Orbit and Eyeball Anatomy

Orbit and Eyeball

• The eyeball is a slightly asymmetrical sphere located in the anterior part of the orbit; its sagittal diameter is 22-27 mm and volume is 6.5 cc.
• The orbit is pyramidal in shape and formed by seven bones namely: Frontal, Sphenoid, Palatine, Ethmoid, Maxillary, Lacrimal, and Zygomatic

Orbit Features

• The orbit contains nine fissures: Naso-lacrimal, Optic Foramen, Superior Orbital Fissure, and passages for CN III, IV, VI, and the Ophthalmic Branch of CN V.
• The ocular globe occupies only one-fifth of the orbital space, with the remaining space filled by extraocular muscles (EOM), nerves, blood vessels (BV), and adipose tissues.
• Tenon's Capsule is a thin membranous sac found in the posterior two-thirds of the globe; also called bulbar fascia or fascia bulbi, it starts at the limbus and lid muscles, initially fusing to conjunctiva, has a loose matrix, follows the sclera, sleeves around rectus and oblique muscles, and attaches to optic nerve sheaths.

Sclera

• The sclera is the white part of the eye.
• It is a tough layer made of bundles of white connective tissue (CT) fibers.
• The sclera is approximately 1mm thick at the optic nerve (ON).
• The optic nerve pierces the sclera about 2-3mm to the nasal side of the posterior pole, 1mm below the horizontal plane.
• Appears bluish in youth due to underlying pigments; yellowish in old age because of fat deposits.
• Accounts for one-fourth of the dry weight of the eyeball
• Composition: 72.24% water and 27.76% solids.
• Collagen forms 22% of its organic materials.
• The lamina cribrosa is the weakest part of sclera, perforated by optic nerve fibers in a basket-like weave.
• Functions to provide a firm, unyielding wall for the retina, protects against injury (mechanical & bacterial), furnishes a firm surface for EOM attachment, and aids in excluding extraneous light.

Cornea

• The cornea is transparent with a diameter of 11-12mm, radius of curvature of 8mm, center thickness of 0.8mm, and edge thickness of 1.1mm.
• Devoid of blood vessels, tactile, and thermal nerves, but abundant with nerves for pain
• Layers: Anterior epithelium (like skin), Bowman's membrane (thin, anterior limiting layer), Corneal Stroma (substantia propria, 90% of cornea), Descemet's membrane (structureless, elastic, resistant to inflammation), and Endothelium (direct contact with aqueous humor, water imbibition role).
• Functions as the first refracting media of the eye, gives the eyeball a constant shape, permits light to reach the interior, and protects the eye with its sensitivity.
• Transparency is due to the absence of blood vessels and pigments, the regular arrangement of epithelial and endothelial cells, and the dynamic balance between ions and water controlled via the endothelial pump

Corneoscleral Limbus

• The limbus is the transition area from the cornea to the sclera where:
  • Nourishment of the cornea occurs
  • It serves as an anatomical site for surgical procedures, such as cataract surgery

Iris

• The iris is a diaphragm that controls the amount of light entering the eye and is the colored part.
• Its color is due to melanin pigment.
• Blue eyes are more prone to photophobia(light sensitivity) because they have less melanin.
• There is an opening at the center called the pupil.
• The sphincter pupillae constricts the pupil, and the dilator pupillae dilates it.

Ciliary Body

• The ciliary body is where the ciliary muscle controls the crystalline lens
• The ciliary processes is where the aqueous humor is being manufactured or produced

Crystalline Lens

• Suspended by ligaments (zonule fibers or Zonules of Zinn) attached to the anterior portion of the ciliary body.
• Ligament actions change the lens shape, a process called accommodation that allows us to form a sharp image on the retina.

Choroid

• The choroid is the vascular layer between the retina and sclera; it provides oxygen and nourishment to the outer retinal layers.
• Known as the choroidea or choroid coat, it has a thickness of about 0.5 mm.
• Along with the ciliary body and iris, the choroid forms the uveal tract.
• Layers: Haller's Layer (outermost, larger blood vessels), Sattler's Layer (medium diameter blood vessels), Choriocapillaris (capillaries), and Bruch's Membrane (innermost).

