ABOUT YOUR EYES AND VISION

ABOUT YOUR EYES

Vision is the most complex of the five senses, a result of sensory reception and intellectual judgment. Light rays enter the eye's pupil and register on the retina at the back of the eye, to create two-dimensional images. These images are then converted into electrical impulses, that are transported through the eye's optic nerve to parts of the brain—in particular the occipital lobe—where they are interpreted.

Structure of the Eye

The eye is composed of two spheres; the front sphere is smaller, more curved, and transparent and is called the cornea. The posterior sphere is a white opaque fibrous shell called the sclera. The cornea and sclera encase the eye and form a protective covering. Inside this protective covering are the iris, ciliary body and choroid. The choroid is a vascular structure that supplies the nourishment to the inner aspect of the eye. The lens of the eye is located behind the iris and is responsible for focusing the light rays onto the retina. The retina, which is really part of the brain, is located in the posterior aspect of the eye adjacent to the choroid. . The retina contains sensory receptors that convert the light images to electrical impulses that are then transmitted via the optic nerve to the brain.

The Cavities of the Eye

Both the anterior and posterior chambers of the eye's front cavity are filled with aqueous humor, a fluid that provides oxygen, glucose, and proteins. The back cavity of the eye is filled with a clear gel, called vitreous humor. These humors contribute to the constant internal pressure that maintains the shape of the eye.

ABOUT YOUR VISION

Normal Vision

Light enters the eye and is refracted (bent) by both the cornea and the lens to focus the light rays onto the retina.

Myopia

Myopia, commonly known as nearsightedness, is a common eye condition, where patients can see objects close to them quite clearly or even perfectly. In a myopic individual distant objects —a street sign, a movie screen, a crowd, even the big "E" on old-fashioned eye charts—may be blurred or indistinct.

In a myopic patient the light rays entering the eye are not focused on the retina, rather they are focused in front of the retina.

Myopia is easily corrected with prescription glasses, rigid or soft contact lenses, or a variety of new surgical refractive procedures, such as LASIK.

Hyperopia

Hyperopia, commonly known as farsightedness, is perceived to be the opposite of myopia. Farsighted patients have difficulty seeing objects close at hand - a book, a computer screen, keys - in sharp focus. In addition, depending on the degree of farsightedness and the age of the patient, they may also experience difficulty in seeing distant objects.

In hyperopia, the light rays are focused behind the retina. In individuals under the age of 40 the eye's accommodative ability is usually able to refocus the light rays on the retina and thus the image is in focus without the need of refractive correction.

Hyperopia can be corrected with glasses, contact lenses or surgical refractive procedures.

Astigmatism

Astigmatism is another quite common condition, one which patients may have in addition to myopia or hyperopia. Astigmatic patients may have difficulty in seeing both distant and near objects. Like myopia and hyperopia astigmatism can be corrected with glasses, contact lenses or refractive procedures.

Presbyopia

Presbyopia is a natural byproduct of the aging process and commonly occurs when patients reach their forties. It is the difficulty an individual experiences in changing his or her focus from distant objects to near ones. Thus patients may experience difficulty in reading.

Presbyopia can be corrected with reading glasses, bifocal contact lenses, or glasses.