What is the structure of the human eye?

The eyeball is an ovoid sphere, around the size of a ping-pong ball, of 1" in length. It consists of a clear cornea with a variable-sized opening, a pupil and a lens. Basically, it has three coats behind: (I) A firm white protective layer, the sclera; (II) A layer of blood vessels, supplying nutrition to the eye; (III) The all-important retina. The nerve fibres of the retina collect together and pass out of a hole in the white of the eye, behind, forming the optic nerve.

Light enters via the clear cornea, its intensity modified by the variable-sized opening of the pupil, and is focused by the lens on the retina.

What is the range of vision of an eye?

Virtually infinite. The eye can see in bright sunshine and in almost total darkness, covering a brightness range of 10 million to 1. The eye has no distance limitation and can see up to infinity. You look up at the night sky and see a galaxy so far away that the light may have taken thousands of years to travel down to our planet. Without much trouble the eye can also see objects only a few inches from your face in great detail.

Is the brain the controller of the eye?

A camera can only reproduce what it sees. The control of the eye, its movement, focus, and evaluation of details jointly with its partner eye require constant effort by the brain to maintain the required coordination. After all, the eye only essentially converts light into electrical impulses. It takes the brain to translate the impulses into a close-knit coherent picture.

Do I see better keeping the eyes stationary or letting them move around?

The eyes are in almost constant movement and yet we see the world as a stable entity. The visual cells in the retina respond best to continuous change—change in contour, shape, orientation or brightness. As an experiment, keep your eyes fixed at an object. Gradually you will notice that the scene around the object you are looking at will start blurring and fading. A quick flick and the world slides into its proper perspective.

The ability to recognise an object depends upon rapid eye movement termed as scanning. To recognise an object, say, a motorcycle, the eye quickly moves over it, deciphering and comparing it in the mind with a known pattern before recognition occurs. Often it can be misleading.

Dustin Flores

Copyrighted material; do not reprint without permission.

 

View all articles by Dustin Flores