupied by fatty tissue. The bony wall of the orbit and the fat helps to protect the eye from injury. Structurally the two eyes are separate but they function as a pair. It is possible to see with only one eye, but three-dimensional vision is impaired when only one eye is used specially in relation to the judgement of distance. Structure of the eye Structure of the Eye The eyeball has three layers namely: 1. The outer fibrous layer—Sclera and cornea 2. The middle vascular layer—Iris, ciliary body and choroid 3. The inner nervous tissue layer—Retina. Interior of the Eyeball The structures inside the eyeball are: 1. Aqueous humour 2. Lens 3. Vitreous. Accessory Structures of the Eye 1. Eyebrows 2. Eyelids and eyelashes 3. Lacrimal apparatus Side view of some structures which protect the eye 4. Extraocular muscles of the eye. 4 Basic Ophthalmology STRUCTURE OF THE EYE 1. The Outer Fibrous Layer 1. Sclera—The sclera or white of the eye forms the firm, fibrous outermost layer of the eye. It maintains the shape of the eye and gives attachment to the extraocular muscles. It is about 1 mm thick. The sclera becomes thin (seive-like membrane) at the site where the optic nerve pierces it. It is called Lamina cribrosa. Schematic diagram of three layers of the eyeball 2. Cornea—Cornea forms the anterior 1/6 of the eye. The transparent, ellipsoid, anterior part of the eyeball is known as the cornea. It is the main refracting surface of the eye. The dioptric power is + 43 to + 45 D. 3. Limbus—The junction of cornea and sclera is known as the limbus. There is a minute arcade of blood vessels about 1 mm broad present at the limbus. 2. The Middle Vascular Layer 1. Iris—Iris is a coloured, free, circular diaphragm with an aperture in the centre—the pupil. It divides the anterior segment of the eye into anterior and posterior chambers which contain aqueous humour secreted by the ciliary body. It consists of endothelium, stroma, pigment cells and two groups of plain muscle fibres, one circular (sphincter pupillae) and the other radiating (dilator pupillae). 2. Ciliary body—Ciliary body is triangular in shape with base forwards. The iris is attached to the middle of the base. It consists of non-striated muscle fibres (ciliary muscles), stroma and secretory epithelial cells. It consists of two main parts, namely pars plicata and pars plana. 3. Choroid—Choroid is a dark brown, highly vascular layer situated between the sclera and retina. It extends from the ora serrata up to the aperture of the optic nerve in the sclera. 3. The Inner Nervous Tissue Layer 1. Retina—Retina is composed of ten layers of nerve cells and nerve fibres lying on a pigmented epithelial layer. It lines about 3/4 of the eyeball. Macula lutea is a yellow area of the retina situated in posterior part with a central depression called fovea centralis. It is the most sensitive part of retina.  Embryology and Anatomy 5 The sclera, ciliary body and iris The lens and suspensory ligament (Cornea has been removed) (Iris has been removed) 2. Optic disc—Optic disc is a circular, pink coloured disc of 1.5 mm diameter. It has only nerve fibre layer so it does not excite any visual response. It is known as the blind spot. 3. The optic nerve—The optic nerve extends from the lamina cribrosa up to the optic chiasma. The total length of the optic nerve is 5 cm. It has four parts namely, Intraocular — 1 mm Intraorbital — 25 mm Intraosseous — 4-10 mm Intracranial — 10 mm (Duke–Elder). INTERIOR OF THE EYEBALL 1. Aqueous Humour Both anterior and posterior chambers contain a clear aqueous humour fluid secreted into the posterior chamber by the ciliary epithelium. It passes in front of the lens, through the pupil into the anterior chamber and returns to the venous circulation through the canal of Schlemm situated in the angle of anterior chamber. 2. Lens Lens is a transparent, circular, biconvex structure lying immediately behind the pupil. It is suspended from the ciliary body by the suspensory ligament or zonule of Zinn. It is enclosed within a transparent capsule. 3. Vitreous Vitreous is a transparent, colourless, inert gel which fills the posterior 4/5 of the eyeball. It contains few hyalocytes and wandering leucocytes. It consists of 99% water, some salts and mucoproteins. ACCESSORY STRUCTURES OF THE EYE The eye is a delicate organ which is protected by several structures such as eyebrows, eyelids, eyelashes and extraocular muscles. 6 Basic Ophthalmology 1. Eyebrows Eyebrows are two arched ridges of the supraorbital margins of the frontal bone. Numerous hair (eyebrows) project obliquely from the surface of the skin. They protect the eyeball from sweat, dust and other foreign bodies. 2. Eyelids and Eyelashes The eyelids are two movable folds of tissue situated above and below the front of each eye. There are short curved hair, the eyelashes situated on their free edges. The eyelid consists of: A thin covering of skin Three muscles—the orbicularis oculi, levator palpebrae superioris and Müller’s muscles A sheet of dense connective tissue, the tarsal plate A lining of the conjunctiva. 3. Lacrimal Apparatus Lacrimal apparatus consists of: Lacrimal gland and its ducts Accessory lacrimal glands Gross anatomy of the eyelid Lacrimal canaliculi Lacrimal sac Nasolacrimal duct The tears are secreted by the lacrimal gland and accessory lacrimal glands. They drain into the conjunctival sac by small ducts. The tears then pass into the lacrimal sac (via the two canaliculi), nasolacrimal duct and finally into the nasal cavity (inferior meatus). Section of the eye and its accessory structures  Embryology and Anatomy 7 4. Extraocular Muscles of the Eye The eyeballs are moved by six extrinsic muscles, attached at one end to the eyeball and at the other to the walls of the orbital cavity. There are four straight and two oblique muscles. They consist of striated muscle fibres. Movement of the eyes to look in a particular direction is under voluntary control but co-ordination of movement needed for convergence and accommodation to near or distant vision, is under autonomic control. The extraocular muscles of the eye The medial rectus rotates the eyeball inwards. The lateral rectus rotates the eyeball outwards. The superior rectus rotates the eyeball upwards. The inferior rectus rotates the eyeball downwards. The superior oblique rotates the eyeball so that the cornea turns in a downward and outward directions. The inferior oblique rotates the eyeball so that the cornea turns upwards and outwards. BLOOD SUPPLY TO THE EYE Arterial Supply The eye is supplied by the short (about 20 in number) and long ciliary (2 in number) arteries and the central retinal artery. These are branches of the ophthalmic artery, which is one of the branch of the internal carotid artery. Venous Drainage Venous drainage is done by the short ciliary veins, anterior ciliary veins, 4 vortex veins and the central retinal vein. These eventually empty into the cavernous sinus. 8 Basic Ophthalmology Blood supply of the eye NERVE SUPPLY TO THE EYE The eye is supplied by three types of nerves, namely motor, sensory and autonomic. 1. The Motor Nerves i. The third cranial nerve (oculomotor) ii. The 4th cranial nerve [trochlear]—It supplies the superior oblique muscle. iii. The 6th cranial nerve [abducens]—It supplies the lateral rectus muscle. iv. The 7th cranial nerve [facial]—It supplies the orbicularis oculi muscle. 2. The Sensory Nerve The 5th cranial nerve [trigeminal]—The ophthalmic division supplies the whole eye. 3. The Autonomic Nerves 1. The sympathetic nerve supply is through the cervical sympathetic fibres to: i. Iris—Dilator pupillae muscle ii. Ciliary body iii. Müller’s muscle in the lids iv. Lacrimal gland. 2. The parasympathetic nerve supply originates from the nuclei in the midbrain. It gives branches to: i. Iris—Sphincter pupillae muscle ii. Ciliary body iii. Lacrimal gland. Light waves travel at a speed of 300,000 kilometres per second. Light is reflected into the eyes by objects within the field of vision. White light is a combination of all the colours of the visual spectrum, i.e. red, orange, yellow, green, blue, indigo, and violet. This can be demonstrated by passing white light through a glass prism which refracts or bends the rays of the different colours to a greater or lesser extent, depending on their wavelengths. Red light has the longest wavelength and violet the shortest. This range of colours is the spectrum of visible light. In a rainbow, white light from the sun is broken up by raindrops which act as prisms and reflectors. White light broken into the colours of the visible spectrum when passed through a prism The Spectrum of Light The spectrum of light is broad but only a small part is visible to the human eye. The visible spectrum extends from 723 nm at the red end to 397 nm at the violet end or roughly 700 to 400 nm. Beyond the long end there are infrared (heat), radar and radio waves. Beyond the short end there are ultraviolet (UV), X-ray and cosmic waves. UV light is not normally visible because it is absorbed by a yellow pigment in the lens. Following removal of the lens (cataract operation), UV light is visible and it has been suggested that long-term exposure may damage the retina. A specific colour is perceived when only one wavelength is reflected by the object and all the others are absorbed, e.g. an object appears red when only the red wavelength is reflected. Objects appear white when all wavelengths are reflected, and black when they are all absorbed. 