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Anatomy of The Eye

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INTRODUCTION

The Eye is the The Eye is the organ of vision.organ of vision.

Composed of :Composed of :

1.1. Eyeball.Eyeball.

2.2. The adnexa. The adnexa.

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THE POSITION

In the Predatory species: In the Predatory species: have set well forwardhave set well forward

In Herbivores , In Herbivores , Ruminant and rabbits: Ruminant and rabbits: have eyes more laterally have eyes more laterally to have wide area of to have wide area of vision vision

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Terminology of the eye CorneaCornea : the transparent : the transparent

part of the eyeball .part of the eyeball . Anterior poleAnterior pole: the highest : the highest

point on cornea .point on cornea . Posterior polePosterior pole : the : the

highest point on posterior highest point on posterior surface .surface .

Optic axisOptic axis: the straight : the straight line passing through both line passing through both poles poles

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The Eyeball EquatoEquator :an imaginary line about r :an imaginary line about

the eyeball, which is the equidistant the eyeball, which is the equidistant from the poles.from the poles.

MeridianMeridian: is one of many lines : is one of many lines

passing from pole to pole that passing from pole to pole that intersects the equator at right angles.intersects the equator at right angles.

• Optic nerveOptic nerve :leaves the :leaves the eyeball slightly ventral to eyeball slightly ventral to the posterior pole the posterior pole

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Eyeball

The three tunics are:The three tunics are:

I- I- An external fibrous tunicAn external fibrous tunic

II- A middle vascular tunicII- A middle vascular tunic

III- III- An internal tunicAn internal tunic

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Eyeball The three tunics are:The three tunics are:I. I. An external fibrous tunic: An external fibrous tunic: that gives form to and protects that gives form to and protects

the eyeball; it’s the only complete tunic.the eyeball; it’s the only complete tunic.

II.II. A middle vascular tunic:A middle vascular tunic: that consist largely that consist largely of blood vessels and smooth muscle of blood vessels and smooth muscle

concerned with the nutrition of the eyeball and concerned with the nutrition of the eyeball and the regulation of the shape of the lens and size the regulation of the shape of the lens and size of pupil.of pupil.

                

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Eyeball

              

  III. III. An internal tunic:An internal tunic: that consists largely that consists largely of nervous tissue of nervous tissue concerned with vision and concerned with vision and

translation of visual stimuli into nerve translation of visual stimuli into nerve impulses for interpretation by the brain.impulses for interpretation by the brain.

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The Fibrous Tunic

It consists of the It consists of the sclera sclera and the and the cornea, cornea, which meet at the which meet at the limbus.limbus.

1. The sclera 1. The sclera is the opaque posterior part of is the opaque posterior part of the fibrous tunic and consists of a dense felt the fibrous tunic and consists of a dense felt work of colagenous and elastic fibers and is work of colagenous and elastic fibers and is generally white but in some species it generally white but in some species it contain pigment cells contain pigment cells

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The fibrous tunic

The corneaThe cornea forms about one quarter of the forms about one quarter of the fibrous tunic and bulges forward. It is fibrous tunic and bulges forward. It is composed off dense connective tissue composed off dense connective tissue arranged in lamellar form .arranged in lamellar form .

The cornea doesn’t contain blood vessels; The cornea doesn’t contain blood vessels; nutrients for its cells permeate from vessels nutrients for its cells permeate from vessels in the limbus or are carried to it its surface in the limbus or are carried to it its surface in the lacrimal fluid and aqueous humor .in the lacrimal fluid and aqueous humor .

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The vascular Tunic (uvea)

Deep to the sclera, which it composed of Deep to the sclera, which it composed of three zones .three zones .

