Ophthalmology.pdf

Basics of Ophthalmology for Dental Students Background • The eye is the organ of sight. • It is designed to allow light rays to stimulate the retina where is converted into electric impulses using specialized nerve ending and it is conveyed to the brain via the optic nerve. • It is protected within...

Basics of Ophthalmology for Dental Students Background • The eye is the organ of sight. • It is designed to allow light rays to stimulate the retina where is converted into electric impulses using specialized nerve ending and it is conveyed to the brain via the optic nerve. • It is protected within the bony orbit and it is surrounded by orbital pad of fat. • It can freely move in all directions by extraocular muscles. Anatomy of the eyeball • The eyeball is about 24 mm in diameter. It has 3 coats: 1. Outer protective coat: Cornea and sclera. 2. Middle vascular and pigmented coat: Uveal tract (Iris, ciliary body and choroid) 3. Inner receptive coat: Retina. 1. Outer coat of the eyeball Cornea: • Anterior 1/6 of the outer coat. • Transparent and avascular. • 11 mm in diameter, 0.5 mm in thickness. • It admits light into the eye and it is the main refractive surface of the eye. Sclera • Posterior 5/6 of the outer coat. • White opaque tough coat of the eyeball. • 1 mm in thickness. • Posteriorly, it is pierced by the optic nerve. 2. Middle layer of the eyeball • It is the vascular, pigmented and nutritive layer. • It is called the uveal tract and it is divided anatomically into: Iris, ciliary body and choroid. Iris: • Formed the colored part of the eye. • It is a diaphragm with a central opening called the pupil which controls the amount of light entering the eye. • Its root is attached to the ciliary body. • It contains 2 types of plain muscles; sphincter pupillae supplied by the parasympathetic system and dilator pupillae supplied by sympathetic system. Ciliary body: • It is the part between the iris and the choroid. • It has an anterior part with ciliary processes to be attached the lens and posterior plane part. • Functions: 1. Secretes aqueous humor to control the intraocular pressure. 2. Contains the ciliary muscles responsible for accommodation to allow seeing near objects. Choroid: • It extends backwards from the ciliary body. • It is highly vascular and responsible for nutrition of adjacent structures. • It is highly pigmented. 3. Inner layer of the eyeball Retina: • It contains 3 layers of cells and responsible for converting the light rays into electric impulses. • 2 types of light receptors: 1. Cones: responsible for day vision and color vision. 2. Rods: responsible for night vision.  Structure of the retina: • Macula lutea: most posterior part, rich in cones and responsible for acute sharp vision, reading and differentiating colors. • Optic disc: is the point where the optic nerve leaves the eye and it is insensitive to light “blind spot”. • Peripheral retina: rich in rods and responsible for night vision. Protective mechanisms of the eye ball 1. Eyelids and the conjunctiva  The upper and lower eyelids act as a curtain to protect the front surface of the globe.  The lids are connected to the eyeball by a mucus membrane called the conjunctiva.  The 2 lids join at the medial and lateral ends by the medial and lateral canthus.  The conjunctiva lines the posterior surface of each lid and reflected back to cover the eyeball.  Palpebral conjunctiva: lining the eyelid.  Bulbar conjunctiva: covering the sclera. • Lid muscles: o Orbicularis oculi: a sphincter like muscle which closes the eyelid. Supplied by the facial nerve. o Levator palpebrae superioris: it raises the eyelid and supplied by the oculomotor nerve. • Arterial supply: branches from ophthalmic artery. • Venous drainage: partly to the cavernous sinus through the ophthalmic vein and partly to the pterygoid plexus. • Lympahtic drainage: 1. Preauricular lymph nodes: drain the upper lid and outer canthus 2. Submandibular lymph nodes: drain the lower eyelid and the inner canthus 2. The lacrimal apparatus It consists of: 1. Secretory part: the lacrimal gland in the upper outer part of the orbit. 2. Excretory part: consists of the puncta on the medial aspect of the upper and lower lids, canaliculi, lacrimal sac and nasolacrimal duct. 3. The bony orbit  There are 2 orbital cavities placed on either sides of the midline of the skull.  Each orbit has the shape of quadrilateral pyramid whose base directed forward and it is called the orbital margin.  