10 Basic Ophthalmology PHYSIOLOGY OF VISION In order to achieve clear vision, light reflected from objects within the visual field is focused on to the retina of both eyes. The processes involved in producing a clear image are: 1. Refraction of the light rays 2. Accommodation of the eyes to light. Although these may be considered as separate processes, effective vision is dependent upon their coordination. 1. REFRACTION OF THE LIGHT RAYS When light rays pass from a medium of one density to a medium of a different density they are refracted or bent. This principle is used in the eye to focus light on the retina. Before reaching the retina light rays pass successively through the conjunctiva, cornea, aqueous fluid, lens and vitreous. They are all more dense than air and with the exception of the lens, they have a constant refractory power similar to that of water. Lens The lens is a biconvex elastic transparent structure suspended behind the iris from the ciliary body by the suspensory ligament. Lens is the only structure in the eye that changes its refractive power. All light rays entering the eye need to be bent (refracted) to focus them on the retina. Light from distant objects needs least refraction and as the object comes closer, the amount needed is increased. To increase the refractive power the ciliary muscle contracts, releasing its pull on the suspensory ligament and the anterior surface of the lens bulges forward, increasing its convexity. When the ciliary muscle relaxes it slips backwards, increasing its pull on the suspensory ligament, making the lens thinner. Section of the eye showing the focussing of light rays on the retina  Physiology of Vision 11 Diagram of the difference in the shape of the lens for distant and near vision Looking at near objects ‘tires’ the eyes more quickly due to the continuous use of the ciliary muscle. 2. ACCOMMODATION OF THE EYES TO LIGHT There are three factors which are involved in accommodation 1. Pupil 2. Movement of the eyeballs-convergence 3. Lens. 1. Size of the Pupil Pupil size influences accommodation by controlling the amount of light entering the eye. In a bright light the pupils are constricted. In a dim light they are dilated. If the pupils were dilated in a bright light, too much light would enter the eye and damage the retina. In a dim light, if the pupils were constricted, insufficient light would enter the eye to activate the photosensitive pigments in the rods and cones which stimulate the nerve endings in the retina. The iris consists of one layer of circular and one of radiating smooth muscle fibres. Contraction of the circular fibres constricts the pupil, and contraction of the radiating fibres dilates it. The size of the pupil is controlled by the nerves of the autonomic nervous system. Sympathetic stimulation dilates the pupil and parasympathetic stimulation causes contraction of the pupil. 2. Movements of the Eyeballs-convergence Light rays from objects enter the two eyes at different angles and for clear vision they must stimulate corresponding areas of the two retinae. Extraocular muscles move the eyes and to obtain a clear image they rotate the eyes so that they converge on the object viewed. This co-ordinated muscle activity is under autonomic control. When there is voluntary movement of the eyes both eyes move and convergence is maintained. The nearer an object is to the eyes the greater the eye rotation needed to achieve convergence. If convergence is not complete there is double vision, i.e. diplopia. After a period of time during which convergence is not possible, the brain tends to ignore the impulses received from the divergent eye. 12 Basic Ophthalmology FUNCTIONS OF THE RETINA The retina is the photosensitive part of eye. The light sensitive cells are the rods and cones. Light rays cause chemical changes in photosensitive pigments in these cells and they emit nerve impulses which pass to the occipital lobes of cerebrum via the optic nerves. The rods are more sensitive than the cones. They are stimulated by low intensity or dim light, e.g. by the dim light in the interior of a darkened room (scotopic vision). The cones are sensitive to bright light and colour. The different wavelengths of light stimulate photosensitive pigments in the cones, resulting in the perception of different colours. In a bright light the light rays are focused on the macula lutea (photopic vision). The rods are more numerous towards the periphery of the retina. Visual purple (rhodopsin) is a photosensitive pigment present only in the rods. It is bleached by bright light and when this occurs the rods cannot be stimulated. Rhodopsin is quickly reconstituted when an adequate supply of vitamin A is available. When the individual moves from an area of bright light to one of dim light, there is variable period of time when it is difficult to see. The rate at which dark adaptation takes place is dependent upon the rate of reconstitution of rhodopsin. In dim evening light different colours cannot be distinguished because the light intensity is insufficient to stimulate colour sensitive pigments in cones. VISUAL PERCEPTIONS Visual perceptions are of four types namely, 1. Light Sense Light sense is the faculty which permits us to perceive light as such and in all its gradation of intensity. Light Minimum Light minimum is the minimum intensity of light appreciated by the retina. If the light which is falling on the retina is gradually reduced in intensity, a point comes when light is no longer perceived. Dark Adaptation Dark adaptation is the ability of the eye to adapt itself to decreasing illumination. If one goes from a bright light into a dimly lit room, one cannot perceive the objects in the room until sometime has elapsed. This time interval is known as dark adaptation. 2. Form Sense Form sense is the faculty which enables us to perceive the shape of objects. Visual acuity is a record of form sense. 3. Sense of Contrast Sense of contrast is the ability to perceive slight changes in luminance between regions which are not separated by definite borders.  Physiology of Vision 13 4. Colour Sense Colour sense is that faculty which helps us to distinguish between different colours as excited by light of different wavelengths. Three important factors influence colour vision: i. Wavelength ii. Brightness or luminosity iii. Saturation or calorimetric purity The normal colour vision is called “trichromatic” (red, green, blue) and it is the basis of the Young-Helmholtz theory. When red, green, and blue portion of spectrum mix together, they produce white colour. Thus red, green, and blue are known as primary colours. The exact nature of the defect is tested by : 1. Isochromatic chart—These are coloured lithographic plates in which bold numbers are represented in dots of various colours, e.g. Japanese Ishihara lithographic plates, American H-R-R test, Swedish-Bostrom test. Colour blind person finds it difficult to identify the bold numbers. 2. The lantern test—Various colours are shown by a lantern, e.g. Edridge-Green’s lantern. He is judged by the mistakes he makes. 3. Holmgren’s wools—This consists of a selection of skeins of coloured wools from which the candidate is required to make a series of colour matches. 4. Nagel’s anomaloscope—A bright disc coloured yellow, red, and green is used. 5. The Farnsworth-Munsell 100 hue test—This represents hue discrimination by an error score. Patients with toxic optic neuropathy show a characteristic pattern. COLOUR BLINDNESS [ACHROMATOPSIA] It is an inability to recognise colour. Defective colour vision is seen in 1% males and 0.4% females. Etiology 1. Congenital—There is absence of red, green or blue pigments in the cones. It can be either partial or complete. It is an inherited condition being transmitted through females. It is bilateral and incurable. i. Partial colour blindness—A person cannot recognise green, red or blue colours. Green blindness is most common. There is Absorption spectrum of three cone pigments absence of one or two of the photopigments normally found in foveal cones. ii. Total colour blindness—A person cannot recognise any colour and sees everything grey. It is rare and is associated with nystagmus and central scotoma. 