The IOP correction calculator adjusts an intraocular pressure measured by applanation tonometry for the central corneal thickness, using a correction factor per 10 microns around a reference thickness.
How the calculation works
- Enter the measured pressure and the corneal thickness.
- Enter the reference thickness and the correction factor.
- Read the corrected pressure and the correction.
Example
A pressure of 21 mmHg with a thickness of 590 µm is 45 µm above the reference of 545 µm. With 0.25 mmHg per 10 µm the correction is 4.5 × 0.25 = 1.12 mmHg, giving a corrected pressure of 19.9 mmHg.
Why it matters
The calculator helps optometry and ophthalmology students, ophthalmic technicians and patients who want to understand why their pressure and corneal thickness are measured together.
Good to know
No correction formula has been validated for clinical use, and the Goldmann reading itself varies with the cornea’s rigidity, curvature and hydration, which are not captured by the thickness alone. Several studies show that adjusted values do not predict glaucoma better than the measured values, but the thickness stays an important independent risk factor, and ocular hypertension treatment studies used it. Most clinicians therefore interpret the measured pressure and the thickness together, without computing a corrected figure. Other tonometers, such as dynamic contour or rebound devices, are less affected by the cornea. This page is educational only and gives no diagnosis or treatment advice. Corneal thickness also changes with age, with corneal disease and after refractive surgery, so a single correction factor cannot be trusted in these cases. The treatment target is set by the ophthalmologist from the optic nerve and the visual field, not from the pressure alone.
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The keratometry calculator treats corneal curvature, the visual acuity calculator converts notations, the mean arterial pressure calculator treats blood pressure and the spherical equivalent calculator converts prescriptions.