HISTOLOGY OF CORNEA & RETINA

CORNEA

Corneal epithelium (Anterior epithelium) Bowman’s membrane Corneal Stroma Descement’s Membrane Endothelium (Posterior epithelium)

Corneal epithelium: Stratified squamous non keratinised epithelium 1mm thick Highly sensitive Irritation or injury causes pain,lacrimation,photophobia,blinking….

Bowman’s capsule: Also called anterior limiting membrane 10 to 12 micrometer. Dense mass of collagen fibers Acts barrier—spread of infection Damaged—can’t regenerate

Corneal stroma: 90% thickness 200—230 sequentially arranged lamellae Bundles of collagen fibers—highly ordered. Transparent Flattened fibroblasts are located b/w lamellae.

Posterior limiting membrane: Also called Descemet’s membrane. Acellular Regarded has BM of endothelium

Endothelium: Single layer of cuboidal cells. Metabolic exchange….

Cornea Stratified squamous epithelium Bowman’s membrane Substantia propria Descemet’s membrane Mesothelium Corneal corposcles

RETINA Neural sensory layer. Inner coat—posterior 3/4th surface. Specialized area—fovea centralis—only cones-most acute vision. Also ‘blind spot’, ‘optic disc’….

LAYERS OF RETINA Pigment cell layer Layer of rods & cones External limiting membrane Outer nuclear layer Outer plexiform layer Inner nuclear layer Inner plexiform layer Ganglion cell layer Nerve fiber layer Internal limiting membrane

Pigment layer…. Lined by cuboidal epithelium Cytoplasm contains melanin pigment. Melanin pigment—absorbs light Forms blood retinal barrier b/w retina and vascular system of choroid.

Functions: absorption of light Phagocytosis of tips of rods and cones Structural and metabolic support Storage, esterification and release of Vitamin A

Layer of rods and cones… Rod and cone cells—photoreceptors Tip of rods and cones are surrounded—processes of pigment cell layer.

External limiting membrane… Junctional zone b/w Muller’s cells and photoreceptor processes

Outer nuclear layer….. Consist of cell bodies and nuclei of rods and cones. Darkly stained area Cone cell---color vision in good lighting condition (Iodopsin) Rod cell---sensitive to lower intensities of light. (Rhodopsin)

Outer plexiform layer… Consist of axons of rods & cones + dendrites of bipolar neurons + horizontal cells.

Inner nuclear layer…. Consist ----bipolar neurons + Amacrine cells +Muller’s cell + Horizontal cell

Inner plexiform layer; Consist of axons of bipolar + dendrites of ganglionic cells + displaced amacrine cells.

Ganglionic cell layer…. Consist body nuclei of large ganglion cell Nerve fiber layer Consist of axons of ganglion cell gather together and leave eye as OPTIC NERVE..

Internal limiting membrane… Seperates retina from vitreous humour Formed by union of terminal expansions of Muller cells and their BM…….

Other cells of Retina….. Horizontal cells- association neurons , inhibitory interneurons , GABA Amacrine cells –’no axons’ - modulate the photoreceptive signals Muller’s cells – Glial cell - Mechanical support - stores glycogen

Retina Layer of rods and cones Outer nuclear layer Outer plexiform layer Inner nuclear layer Inner plexiform layer Ganglionic cell layer Layer of optic nerve fibers