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8/9/2019 Anatomy & Physiology of the Eye
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Anatomy & Physiology of the Eye
an OverviewBy:
Haslinda A.Rahim
Medical Officer
Ophthalmology Department
Queen Elizabeth Hospital
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Can be divided into 2 segments :
Anterior segment in front of lens
Posterior segment behind the lens
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There are grossly 3 layers of specialized
tissues in the posterior segment :
Sclera outermost layer
Choroid intermediate layer
Retina innermost layer
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CORNEA
1/6 of the outer layer of the eye
Transparent
Composed of 5 layers:
epithelium Bowmans (anterior limiting) membrane
stroma (substantia propria)
Descemets (posterior limiting) membrane
endothelium Primary structure focusing light
Barrier to trauma & infection
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CONJUNCTIVA
Mucous membrane
Transparent
3 sections:
palpebral conjunctiva
bulbar conjunctiva
fornix
Within the bulbar conjunctiva are goblet cellswhich secrete mucin, an important component
that protects and nourishes the cornea
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IRIS
Thin diaphragm composed mostly of connective tissue and
smooth muscle fibers
Divide the anterior compartmentinto the anterior
chamberand theposterior chamber
Eye color
Rarely, one iris can be a different color than the other iris.
This is known as heterochromia irides and is determined
genetically. Also, a section of one iris may be a different
color from the rest of that iris; this is known asheterochromia iridum or sectoral heterochromia iridis.
Control the size of the pupils
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PUPILS
The iris acts like the shutter of a camera
Regulate the amount of light passing
through to the retina
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LENS
Immediately behind the iris
Transparent
Composed of 4 layers: capsule
subcapsular epithelium
cortex
nucleus
Hold in place by suspensory ligaments (zonules), which
attach at one end to the lens capsule and at the otherend to the ciliary processes of the circular ciliary bodyaround the inside of the eye
2nd powerful in light focusing
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VITREOUS HUMOUR
Clear gel which occupies the posterior
compartment of the eye
80% of the volume of the eyeball
Functions:
Transmit light to the retina
Contributes to the dioptric power of the eye
Supports the posterior part of the lens
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RETINA
Innermost layer of the eye
Comparable to the film inside of a camera
Composed of nerve tissue which senses the lightentering the eye. This complex system of nerves sends
impulses through the optic nerve back to the brain The macula lutea is the small, yellowish central portion
of the retina, and it is the area providing the clearest,most distinct vision.
The very center of the macula is called the foveacentralis, an area where all of the photoreceptors arecones
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SCLERA
Makes up the back five-sixths of the eyes
outer layer
White, opaque portion of the eye
Continuous with the cornea
It provides protection & attachment for the
extraocular muscles
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EXTRA OCULAR MUSCLES
medial rectus (MR)lateral rectus
(LR)superior rectus (SR)inferior rectus
(IR)superior oblique (SO)inferior
oblique (IO)
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medial rectus (MR) moves the eye inward, toward the nose (adduction)
lateral rectus (LR) moves the eye outward, away from the nose (abduction)
superior rectus (SR) primarily moves the eye upward (elevation) secondarily rotates the top of the eye toward the nose (intorsion)
tertiarily moves the eye inward (adduction)
inferior rectus (IR) primarily moves the eye downward (depression) secondarily rotates the top of the eye away from the nose (extorsion) tertiarily moves the eye inward (adduction)
superior oblique (SO) primarily rotates the top of the eye toward the nose (intorsion)
secondarily moves the eye downward (depression) tertiarily moves the eye outward (abduction)
inferior oblique (IO) primarily rotates the top of the eye away from the nose (extorsion) secondarily moves the eye upward (elevation) tertiarily moves the eye outward (abduction)
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VISUAL PATHWAY
Optic nerve Optic chiasm (nasal retinal
fibers cross over) Optic tract
Thalamus Optic radiation Visual
cortex (occipital lobe)
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