PS262 Chapter Notes -Far-Sightedness, Presbyopia, Opsin
Document Summary
The lens is the transparent focusing element at the front of the eye behind the lens cornea: controls 20% of eyes focusing power, can change its shape to adjust the eyes focus for objects, change in shape is achieved by the ciliary muscles increasing curvature. Presbyopia (old eye) is when the distance of the near point increases as a person gets older: near point for 20yr olds is 10cm, 30yr olds is 14cm, 40yr olds 22cm, 60yr olds 100cm, loss of ability to accommodate occurs because the lens hardens and the ciliary muscles weaken, solution: view things at a farther distance or get glasses. These results demonstrated two important connections between perception and physiology: our sensitivity to light depends on the concentration of a chemical the visual pigment, the speed at which our sensitivity increases in the dark depends on a chemical reaction the regeneration of the visual pigment.
