Eye Function

​​​​​Normal Eye

The cornea and lens of the eye focus light like a camera lens to form an image on the retina at the back of the eye. The cornea, where light first enters the front of the eye, provides about two-thirds of the eye’s focusing power, and the lens inside the eye provides one-third.

Nearsighted Eye

Some eyes focus, or refract, the light too much so the images of distant objects are formed in front of the retina, and the image on the retina is blurred. This condition is called nearsightedness or myopia. Myopia usually starts in childhood and gets progressively worse through adolescence. It usually stops changing by the late teens, but it can sometimes continue to get worse into the middle 20s.

Nearsightedness can be corrected by any method that reduces the total refractive power of the eye. Eyeglasses and contact lenses do this by putting in front of the eye negative lenses that are thicker at the edge than in the center. Refractive surgery corrects nearsightedness by flattening the central part of the cornea to reduce the total refractive power of the eye.

Farsightedness

In farsightedness, the image focuses beyond the retina. In our youth, the natural accommodating (focusing) power of the eyes often compensates for farsightedness. As we age, our eyes become less able to accommodate. For this reason, farsightedness most commonly becomes a problem later in life. Many farsighted eyes do not need correction until the individuals reach their 40s or 50s. Farsightedness can be corrected by any method that increases the total refractive power of the eye. Eyeglasses and contact lenses do this by putting in front of the eye positive lenses that are thicker in the center than at the edge. Refractive surgery corrects it by making the central part of the cornea more steeply curved.

Astigmatism

Astigmatism corrections bring all rays of light from different focal points to one focal point. Astigmatism may be all myopic (nearsighted), hyperopic (farsighted) or a combination of both (mixed).

Refractive surgery corrects astigmatism by altering the central cornea by different amounts at different radial orientations to correct for the uneven focus of light rays.

Presbyopia

Presbyopia is a normal age-related change that occurs with a weakening in our focusing systems. This usually begins in our late 30s and progresses through our mid to late 50s. The optical lens becomes less elastic and loses its ability to change focus for up close objects. Presbyopia will occur regardless of refractive surgery options.