Retina

• The retina is the inner nervous coat where images are cast.
• At the center is the macula lutea, also called the yellow spot, owing to the abundance of cones.
• A "dip" at the center is the fovea centralis, the area of keenest/sharpest vision, and corresponds to the central vision.
• Contains the photoreceptors called rods & cones.

Fovea Centralis

• The fovea centralis is densely packed with cone cells.
• It is largely responsible for color vision and enables high acuity for reading and similar tasks.

Optic Disc

• The optic disc is referred to as the anatomical blind spot because no photosensitive cells exist there.
• It is where the optic nerve pierces the retina to connect to the nerve cells on its inside (lamina cribrosa).

Chambers of the Eye

• Anterior: Located between the cornea and iris, filled with aqueous humor.
• Posterior: Located between the iris, zonule fibers, and lens, filled with aqueous humor, and is the smallest chamber.

Ocular Adnexa

• The ocular adnexa are accessory visual structures.
• Serve to protect and support structures of the eye.
• They play a crucial role with regards to globe protection, lubrication, and minimizing the risk of ocular infection.
• Includes all orbital contents except the eyeball & optic nerve
• Eyebrow, Eyelids, Eyelashes, Lacrimal gland/apparatus, Conjunctiva

Eyebrow

• The eyebrows are areas of short hairs above each eye that follows the shape of the lower margin of the brow ridges of some mammals.
• Keeps moisture and light out of the eyes and communicates emotions and facial recognition.

Lids

• Lids are thin folds of skin that covers/ protects the eye, which can voluntarily or involuntarily close over the eyeball.
• Has one of the most important jobs in the human vision system: protection from impacts, trauma, infections and the harsh rays of the sun.
• Uses skin, muscles, glands, nerves and other tissues to keep the eyes mobile, moist and lubricated.

Lashes

• Lashes are fine hairs sticking out of the upper and lower lid
• Eye's first line of defense
• Keeps water and sweat out of the eyes.
• Triggers a reflex to close the eyelids when insects and other threats get too close.

Lacrimal Apparatus

• Captures dust particles and other pollutants to keep them away from the eyeballs
• Keeps the eyes lubricated by reducing the evaporation of tears.
• A physiological system in the eye that includes the following structures: Lacrimal gland, Excretory ducts, Lacrimal sac, and Lacrimal lake.

Conjunctiva

• The conjunctiva is the eyes' invisible lubrication layer.
• It is a see-through layer found in the innermost layer of the eyelids (palpebral) and white of the eye (bulbar).

• Keeps the eyes moist, lubricated and free of small matter and pollutants
  

• Moisture and lubrication keep the eye surface healthy and make it easier for the eyeballs to move around.
  

• Prevents strain and discourages infections that place extra stress on the vision system
  

• Includes the regions of internal folding, palpebral conjunctiva, fornix conjunctiva, and bulbar conjunctiva

Other orbital contents:

• Adipose Tissue (fat) serve to protect & cushion the eye from injury
• Extrinsic Muscles (4 Recti & 2 Oblique) Intrinsic Muscles Ciliary Muscle Sphincter Pupillae Muscle Dilator Pupillae Muscle

Oblique: SO, IO (Superior Oblique, Inferior Oblique)

• Elevation: Eye looks up, Superior Rectus (SR)
• Depression Eye looks down, Inferior Rectus (IR)
• Abduction eye looks away from the nose Lateral Rectus (LR)
• Adduction eye looks towards the nose Medial Rectus (MR)
• Both superior muscles Intort SR & SO
• Both inferior muscles Extort IR & IO
• Both oblique muscles Abduct SO & IO
• Vertical recti Adduct SR and IR

Optic Nerve

• Cranial Nerve III: Carries the visual impulse to the visual cortex

Orbital Fascia

• Bound together & supported by CT

• Divides orbit into spaces of clinical importance
  

• Limits spread of hemorrhage & inflammation
  

• Supports & protects- Fascia is a layer of connective tissue that surrounds all the cells, nerves, joints, and organs in our body
  

Types of Orbital Fascia

• Periorbita (Periosteum of the Orbit)
• Periosteal lining of the orbit Derived from the dura mater
• Orbital Septum (Palpebral Fascia)
• Stretches from the bony orbit to the eyelid In close relationship with the posterior surface of the palpebral portion of the Orbicularis Oculi muscle
• Bulbar Fascia (Tenon's Capsule)

• Separates the globe from the orbital fat and provides the socket in which the eye moves.
  

