Corneal Topography: What It’s Used for Before Surgery
Dr. Guillermo Enríquez TostadoNovember 5, 20269 min read
In this article
Summary: The corneal topography for surgery is a test that creates a map of the shape and curvature of the cornea. Before refractive surgery or another procedure involving the cornea, it can provide information to assess eye anatomy, detect irregularities, and help determine whether surgery may be appropriate. However, a single image does not, by itself, confirm a diagnosis or automatically determine whether a person is a candidate.
What Is Corneal Topography?
The cornea is the transparent layer at the front of the eye and plays an important role in focusing light. Corneal topography uses imaging systems to measure mainly the curvature of its front surface and display the data using maps and color scales. According to the American Academy of Ophthalmology, EyeWiki: Corneal Topography, many devices use patterns of rings reflected on the corneal surface to estimate its characteristics.
Simply put, the test helps show whether the cornea has a relatively regular shape or has changes that require a more detailed evaluation. The colors on the map should not be interpreted as a universal sign of “good” or “bad”: they depend on the type of map, the scale used, the quality of the measurement, and the clinical context.
It is also important to distinguish between topography and corneal tomography. Topography primarily describes the front surface. Tomography can provide three-dimensional information, including the back surface and the distribution of corneal thickness. This difference may be relevant when evaluating the risk of ectasia or assessing candidacy for refractive surgery. A review published in Applications of corneal topography and tomography: a review describes these differences and their clinical applications.
Why might it be requested before surgery?
Before surgery, the specialist needs to consider several pieces of information: medical and eye history, eyeglass prescription, refractive stability, slit-lamp examination, the condition of the ocular surface, corneal thickness, and the characteristics of both corneas, among other factors.
Topography can help:
- •Describe the shape and regularity of the cornea.
- •Assess corneal astigmatism and its distribution.
- •Identify patterns that may warrant further evaluation.
- •Look for signs consistent with corneal irregularities, such as suspected keratoconus or ectatic degeneration.
- •Help plan some corneal procedures or treatments guided by the corneal surface.
In the evaluation for refractive surgery, the American Academy of Ophthalmology, EyeWiki: Preoperative Evaluation for LASIK Surgery notes that topography and tomography are part of the corneal analysis and that findings consistent with ectatic diseases may change or rule out the recommendation for certain procedures.
This does not mean that a topography scan alone “authorizes” or “prohibits” surgery. The decision should take into account the imaging findings, examination, symptoms, eyeglass prescription, eye health, and the procedure being considered.
What might the ophthalmologist look for on the map?
A professional analysis may include the symmetry of the cornea, the distribution of steeper or flatter areas, the regularity of astigmatism, and the relationship between different study parameters. In some cases, the equipment may flag patterns that warrant ruling out a condition such as keratoconus or a predisposition to corneal ectasia.
Keratoconus is a disease in which the cornea may become thinner and change shape. In early stages, some patients may have few symptoms or an apparently normal examination. For this reason, corneal imaging can be useful, although it does not eliminate diagnostic limitations. A review of tomographic parameters for detecting keratoconus notes that information about the posterior surface and full thickness may improve the ability to identify subtle changes, but also acknowledges that challenges remain in diagnosing early forms with certainty (Tomographic parameters for the detection of keratoconus).
In addition, an abnormal measurement does not always mean that a disease is present. Tear film quality, contact lens use, poor fixation during the test, accidental pressure on the eye, or incorrect alignment can affect the result. The American Academy of Ophthalmology, EyeWiki: Refractive Surgery Pearls in Topography describes several artifacts that can resemble certain corneal patterns.
Topography, Tomography, and Surgical Candidacy
- •Corneal topography — What it provides: A map mainly of the curvature of the front surface and corneal astigmatism. · What it cannot determine on its own: It does not, by itself, confirm a disease or determine whether surgery is safe.
- •Corneal tomography — What it provides: It may show the front and back surfaces, as well as a map of corneal thickness. · What it cannot determine on its own: It does not replace a clinical examination or an individual risk assessment.
- •Refraction and eyeglass prescription stability — What it provides: Helps identify the refractive error and whether it has remained stable. · What it cannot determine on its own: It does not, by itself, describe the cornea’s strength or overall shape.
- •Eye examination — What it provides: Allows assessment of the ocular surface, eyelids, natural lens, retina, and other aspects. · What it cannot determine on its own: It does not replace imaging studies when they are needed.
Taken together, these findings help determine whether surgery may be reasonable, whether additional tests should be requested, or whether alternatives should be discussed. In some cases, the conclusion may be that corneal surgery is not advisable, that it is better to wait until the measurements are confirmed as stable, or that a second specialist opinion should be sought.
Topography also cannot precisely predict how each person will see after surgery. Even with appropriate testing, symptoms may persist, optical correction may still be needed, or complications may occur. Risks and benefits depend on the procedure, the condition of the eye, and individual characteristics.
How is it performed, and what can affect the result?
The test is generally noninvasive and involves looking straight ahead while the device takes images of the cornea. It does not involve an incision. The test may take different amounts of time depending on the device and whether additional measurements are performed.
Contact lenses can temporarily change the shape of the cornea and affect the measurement. For this reason, the amount of time to stop wearing them before the test should be determined based on the type of lens, how long it has been worn, and the specialist’s assessment; there is no single time frame that applies to everyone. Dry eye, makeup residue, insufficient blinking, or loss of fixation can also affect the measurement.
If the result is uncertain or does not match the examination findings, the specialist may repeat the measurement or supplement it with tomography, pachymetry, an ocular surface evaluation, or other tests. Repeating the test does not necessarily mean that a disease is present; it may be a way to improve the reliability of the process.
Frequently asked questions
Does a normal corneal topography guarantee that I can have surgery?
No. The map may be reassuring, but candidacy depends on other factors, such as the refractive error, its stability, corneal thickness and biomechanics when evaluated, the ocular surface, age, overall health, and the type of surgery. The decision should be individualized.
Does an image with “irregular” colors mean I have keratoconus?
Not necessarily. Color scales vary among devices, and some artifacts can produce misleading patterns. A suspicious result should be reviewed along with the quality of the study, the examination, and, when appropriate, tomography or another evaluation. It is not advisable to make a diagnosis based on an isolated photograph or screenshot.
Is topography also useful for a second opinion?
It can be useful as part of the medical record, but a second opinion requires reviewing the complete study, not just the main image. It is helpful to ask which procedure is being proposed, what alternatives are available, which findings limit candidacy, and which risks are especially relevant in that case.
Conclusion
Corneal topography for surgery provides a map of the cornea’s shape and can help identify irregularities, assess astigmatism, and supplement the candidacy evaluation. It is most useful when interpreted along with the medical history, eye examination, refractive error, and other tests, especially when refractive surgery is being considered.
If you have a corneal study or are considering surgery, you can request an ophthalmology consultation to review your results comprehensively. A second opinion may be reasonable when there are uncertain findings, different surgical recommendations, or uncertainty about the alternatives.
If you would like an individual assessment, you can request information via WhatsApp.
References
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- •Applications of corneal topography and tomography: a review. Clinical & Experimental Ophthalmology.
- •Tomographic parameters for the detection of keratoconus: suggestions for screening and treatment parameters. Eye & Contact Lens, 2014.
This content is for informational purposes only and does not replace a medical consultation or constitute a diagnosis.
This information is for guidance only and does not replace a medical consultation, diagnosis, or treatment. Each case is assessed in person.
