Central Corneal Thickness and IOP: Why There Is No Correction Formula
Last updated: October 2026
Short answer: Goldmann tonometry assumes an average corneal thickness, so thin corneas read falsely low and thick corneas falsely high. However, there is no reliable formula to "correct" IOP for central corneal thickness (CCT). Use CCT as a risk factor (thin CCT increased glaucoma risk in OHTS) rather than as a correction, and remember that corneal biomechanics also matter.
How CCT affects tonometry
| Cornea | Goldmann reading | Example |
|---|---|---|
| Thin | Underestimates true IOP | Thin corneas, after myopic LASIK or PRK |
| Thick (healthy) | Overestimates true IOP | Some "ocular hypertension" patients with thick corneas |
| Thick but oedematous | Often underestimates | Corneal oedema makes the cornea softer despite being thicker |
Why not use a correction formula?
- Many correction formulas have been proposed, but none is accurate enough for individual patients.
- The relationship between CCT and measured IOP is not linear and varies between people.
- Corneal stiffness and hysteresis affect readings independently of thickness.
- Applying a formula can give a false sense of precision. Treat the patient, not a corrected number.
CCT as a risk factor
- In the Ocular Hypertension Treatment Study, a thinner CCT was an independent risk factor for developing glaucoma.
- Use CCT, together with IOP, age, disc appearance and other factors, when deciding whether to treat ocular hypertension.
- Measure CCT at least once in every glaucoma suspect and glaucoma patient, and after corneal refractive surgery.
Corneal hysteresis
- Corneal hysteresis (measured with the Ocular Response Analyzer) reflects the cornea's ability to absorb and release energy.
- Lower hysteresis has been associated with a higher risk of glaucoma progression.
Alternative tonometers
- Dynamic contour tonometry and corneal-compensated IOP measurements are designed to be less dependent on corneal properties.
- Rebound tonometry (for example, iCare) is useful in children and at home, but is also affected by corneal properties.
- Use the same tonometer for follow-up whenever possible.
Frequently asked questions
Should IOP be corrected for corneal thickness?
No validated formula is accurate enough for individual patients. Use CCT as a risk factor and interpret IOP readings with it in mind, rather than applying a correction.
Is IOP falsely low after LASIK?
Yes. After myopic laser refractive surgery the cornea is thinner and Goldmann tonometry tends to underestimate IOP. Record pre-operative IOP and CCT if possible.
Why is thin CCT a risk factor for glaucoma?
Thin corneas lead to IOP being underestimated, and thin CCT was also an independent risk factor for developing glaucoma in OHTS.
Related: target IOP, refractive surgery and landmark trials.
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