Cataracts One or both lenses often become cloudy as one ages. When a cataract seriously interferes with seeing, the cloudy lens is easily removed and a plastic one substituted. The entire process can be done in a few minutes as an outpatient under local anesthesia. Each type of receptor has its own special pigment for absorbing light. The amino acid sequence of each of the four types of opsin are similar, but the differences account for their differences in absorption spectrum.
Ganglion cells are always active.
Even in the dark they generate trains of action potentials and conduct them back to the brain along the optic nerve . Vision is based on the modulation of these nerve impulses. There is not the direct relationship between visual stimulus and an action potential that is found in the senses of hearing, taste, and smell. In fact, action potentials are not even generated in the rods and cones. Rod Vision Rhodopsin is the light-absorbing pigment of the rods.