The medial walls are parallel while the lateral walls form an angle of 90 degrees. Bony orbit has 4 walls: • Roof. • Medial wall. • Lateral wall. • Floor. Contents of the bony orbit: • The eyeball. • The extraocular muscles. • Nerves and vessels. • Fat and fascia. Extraocular muscles: 6 in number • 4 recti: superior, inferior, medial, lateral. • 2 obliques: Superior and inferior. All muscles are supplied by the oculomotor nerve except superior oblique ( 4 th trochlear nerve) and lateral rectus (6th abducent nerve). Bony fissures • Superior orbital fissure: separates the roof from the lateral wall. • Inferior orbital fissure: separates the floor from the lateral wall. Ophthalmic examination a- Clinical examination • Examination of face and eyelids. • Pressure on the lacrimal sac to note any inflammation. • Extraocular muscle motility in all directions of gaze. • Examination of the surface of the conjunctiva and cornea. • The texture of the iris and pupillary reaction to light. • Examination of the visual acuity using special charts (Snellen’s chart). • Estimation of the intraocular pressure by gentle palpation with both index fingers. b- Instrumental examination i-Slit lamp biomicroscopy • It is used for detailed ocular examination till the level of the crystalline lens. ii-Optical examination of errors of refraction: 1. Retinoscope. 2. Autorefractometer. iii-Fundus examination: 1. Direct ophthalmoscope. 2. Indirect ophthalmoscope. iv-Testing of color vision • Ischihara plates. v-Measurement of intraocular pressure (IOP) • Applanation tonometer. Eye Diseases provoked by oro-dental disease Orbital cellulitis Definition: Inflammation of the fatty tissues of the orbit, characterized by proptosis and varying signs of inflammation. It is usually unilateral. Etiology: 1. Extension of inflammation from the maxillary sinus in connection with dental infections. 2. Inflammation of ethmoidal and frontal sinuses. 3. Spread of infection from lids, brows. 4. Spread of oral infections, tonsils or pharynx. 5. Deep injuries of the orbit with retained FBs. 6. Metastatic: pyemia. Clinical picture: 1. General symptoms: fever, rigors. 2. Localized pain in the eye or frontal headache. 3. Swelling of the eyelids and conjunctiva. 4. Proptosis with painful or limited eye movements. 5. Vision may be affected in neglected cases. Complications: 1. It may point anteriorly. 2. Posterior extension to the brain leading to brain abscess or meningitis. 3. Corneal ulceration due to exposure of the cornea by severe proptosis. Treatment: 1. Investigations and treatment of the cause (examination of the teeth and oral cavity). 2. Complete bed rest and fluids. 3. Broad spectrum antibiotics as early as possible. 4. Local treatment (hot fomentation and antibiotic eye ointment). 5. Drainage may be necessary by surgical incision in case of pointing. Phlyctenular Kerato-conjunctivitis Clinical picture: 1. Symptoms of photophobia, lacrimation in addition to pricking pain. 2. A solitary phlecten is typical as small yellowish nodule variable in size and present and the corneoscleral junctions surrounded by conjunctival inflammation. Treatment: 1. Treatment of the septic focus. 2. Local steroids eye drops and ointment. 3. Antibiotic eye drops or ointment. Iridocyclitis Definition: inflammation of the iris and ciliary body. Causes: 1. Due to systemic disease: septic focus in the teeth and oral region. 2. Due to localized eye disease: corneal ulcers, perforating corneal wounds, or following intraocular operations. Clinical picture:  Symptoms of pain, photophobia, headache and blurring of vision.  Signs: 1. Circum-corneal congestion with corneal clouding. 2. Cloudiness of the anterior chamber (aqueous flare). 3. Pus in the anterior chamber (hypopyon). 4. Muddy iris with constricted pupils. 5. Increased intraocular pressure. Treatment: 1. Local corticosteroid eye drops and ointment. 2. Cycloplegic eye drops to relax ciliary muscles and ciliary spasm. 3. Hot foments and dark glasses. 4. Systemic steroids may be needed in some cases. 5. Treatment of elevated intraocular pressure. Optic neuritis Definition: inflammation of the optic nerve. Etiology: 1. Disseminated sclerosis (multiple sclerosis). 2. Septic focus (dental infections or sinusitis. • Papillitis: inflammation of the optic nerve head characterized by edema of the optic disc, engorgement of retinal vessels and hemorrhages. Marked diminution of vision is seen followed by optic atrophy. • Retrobulbar neuritis: inflammation of the optic nerve behind the eye ball. Characterized by rapid diminution of vision, with pain with ocular movements. Fundus examination may appear normal or followed by optic atrophy. Effects of oro-dental diseases on eye surgeries • After intraocular surgeries, the resistance of the eye to infections is lowered due to disruption of the blood ocular barrier by operative trauma, so it is liable to infection from any septic focus in the teeth or oral cavity. • Eye infection may be in the form of: iridocyclitis, choroiditis or endopthalmitis. • Every septic focus in the teeth or oral cavity should be treated before any surgeries. • Detailed reports from the dentist should be sent regarding exclusion of any septic focus. Some important and common eye diseases Glaucoma • It is an increase in the intraocular pressure more than the normal limits (1021 mmHg) with affection of the optic nerve head and the visual field. • Types: 1. Primary glaucoma: where there is no primary cause found. 