As the cochlear duct is displaced by perilymph pressure waves, the created shearing forces cause stereocilia to move and bend, opening up ion channels, leading to depolarization, etc. More bending occurs from louder sounds. The eye takes visible light and turns that into nerve impulses. Light is refracted at the cornea and lens, so that the image formed on the retina is upside down, right to left, hence making the visual field reversed . Correct by concave lens which cause light rays to diverge and hence, with a longer focal length.
Convex lens increase light convergence and so shorten the focal length.
Uneven cylindrical lens needed to correct. In the retina there are two types of photoreceptors . Neural layers of retina are a forward extension of the brain, and so the light must pass through several layers before reaching the photoreceptors. Bipolar cells connect them to the photoreceptors. Rods contain the purple pigment rhodopsin .