1) The choroids: 1) The choroids: lies on the sclera from the lies on the sclera from the optic nerve to the limbus and contains a optic nerve to the limbus and contains a dense network of blood vessels embedded dense network of blood vessels embedded in heavily pigmented connective tissue in heavily pigmented connective tissue

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The vascular Tunic (uvea)

In the dorsal part of the fundus the choroids forms colored, In the dorsal part of the fundus the choroids forms colored, light-reflecting area known as light-reflecting area known as tapetum lucidumtapetum lucidum is avascular layer (cellular in the carnivores, fibrous in is avascular layer (cellular in the carnivores, fibrous in

ruminants and horses) between the capillaries and the ruminants and horses) between the capillaries and the vessels. vessels.

The tapetum makes the eyes of animals shine when they The tapetum makes the eyes of animals shine when they look toward the light. look toward the light.

Our eyes and those of the pig don’t have a tapetum so they Our eyes and those of the pig don’t have a tapetum so they don’t reflect the light. don’t reflect the light.

This reflecting of light is a night vision adaptation because This reflecting of light is a night vision adaptation because of stimulation of the light sensitive receptors in the retina. of stimulation of the light sensitive receptors in the retina.

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The vascular Tunic (uvea)2) The ciliary body2) The ciliary body : :

toward the limbus the choroids toward the limbus the choroids thickness to form it. thickness to form it.

3) The Iris: 3) The Iris: the smallest part of the the smallest part of the vascular tunic, which extends from vascular tunic, which extends from the cornea to the lens. the cornea to the lens.

It attached to sclera and ciliary It attached to sclera and ciliary body by pectinate ligament. body by pectinate ligament.

the opening in the center is the the opening in the center is the pulpi pulpi

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The vascular Tunic (uvea) The iris divided the space between the The iris divided the space between the

lens and cornea into anterior and lens and cornea into anterior and posterior chambers tat communicate posterior chambers tat communicate through pupil and filled with, aqueous through pupil and filled with, aqueous humor (a clear watery fluid).humor (a clear watery fluid).

The color of the iris determines the The color of the iris determines the color of the eye color of the eye

depends on the number of the depends on the number of the pigmented cells present in its pigmented cells present in its stroma stroma

the type of the pigment in the the type of the pigment in the cells. cells.

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The internal tunic

The internal tunic of the eyeball contains The internal tunic of the eyeball contains the light-sensitive receptor cells (known as the light-sensitive receptor cells (known as retina). retina). It’s an extension of the brain to which It’s an extension of the brain to which

remains connected by the optic nerve.remains connected by the optic nerve.

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The internal tunic The layers in retina are:The layers in retina are: A single layer of pigmented cells.A single layer of pigmented cells. Aneuroepithelialm layer containing the receptor Aneuroepithelialm layer containing the receptor

cells, rods and cones and their nuclei.cells, rods and cones and their nuclei. the rods for black and whit the rods for black and whit the cones for the color vision.the cones for the color vision.

A layer of bipolar ganglion cells.A layer of bipolar ganglion cells. A layer of multipolar ganglion cells nonmyelinated A layer of multipolar ganglion cells nonmyelinated

axons lying internal to the cells and pass to the axons lying internal to the cells and pass to the optic disc where they form the optic nerve. optic disc where they form the optic nerve.

The optic disc is a blind area because there is no The optic disc is a blind area because there is no receptor cellreceptor cell..

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  The adnexa of the eye1.1. The orbital fasciaeThe orbital fasciae :: a. a. The periorbital:The periorbital: is attached near is attached near

the optic foramen at the apex of the the optic foramen at the apex of the cone .cone .

b. b. The superficial muscular fascia:The superficial muscular fascia: lies within the periorbital. It’s loose lies within the periorbital. It’s loose and fatty. And envelops in the and fatty. And envelops in the levator palpebrae superioris and the levator palpebrae superioris and the lacrimal gland. lacrimal gland.

c. c. The deep muscular fascia: The deep muscular fascia: is is more fibrous and arises from the more fibrous and arises from the eyelids and from the limbus of the eyelids and from the limbus of the eyeball.eyeball.

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  The adnexa of the eye

2. 2. The muscles of the eyeball:The muscles of the eyeball: The rectus muscles: dorsal, The rectus muscles: dorsal,

ventral, medial and lateral ventral, medial and lateral are inserted anterior to the are inserted anterior to the equator by wide but very equator by wide but very thin tendons.thin tendons.