2. Secondary glaucoma: the increase in IOP is secondary to an ocular disease (e.g. iridocyclitis). Primary glaucoma Congenital glaucoma: • Large opaque cornea. • May be bluish in color. • May present since birth. Acute primary glaucoma: • Elderly patients (over 60 years). • Acute rise in IOP within 1-2 hours. • Accompanied by severe ocular pain, headache, vomiting, fever and malaise. • Colored haloes around lights with hazy cornea and stony hard IOP. Treatment • Considered as an ophthalmic emergency. • Systemic carbonic anhydrase inhibitors. • Intravenous mannitol to reduce aqueous secretion. • Topical eye drops as B-blockers and miotics (pilocarpine). Chronic primary glaucoma: • Gradual onset over months and years. • Gradual limitation of vision and may be discovered accidentally. • Loss of field is prominent and may end in glaucomatus optic atrophy. Treatment • Local miotic drugs. • B-blocker eye drops. • Topical carbonic anhydrase inhibitors. • Local prostaglandins. • Surgical treatment in resistant cases. Cataract • It is development of opacity in the crystalline lens. • Normally, the lens is clear and with age its fibers become harder (nuclear sclerosis) but it remains clear. • It is presented with haloes and glare around light, difficulty in night vision, followed by gradual diminution of vision. Etiology: • Congenital due to prenatal infection (rubella or toxoplasma). • Complicated cataract due to iridocyclitis or diabetes. • Traumatic due to blunt or penetrating trauma. • Senile cataract due to old age. Treatment: • Cataract extraction operation by phacoemulsification. • Intraocular lens implantation. Retinal detachment • It is separation of the neurosensory retina from the underlying choroid, thus losing its function. • It is common in high myopia. • A common predisposing factor is blunt trauma to the eye. • The first complain may be flashes of light with increase in floaters. • By fundus examination, the detachment is seen as raised greyish fold of retina with a tear of the retina can be seen in the retinal periphery. Proptosis (exophthalmos) • Protrusion of the eyeball forward. • It may be unilateral or bilateral Causes: • Congenital: due to lack of orbital cavity (Crozen’s disease). • Inflammatory: orbital cellulitis. • Orbital tumors or maxillary tumors invading the orbit. • Endocrine: toxic goiter. • Traumatic: retrobulbar hemorrhage. Squint (strabismus) • It is the condition where the two visual axes are not parallel to each other in any direction of gaze. • Types:  Comitant squint: where there is no paralysis or restriction in any extraocular muscle and the angle of squint is constant in any direction of gaze.  Incomitant squint: due to paralysis or restriction of one or more of extraocular muscles. Orbital fractures • Causes: road traffic accidents, sports injuries or civil violence. • Types: 1. Blow out fracture: fracture of the orbital floor accompanied by herniation of orbital contents into the maxillary sinus and enophthalmus. 2. Medial wall fracture: due to ethmoidal bone fractures accompanied by lacrimal sac injuries. 3. Lateral wall fracture: caused by zygomatic bone fracture and displacement. 4. Upper wall fractures: result from fracture of the frontal bone and may be accompanied by meningeal injury. Errors of refraction • Emmotropia: it is the condition where parallel rays entering the eye are focused on the retina at rest (with no accomodation) • Ametropia: parallel rays don’t focus on the retina. • Thus, there is no sharp distinct retinal image. • Myopia (near-sightedness): Parallel rays focus in front of the retina, near objects are seen clearly, whereas distant objects are indistinct. Correction is by concave lenses. • Hyperopia (far-sightedness): Parallel rays focus behind the retina, far objects are seen more clearly, whereas near objects are indistinct. Correction is by convex lenses. • Astigmatism It is the condition in which the image focused on the retina in different points due to unequal refraction power of different corneal planes. Correction is by cylindrical lenses. • Presbyopia It is a physiological condition occurring in every person above the age of 40 in which there is difficulty in focusing or accomodation at near tasks as reading. Treatment is by convex lenses to be used only at reading or by bifocal or multifocal glasses.