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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