Extends anteriorly to the insertion of the conjunctiva at the limbus. Its lower portion is thickened to form a sling (called the Ligament of Lockwood) upon w/c the globe rests

• Muscular Fascia Surrounds the ocular muscles Like a sleeve of a coat that surrounds an arm

Nerve Supply of the Eye

• CN II (optic nerve): Carries impulses from retina to the brain.

• CN III (oculomotor): Innervates EOMs, LPS.

• CN IV (trochlear): Innervates SO muscle.

• CN VI (abducens): Innervates only the lateral rectus muscle.

• CN V (trigeminal nerve): Ophthalmic nerve (1st branch) supplies sensory innervation to the structures of the eye, including the cornea, ciliary body, lacrimal gland, and conjunctiva.

Blood Supply of the Eye

• Ophthalmic Artery: First branch of Internal Carotid artery.

Bones of the Orbit

• Roof of the Orbit composed of 2 bones: Frontal & Sphenoid.

• Frontal Bone: Comprises the anterior and main part of the roof of the orbit.

  Includes:

  :Smooth area between the eyes. :The opening above each orbit allowing blood vessels & nerves to pass through. :A fibrous tissue that forms a pulley for the tendon of the SO muscle; situated medially near the anterior portion of the frontal bone.

The bat shaped bone forming the anterior plateau of the middle cranial cavity across the width of the skull

Lesser wing of the Sphenoid surrounds the optical canal and forms the posterior part (apex) of the roof.

Includes: The jagged openings in the orbit providing passage for CN's III, IV, V & VI.

The openings in the base of the lesser wing where CN II enter the orbit.

The medial wall of the orbit is quadrilateral in shape composed of 4 bones :The Lesser Wing of the Sphenoid most posterior & is joined to the Ethmoid bone , moving anteriorly to the Lacrimal bone and to the Maxillary bone. the orbital plate forms main part of the medial wall.

:Is extremely thin, the sinus may rupture into the orbit when inflamed or fractured and allow air to enter the orbit :Are fingernail sized bones forming a part of the medial wall & ethmoid.

   Each which bears a groove or furrow

called the Lacrimal Sulcus which serves as passageway of tears

two bones fused in a median suture which forms the upper jawbone and part of the orbit.

 O:Opening under the

orbit carrying nerves to the nasal region

The floor of the orbit does not extend to the apex and is composed of 3 bones O:Main bone O:Infra-orbital fissure weakest area of the orbit and may incarcerate the IR muscle in fractures of the orbital floor.

borders on the inferior orbital fissure, which narrows posteriorly

located lateral to the maxilla, forms the portion of the face called the cheekbone and part of the lateral orbit.

   The lateral wall of the orbit is composed of

O: composed of dense bone that separate the orbit from the fossa of the temporalis muscle.

Ois the portion of Sphenoid seen exteriorly, and forms posterior 2/3 of the lateral wall; is extremely thin and separates the orbit from the temporal

Physical Optics

• Refers to the properties of light itself, like the electromagnetic spectrum. Geometric Optics
• Refers to how light behaves when affected by various media. Optics
• Pertains to light

Introduction to Physiological Optics

• Science concerned with the genesis & propagation of light: the changes it undergoes and produces, and other phenomena closely associated with it.
• The study of the mechanics and function of the eye in relation to the process of seeing
• Aims at a scientific understanding of how information is extracted: from entering the eye to produce sensations such as brightness, shape, color, or movement
• Study of the function of vision divided into the following:

1. The path the light takes on its way through the eye to reach the retina.
2. The molecular changes in the retina which give rise to stimulation of optic nerves.
3. The sensations arising in the sensorium (interpretations)as the result of the molecular changes set up in the cerebral nerve cells by the impulses from the optic nerve.
4. The visual perceptions and judgments which our consciousness is of elaborating from the visual sensations.