2. Acquired—This is due to the diseases of the macula and optic nerve, e.g. macular degenerations, toxic amblyopias. Blue blindness occurs in sclerosing black cataracts which is said to affect the paintings of artists in old age. 14 Basic Ophthalmology Types In most cases red and green colours are confused. i. Protanopes—The red sensation is defective. ii. Deuteranopes—The green sensation is defective. iii. Tritanopes—There is absense of blue sensation. It is very rare. It is important to test colour vision in certain occupations like drivers, pilots, sailors, etc. as they can be a source of danger to the society. Diagram of the parts of the visual field monocular and binocular BINOCULAR VISION Binocular or stereoscopic vision has certain advantages. Each eye ‘sees’ a scene slightly differently. There is an overlap in the middle but the left eye sees more on the left than can be seen by the other eye and vice versa. The images from the two eyes are fused in the cerebrum so that only one image is perceived. Binocular vision provides a much more accurate assessment of one object relative to another, e.g. its distance, depth, height and width. This is done by mechanisms of: 1. Simultaneous macular perception 2. Fusion 3. Stereopsis. Some people with monocular vision may find it difficult to judge the speed and distance of an approaching vehicle.  THE VISUAL PATHWAY AND ITS LESIONS The visual pathway consists of: 1. The optic nerves 2. The optic chiasma 3. The optic tracts 4. The lateral geniculate bodies 5. The optic radiations 6. The occipital cortex. The optic chiasma 1. THE OPTIC NERVES The fibres of the optic nerve originate in the retina. The retina is divided into the temporal and nasal halves at the level of the fovea centralis. The optic nerves join the optic chiasma at the anterolateral angle. 2. THE OPTIC CHIASMA It is a flat band-like structure lying above the pituitary fossa. In the optic chiasma there is semi- decussation of the nerve fibres. i. The nerve fibres from the nasal side of each retina cross-over to the opposite side. ii. The nerve fibres from the temporal side do not cross but pass into optic tracts of the same side. 3. THE OPTIC TRACT The optic tracts originate from the postero-lateral angle of the optic chiasma. They are cylindrical bands running outwards and backwards to end in the lateral geniculate bodies. They consist of the temporal fibres of the same side and the nasal fibres of the opposite side. 4. THE LATERAL GENICULATE BODIES These are oval structures situated at the posterior end of the optic tracts. The fibres of the optic tracts end in the lateral geniculate bodies and new fibres of the optic radiations originate from them. 5. THE OPTIC RADIATIONS The nerve fibres proceed backwards and medially as the optic radiations to terminate in the visual centres situated in the occipital lobes. 16 Basic Ophthalmology The visual nerve pathway 6. THE OCCIPITAL CORTEX It is situated above and below the calcarine fissure in the occipital lobes extending up to the occipital pole. The visual nerve pathway can be divided into three parts: 1. The neuron of the first order is the bipolar cell in the retina. The rods and cones are the sensory end organs. 2. The neuron of the second order is the ganglion cell in the retina, the process of which pass along the optic nerve, optic chiasma and optic tract to the lateral geniculate body. 3. The neuron of the third order takes up the impulses via the optic radiations to the occipital lobe (visual centre). LESIONS OF THE VISUAL PATHWAY Lesions of the visual pathway usually cause defects in the visual fields and diminution of visual acuity depending on the site of lesion. 1. Hemianopia 2. Amblyopia 3. Amaurosis. 1. HEMIANOPIA Hemianopia is a condition of loss of half the field of vision of both eyes. Etiology Lesions in the visual pathway may be commonly due to: i. Trauma, e.g. injury by the falls on the back of the head, gun shot wounds. ii. Tumour, e.g. cerebral tumour, pituitary gland tumour.  Neurology of Vision 17 iii. Vascular lesion, e.g. aneurysms, atheroma of carotids, cerebral thrombosis. iv. Inflammation, e.g. meningitis, chronic arachnoiditis, encephalitis. v. Degeneration, e.g. multiple sclerosis. Types 1. Homonymous hemianopia—There is loss of right or left half of binocular field of vision. Lesions of the occipital lobe often result in homonymous hemianopia with sparing of the fixation area. Site of lesion—Optic tract, optic radiations and occipital lobe, e.g. vascular lesions. 2. Bitemporal hemianopia—There is loss of both the temporal fields. Site of lesion—Lesions of the central part of optic chiasma, e.g. pituitary tumour, aneurysms. 18 Basic Ophthalmology 3. Binasal hemianopia—There is loss of both the nasal fields. It is a rare condition. Site of lesion—Lesions situated on the either side of the optic chiasma destroying the temporal fibres of each retina, e.g. distension of the third ventricles, atheroma of the carotids or posterior communication arteries. 2. AMBLYOPIA (BLUNT) There is partial loss of sight in one or both eyes in the absence of ophthalmoscopic or other marked objective signs. It is basically a deprivation phenomenon whereby fixation reflexes are not developed. Etiology 1. Unilateral amblyopia i. Congenital error in visual pathway ii. Psychical suppression of the retinal image (amblyopia ex anopsia) iii. High refractive error—It is curable with suitable spectacles in early life. iv. Retrobulbar neuritis—There is the acute inflammation of the optic nerve situated behind the eyeball. 2. Bilateral amblyopia i. Toxic amblyopia—Optic nerve fibres are damaged by the exogenous poisons, e.g. tobacco, ethyl alcohol, etc. ii. Hysteria—It is due to psychogenic cause. It exhibits protean manifestations such as characteristic spiral visual fields, blinking, blepharospasm, etc. 3. AMAUROSIS (DARK) There is complete loss of sight in one or both eyes in the absence of ophthalmoscopic or other marked objective signs. Etiology 1. Unilateral amaurosis i. Amaurosis fugax—There is sudden loss of vision due to embolisation of retinal circulation. The episode lasts for few minutes. ii. Cardiovascular abnormalities such as valvular defect, arrhythmias. iii. Migraine—There may be vasospasm of retinal vessels. iv. Gaze-evoked amaurosis—Transient loss of vision occurs in a particular direction of eccentric gaze. 2. Bilateral amaurosis i. Uraemia—It occurs in acute nephritis and chronic renal disease due to circulation of toxins, which act on visual centres. ii. Meningitis, encephalitis—The visual pathway and centre are affected. iii. Hysteria—Psychogenic aspect of the disease is often treated but great care is taken to eliminate any organic disease. iv. Lebers congenital amaurosis (retinal aplasia)—It is characterised by reduced visual acuity, head nodding and nystagmus.  Neurology of Vision 19 MULTIPLE CHOICE QUESTIONS 1. Lens develops from a. neural ectoderm b. surface ectoderm c. optic vesicle d. all of the above 2. Retina develops from a. surface ectoderm b. mesoderm c. optic vesicle d. embryonic fissure 3. Muscles controlling pupil arise from a. mesoderm b. ectoderm c. endoderm d. none of the above 4. The avascular structure of eye is a. choroid b. lens c. conjunctiva d. ciliary body 5. Aqueous humour is secreted by a. angle of anterior chamber b. choroid c. ciliary body d. iris 6. Optic disc is also known as a. macula lutea b. blind spot c. fovea d. rods and cones 7. Superior oblique muscle is supplied by the a. optic nerve b. third cranial nerve c. fourth cranial nerve d. sixth cranial nerve 8. The sensory nerve supply of the eye is by the a. optic nerve b. third cranial nerve c. fifth cranial nerve d. seventh cranial nerve 9. Optic nerve contains a. pigment layer b. ganglion cell layer c. nerve fibre layer d. all of the above 10. The junction of cornea and sclera is known as a. angle of anterior chamber b. ciliary body c. pupil d. limbus 11. Tarsal plate is situated in a. eyebrow b. eyelid c. lacrimal apparatus d. conjunctiva 12. Between epithelium and stroma of cornea lies a. Bowman’s membrane b. Descemet’s membrane c. endothelium d. none of the above 13. Lamina cribrosa is present in a. choroid b. ciliary body c. sclera