The ventral and dorsal The ventral and dorsal oblique muscles: attach to oblique muscles: attach to the eyeball near the equator. the eyeball near the equator.

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  The adnexa of the eye2. 2. The muscles of the eyeball:The muscles of the eyeball:

The retractor bulbi arises from The retractor bulbi arises from the vicinity of the eyeball and the vicinity of the eyeball and inserted on the eyeball posterior inserted on the eyeball posterior to the equator.to the equator.

The levator palpebrae The levator palpebrae superioris: striated muscle superioris: striated muscle within the orbit that doesn’t within the orbit that doesn’t attach to the eyeball but passes attach to the eyeball but passes over it to enter and elevate the over it to enter and elevate the upper eyelid upper eyelid

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  The adnexa of the eye3. 3. The eyelids and conjunctivaThe eyelids and conjunctiva : : The eyelids (palpebrae) are two The eyelids (palpebrae) are two

musculofibrous folds of which the musculofibrous folds of which the upper is the more extensive and upper is the more extensive and more mobile.more mobile.

The free margins of the lids are The free margins of the lids are

meet at the medial and lateral angles meet at the medial and lateral angles of the eye and bound an opening of the eye and bound an opening known as the palpebral fissure.known as the palpebral fissure.

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  The adnexa of the eye3. The eyelids and conjunctiva3. The eyelids and conjunctiva : : They are consist of three layers:They are consist of three layers:

1.The skin: is thin and delicate and is 1.The skin: is thin and delicate and is covered with short hairs: it may also covered with short hairs: it may also carry a few prominent tactile airs.carry a few prominent tactile airs.

2.The musculofibrous layer: is formed by 2.The musculofibrous layer: is formed by the orbicularis oculi, the orbital the orbicularis oculi, the orbital septum, the aponeurosis of the levator septum, the aponeurosis of the levator muscle and the smooth tarsal muscle.muscle and the smooth tarsal muscle.

3.The mucous (palpebral conjunctiva) a 3.The mucous (palpebral conjunctiva) a thin, transparent mucous membrane thin, transparent mucous membrane

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  The adnexa of the eye3. The eyelids and 3. The eyelids and

conjunctivaconjunctiva : : The third eyelid is supported The third eyelid is supported

by a T-shaped piece of by a T-shaped piece of cartilage.cartilage.

Bar lies in the free edge of the Bar lies in the free edge of the fold and stem points backward fold and stem points backward into the orbit medial to the into the orbit medial to the eyeballeyeball. .

The stem of cartilage is The stem of cartilage is surrounded by lacrimal gland surrounded by lacrimal gland (the gland of the third eyelid).(the gland of the third eyelid).

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  The adnexa of the eye4.4. The lacrimal apparatus:The lacrimal apparatus: This consists of lacrimal gland properThis consists of lacrimal gland proper

The lacrimal gland is flat and lies The lacrimal gland is flat and lies between the eyeball and the between the eyeball and the dorsolateral wall of orbit.dorsolateral wall of orbit.

The glands associated with the third The glands associated with the third eyelids eyelids

several small accessory glands several small accessory glands • duct system that conveys the lacrimal duct system that conveys the lacrimal

fluid after it has washed over the eye fluid after it has washed over the eye into the nasal cavity for evaporation.into the nasal cavity for evaporation.

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    The blood supply of the eye: The arteries can be divided into three groups:The arteries can be divided into three groups:

1.1. THOSE SUPPLY EYEBLLTHOSE SUPPLY EYEBLL

2.2. SUPPLY OCULR MUSCLESSUPPLY OCULR MUSCLES

3.3. THOSE LAEVING THE ORBIT TO SUPPLY THOSE LAEVING THE ORBIT TO SUPPLY ADJCENT STRCTURES. ADJCENT STRCTURES.

The external ophthalmic artery carries the principle supply The external ophthalmic artery carries the principle supply of the blood to the eye, which is a branch of the maxillary of the blood to the eye, which is a branch of the maxillary artery.artery.

