Download - Cornea .....pptx

  • 8/14/2019 Cornea .....pptx


  • 8/14/2019 Cornea .....pptx


    The cornea is a transparent, avascular, watch glass

    like structure. It forms anterior 1/6 th of the outer fibrous coat of

    the eyeball.

  • 8/14/2019 Cornea .....pptx


  • 8/14/2019 Cornea .....pptx


    o The anterior surface : elliptical with an average

    horizontal diameter of 11.7 mm and vertical

    diameter of 11 mm


    The posterior surface of cornea is circular with anaverage diameter of 11.5 mm

    o Thickness : in the center 0.52 mm

    at periphery 0.7 mm

  • 8/14/2019 Cornea .....pptx


    It composed of the following 5 layers from

    outside inwards.

    1) Corneal epithelium

    2) Bowmans membrane or anterior limitingmembrane

    3) Substantia propria {corneal stroma}

    4) Descemets membrane or posterior limiting


    5) Endothelium

  • 8/14/2019 Cornea .....pptx


  • 8/14/2019 Cornea .....pptx


    It consists of non keratinized stratified squamousepithelium,{5 to 6 cells thick}At the sclera corneal junction

    {limbus} epithelium continuous with epithelium of bulbar

    conjunctiva.{ 10 cell thick}

    The deepest layer is made up of columnar cells,

    next 2 to 3 layers of wing or umbrella cell

    Most superficial two layers of flattened cellThe surface

    cells present microvilli which help retention of an

    unbroken film of tear fluid to increase the refractive

    surface of the eye.

    The corneal epithelium regenrates rapidly &

    is replaced continuously.

  • 8/14/2019 Cornea .....pptx


  • 8/14/2019 Cornea .....pptx


    2. Bowmans membrane

    It forms an acellular, densely packed layer of fine

    collagen fibres

    12 m in thickness and binds

    Covers the under lining substantia propri. It is not a true elastic membrane but simply a

    condensed superficial part of the stroma.

    It shows considerble resistance to infection. But

    once destroyed, it does not regenerate.

  • 8/14/2019 Cornea .....pptx


    3. Stromao This layer is about 0.5 mm thickness and constitutes most of

    the cornea [90% OF total thickness]o It consists collagen fibrils [ lamellae ] embedded in hydrated

    matrix of proteoglycans.

    o The lamella is arranged in many layers. In each layer they are

    not only parallel to each other but also to the corneal planeand become continuos with scleral lamellae at the limbus.

    o The alternating layers lamellae are at right angel to each


    o Among the lamellae keratocytes , wandering macrophages,

    histiocytes, & a few leucocytes.

    o All fibrils are of uniform size & embedded in a ground

    substance rich in chondroitin sulphate and keratosulphate,

    which helps to make the cornea transparent.

  • 8/14/2019 Cornea .....pptx


    4. Descemets membrane or posterior limiting membrane

    It is a strong homogenous layer which bounds the stromaposteriorly.

    It is very resistant to chemical agents, trauma and

    pathological processes.Therefore, Descemetocele can maintain the integrity of

    eyeball for long.

    It consist of collagen and glycoprotineins. Unlike Bowmans

    membrane it canregenerate.

  • 8/14/2019 Cornea .....pptx


    5. EndotheliumIt consists of a single layer of flat polygonal { mainly

    hexagonal} cells .The cell density of endothelium is around 3000 cells /mm in

    young adults,

    Which decreases with the advancing age. This is a

    considerable function rese

    rve for the endothelium. Therefore, corneal

    decompensation occurs only after

    more then 75 % of cells are lost.

    Because of the stroma tends to absorb water ,the

    endothelium primary task isto pump excess water out of the stroma .

    with out this pumping action, the stroma would swell with

    water , become hazy, & ultimately opaque.

  • 8/14/2019 Cornea .....pptx


  • 8/14/2019 Cornea .....pptx


    Nutrition of cornea

    Since the cornea is avascular, it gets nutrition by three

    sources.1) Loop of capillaries at the periphery of conjuntivo corneal

    junction .

    2) Aqueous humor from the anterior chamber of the eye.

    3) The lacrimal secretion spreading as fluid film over theanterior surface of cornea.

    4) Solutes { glucose etc} enter the cornea by either simple

    diffusion or active transport trough aqueous humor and by

    diffusion from the perilimbal capillaries.

    5) Oxygen is derived directly from air through the tear film.

    This is an active process undertaken by the epithelium.

  • 8/14/2019 Cornea .....pptx


    Blood supply Cornea is avascular structure

    Small loops derive from the anterior cilliary vessels invedeits periphery

    For about 1 mm. actually these loops are not in the cornea

    but in the sub

    conjunctival tissue which overlaps the cornea.

    Nerve supplyAnterior ciliary nerves { branches of opthalamic division of

    5 th cranial n.

    After going about 2mm in cornea the nerves lose theirmyelin sheath and divide dichotomously & form three

    plexuses ..the stromal , subepithelial and


  • 8/14/2019 Cornea .....pptx


    Corneal transparencyIt is due to.

    .the smoothness of the epithelium.the absence of blood vessel

    .the uniform organisation of collagin fibrils of the

    substantia propria

    .the type of the ground substance.

  • 8/14/2019 Cornea .....pptx


    Note .New layer of human cornea discovered by researches in

    university ofNottingham , by pro..Harminder Dua.

    That is Duas layer

    Between the corneal stroma & desment membrane.

    Duas layer is a very thin layer of collagen which is

    impervious to air.

  • 8/14/2019 Cornea .....pptx


    By :!!!