d. retina 20 Basic Ophthalmology 14. Suspensory ligament extends between lens and a. iris b. ciliary body c. choroid d. limbus 15. Oculomotor nerve palsy features include all, EXCEPT a. facial weakness b. divergent squint c. dilated fixed pupil d. absent accommodation 16. The normal trichromatic colour vision consists of following colours a. red, blue, yellow b. red, blue, green c. red, blue, white d. red, green, yellow 17. The trichromatic theory of colour vision has been propounded by a. Schiotz b. von Graefe c. Young-Helmholtz d. none of the above 18. The intraorbital length of the optic nerve is a. 1 mm b. 5 mm c. 10 mm d. 25 mm 19. The total length of the optic nerve is a. 2.5 cm b. 3 cm c. 4.5 cm d. 5 cm 20. The neuron of the 1st order in the visual pathway lies in which layer of retina a. inner plexiform b. outer plexiform c. optic nerve fibre d. none of the above 21. Lesion of the optic tract causes a. homonymous hemianopia b. bitemporal hemianopia c. binasal hemianopia d. ipsilateral blindness 22. Scotopic vision is due to a. cones b. rods c. both d. none 23. Visual acuity is a record of a. light sense b. form sense c. contrast sense d. colour sense 24. Visual centre is situated in a. parietal lobe b. frontal lobe c. midbrain d. occipital lobe 25. Optic nerve extends up to a. optic chiasma b. optic tracts c. lateral geniculate body d. optic radiations 26. Visible spectrum extends from a. 100-300 nm b. 300-650 nm c. 400-700 nm d. 720-920 nm 27. Vortex vein drain a. iris and ciliary body b. sclera c. uveal tract d. retina  Neurology of Vision 21 28. Highest visual resolution is seen in a. macula lutea b. fovea centralis c. optic disc d. ora serrata 29. Second order neurons in the optic pathway are present in a. superior colliculus b. retina c. medial geniculate body d. lateral geniculate body 30. Bitemporal hemianopia is seen with a. aneurysm of circle of Willis b. temporal SOL c. frontal SOL d. retinoblastoma ANSWERS 1—b 2—c 3—b 4—b 5—c 6—b 7—c 8—c 9—c 10—d 11—b 12—a 13—c 14—b 15—a 16—b 17—c 18—d 19—d 20—d 21—a 22—b 23—b 24—d 25—a 26—c 27—c 28—b 29—b 30—a  HISTORY Patient is encouraged to narrate his complaints but relevant enquiries are made. PRESENT HISTORY 1. Name, Age, Sex, Occupation 2. Dimness of Vision Mode of onset—It may be sudden or gradual: Sudden loss of vision commonly occurs in central retinal artery occlusion and central retinal vein occlusion, retinal detachment, papillitis, acute congestive glaucoma, vitreous haemorrhage, etc. Gradual loss of vision commonly occurs in cataract, open angle glaucoma, uveitis maculo- pathy, toxic amblyopia, chorioretinal degenerations, optic atrophy, etc. Duration—Short or long For distance or near Seeing double objects—This commonly occurs in cases of paralytic squint. Seeing flashes of light—It is usually due to retinal disease or high myopia. Night blindness—It is common in vitamin A deficiency, liver disorders (cirrhosis), retinitis pigmentosa, congenital night blindness, extensive chorioretinitis. Associated with photophobia, lacrimation, blepharospasm as in keratitis. 3. Pain in the Eyes Mode of onset—It may be sudden or gradual Severity and duration—It may be mild, moderate or severe Relation to close work—It is common in refractive errors Time of the day when maximum—Eye strain is maximum in the evening in refractive errors Associated nausea, vomiting, photophobia, impaired vision occurs in acute glaucoma. 4. Redness, Congestion or Inflammation Of the eyelids Of the area surrounding the eye Of the eyeball. 5. Secretion Excessive normal secretion Type of altered secretion (discharge), e.g. mucopurulent, purulent, ropy Common causes of dimness of vision  Examination of the Eye 23 Sticking together of lids in the morning is suggestive of acute conjunctivitis Associated crusts or flakes in the lid margin are seen in blepharitis. 6. Disturbances of the Eyeball Eyelids Altered position—drooping of the lids below the normal position occurs in ptosis Altered direction of the margin, e.g. entropion, ectropion Disturbance in function, e.g. inability to close the lids leading to exposure Direction Eyes are turned out, in, up or down in squint Fixation Eyes “shakes” due to involuntary movements as in nystagmus. 7. Headache Location—frontal or occipital Severity and type—dull or throbbing Relation to near work Time of the day when maximum Factors which relieve or aggravate it Associated nausea, vomiting, blurred vision. PAST HISTORY Previous diseases, treatment or operation history of using glasses for distance or near. Ocular causes of headache 1. Refractive errors PERSONAL HISTORY 2. Poor accommodation and conver- Habits—Sleep, tobacco and alcohol intake, diet, gence digestion and bowel habits. 3. Contact lens overwear Blood pressure and diabetes mellitus. 4. Acute congestive glaucoma Kidney, blood and heart diseases. 5. Iritis 6. Herpes zoster Foci of infection in teeth, tonsils, ears and sinuses. 7. Orbital cellulitis 8. Superior orbital fissure syndrome FAMILY HISTORY Diabetes mellitus, hypertension, myopia, glaucoma, congenital cataract. EXAMINATION OF THE EYE 1. EXAMINATION OF THE ANTERIOR SEGMENT OF THE EYE 1. Inspection 2. Palpation 3. Intraocular tension 4. Binocular loupe and slit-lamp examination 5. Gonioscope examination 6. Transillumination. 24 Basic Ophthalmology 2. EXAMINATION OF THE POSTERIOR SEGMENT OF THE EYE II. Examination of the Fundus Oculi EXAMINATION OF THE ANTERIOR SEGMENT OF THE EYE 1. INSPECTION Examination of the anterior segment of the eye is made by general inspection in good diffuse light. 1. Head—Position is characteristic in paralysis of extraocular muscles and ptosis. 2. Face—Asymmetry, facial paralysis, affections of the skin, e.g. herpes zoster. 3. Eyebrows—Loss of hair or depigmentation, e.g. leprosy. They are elevated due to the overaction of frontalis muscle, e.g. ptosis. 4. Orbits—Exophthalmos, enophthalmos, orbital cellulitis. 5. Eyeballs i. Position and direction—They are abnormal in cases of squint, exophthalmos, enophthalmos, phthisis bulbi, etc. ii. Movements—Involuntary oscillations are present in nystagmus. iii. Size and shape—Eyeball is small in microphthalmia It is large in buphthalmos (infantile glaucoma), myopia, staphyloma. 6. Eyelids i. Position—Drooping of the upper lid below its normal position occurs in ptosis There is outrolling of lid margin (ectropion) There is inrolling of lid margin (entropion) ii. Palpebral aperture—It may be narrow, e.g. ptosis It may be wide, e.g. exophthalmos, Bell’s palsy iii. Movement—It is restricted in symblepharon, i.e., adhesion of the lids to the globe as in acid burn cases. iv. Margins—Crusts are seen in blepharitis, i.e., inflammation of lid margin It may be thickened (tylosis) as in trachoma. v. Lashes—These are misdirected backwards and rub against the cornea (trichiasis) Scanty (madarosis)  Examination of the Eye 25 The lashes are white in colour (poliosis) Multiple rows of eyelashes are present which rub against the cornea (distichiasis). Section of the upper eyelid showing normal and abnormal position of tarsus and eyelashes vi. Glands—Stye is situated at or near the lid margin Chalazion is situated a little away from the lid margin. vii. Lacrimal puncta—Eversion of the puncta is seen in ectropion Occlusion may be present due to scarting or eyelash. 7. Lacrimal Sac Swelling and redness (mucocele). Regurgitation test—There is watery, mucoid or purulent discharge through the puncta on pressure over the sac area. Fistula may be present due to repeated rupture or leakage from the infected sac with epitheliazation of the fistulous track. 8. Conjunctiva i. Bulbar—Congestion (conjunctival and ciliary) Secretion, chemosis or oedema or subconjunctival haemorrhage may be present Phlycten, growth, pterygium, cyst or Bitot’s spot (vitamin A deficiency). ii. Palpebral—The upper lid is everted by asking the patient to look downwards. A gentle pull on the eyelashes and simultaneous pressure over the skin of the upper lid by index finger or glass rod is given to evert the upper lid.The lower palpebral conjunctiva and fornix are exposed by pulling the lower lid downwards. Both upper and lower lids are examined for, Congestion as in conjunctivitis. Follicles, papillae, foreign body, concretions Scarring, e.g. trachoma, chemical burn Membrane as in diphtheria, streptococcal conjunctivitis Symblepharon, i.e. adhesion of the lids to the Eversion of upper eyelid globe, e.g. chemical burn. iii. Plica semilunaris—It may be displaced by pterygium growth. iv. Caruncle—There may be inflammation or growth. 