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    The blood supply of the eye: 1) The branches of the external 1) The branches of the external

ophthalmic for the eyeball penetrate ophthalmic for the eyeball penetrate the sclera to reach the vascular the sclera to reach the vascular tunic and retina.tunic and retina.

-Short posterior ciliary a. / -Short posterior ciliary a. / supply supply the adjacent choroids in addition to the adjacent choroids in addition to branches to the optic nerve.branches to the optic nerve.

--Long posteriorLong posterior ciliary a. /ciliary a. /pass pass close the sclera closer to the close the sclera closer to the equator.equator.

-The anterior ciliary a. / -The anterior ciliary a. / supply supply the anterior potion of the choroids, the anterior potion of the choroids, the ciliary body and the iris the ciliary body and the iris

These arteries anastomose to form These arteries anastomose to form the greater arterial circle of the the greater arterial circle of the iris.iris.

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    The blood supply of the eye:

2) The arteries that supply the ocular muscles. 2) The arteries that supply the ocular muscles. Which the absence of the large vessels in Which the absence of the large vessels in distal ends reduces bleeding when the distal ends reduces bleeding when the muscles are cut during the enucleating.muscles are cut during the enucleating.

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    The blood supply of the eye:

3) The arteries that leave the orbit: 3) The arteries that leave the orbit: -The lacrimal a. /-The lacrimal a. / supply the lacrimal gland in supply the lacrimal gland in

route.route. --The supraorbital a. /The supraorbital a. / send branches to the upper send branches to the upper

eyelidseyelids -The malar a. /-The malar a. /supply the eyelids and also adjacent supply the eyelids and also adjacent

area of the face.area of the face. -The external ethamoid a. / -The external ethamoid a. / supply the ethamoid supply the ethamoid

labyrinth of the nasal cavity.labyrinth of the nasal cavity.

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The nerve supply of the eye:

The optic nerve II:The optic nerve II: enters the orbit through enters the orbit through the optic foramen and passes to the light the optic foramen and passes to the light receptor cells in the retina.receptor cells in the retina.

It allows the movements of the eye and is It allows the movements of the eye and is covered by meninges that it acquired during its covered by meninges that it acquired during its development.development.

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The nerve supply of the eye:

The Oculomoter nerve III: The Oculomoter nerve III: control the movement of the control the movement of the eyeball. it enters the orbit through the orbital fissure.eyeball. it enters the orbit through the orbital fissure. Supply: dorsal, medial, ventral Rectus muscleSupply: dorsal, medial, ventral Rectus muscle Ventral oblique muscleVentral oblique muscle Part of retractor musclePart of retractor muscle

The abducent nerve VI: The abducent nerve VI: enters through the orbital enters through the orbital foramen and innervates most of retractor bulbi and lateral foramen and innervates most of retractor bulbi and lateral rectus muscles.rectus muscles.

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The nerve supply of the eye:

The trochlear nerve IV: The trochlear nerve IV: innervate innervate Dorsal oblique muscleDorsal oblique muscle

The trigeminal nerve V: The trigeminal nerve V: send branches to the eye.send branches to the eye. Opthalmic divisionOpthalmic divisionGive sensory branches to:Give sensory branches to:

1- long ciliary nerve of the eye, lacrimal and supraorbital nerves.1- long ciliary nerve of the eye, lacrimal and supraorbital nerves. Maxillary divisionMaxillary division

Zygomatic branch supply ventrolateral segment of the eyelids Zygomatic branch supply ventrolateral segment of the eyelids and conjunctivaand conjunctiva

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The nerve supply of the eye:

The facial nerve VII:The facial nerve VII: passes between the eye and the ear gives passes between the eye and the ear gives

auriculopalpebral branch auriculopalpebral branch

innervates the orbicularis oculi innervates the orbicularis oculi