Several days prior to a night op, dim the lights inside your house and wear polarizing sun
glasses outside. Eat more carrots, dark leafy greens, fortified milk, and cheese to boost your
intake of vitamin A. Avoid all bright light after sunset. Rod cells require 30 minutes or more
to readjust after even a brief burst of light, and can take hours to adapt completely in the
dark. Use red filtered flashlights, since rod cells don't react to red wavelengths. Scan the
horizon with your peripheral vision, since scanning prevents the rods from becoming saturated
with light.
The rod cell in the retina of the eye contains a protein called opsin, which combines with the
organic molecule retinal to form a complex know as rhodopsin. Retinal can undergoe a reversible
isomerism around one of its five double bonds when hit by light energy. This, in turn, stimulates
nerve cells to the brain, which records the data from the light. The process is reversed by a
type of protein known as an enzyme (a biological catalyst), and the retinal is ready to change
again. Opsin is regenerated by the replacement of the all-trans retinal by a newly synthesized
11-cis-retinal provided from the retinal epithelial cells.
Retinal can be made in the body from beta-carotene, a yellow pigment found in many vegetables,
especially carrots and sweet potatoes. Beta-carotene is cleaved in half by enzymes to form
retinol, or vitamin A. The retinol is then oxidized to retinal and combines with opsin for your
viewing pleasure.
Excesses of vitamin A, which are stored in the liver and fat tissue of the body, can also be
toxic, leading to yellowing and peeling of the skin, headaches, and vomiting.