The eye is the photosensory organ of the body. It is composed of three tunics (coats): 1.Fibrous coat (sclera and cornea) forming the tough outer coat. 2.Vascular coat (choroid, ciliary body and iris) forming the pigmented and vascular middle layer. 3.Neural coat (retina), forming the innermost layer. The eye is the photosensory organ of the body. It is composed of three tunics (coats): 1.Fibrous coat (sclera and cornea) forming the tough outer coat. 2.Vascular coat (choroid, ciliary body and iris) forming the pigmented and vascular middle layer. 3.Neural coat (retina), forming the innermost layer.
ScleraSclera Tough white fibrous coat. Forms the posterior 5/6 of the eye ball. About 0.5 mm in thickness. Composed of flat bundles of collagen fibers running in directions parallel to the surface. Functions: –Protection of the internal structures. –Maintains the shape of the eye. –Gives attachment to the extrinsic muscles. Tough white fibrous coat. Forms the posterior 5/6 of the eye ball. About 0.5 mm in thickness. Composed of flat bundles of collagen fibers running in directions parallel to the surface. Functions: –Protection of the internal structures. –Maintains the shape of the eye. –Gives attachment to the extrinsic muscles.
CorneaCornea The cornea is transparent, avascular and forms the anterior 1/6 of the eye ball. Its is composed of five layers: 1.Corneal epithelium. 2.Bowman’s membrane. 3.Stroma (substantia propria). 4.Descemet’s membrane. 5.Corneal endothelium. The cornea is transparent, avascular and forms the anterior 1/6 of the eye ball. Its is composed of five layers: 1.Corneal epithelium. 2.Bowman’s membrane. 3.Stroma (substantia propria). 4.Descemet’s membrane. 5.Corneal endothelium.
Corneal epithelium Stratified squamous non-keratinized. About five-cells thickness. The lateral membranes of the adjacent cells are extensively interdigitated and joined by desmosomes. The epithelium has many free nerve endings and is very sensitive to stimuli specially pain. Stratified squamous non-keratinized. About five-cells thickness. The lateral membranes of the adjacent cells are extensively interdigitated and joined by desmosomes. The epithelium has many free nerve endings and is very sensitive to stimuli specially pain.
Bowman’s membrane A thin membrane below the corneal epithelium. Appears homogenous on light microscope. With electron microscope, it appears to be formed of type I collagen fibers arranged in random fashion. It is synthesized by the corneal epithelial cells and underlying stroma. A thin membrane below the corneal epithelium. Appears homogenous on light microscope. With electron microscope, it appears to be formed of type I collagen fibers arranged in random fashion. It is synthesized by the corneal epithelial cells and underlying stroma.
Substantia propria The thickest layer of the cornea. Composed of type I collagen fibers and corneal cells (modified fibroblasts). The fibers are arranged in lamellae which run parallel to the corneal surface. The matrix consists of sulfated proteoglycans rich in chondroitin sulfate and keratin sulfate. The thickest layer of the cornea. Composed of type I collagen fibers and corneal cells (modified fibroblasts). The fibers are arranged in lamellae which run parallel to the corneal surface. The matrix consists of sulfated proteoglycans rich in chondroitin sulfate and keratin sulfate.
Descemet’s membrane It is a thin membrane containing an atypical type of collagen fibers which have elastic character. It is considered as the basement membrane of the corneal endothelium. It is a thin membrane containing an atypical type of collagen fibers which have elastic character. It is considered as the basement membrane of the corneal endothelium.
Corneal endothelium It is the innermost layer of the cornea. Composed of a single layer of large hexagonal squamous cells. This layer is involved in transport of materials from the anterior chamber. It is the innermost layer of the cornea. Composed of a single layer of large hexagonal squamous cells. This layer is involved in transport of materials from the anterior chamber.
The cornea is avascular, it derived its nutrition from the aqueous humour and the blood vessels of the surrounding limbus. Corneal epithelial cells divide repeatedly by mitotic division, but the endothelial cells do not divide after birth the are not replaced. The transparency of the cornea is due to: 1.Its uniform diameter. 2.Regular arrangement of the collagen fibers. 3.Properties of ground substance (matrix). 4.Absence of blood vessels. 5.Ion pumps of the corneal endothelial cells maintains a critical fluid level within the substantia propria. The cornea is avascular, it derived its nutrition from the aqueous humour and the blood vessels of the surrounding limbus. Corneal epithelial cells divide repeatedly by mitotic division, but the endothelial cells do not divide after birth the are not replaced. The transparency of the cornea is due to: 1.Its uniform diameter. 2.Regular arrangement of the collagen fibers. 3.Properties of ground substance (matrix). 4.Absence of blood vessels. 5.Ion pumps of the corneal endothelial cells maintains a critical fluid level within the substantia propria.
Vascular (uveal) layer It is the middle layer of the eye. Highly vascular layer. Composed of three components: choroid, ciliary body and iris. Choroid provides nutrition for the retina and absorbs the light which has passed through it. Ciliary muscles contract to change the convexity of the lens. Ciliary body is responsible for secretion of aqueous humour. The Iris control the amount of light entering the eye by the dilator and sphincter pupillae muscles. It is the middle layer of the eye. Highly vascular layer. Composed of three components: choroid, ciliary body and iris. Choroid provides nutrition for the retina and absorbs the light which has passed through it. Ciliary muscles contract to change the convexity of the lens. Ciliary body is responsible for secretion of aqueous humour. The Iris control the amount of light entering the eye by the dilator and sphincter pupillae muscles.
RetinaRetina It is the innermost layer of the eye. Is a delicate sheet of nervous tissue that forms the photoreceptor of the eye. Anteriorly, it decreases in thickness and becomes continuous with the ciliary body and called ora serrata. Posteriorly, it forms the optic disc, where the nerve fibers merge to form the optic nerve. Fovea lies in the center of the retina and lies on the visual axis and represent the area of the maximum focus and visual acuity. The retina is formed of 10 histological layers. It is the innermost layer of the eye. Is a delicate sheet of nervous tissue that forms the photoreceptor of the eye. Anteriorly, it decreases in thickness and becomes continuous with the ciliary body and called ora serrata. Posteriorly, it forms the optic disc, where the nerve fibers merge to form the optic nerve. Fovea lies in the center of the retina and lies on the visual axis and represent the area of the maximum focus and visual acuity. The retina is formed of 10 histological layers.
Layers of the Retina 1. Pigment epithelium. 2. Rods and cones. 3. Outer limiting membrane. 4. Outer nuclear layer. 5. Outer plexiform layer. 6. Inner nuclear layer. 7. Inner plexiform layer. 8. Ganglion cell layer. 9. Nerve fibers (optic nerve) layer. 10. Inner limiting membrane. 1. Pigment epithelium. 2. Rods and cones. 3. Outer limiting membrane. 4. Outer nuclear layer. 5. Outer plexiform layer. 6. Inner nuclear layer. 7. Inner plexiform layer. 8. Ganglion cell layer. 9. Nerve fibers (optic nerve) layer. 10. Inner limiting membrane.
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