9. Cornea—In children and in marked blepharospasm, lid retractor may be used for examination after instillation of local anaesthetic. i. Size—Normal vertical diameter is 11 mm and horizontal diameter is 12 mm. 26 Basic Ophthalmology DIFFERENCES BETWEEN CONJUNCTIVAL AND CILIARY CONGESTION CONJUNCTIVAL CONGESTION CILIARY CONGESTION 1. Site Most marked in fornix Most marked around the limbus 2. Colour Bright red, well-defined Greyish red (violet), ill-defined 3. Vessels and branches Superficial vessels Deep vessels (anterior ciliary) (anterior and posterior conjunctival) Branch dichotomously Branches are parallel or radially forming arborescent pattern arranged 4. Pressure effect After emptying the vessels Vessels fill from the limbus by pressure, (glass rod) they fill from the fornix 5. Common causes Acute conjunctivitis Keratitis Acute and chronic iridocyclitis Acute congestive glaucoma It is measured by the keratometer. It is small in microphthalmos. It is large in buphthalmos, megalocornea and myopia. ii. Curvature—Normal radius of curvature is 7.8 mm. It is measured by the keratometer—It may be conical, globular or flat. iii. Surface—It is examined by the Placido’s disc (keratoscope) or window reflex. iv. Transparency—Facet, ulcers, opacities (nebula, macula, leucoma) may be present. Position—The situation and extent of the opacity is noted in relation to iris. Pigmentation over the opacity is seen in adherent leucoma Any iris adhesion or anterior synechia. Pannus or vascularisation Striate keratitis (postoperative) are noted. v. Sensation—It is tested by touching the cornea with a wisp of cotton wool. Normally there is a brisk reflex closure of the lids. This is known as the corneal reflex.  Examination of the Eye 27 Placido disc Normal corneal reflex Irregular corneal reflex in keratoconus Placido’s disc (Keratoscope) Common causes of loss or diminished corneal sensation 1. Herpes simplex 2. Herpes zoster 3. Acute congestive glaucoma 4. Absolute glaucoma 5. Leucomatous corneal opacity 6. Leprosy 7. Following alcohol injection in the Gasserian ganglion (Trigeminal neuralgia) vi. Thickness—The thickness of the periphery of the cornea is 0.67 mm. It is 0.52 mm thick in the centre. It is measured by the pachymeter. vii. Staining of the cornea by vital stains a. Fluorescein 2%—It is the most useful and commonly used vital stain. It marks the areas of denuded epithelium due to abrasions, corneal ulcer, etc. It is available as drops or disposable strips. i. Superficial staining—A drop of fluorescein is instilled in the conjunctival sac. Excess dye is washed with normal saline after few seconds. The lesion is stained bright or brilliant green. ii. Deep staining—After instilling the dye the lids are kept closed for about 5 minutes. The dye penetrates the intact epithelium and any infiltration in the stroma takes up the dull grass green colour. The defects in the endothelium appear as green-yellow dots. b. Bengal rose1%—It is a red aniline dye. It stains the diseased or devitalized cells red, e.g. as in superficial punctate keratitis and filaments, e.g. keratoconjunctivitis sicca. c. Alcian blue—It stains only excess mucus, e.g. as in keratoconjunctivitis sicca (dry eye). 10. Sclera i. Curvature and colour—There is thinning, pigmentation and ectasia of the sclera in myopia, staphyloma and blue sclerotics. ii. Vessels—Ciliary injection and nodule is seen in episcleritis and scleritis. 28 Basic Ophthalmology 11. Anterior Chamber i. Depth—The normal depth is 2.5 mm. It is estimated by the position of the cornea and plane of the iris. Shallow (closed angle glaucoma, anterior synechia) Deep (buphthalmos, chronic iridocyclitis) Irregular (subluxation of lens, iris bomb) ii. Content—Cloudy aqueous (acute iridocyclitis) Pus (hypopyon corneal ulcer) Blood (hyphaema due to trauma) Lens matter (following extracapsular lens extraction and trauma) Foreign body. Heterochromia iridium 12. Iris i. Colour—Heterochromia iridium—The two irides are of different colour. Heterochromia iridis Heterochromia iridis—Parts of the same iris are of different colour, e.g. congenital, chronic iridocyclitis. Muddy (iritis) White atrophic patches (glaucoma, chronic iridocyclitis). ii. Pattern—Ill-defined or loss of pattern (chronic iridocyclitis) iii. Position—Plane of the iris is noted. Anterior synechia—There is adhesion of the iris to the posterior surface of cornea. Anterior synechia Posterior synechia—There is adhesion of the iris to the lens capsule.  Examination of the Eye 29 Posterior synechia iv. Tremulousness (Iridodonesis)—Excessive movements or tremors of iris are seen best in a dark room (with oblique illumination) when eyes move rapidly, e.g. in aphakia or absence, shrinkage, dislocation and subluxation of lens. 13. Pupil Size—Normal size of the pupil is 2-4 mm Anisocoria—Unequal size of both the pupil is called anisocoria Miosis—The pupil is small and constricted Mydriasis—The pupil is dilated Miosis—The pupil is small and constricted due to the action of sphincter pupillae muscle. Etiology 1. Physiological—Babies, old age, blue eyes 2. Pharmacological i. Local—Miotic, e.g. pilocarpine ii. General—Morphia 3. Pathological i. Unilateral—Acute iritis Healed iritis Horner’s syndrome ii. Bilateral—Pontine haemorrhage Argyll Robertson pupil Mydriasis—The pupil is dilated due to the action of dilator pupillae muscle. Etiology 1. Physiological—Myopia, nervous excitement 2. Pharmacological—Mydriatics, e.g. atropine, phenylephrine, cyclopentolate, tropicamide 3. Pathological i. Retina and optic nerve diseases Optic nerve atrophy Absolute glaucoma Acute congestive glaucoma 30 Basic Ophthalmology ii. Central lesion (above lateral geniculate body) Meningitis, haemorrhage, uraemia The light reaction is present but the patient is blind iii. Third cranial nerve paralysis—Trauma, syphilis, diphtheria, meningitis iv. Irritation of cervical sympathetics, e.g. apical pneumonia, pleurisy, cervical rib. 2. Shape Normally the pupil is central and circular. Irregular (posterior synechia). 3. Pupillary reactions (reflexes) a. Light reflex i. Direct light reflex—If light enters an eye, the pupil of this eye contracts. Afferent pathway—The optic nerve Centre—Edinger-Westphal nucleus in midbrain (third nerve nucleus). Efferent pathway—The oculomotor nerve. Pathway of the pupillary light reflex ii. Indirect (consensual) light reflex—If light enters an eye, the pupil of the other eye also contracts. The decussation of the nerve fibres in the midbrain explains the mechanism of the indirect reflex. b. Near reflex (accommodation reflex)—Contraction of the pupil occurs on looking at a near object. c. Psychosensory reflex—A dilatation of the pupil occurs on psychic or sensory stimuli, e.g. as in fear, pain, excitement, etc. Argyll-Robertson pupil—Accommodation reflex is retained but light reflex is lost. The pupil is small. There is damage to the relay path in tectum between afferent and efferent nerve pathways, e.g. in syphilis.  Examination of the Eye 31 Horner’s syndrome—All sympathetic functions are lost on one side causing, Miosis Enophthalmos Narrow palpebral fissure Unilateral absence of sweating Marcus-Gunn pupil—There is ill-sustained contraction of the pupil in swinging flashlight test, e.g. as in retrobulbar neuritis. Adie pupil—It presents as unilateral dilated pupil usually in young women. It is of unknown etiology. 14. Lens i. Colour—Jet black—Normal, aphakia Grey—Immature cataract White—Mature cataract, retinoblastoma, pseudogliomas, etc. Brown/black—Nuclear cataract, Morgagnian cataract Dislocation into anterior chamber Posterior dislocation Yellowish—Shrunken lens in hypermature cataract. ii. Opacity—Central, peripheral or total. iii. Position—Dislocation occurs commonly in lower part of the vitreous or in the anterior chamber due to complete rupture of the zonule as following trauma. Subluxation—It is due to the partial rupture of the zonule. The lens is tilted causing astigmatism and uniocular diplopia (seeing double objects). iv. Purkinje-Sanson images—When bright light falls obliquely on the eye (dilated pupil) in a dark room images are formed by the a. Anterior surface of cornea b. Posterior surface of cornea Concave surface Erect (virtual) image c. Anterior surface of lens d. Posterior surface of lens Concave surface Inverted (real) image In clear transparent lens—There is presence of all 4 images. In aphakia—There is absence of 3rd and 4th images. In opaque lens—There is absence of 4th image. Purkinje-Sanson images 32 Basic Ophthalmology 2. PALPATION Orbit—Irregular margin, swelling growth, tenderness are noted. Eyeball—Tenderness, pulsation are noted. Digital tension—It is assessed by fluctuation method. Lymph nodes—Preauricular lymph nodes may be enlarged. 