The diagram of the eye above shows the clear cornea at the front of the eye, and its relation with the iris. The Angle produced where the posterior (back) of the cornea intersects the anterior (front) of the iris is significant. If the angle is too narrow it can block the normal flow of aqueous fluid produced in the anterior chamber from escaping into the Canal of Schlemm, causing the pressure to increase in the eye and producing narrow angle or angle closure glaucoma. Covering the sclera at the front of the eye is a clear tissue called the bulbar conjunctiva (labelled conjunctiva in the illustration). The conjuctiva also covers the inside portion of the lids, where the lids make contact with the eye and where it is known as the palpebral conjunctiva. The cornea, crystalline lens inside the eye, and the vitreous normally have no blood vessels, but the conjunctiva is highly vascularized, and becomes easily inflammed (a condition known has conjunctivitis). The most posterior and most central part of the retina is the macula, and the center of the macula is the fovea. The greatest concentration of the photoreceptive cells, especially cones, is in this area, and the high density of these cells in this area is necessary to produce sharp visual acuity.
The picture on the left from biology.clc.uc.edu shows a 400x magnified Cross section of the retina. The photoreceptors (rods and cones) are seen as the back layer of the retina, behind Muller's fibers, Ganglion cells, Amacrine cells, bipolar cells, Horizontal cells and the Outer limiting membrane. Behind the photoreceptors are pigment cells and the two layers of the eye behine the retina--the vascularized choroid and the connective tissue outer layer, the Sclera. Not shown are the retinal blood vessels in front of the Muller's fibers. Although light must travel through retinal blood vessels and all the cells in front of the photoreceptors the brain filters out the cells and vessels in front of the photoreceptors.
The interactive diagram presented on Peter Kaiser's Joy of Visual Perception is a wonderful aid in illustrating the parts of the eye and how they function. Click the underlined title above to go to Kaiser's ingenious creation. It is best to refer to the pictures when reading descriptions of eye conditions and diseases, as well as the workings of the normal eye.
