The Human Eye Essay Example | Topics and Well Written Essays - 750 words

The Human Eye - Essay Example The genes that govern many aspects of light detection, eye development, and neural development are the ones directing these processes in jawed vertebrates. These outstanding similarities to the eye of jawed vertebrates are far too many to have emerged separately. There are no living representatives of ancestry that split off from our line in the past 50 million years. Eyes of the hagfish differ intensely from the vertebrate standard even though they are vertebrates. This is because the eye of the hagfish lacks a cornea, iris, lens and all of the normal supporting muscles. Its retina consists of just two layers of the cell instead of three. Each eye is buried deep beneath a translucent patch of skin. The eye can undergo enormous degeneration and can be even lost altogether in as little as 10,000 years. The hagfish eye is not involved in vision but instead offers input to the part of the animal’s brain that controls crucial circadian rhythms, as well as seasonal events like breeding and feeding based in part on this parallel to the pineal gland. Mammalian eye also shows telltale clues to its evolutionary origin during embryological development. The circuit of the mammalian retina starts out in contrast to that of the hagfish, with the photoreceptors linking directly to the output neurons. Photoreceptor cells across the animal kingdom fall into two different classes- ciliary and rhabdomeric. Ciliary photoreceptors are accountable for sensing light for nonvisual functions in the vast majority of organisms.