Corneal Topography

What is corneal topography?

Corneal topography is a painless test that produces color-coded maps of your cornea. Your cornea is the clear, outer surface of your eye. It has a slightly curved shape that refracts (bends) light as it enters your eye, allowing you to see the world around you. Corneal topography evaluates the shape of your cornea to diagnose and manage various eye conditions.

The word “topography” usually refers to surface features on land (like mountains or rivers), or maps that describe those features. So, you might wonder what this term has to do with your eyes.

Think of your cornea as a miniature version of a sprawling stretch of land. Like land, your cornea can be smooth or dotted with bumps or other unusual features. On land, you can spot trees or elevation changes. But you normally can’t see such surface features on your cornea. That’s where corneal topography comes in. This technology allows eye care specialists to map and measure your cornea, including its thickness and elevation changes.

Corneal topography is the gold standard for mapping subtle changes in your cornea that occur suddenly or over time. Computerized corneal topography is another name for this test.

What is corneal topography used for?

Corneal topography serves many purposes. This test helps eye care specialists:

• Diagnose and monitor conditions that affect your cornea.
• Plan for surgery on your cornea and evaluate the surgery’s results.
• Fit contact lenses to the shape of your eyes.

Diagnosing and monitoring conditions

Corneal topography plays an essential role in diagnosing and checking the progression of:

• Astigmatism.
• Keratoconus.
• Pellucid marginal degeneration (PMD).
• Scarring from injuries or infections.
• Growths, such as pterygium (surfer’s eye).

Surgical planning and evaluation

Corneal topography allows providers to identify issues that could affect the success of certain eye surgeries. For example, this test can diagnose conditions like keratoconus in the early stages, even before you have symptoms. People with keratoconus face a higher risk of complications after refractive eye surgeries such as LASIK.

Corneal topography helps providers plan:

• Refractive surgery, such as LASIK or PRK, to correct your vision.
• Cataract surgery to replace your eye’s natural lens with an intraocular lens.
• Cornea transplant to give you a new cornea.
• Corneal cross-linking surgery to treat keratoconus and other conditions that weaken your cornea.

Fitting contact lenses

Corneal topography provides precise measurements of your cornea. These measurements allow your provider to find the best fit for contact lenses. They’re especially helpful for fitting rigid gas-permeable (RGP) lenses. These are hard, durable contacts that help people with irregularly shaped eyes or conditions like keratoconus.

Who needs corneal topography?

You may need corneal topography if:

• You’d like to have laser refractive surgery (like LASIK). This test is a crucial part of pre-operative evaluations to make sure you’re a good candidate for the surgery. Underlying problems with your cornea can lead to complications after your surgery.
• You need surgery to treat corneal disease. This test helps your provider plan your surgery to give you the best possible outcomes.
• You’ve already had surgery. Providers use this test to evaluate the results of your surgery.
• You need contact lenses. This test allows your provider to fit contact lenses to the shape of your eyes. Such testing is especially important if your corneas have an irregular shape.

Who performs this procedure?

An eye care specialist, often an ophthalmologist, performs corneal topography.

How do I prepare?

You typically don’t need to do anything to prepare for this test. However, your provider will tell you if you need to stop wearing your contact lenses for a while before the test. Over time, contacts can temporarily change the shape of your cornea (corneal warpage). So, you may need to stop wearing them for several weeks to gain the most accurate measurements of your cornea.

How is corneal topography done?

Corneal topography is quick and painless. You can think of it as a specialized photo shoot for your eyes. Here’s what to expect:

1. You sit in front of a device that looks like a large bowl.
2. You rest your forehead and chin in designated spots.
3. You stare at a point inside the bowl as the device captures images of your eyes.
4. The device converts these images to a series of color-coded maps.

The whole process takes just a couple of minutes. You feel no pain, and the device never touches your eyes.

What can I expect after the test?

Your provider will discuss the results of your test at your exam or at a follow-up appointment. They may show you the maps and explain what they mean.

What are the risks of this test?

This is a safe test with no known risks. The test is painless and quick, and the device doesn’t touch your eyes.

What do the results mean?

Your corneal topography test produces a series of maps that display colors and numbers. These maps show the surface features of your cornea, including spots where your cornea is steep or flat. The test can produce many different types of maps, depending on what your provider needs to learn.

Common maps include:

• Axial map (sagittal map): This is the type of map providers use most often. It shows the curvature of your cornea, or what you might think of as the peaks and valleys. Warm colors like red and orange show steep areas. Cool colors like green and blue show flatter areas. The map also shows numbers that measure the curvature. Normal corneal topography on an axial map is mostly green.
• Elevation map: This map compares your cornea to a “best fit” reference. It tracks elevation, or how much your cornea curves outward. Warm colors and positive numbers indicate your cornea’s measurements are higher than the reference. Cool colors and negative numbers indicate they’re lower than the reference. There’s one map for the anterior (front) surface of your cornea and another map for the posterior (back) surface.
• Corneal thickness map (pachymetry map): This map shows the thickness of your cornea. There’s no one thickness cutoff for a healthy vs. unhealthy cornea, but significant thickening or thinning can be abnormal. Certain conditions like keratoconus cause thinning of your cornea. On this map, cool colors show thick areas of your cornea. Warm colors show thinner areas of your cornea.

Corneal topography interpretation involves analyzing the colors and the numbers. Your provider will interpret the results and explain to you what they mean.

When should I call my doctor?

Call your provider if:

• You have any questions or concerns about the test results.
• You have new or worsening symptoms.

A note from Cleveland Clinic

Corneal topography is a valuable test that shows the landscape of your eyes. It’s quick and painless, and it provides a wealth of data that helps your provider plan the best possible care for you. Talk to your provider if you have questions or concerns about the test results or any aspect of your eye health.