3. INTRAOCULAR PRESSURE The normal intraocular pressure is 10-20 mm Hg (Schiotz). Suspicious cases = 20-25 mm Hg (Schiotz). Glaucoma = above 25 mm Hg (Schiotz). 1. Digital Tension Principle—The intraocular tension is estimated by palpation of the eyes with fingers. Method—The patient is asked to look down. The sclera is palpated through the upper lid beyond the tarsal plate. The tension is estimated by the amount of fluctuation. 2. Schiotz Tonometer Principle—The depth of indentation of the cornea is measured. Method— The cornea is anaesthetized with suitable local anaesthetic, e.g., xylocaine 4% eyedrops. Lids are separated and a tonometer carrying a weight of 5.5 gm is gently placed on the cornea. (There are 3 more weights available 7.5, 10 and 15 gm) The deflection is measured and reading in millimeter of mercury can be read from a chart. Advantages—It is cheap, easy to use, convenient to carry and does not require a slitlamp. Disadvantage—There may be error due to ocular rigidity. 3. Applanation Tonometer It is a more accurate method. The cornea is flattened by a plane surface. This is based on the principle of Imbert-Fick’s law. It states that for an ideal, thin-walled sphere, the pressure inside the sphere (P) equals to force necessary to flatten its surface (F) divided by the area of flattening (A), i.e. P = F/A. Force applied F Pressure = _______________________________ P = ____ Area of flattened cornea A An applanation tonometer measures the intraocular pressure by flattening (rather than indent) the cornea over a specific area (3.06 mm). This is more accurate since the pressure values recorded are uninfluenced by scleral rigidity. Six applanation tonometers are currently in use namely, 1. The Goldmann applanation tonometer 2. The Perkins tonometer 3. The pneumatotonometer 4. The air-puff tonometer 5. The MacKay-Marg tonometer  Examination of the Eye 33 Goldmann applanation tonometer Schiotz tonometer 6. The Microelectronic Tono-pen Goldmann applanation tonometer—It is the most popular and accurate tonometer. It consists of a double prism mounted on a standard slit-lamp. The prism applanates the cornea in an area of 3.06 mm diameter. The normal IOP as measured by applanation tonometer is 15 + 3 Hg. Method 1. Anaesthetise the cornea with a drop of 2% xylocaine and stain the tear film with fluorescein. 2. Patient is seated in front of a slit-lamp. The cornea and biprisms are illuminated with cobalt blue light from the slit-lamp. 3. Biprism is then advanced until it just touches the apex of the cornea. At this point two fluorescent semicircles are viewed through the prism. 4. The applanation force against the cornea is adjusted until the inner edges of the two semicircles just touch. This is the end point. 5. The intraocular pressure is determined by multiplying the dial reading with 10. Perkins (hand-held) applanation tonometer—It is same as above except that it does not require a slit- lamp and it can be used even in supine position. It is small and easy to carry. Pneumatic tonometer—The cornea is applanated by touching its apex by a silastic diaphragm covering the sensing nozzle which is connected to a central chamber containing pressurised air. There is a pneumatic-to-electronic transducer which converts the air pressure to a recording on a paper-strip from where IOP is read. 34 Basic Ophthalmology Air-puff tonometer—It is a non-contact tonometer based on the principle of Goldmann tonometer. The central part of cornea is flattened by a jet of air. This tonometer is very good for mass screening as there is no danger of cross-infection and local anaesthetic is not required. MacKay-Marg Pulse air tonometer—It is a hand held, non-contact tonometer that can be used on the patients in any position. Microelectronic Tono-pen—It is a computerised pocket tonometer. It employs a microscopic transducer which applanates the cornea and converts IOP into electrical waves. 4. BINOCULAR LOUPE AND SLIT-LAMP EXAMINATION Examination of the eye is done in focal or oblique illumination under magnification. Binocular loupe—A stereoscopic effect is obtained and the depth of opacities can be assessed. Magnification = 3-4 times. Slit-lamp examination—It is essential when minute examination of the eye is necessary. A brilliant light is brought to a focus as a slit or point by an optical system supported on a movable arm and observations are made by a binocular microscope. Magnification = 16, 25 times. 5. GONIOSCOPE EXAMINATION The purpose of gonioscopy is to identify abnormal angle structures, e.g. anterior synechiae, foreign body, tumour and to estimate the width of the angle of anterior chamber as in closed angle glaucoma. Optics—Normally, the angle cannot be visualized directly through an intact cornea because light rays emitted from angle structures undergo total internal reflection. A gonioscope eliminates total internal reflection by replacing the ‘cornea-air interface’ by a new ‘lens-air interface’ that has a greater refractive index than that of the cornea and tears. Types of Gonioscopy i. Direct gonioscopy with goniolenses—They provide a direct view of the angle. They are used both for diagnostic and operative purposes, e.g. Koeppe, Barkan goniolens, etc. ii. Indirect gonioscopy with gonioprisms—The rays are reflected by the mirror and the angle of anterior chamber is seen. They provide a mirror image of the opposite angle, and can only be used at a slit-lamp, e.g. Goldmann single mirror or three mirror gonioscope, Zeiss four mirror gonioscope, etc.  Examination of the Eye 35 Gonioscopic examination of the angle of anterior chamber Normal angle structures (from anterior to posterior)—Normal angle structures are: 1. Schwalbe’s line—It is an opaque line which represents the peripheral termination of the Descemet’s membrane. 2. Trabecular meshwork—The degree of pigmentation varies. It is a sieve-like structure with occasional visibility of the Schlemm’s canal. 3. Scleral spur—It is a prominent white line which represents the most anterior projection of the sclera. 4. Ciliary band—A grey or dull brown band of ciliary body is seen at the insertion of iris root. The presence of a narrow angle of the anterior chamber, as evident from gonioscopy, is invaluable in the diagnosis of the disease. 6. TRANSILLUMINATION 1. Trans-scleral—When an intense beam of light is thrown through the sclera, the pupil appears red in colour. If there is a solid mass in the path of light, the pupil remains black, e.g. as in intraocular tumour. 2. Trans-pupillary—When an intense beam of light is allowed to pass obliquely through the dilated pupil, the pupil becomes illuminated uniformly in the normal cases. EXAMINATION OF THE POSTERIOR SEGMENT OF THE EYE 1. Subjective Examination of Retinal Functions 1. VISUAL ACUITY It is a measure of smallest retinal image which can be appreciated. It tests the form sense. Snellen’s Test Type Snellen’s chart consists of a series of letters arranged in lines each diminishing in size. The lines from above downwards should be read at 60, 36, 24, 18, 12, 9, 6, 5 m, respectively. At these distances the letters subtend a visual angle of 5' at the nodal point. It is kept at a distance of 6 m so that the rays of light are parallel for practical purpose. The minimum illumination of the test type accepted for satisfactory vision should be 15-20 foot candles. 36 Basic Ophthalmology Structures forming angle of the anterior chamber 1. Recording of Visual Acuity for Distance Each eye is tested separately. A normal person can read all the lines, i.e. up to 6 m line. Thus the normal visual acuity is = 6/6. When the patient can only read the 18 m line, his distant vision is defective = 6/18. When the patient cannot read the largest letter, he is asked to walk slowly towards the chart. If he can read the top most letter at 5, 4, 3 or 2 m, his visual acuity = 5/60, 4/60, 3/60, 2/60 respectively. If the patient is unable to see the top letter when close to it, he is asked to count the surgeon’s fingers held at 1 m against a dark background. If he can count the fingers, the visual acuity = 1/60. If he can count fingers only at 50 cm, the visual acuity = counting fingers at 50 cm. If he cannot count fingers, the surgeon’s hand is moved in front of the eyes close to face. If he can appreciate the movements, the visual acuity = hand movements. In a dark room, light is concentrated on his eyes. He is asked to say when the light is on the eye or when it is off. If he tells correctly, the visual acuity = PL (perception of light). If he gives correct indication of the direction from where the light is coming the visual acuity = PL (perception of light) and projection of rays is good. If he fails to see the light, he is blind. The visual acuity = no PL (no perception of light). Other Test Types 1. Landolt’s chart—‘C’ type—It is used for illiterate persons. 