With just a quiver

摘要

Nutrition is expensive. There is a price to pay to nourish any cell, and this is especially true of the eye. Evolution has had to be creative to nourish portions of the eye so as not to interfere with vision. If the retina is relatively simple and is thinner than about 150 mu m, diffusion from the chor-oid is sufficient. But, if the ecology demands better vision, the retina must thicken to permit more amacrine and horizontal cells to increase retinal processing. To assure inner retinal cells have adequate nutrition and proper cellular metabolism, evolution has found creative and seemingly contradictory mechanisms.