Anatomy of The Eye

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Anatomy of The Eye
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INTRODUCTION

• The Eye is the organ of vision.
• Composed of
• Eyeball.
• The adnexa.

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THE POSITION

• In the Predatory species have set well forward
• In Herbivores , Ruminant and rabbits have eyes
  more laterally to have wide area of vision

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Terminology of the eye

• Cornea the transparent part of the eyeball .
• Anterior pole the highest point on cornea .
• Posterior pole the highest point on posterior
  surface .
• Optic axis the straight line passing through
  both poles

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The Eyeball

• Equator an imaginary line about the eyeball,
  which is the equidistant from the poles.
• Meridian is one of many lines passing from pole
  to pole that intersects the equator at right
  angles.
• Optic nerve leaves the eyeball slightly ventral
  to the posterior pole

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Eyeball

• The three tunics are
• I- An external fibrous tunic
• II- A middle vascular tunic
• III- An internal tunic

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Eyeball

• The three tunics are
• I. An external fibrous tunic that gives form to
  and protects the eyeball its the only complete
  tunic.
• A middle vascular tunic that consist largely
• of blood vessels and smooth muscle
• concerned with the nutrition of the eyeball and
  the regulation of the shape of the lens and size
  of pupil.
•         

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Eyeball

•        
•  III. An internal tunic that consists largely of
  nervous tissue
• concerned with vision and translation of visual
  stimuli into nerve impulses for interpretation by
  the brain.

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The Fibrous Tunic

• It consists of the sclera and the cornea, which
  meet at the limbus.
• 1. The sclera is the opaque posterior part of the
  fibrous tunic and consists of a dense felt work
  of colagenous and elastic fibers and is generally
  white but in some species it contain pigment
  cells

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The fibrous tunic

• The cornea forms about one quarter of the fibrous
  tunic and bulges forward. It is composed off
  dense connective tissue arranged in lamellar form
  .
• The cornea doesnt contain blood vessels
  nutrients for its cells permeate from vessels in
  the limbus or are carried to it its surface in
  the lacrimal fluid and aqueous humor .

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The vascular Tunic (uvea)

• Deep to the sclera, which it composed of three
  zones .
• 1) The choroids lies on the sclera from the
  optic nerve to the limbus and contains a dense
  network of blood vessels embedded in heavily
  pigmented connective tissue

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The vascular Tunic (uvea)

• In the dorsal part of the fundus the choroids
  forms colored, light-reflecting area known as
  tapetum lucidum
• is avascular layer (cellular in the carnivores,
  fibrous in ruminants and horses) between the
  capillaries and the vessels.
• The tapetum makes the eyes of animals shine when
  they look toward the light.
• Our eyes and those of the pig dont have a
  tapetum so they dont reflect the light.
• This reflecting of light is a night vision
  adaptation because of stimulation of the light
  sensitive receptors in the retina.

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The vascular Tunic (uvea)

• 2) The ciliary body
• toward the limbus the choroids thickness to
  form it.
• 3) The Iris the smallest part of the vascular
  tunic, which extends from the cornea to the lens.
  
• It attached to sclera and ciliary body by
  pectinate ligament.
• the opening in the center is the pulpi

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The vascular Tunic (uvea)

• The iris divided the space between the lens and
  cornea into anterior and posterior chambers tat
  communicate through pupil and filled with,
  aqueous humor (a clear watery fluid).
• The color of the iris determines the color of the
  eye
• depends on the number of the pigmented cells
  present in its stroma
• the type of the pigment in the cells.

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The internal tunic

• The internal tunic of the eyeball contains the
  light-sensitive receptor cells (known as retina).
  
• Its an extension of the brain to which remains
  connected by the optic nerve.

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The internal tunic

• The layers in retina are
• A single layer of pigmented cells.
• Aneuroepithelialm layer containing the receptor
  cells, rods and cones and their nuclei.
• the rods for black and whit
• the cones for the color vision.
• A layer of bipolar ganglion cells.
• A layer of multipolar ganglion cells
  nonmyelinated axons lying internal to the cells
  and pass to the optic disc where they form the
  optic nerve.
• The optic disc is a blind area because there is
  no receptor cell.

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v  The adnexa of the eye

• The orbital fasciae
• a. The periorbital is attached near the
  optic foramen at the apex of the cone .
• b. The superficial muscular fascia lies
  within the periorbital. Its loose and fatty. And
  envelops in the levator palpebrae superioris and
  the lacrimal gland.
• c. The deep muscular fascia is more
  fibrous and arises from the eyelids and from the
  limbus of the eyeball.

