IOP Adjusted for Corneal Thickness
Ophthalmology
Three published nomograms side by side.
How it is calculated
- Goldmann applanation assumes a cornea of about 520 µm. A thicker cornea resists flattening and over-reads; a thinner one under-reads.
- Ehlers (1975): 0.7 mmHg per 10 µm away from 520 µm.
- Dresden, Kohlhaas (2006): about 0.42 mmHg per 10 µm away from 550 µm — the familiar "1 mmHg per 25 µm" rule, published as ΔIOP = −0.0423 × CCT + 23.28.
- Doughty and Zaman (2000): 0.2 mmHg per 10 µm away from 535 µm in normal corneas, and about 0.5 mmHg per 10 µm in eyes with chronic ocular disease.
- The three disagree by several mmHg at the extremes of corneal thickness, which is why this tool prints all of them rather than choosing one.
- The Ocular Hypertension Treatment Study found that adjusting IOP for corneal thickness did not improve prediction of who goes on to develop open-angle glaucoma. Corneal thickness is treated as a risk factor in its own right, not as a number to subtract from the reading.
References
- Ehlers N, Bramsen T, Sperling S. Applanation tonometry and central corneal thickness. Acta Ophthalmol 1975;53:34-43.
- Kohlhaas M, et al. Effect of central corneal thickness, corneal curvature, and axial length on applanation tonometry. Arch Ophthalmol 2006;124:471-476.
- Doughty MJ, Zaman ML. Human corneal thickness and its impact on intraocular pressure measures. Surv Ophthalmol 2000;44:367-408.
- Brandt JD, et al. Adjusting intraocular pressure for central corneal thickness does not improve prediction models for primary open-angle glaucoma. Ophthalmology 2012;119:437-442.
About these tools
OcuLearning Clinical Tools is part of an educational platform. These calculators are provided for learning and reference, and are not medical advice, a diagnosis, or a treatment recommendation.