Eventally patients are reduced to tunnel vision with only the fovea spared the disease process. Both Helmholtzs trichromatic theory and Herings opponent-process theory are therefore correct but trichromacy arises at the level of the receptors and opponent processes arise at the level of retinal ganglion cells and beyond. 2 Types Of Photoreceptor Cells Unevenly Distributed In Density Location And Amount Light In The Dark Electromagnetic Spectrum Light Rays The rods of the peripheral retina begin to degenerate in early stages of the disease. . Characteristic pathology is the occurence of black pigment in the. Patients become night blind gradually as more and more of the peripheral retina where the rods reside becomes damaged. Color processing begins at a very early level in the visual system even within the retina through initial color opponent mechanisms.
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