Topography of the Eye

Topography of the eye is also called corneal topography or videokeratography. It is a computer-assisted method of mapping the surface curvature of the cornea, a clear membrane covering the front of the eye and accounting for approximately 70 percent of the eye's focusing power. Much like making a map of land, corneal topography creates a detailed description of the cornea's shape. It is used to diagnose, evaluate, monitor and treat several visual diseases and injuries.

Conditions of the Cornea

• The cornea is sometimes referred to as the front window of the eye. When an eye has normal vision, the cornea is evenly rounded. When the cornea is uneven, too flat or too steep, vision is less than perfect. This often results in someone only needing corrective lenses. However, the cornea is also vulnerable to abrasions, curvature abnormalities and diseases and conditions that cause cloudy vision, permanent swelling of the cornea and thinning and weakening of its central region.

Purpose of Testing

• Corneal topography is not a standard, routine test offered by ophthalmologists. When a patient undergoes this test, it is because certain conditions or diseases are suspected or may have already been diagnosed and require monitoring. Corneal topography is also used to evaluate corneal deformities, an irregular astigmatism in patients who have undergone corneal transplants, and sometimes in the fitting of contact lenses. It is frequently used in preparation for refractive eye surgery, combined with other testing to ascertain precisely how much corneal tissue will be removed to correct the visual defect.

How It Works

• Corneal topography uses a computer that is linked to a lighted bowl containing a pattern of concentric rings. Using imaging technology and software, it produces a detailed, three-dimensional view of the cornea's shape. This view is referred to as a map and uses different colors to identify the elevations of the cornea's shape. It is similar to a topographic map of the earth that shows variations and changes in the land surface.

What to Expect

• Corneal topography is a noncontact test. Brief and painless, it requires the patient to sit in front of the bowl that contains the ring pattern and press his head against a support bar. Using normal light to photograph the surface of the eye, a series of data points are generated on a placido disk (an instrument specific in examining corneal curvature) that has been projected onto the cornea.

Advantages

• Before corneal topography was available, several tests and a lot of time were required to photograph and calculate the cornea's shape. Besides its advent allowing for faster and more effective diagnostic benefits, it's most important advantage is that it can expose conditions that remain invisible under conventional types of testing.