Corneal Topography

Corneal topography is a non-invasive imaging technique that creates a detailed map of the surface curvature of the cornea—the clear front window of the eye. It helps diagnose and monitor conditions like astigmatism, keratoconus, and corneal irregularities.

Why It's Done

Corneal topography is performed to:

• Evaluate astigmatism—regular vs. irregular
• Screen for keratoconus and other corneal ectasias
• Plan refractive surgery (LASIK, PRK)
• Fit specialty contact lenses
• Monitor corneal ulcer healing and scarring
• Assess corneal shape after surgery or injury
• Evaluate corneal transplant outcomes

What to Expect

Before the Test

• Remove contact lenses ahead of time (soft lenses: 1-2 weeks; rigid lenses: 3-4 weeks before refractive surgery evaluation)
• No special preparation for routine topography
• No eye drops are needed

During the Test

1. Sit comfortably with chin on the chin rest
2. Look at a target (usually a central fixation light)
3. The instrument projects rings of light onto your cornea
4. A camera captures the reflected pattern
5. The computer generates a map from the reflections
6. Both eyes are typically tested
7. Takes approximately 5-10 minutes total

After the Test

• No recovery time needed
• Resume all normal activities immediately
• Results are available right away
• No side effects

Understanding Results

Color-Coded Maps

Topography maps use colors to represent curvature:

Color	Meaning
Cool colors (blue/green)	Flatter areas
Warm colors (red/orange)	Steeper areas
Uniform colors	Regular corneal shape
Irregular patterns	Corneal irregularity

Common Patterns

Normal Cornea:

• Symmetric bowtie pattern
• Slightly steeper centrally
• Regular, smooth contours

Regular Astigmatism:

• Symmetric bowtie pattern
• Steepest and flattest meridians 90° apart
• Correctable with glasses or standard contacts

Irregular Astigmatism:

• Asymmetric or skewed patterns
• May indicate keratoconus or corneal scarring
• Often requires specialty contact lenses

Keratoconus:

• Inferior steepening
• Asymmetric bowtie
• Progressive thinning and protrusion

Corneal Topography vs. Other Corneal Tests

Test	What It Measures
Corneal topography	Front surface curvature
Corneal tomography (Pentacam)	Front and back surface + thickness
Corneal pachymetry	Corneal thickness only
OCT	Cross-sectional corneal layers

Frequently Asked Questions

Is corneal topography the same as corneal tomography?

No. Topography maps only the front surface of the cornea. Tomography (such as Pentacam) maps both front and back surfaces and also measures corneal thickness, providing more comprehensive information.

How often do I need corneal topography?

Frequency depends on your condition. For stable conditions, annual testing may be sufficient. For progressive conditions like keratoconus or after surgery, more frequent testing may be needed.

Will I need this test before cataract surgery?

Often yes. Corneal topography helps your surgeon select the best intraocular lens and plan the surgical approach, especially if you have astigmatism.

Can I wear contacts before the test?

For routine monitoring, your doctor may test with your usual lens wear schedule. For refractive surgery evaluation, contacts must be removed well in advance because they temporarily reshape the cornea.

Is the test safe?

Yes. Corneal topography is completely non-invasive. No instruments touch your eye, no drops are used, and there are no risks or side effects.