Eye Structure

For maintain the eyes human must enough of Vitamin A. Vitamin A has the structure of one-half molecule of beta-carotene, a pigment found in almost all plants. It cannot be made by animals and must be present in the food or be made from plant carotene seems to be responsible for the growth toward light, and it also plays a role in photosynthesis, the process by which sun light and water are combined to produce organic nutrients. Remarkably, evolution has adapted this almost universal plant pigment to animal vision.

The eyes of vertebrates differ in some details, yet they are all build to a common plan. More is known about the human eye than about that of any other vertebrate, and it may therefore serve as an example. There are many different between animals eye and human eye.

Protecting the eyeball is a bony socket called the orbit. Each eye is suspended within its orbit and is surrounded by a cushion of fat and blood vessels and motor and sensory nerves, including the optic nerve. These are six small muscle attached to each eye to allow coordinated movement of the pair. The eyelids provide some protection in the front and also serve to keep the cornea lubricated by spreading the tear fluid with each blink, as well as an only fluid produced by Meibomian gland in the lid. The tear fluid is produced by the lacrimal glands near the outer portion of each eyebrow and is collected and drained through tiny canals within the upper and lower lids near the nose. The tears eventually flow into the nasal passages and are swallowed.