OUR EYE

The human eye is a complex sense organ whish has evolved over the ages from a primitive light sensitive spot on the surface of simple prehistoric animals. It is among the most versatile of nature's accomplishments.

HOW THE EYE WORKS :

The sense of sight is one of the five senses with which most human beings are endowed. Sight, like the other senses, requires more than just the eye. There must be light by which we see an object, and our brain must interpret what is seen. Light striking an object to the eye. The light rays pass through the cornea (or clear front window), the aqueous (or watery liquid behind the cornea), the pupil (or opening in the colored iris). the lens, and the vitreous. The cornea and the lens of the eye bend the light rays as they pass through and focus them on the retina (or rear inner lining of the eye), which contains approximately 127 million light sensitive rod and cone cells. These cells have fibers which extend to make the optic nerve.

The eye has been well-described as a camera which automatically adjusts to different levels of light and focuses light on the 'camera film' or retina of the eye. Retinal cells then send electrochemical impressions of the light ray image through several processing layers, and then through the optic nerve to the brain. As with a camera, the image is received upside down because the lens inverts it, but as a life long habit, the brain interprets it correctly, and we see objects right side up.
 

COMMON ERRORS OF REFRACTION:

Nearly every person has some type of refractive error or other slight ocular imperfection of focusing. These errors are clinically significant when they produce blurring which might cause symptoms and require corrective lances. Generally, each person can accommodate to compensate for minor refractive errors. Focusing occurs by the changing of the shape of the lance by contraction or relaxation of the ciliary muscles.
 

MYOPIA (Near-Sightedness):

In Myopia, the eye ball is usually larger or longer than average so that light is focused at a point in front of the retina. The symptom of Myopia is inability to see clearly in the distance without lances. Myopia may be present at birth, but usually becomes evident during growth or the early years of school. It may particularly progress during active periods of growth so that new lances, like larger shoes, are required periodically. After adolescence, when the child stop growing, Myopia usually becomes stationary. Contact lances do not slow or alter the progression of Myopia.
 

HYPEROPIA (Far-Sightedness):

In Hyperopia, the eye ball is usually shorter or smaller so that light would be focused at a point behind the retina. The normal ability to accommodate, however, provides enough refractive power to enable many far-sighted person to see at a distance, particularly while young. Because of this abilities, until approximately age 40, correction of moderate Hyperopia is usually unnecessary. Until discomfort is noted and doing close work. 

In children, uncorrected Hyperopia may cause the eyes to cross. Glasses for distance often correct this crossing without surgery.
 

ASTIGMATISM (Irregular Curvature of Cornea):

Most optical surfaces in cameras, telescopes and other precision instruments have spherical surface curves that are equal and symmetrical in all meridians. Unfortunately, the human cornea offten lacks this perfection and is may be more curved in one direction. Such unequal curvature of surfaces create 'astigmatism' or distortion in the focus of light rays, resulting in blurred vision. Generally it is possible to compensate for astigmatism with spectacles or contact lenses. In extreme cases, surgery such as a corneal transplant, may be required in order to produce good vision.
 

PRESBYOPIA:

As people grow older, particularly after the age of 40, the lens becomes less elastic, thus decreasing the ability to accommodate or focus for near vision. Glasses, usually bifocals, compensate for this decreased ability to focus for near. The vision of aging, or presbyopia, is added to any pre-existing refractive errors such as Myopia, Hyperopia or Astigmatism.