MOLECULAR GENETIC ANALYSIS OF LATTICE AND GRANULAR CORNEAL PYSTROPHIES IN IN'DIAN PATIENTS

Abstract

The cornea is a clear tissue pres,el1t at the front of the eye as shown in Figure 1.1. It provides 85% of the refractive power of the eye. It is approximately half a millimeter (550 microns) thick and has a diameter of 12 mm. The adultlilwmal1 cornea measures 11 to 12 mm horizontally and 9 to 11 mm vertically. The thickness of the cornea increases from center to periphery where it is about 0.7 mm thick. It is made up of tissue similar to that of the sclera but it has 110 blood vessels. Absence of blood vessels and orderly ar.raRgerTJent of collagel1 fibers are responsible for cormeal transparemcy. The mean diameter of collagen fibers and the mean distamce between the collagen fibers are less than half of tl7le wavelength of visible light (400-700 nm). Due to tmis orderly arramgemel1t, the scattering of incident light by one collagen fiber is canceled by the interference from the other which allows light to pass tmrough the cornea. The cornea consists of 3 main and 2 auxiliary layers as shown in Figwre 1.2. The rnainlayers from the surface to the inner eye are epithelium, stroma and endotmelium. Bowman's membrane lies between the epithelium and tl7le stroma and the Descemet's membrane is between the stroma aRd the endotmelium.