2. E chart—It is used for illiterate persons. 3. Simple picture chart—It is used for children. 2. Recording of Visual Acuity for Near The patient reads Snellen’s test type for reading or printer’s types (N series) at a distance of about 25 cm in good illumination. The normal vision is recorded as N/6.  Examination of the Eye 37 N.5. The streets of London are better paved and better lighted than those of any metropolis in Europe: there are lamps are both sides of every street, in the mean proportion of one lamp to three doors. The effect pro- cave scorn veneer succour N.8. Water Cresses are sold in small bunches, one penny each, or three bunches for two pence. The crier of Water Cresses frequently travels seven or eight miles rose sauce cannon reverse N.10. Hearth Brooms, Brushes, Sieves, Bowls, Clothes-horses, and Lines, and almost every household article of turnery, are cried in the noen verse runner caravan N.12. Strawberries, brought fresh gathered to the market in the height of their season, both morning and after noon, nuns score severe careers N.18. Doors-mats of all kinds, rush and rope, from sixpence to four shillings crave savour concern Snellen’s near type The minimum visual angle The letter of Snellen chart 2. THE FIELD OF VISION The normal visual field is described as ‘island of vision surrounded by a sea of blindness’. The Normal Field of Vision Upwards = 60° Inwards = 60° Downwards = 70° Outwards = more than 90° Normal visual field—The normal visual field is described by Traquair as “island of vision surrounded by a sea of blindness”. Boundary—The peripheral limits of the visual field, which normally measures from the fixation points are approximately 60° above and inwards, 70° below and more than 90° temporally. Point of fixation—It is the area of maximum visual acuity in the normal visual field. It corresponds to the foveola of the retina. 38 Basic Ophthalmology Blind spot—This is an area of absolute scotoma (non-seeing area) within the boundaries of normal visual field. It corresponds to the region of optic nerve head where there are no rods and cones. It is located approximately 15° temporal to the fixation point. Scotoma—It is an absolute or relative area of depressed visual function (non-seeing area) surrounded by normal vision. It is commonly seen in cases of glaucoma, optic neuritis, papilloedema, etc. i. Absolute scotoma—All vision is lost, i.e. no perception of light (no PL) ii. Relative scotoma—A variable amount of vision remains. iii. Positive scotoma—When the patient appreciates a dark area in his field of vision. iv. Negative scotoma—It is a defect detected only when visual field is recorded. Perimetry The term ‘perimetry’ is used to describe various techniques employed to evaluate both central and peripheral visual fields using targets of various sizes and colours. Two techniques of testing the field of vision are commonly employed: 1. Kinetic perimetry—A target is moved across the field to map out of the two-dimensional extent of field. It involves presentation of a moving stimulus of known luminance or intensity from periphery towards the centre till it is perceived. The point of perception is recorded along different meridians. By joining these points an isopter is plotted for that stimulus intensity. Kinetic perimetry can be performed by Confrontation method Listers perimeter Goldmann perimeter Tangent screen or Bjerrum’s screen 2. Static perimetry—It forms the basis of modern glaucoma assessment. It is a three dimensional assessment of the height of a predetermined area of the ‘hill of vision.’ Non-moving stimuli of varying luminance are presented in the same position to obtain a vertical boundary of the visual field. The stimuli can be presented in two different ways Extent of normal visual field of right eye a. Suprathreshold perimetry—It is used mainly for screening the patients. Visual stimuli are presented at luminance levels above the expected normal threshold values in various locations in the visual field. In cases of moderate to gross loss of sensitivity, the supranormal stimulus is not seen. b. Threshold perimetry—It is used for detailed assessment of the ‘hill of vision’. Target of different and increasing intensities are presented at designated points in the visual fields until just visible to find out the patient’s threshold for that point. This is the principle used in computerized automated perimeters.  Examination of the Eye 39 Uses Charting of the visual fields is very useful in the diagnosis of many disease conditions Glaucoma Retinal diseases e.g. retinitis pigmentosa Follow up of laser treatment for diabetic retinopathy Neurological disorders, e.g. brain tumours, head injury, multiple sclerosis, cerebral thrombosis, aneurysms. 1. Peripheral Field i. Confrontation Method It is a rough but very useful method. It can be done in the clinic or at the patient’s bedside. Principle—The patients field of vision is compared with that of the examiner having a normal field of vision. Method—The surgeon stands facing the patient at a distance of about 60 cm. The patient covers his one eye (left) and the surgeon closes his one eye (right). The surgeon moves his hand from the periphery towards the centre, keeping his hand in the plane halfway between the patient and himself. The surgeon repeats the procedure covering the other eye. ii. The Perimeter—(Lister’s, Goldmann’s) It consists of a half sphere within which a spot of light can be moved (kinetic technique). Method—The patient is seated with his chin supported by the chin rest. One eye is covered by a pad. The other eye fixes an object placed at the centre of the arc. The field is recorded first with a white object 5 mm in diameter from periphery to centre. At least 8 or preferably 16 meridians must be tested. 40 Basic Ophthalmology 2. Central Field (Campimetry) It is limited to 30° from the fixation point. i. Bjerrum’s screen—It consists of a black felt or flannel screen, 2 m in diameter on which central 30° of the visual field can be studied (kinetic technique). Method—The patient sits 2 m away from the screen. He fixes a spot in the centre of the screen. Small white discs (1-10 mm diameter) attached to a long rod are brought in from the periphery towards fixation point until the patient recognises the target. After marking the blind spot, the procedure is repeated in various directions around the fixation point. The isoptres are mapped out and labelled as 1/1000, 2/1000, 3/1000. ii. Automated perimeters, e.g. Friedmann analyser, Ouplot, Auto field perimeters Field master and Humphery field analyser (static technique). In static perimetry, the visual field can be plotted by using a stationary light target of variable brightness against a background whose luminance can be adjusted. Automated perimeters utilize computers to programme visual field sequences, e.g. Baylor visual field programmer attached to standard Goldmann perimeter. Each of them has an electronic fixation control and an automatic recording of missed points. Advantages 1. These are more sensitive than manual perimetry. 2. Examiner bias is eliminated. 3. There is constant monitoring of fixation. 4. Visual field can be always stored and reproduced. 3. COLOUR VISION Electroretinogram The main objective of testing colour vision is: To find out the exact nature of the defect, e.g. red or green colour blind. Whether the patient is likely to be a source of danger to the society, e.g. driver, pilot, sailor. 2. Objective Examination of Retinal Functions The retinal function can be tested objectively by: 1. Electroretinogram (ERG) The changes induced by the stimulation of light in the resting potential of the eye are measured by electroretinography. It is extinguished or absent in complete failure of function of rods and cones, e.g. pigmentary retinal dystrophy, complete occlusion of retinal artery, complete retinal detachment, advanced siderosis, etc. i. Negative ‘a’ wave represents the activity in rods and cones. ii. Positive ‘b’ wave arises in inner retinal layers. iii. Positive ‘c’ wave is associated with the pigmentary epithelium.  Examination of the Eye 41 2. Electro-oculogram (EOG) The changes in the resting current when the eyes are moved laterally are picked up by the electrodes placed at the inner and outer canthi. It is absent in retinal dystrophies and degenerations. EXAMINATION OF THE FUNDUS OCULI Pupil is dilated with a suitable mydriatic, e.g. phenylephrine, tropicamide, homide or cyclopentolate and the examination of the fundus oculi is done in a dark room. Atropine is preferred in children as it results in paralysis of ciliary muscle. Fundus oculi examination 1. Media Media consists of cornea, aqueous humour, lens and the vitreous. Media can be clear, hazy, partially or totally opaque. 