Corneal Topography: What the Map Shows & Why It Matters

What topography maps

A topographer projects rings or a grid of light onto the cornea and analyses the reflections to calculate curvature at thousands of points. The result is a colour-coded map: cooler colours (blues and greens) represent flatter areas; warmer colours (oranges and reds) represent steeper areas.

Regular vs irregular patterns

\n
• Regular astigmatism — a symmetric "bow-tie" pattern; usually correctable with ordinary glasses.
\n
• Irregular patterns — asymmetric or skewed steepening, the hallmark of keratoconus and other ectatic change.
\n

Key uses

Keratoconus screening and monitoring

Topography — and especially tomography, which also images the back corneal surface and thickness — can reveal keratoconus years before symptoms or slit-lamp signs. Serial maps document whether the condition is progressing, which is the key input for cross-linking decisions.

LASIK and refractive surgery planning

Before any laser vision correction, maps confirm the cornea is regular and stable. Early ectatic change is a contraindication to LASIK; missing it risks worsening the cornea. This is why "your eye power alone does not decide your LASIK eligibility" — the map matters as much as the number. More on eligibility.

Other uses

\n
• Fitting rigid and scleral contact lenses
\n
• Evaluating irregular astigmatism after surgery, injury or transplantation
\n
• Guiding suture removal after corneal grafts and assessing cataract-surgery astigmatism
\n

What to expect during the test

The test takes a few minutes per eye: you rest your chin, look at a light target, and the instrument captures the images without touching the eye. Contact lens wearers may be asked to stop lenses for a period beforehand, because lenses temporarily mould the cornea and distort the map. The educational graphics on this site are illustrative; your own maps are interpreted by your doctor in clinical context.

Information on this page is for general education and does not replace an examination, diagnosis or personalised medical advice from a qualified eye-care professional.

Related treatments & topics