Corneal Topography

an eye doctor reviewing a corneal topography map

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Corneal topography is a procedure used to monitor and measure changes that may occur to the shape and integrity of the cornea of your eye.

A corneal topographer projects a series of illuminated rings, referred to as a Placido disc, onto the surface of the cornea. The rings are reflected back into the instrument.

After analyzing the reflected rings of light, the computer generates a topographical map of the cornea. The images produced by the topographer can be helpful for your eye doctor when analyzing the health of your eyes.

About the Cornea

The cornea is the transparent dome-shaped tissue covering the iris and the pupil. The cornea provides two-thirds of the refracting power to the eye. The cornea is a remarkable piece of tissue made up of specialized cells.

There are no blood vessels in the cornea to nourish it. The cornea gets most of its nourishment directly from the tears on the surface of the eye and through the aqueous humor (a fluid that fills the back chamber of the eye) from inside the eye. Because the cornea is like a lens, it must be completely transparent, as blood vessels would interfere with the focusing process.

What Corneal Topography Reveals

Corneal topography gives a wealth of information about the eye in different areas, including the following:

Keratometry

Before computerized corneal topographers were invented, a keratometer was used to measure a small area in the central cornea. It gives the healthcare provider two measurements about the steepness of the cornea.

A keratometer is older technology but you will still find at least one device in every healthcare provider's office today. However, corneal topography has revolutionized corneal shape analysis. Instead of just measuring two points, a corneal topographer can measure hundreds and even thousands of data points to build a much more precise color map of the overall steepness of the eye in any location the healthcare provider is interested in.

A color map is generated showing steeper areas in red and flatter areas in blue. This is not only important in the overall shape, but it will tell the healthcare provider more precisely how much astigmatism (imperfection in the curvature of the eye) you have.

Elevation Maps

Corneal topographers can also show elevation maps. Elevation maps help the healthcare provider see unusual spots on the cornea that are different than normal. Some software displays a 3-dimensional image that the healthcare provider can rotate to get a better understanding of what may be occurring with the cornea.

Contact Lens Fitting

Your eye doctor wants your contact lenses to fit your eyes as well as possible, so knowing the exact shape of your cornea is extremely important. Contact lenses that are too tight may constrict normal tear flow, creating an unhealthy environment for normal cell function. On the other hand, fitting a lens that is too loose may allow for excess movement of the lens on your eye, causing discomfort and possibly damaging the epithelial cells.

Wearing contact lenses requires a great deal of responsibility, by you and by your healthcare provider. You must be diligent in following proper cleaning routines and wearing schedules. Your healthcare provider must closely monitor small changes in your eyes in order to avoid potentially serious contact-related complications.

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  • Elliott, David B. Clinical Procedures in Primary Eye Care, Pp 115-116. Elsevier Limited, 2003.