How The Eye Functions

To better understand refractive surgery, one should understand how the eye focuses light. The eye functions on the same principle as a camera.

The Iris

The iris, or colored portion of the eye, acts as a shutter to regulate the amount of light admitted into the eye.

The Cornea

The cornea (the clear window of the eye) and the lens, located behind the pupil, serve to focus the light rays from the object viewed onto the retina.

The Retina

The retina is a thin structure in the back of the eye that captures the image of light and processes it to be sent to the brain for the interpretation of what we are seeing.

If the light rays do not come to a pinpoint focus on the retina, the patient has what is called a refractive error.

What is Refractive Error?

For many people the focusing power of the cornea, combined with the length of the eye, does not allow the light rays to come to a pinpoint focus on the retina They focus either in front of or behind the retina causing a blurred image. This is called a "refractive error".

Myopia (Nearsightedness) The corneal curvature is too steep so the light rays focus in front of the retina.

Hyperopia (Farsightedness) The corneal curvature is too flat so the light rays focus behind the retina.

Astigmatism The corneal curvature is oval instead of spherical causing a distortion of images. Astigmatism can occur along with myopia or hyperopia.

Presbyopia

After age 42 it becomes progressively more difficult to focus on near objects. If you had not previously needed glasses you would now need reading glasses. If you did wear glasses you would now need two prescriptions, i.e. one for distance and one for reading.

Refractive errors have traditionally been treated with eyeglasses or contact lenses. Refractive surgery is that subspecialty of ophthalmology that aims to decrease or eliminate refractive errors. The most commonly performed refractive surgery procedure is LASIK.