Clear Vision Requires Three Independently Acting Components

• Optical
• Neurochemical
• Neural

The Human Eye

• Complicated, Imperfect optical system Visual Perception is a process of seeing: Requires series of transformations of neural activities in the retina, traversing through the visual pathways & finally to the visual cortex (Brodmann's area), creating patterns of activity that represent info needed for recognition, location, localization and guided actions.

Cardinal Points, Axes, And Angles Of The Eye

• The cardinal points are significant in order to find out the image produced by an object passing through optical lens
  • Every optical system has 6 cardinal points: 2 focal points 2 principal points 2 nodal points

The Schemetic Eye

• Consists of theoretical components: Corneal anterior surf Corneal post surf Lens anterior surf Lens posterior surf

Focal Point Points wherein all light rays from the observed object are bent towards the retina Points at the intersection of two imaginary rays created by extending the ray entering the cryst lens, and extending the exiting rays from the lens (P) = 1.35MM from CORNEAL APEX (P') = 1.60MM from CORNEAL APEX

Nodes A theoretical point within the eye, considered the center of the eye a. Optic Axis - is the line passing through the center of the cornea. It is the center of all the elements of the eyeball. b. Visual Axis - the line joining the fixation point, nodal point and the fovea of the same eye. c. Fixation Axis - the line joining the fixation point and the center of rotation d. Line from the center of curvature of cornea passing through the center of the pupil between optic axis & fixation between optic axis & visual axis

Ocular Physiology

• is the line of sight, line from object of regard and through the center of entrance pupil to that of the fovea

Three Distinct Organs

Functions in vision

• Receptors are sensory organs which receive the stimuli: Activated are stimulated, there'll be activity in the protoplasm EX visual receptors which are

• Physicologic: Connectors the ones that carry the impulses To & From -central nervous system

  (Afferent, Efferent)

• Effectors one's who brings- adjustment to the organism with reflex activity

The Human Eye

• Organs of sight, that detect: light, form, color, and motion.
• The simplest eyes: do nothing but detect light or dark
• More complex eyes:complex eyes can distinguish Shapes & Colors
• Eye Field and Vision- Complex eyes:overlap with depth perception to perform better ,(as in Humans) Has complex eye has minimal overlap, (rabbits and chameleons)
  Opposites have no overlap,(horses)

Functions

• Eyes have their own unique :Lens and Photoreceptor cells - some eyes have up to 28,000 sensory cells with arrangement hexagonally with 360 vision
• Are extremely sensitive to motion: each eye viewing a different angle, a fused image from all the eyes is produced in the brain, providing very wide- angle, high-resolution images.

Simple Eyes

 : Called "ocelli" who cannot actually see in the real sense

Functions

• Have photosensitive cells can detect light dark but no lens
• Enables snails to always to keep out of direct sunlight

Caterpillars

• Have can construct and build different simple images Which provides a rough image
• Source is within the eye itself (or ENTOPTIC) In Helmholtz - "some conditions, light failing on this eye may render ( render - put it in order, get it right, adjust ) Certain Objects and view within the self that is -entropical.

Entopical Images

• Have A physical basis in the image cast upon the retina Different: from from optical illusions one or another

The observers are sharing their specific view & perspective that has a direct view

Floaters and Volitantes

• Is an entopical image.
• Blobs of drifting is with transparency . With varying size, shape
• Which are particularly noticeably when

• viewing a bright,   with featureless or
               With point light   that are source & its diffuse & closed with clear, closed eye
  

Object Image View

• All of a shadow image: the shadow view are view is with retina near but is. It is
• May can individually swollen and over load The eye will respond or do with osmotic and blood pressure

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Purkinje Tree :

• Is a(n object) the in eye's of your

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• is results lens there focused periphery and

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