1. Plane mirror examination at a distance of 1 m—Uniform red glow is seen if there are no opacities in the media. 2. Plane mirror examination at a distance of 22 cm (distant direct ophthalmoscopy)—The exact position of the opacities or black spots in the refractive media is determined by parallactic displacement. 3. Direct ophthalmoscopy—Helmholtz invented the direct ophthalmoscope. Method—The surgeon looks through a self-luminous ophthalmoscope and directs the light upon the pupil. A uniform red reflex or glow is seen. Examination of the fundus is done best at a close distance with accommodation relaxed. Optical principle i. The convergent light beam is reflected from the ophthalmoscopic mirror ii. The incident rays reach the retina causing it to be illuminated. iii. The emergent rays from the fundus then reach the observers retina through the hole in the mirror. The image is virtual, erect and magnified (15 times in emmetrope eye). 42 Basic Ophthalmology Direct ophthalmoscopy 4. Indirect ophthalmoscopy Method—It is done in a dark room with a convex condensing lens (+ 30 D, + 20 D, +14 D) and a concave mirror. The lens is held in between the thumb and forefinger of the left hand. The curved surface of the lens is towards the examiner. The periphery of the retina can be seen by scleral depression with the patient in lying down position. Optical principle i. The convergent beam is cast by a perforated concave mirror. ii. The patient’s eye is made myopic by placing a +13D, +20D or +30D convex lens between the observer and the patient. iii. A real, inverted enlarged (5 times with +13D and 3 times with + 20D lens) image of the fundus is formed between the lens and the observer. Indirect ophthalmoscopy Advantages of indirect ophthalmoscope 1. Strong illumination, superb binocularity and stereopsis. 2. It can be used in high refractive error. 3. The beam passes through the opacities in the media. 4. Total retinal area and pars plana can be examined with the help of scleral indentation. 2. Optic Disc It is circular or oval in shape measuring 1.5 mm in diameter. It is situated at the posterior pole of the fundus. It is pink in colour. There is a funnel-shaped depression ‘the physiological cup’ seen in the centre. The central retinal vessels emerge from the middle. The normal cup : disc ratio is 0.3 or 1:2 i. Size—Optic disc is large in myopia and small in hypermetropia and aphakia. ii. Shape—The normal optic disc is round or oval in shape. iii. Margin—The margin is sharp and clearly defined normally and in primary optic atrophy. It is blurred in cases of secondary optic atrophy, optic neuritis, papillitis and papilloedema. iv. Colour—It is normally pink in colour. It is pale or white in cases of optic atrophy. It is waxy yellow in retinitis pigmentosa v. Cupping—Pathological cupping is seen in glaucoma. Papilloedema is seen in cases of raised intracranial tension (brain tumour) and malignant hypertension.  Examination of the Eye 43 3. Macula Lutea It is situated 3 mm or 2 disc diameter to the temporal side of the optic disc. It is a small circular area, deeper red than the surrounding fundus. There is a bright foveal reflex in the centre due to reflection of light from the walls of the foveal pit. Cystoid macular oedema, macular hole or macular star may be seen. 4. Retinal Vessels These are derived from the central retinal artery and vein, which divide into two branches at or near the surface of the disc. The arteries are brighter red and narrower than veins. The normal artery: vein ratio is 2 : 3. 5. General Fundus Normally the fundus has a uniform red appearance. In albino, the choroidal vessels are seen clearly against the white sclera. In high myopia, tesselated or tigroid fundus is seen due to degenerative changes in retina and choroid. Black pigments resembling bone corpuscles are typically seen in retinitis pigmentosa. EXAMINATION OF THE FUNDUS BY FOCAL ILLUMINATION The ordinary slit-lamp can only explore the eye up to the anterior parts of the vitreous. By interposing a –55 D (approximately) lens in front of the cornea, the posterior part of the vitreous and the central area of the fundus can be examined after full mydriasis. Three types of lenses are available for biomicroscopic examination of the vitreous and fundus. 1. Hruby’s lens—It is a plano-concave lens with a dioptric strength of –58.6 D Hruby lens Posterior fundus contact lens 2. Posterior fundus contact lens—This is a modified Koeppe’s lens. 3. Goldmann three mirror contact lens—Three mirrors are placed in a cone. 4. Indirect slit lamp biomicroscopy using +78D, +90D lens is presently the most commonly employed technique for biomicroscopic examination of the fundus. 44 Basic Ophthalmology MULTIPLE CHOICE QUESTIONS 1. Ciliary congestion is most marked at the a. sclera b. fornix c. bulbar conjunctiva d. limbus 2. Superficial vascularisation of cornea has all the following features, EXCEPT a. irregular and tortuous vessel b. rich dendritic branching c. vessels continuous with conjunctival vessel d. vessels lie deep to Bowman’s membrane 3. Corneal thickness is measured by a. keratometer b. vernier scale c. pachymeter d. none of the above 4. Keratometry is used in the measurement of a. length of eyeball b. curvature of cornea c. diameter of cornea d. thickness of cornea 5. Corneal sensations are reduced in a. hypopyon ulcer b. phlyctenular keratitis c. herpes simplex d. arcus senilis 6. Corneal staining is done by following vital stains a. iodine b. fluorescein c. carbolic acid d. silver nitrate 7. All of the following result in loss of corneal sensation EXCEPT a. acute congestive glaucoma b. absolute glaucoma c. dendritic ulcer d. senile mature cataract 8. The normal depth of anterior chamber is a. 1 mm b. 2.5 mm c. 3 mm d. 3.5 mm 9. Anterior chamber is shallow in a. buphthalmos b. open angle glaucoma c. closed angle glaucoma d. aphakia 10. Dilated pupil is seen in all of the following EXCEPT a. pontine haemorrhage b. optic atrophy c. acute glaucoma d. papillitis 11. Tremulousness of iris is seen in a. chronic iridocyclitis b. closed angle glaucoma c. aphakia d. none of the above 12. Pupil is pinpoint in a. optic atrophy b. absolute glaucoma c. atropine d. iritis 13. White pupillary reflex is seen in a. retinoblastoma b. congenital cataract c. complete retinal detachment d. all of the above  Examination of the Eye 45 14. In a frightened man, the pupil shall a. dilate b. constrict c. remain unaltered d. first dilate and then constrict 15. In aphakia there is absence of following Purkinje-Sanson’s images a. 1st and 2nd b. 3rd c. 4th d. 3rd and 4th 16. The normal intraocular pressure is (Schiotz) a. 10-15 mm Hg b. 10-20 mm Hg c. 25-30 mm Hg d. less than 10 mm Hg 17. The most accurate method of measuring lOP is a. digital b. applanation c. Schiotz d. gonioscopy 18. Near vision is recorded at a distance of a. 10 cm b. 25 cm c. 35 cm d. 50 cm 19. Distant vision is recorded at a distance of a. 1 m b. 2 m c. 3 m d. 6 m 20. Normal field of vision extends on the nasal side to a. 40° b. 50° c. 60° d. 70° 21. Peripheral field of vision is tested by a. Bjerrum’s screen b. Snellen’s chart c. Lister’s perimeter d. indirect ophthalmoscopy 22. Central field of vision is limited up to a. 20° b. 30° c. 40° d. 50° 23. Distant direct ophthalmoscopy is done at a distance of a. 1 m b. 6 m c. 22 cm d. close to the face 24. In indirect ophthalmoscopy the image is a. inverted, real, magnified b. erect, real, magnified c. erect, virtual, magnified d. none of the above 25. In direct ophthalmoscopy the image is a. virtual, erect, magnified b. virtual, inverted, condensed c. real, inverted, magnified d. real, erect, condensed 26. Periphery of retina is best visualized with a. direct ophthalmoscopy b. indirect ophthalmoscopy c. retinoscopy d. USG 46 Basic Ophthalmology 27. ‘A’ wave in ERG corresponds to activity in a. rods b. pigment epitheluim c. inner retinal layer d. nerve bundle layer 28. Campimetry is used to measure a. squint b. angle of deviation c. pattern of retina d. field charting 29. Angle of anterior chamber is studied with a. indirect ophthalmoscopy b. gonioscopy c. retinoscopy d. amblyoscope 30. Direct ophthalmoscopy magnification of image in comparison to indirect type (+13D lens) is —— times in emmetropes. a. 2 b. 3 c. 5 d. 6 ANSWERS 1—d 2—d 3—c 4—b,c 5—c 6—b 7—d