Subsequently the absorbtion of photons by the visual pigment of the photoreceptors is translated into first a biochemical message and then an electrical message that can stimulate all the succeeding neurons of the retina. Light must, therefore, travel through the thickness of the retina before striking and activating the rods and cones (Fig. A radial section of a portion of the retina reveals that the ganglion cells (the output neurons of the retina) lie innermost in the retina closest to the lens and front of the eye, and the photosensors (the rods and cones) lie outermost in the retina against the pigment epithelium and choroid. The optic nerve contains the ganglion cell axons running to the brain and, additionally, incoming blood vessels that open into the retina to vascularize the retinal layers and neurons (Fig. The retina is approximately 0.5 mm thick and lines the back of the eye. A schematic section through the human eye with a schematic enlargement of the retina The total retina is a circular disc of between 30 and 40 mm in diameter (Polyak, 1941 Van Buren, 1963 Kolb, 1991).įig. Retina as seen through an opthalmoscopeĬLICK HERE to see an animation (from the iris to the retina) (Quicktime movie)Ī circular field of approximately 6 mm around the fovea is considered the central retina while beyond this is peripheral retina stretching to the ora serrata, 21 mm from the center of the retina (fovea). Approximately 17 degrees (4.5-5 mm), or two and half disc diameters to the left of the disc, can be seen the slightly oval-shaped, blood vessel-free reddish spot, the fovea, which is at the center of the area known as the macula by ophthalmologists.
From the center of the optic nerve radiates the major blood vessels of the retina. In the center of the retina is the optic nerve, a circular to oval white area measuring about 2 x 1.5 mm across. When an ophthalmologist uses an ophthalmoscope to look into your eye he sees the following view of the retina (Fig.
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