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v  The adnexa of the eye

• 2. The muscles of the eyeball
• The rectus muscles dorsal, ventral, medial and
  lateral are inserted anterior to the equator by
  wide but very thin tendons.
• The ventral and dorsal oblique muscles attach to
  the eyeball near the equator.

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v  The adnexa of the eye

• 2. The muscles of the eyeball
• The retractor bulbi arises from the vicinity of
  the eyeball and inserted on the eyeball posterior
  to the equator.
• The levator palpebrae superioris striated muscle
  within the orbit that doesnt attach to the
  eyeball but passes over it to enter and elevate
  the upper eyelid

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v  The adnexa of the eye

• 3. The eyelids and conjunctiva
• The eyelids (palpebrae) are two musculofibrous
  folds of which the upper is the more extensive
  and more mobile.
• The free margins of the lids are meet at the
  medial and lateral angles of the eye and bound an
  opening known as the palpebral fissure.

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v  The adnexa of the eye

• 3. The eyelids and conjunctiva
• They are consist of three layers
• 1.The skin is thin and delicate and is covered
  with short hairs it may also carry a few
  prominent tactile airs.
• 2.The musculofibrous layer is formed by the
  orbicularis oculi, the orbital septum, the
  aponeurosis of the levator muscle and the smooth
  tarsal muscle.
• 3.The mucous (palpebral conjunctiva) a thin,
  transparent mucous membrane

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v  The adnexa of the eye

• 3. The eyelids and conjunctiva
• The third eyelid is supported by a T-shaped
  piece of cartilage.
• Bar lies in the free edge of the fold and stem
  points backward into the orbit medial to the
  eyeball.
• The stem of cartilage is surrounded by lacrimal
  gland (the gland of the third eyelid).

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v  The adnexa of the eye

• The lacrimal apparatus
• This consists of lacrimal gland proper
• The lacrimal gland is flat and lies between the
  eyeball and the dorsolateral wall of orbit.
• The glands associated with the third eyelids
• several small accessory glands
• duct system that conveys the lacrimal fluid after
  it has washed over the eye into the nasal cavity
  for evaporation.

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v    The blood supply of the eye

• The arteries can be divided into three groups
• THOSE SUPPLY EYEBLL
• SUPPLY OCULR MUSCLES
• THOSE LAEVING THE ORBIT TO SUPPLY ADJCENT
  STRCTURES.
• The external ophthalmic artery carries the
  principle supply of the blood to the eye, which
  is a branch of the maxillary artery.

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v    The blood supply of the eye

• 1) The branches of the external ophthalmic for
  the eyeball penetrate the sclera to reach the
  vascular tunic and retina.
• -Short posterior ciliary a. / supply the adjacent
  choroids in addition to branches to the optic
  nerve.
• -Long posterior ciliary a. /pass close the sclera
  closer to the equator.
• -The anterior ciliary a. / supply the anterior
  potion of the choroids, the ciliary body and the
  iris
• These arteries anastomose to form the greater
  arterial circle of the iris.

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v    The blood supply of the eye

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

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v    The blood supply of the eye

• 3) The arteries that leave the orbit
• -The lacrimal a. / supply the lacrimal gland in
  route.
• -The supraorbital a. / send branches to the upper
  eyelids
• -The malar a. /supply the eyelids and also
  adjacent area of the face.
• -The external ethamoid a. / supply the ethamoid
  labyrinth of the nasal cavity.

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v The nerve supply of the eye

• The optic nerve II enters the orbit through the
  optic foramen and passes to the light receptor
  cells in the retina.
• It allows the movements of the eye and is covered
  by meninges that it acquired during its
  development.

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v The nerve supply of the eye

• The Oculomoter nerve III control the movement of
  the eyeball. it enters the orbit through the
  orbital fissure.
• Supply dorsal, medial, ventral Rectus muscle
• Ventral oblique muscle
• Part of retractor muscle
• The abducent nerve VI enters through the orbital
  foramen and innervates most of retractor bulbi
  and lateral rectus muscles.

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v The nerve supply of the eye

• The trochlear nerve IV innervate
• Dorsal oblique muscle
• The trigeminal nerve V send branches to the eye.
• Opthalmic division
• Give sensory branches to
• 1- long ciliary nerve of the eye, lacrimal and
  supraorbital nerves.
• Maxillary division
• Zygomatic branch supply ventrolateral segment of
  the eyelids and conjunctiva

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v The nerve supply of the eye

• The facial nerve VII
• passes between the eye and the ear gives
  auriculopalpebral branch
• innervates the orbicularis oculi