IOP and Pachymetry Adjustment
The Goldmann baseline
Goldmann applanation tonometry (GAT) is calibrated around an average central corneal thickness (CCT) of approximately 545 microns. The force required to applanate the cornea reflects both true intraocular pressure and corneal biomechanics. Meaningful deviation in CCT can bias measured IOP, so pachymetry is important when risk stratifying glaucoma suspects and patients with ocular hypertension.
Thin and thick corneas in clinical practice
Thin corneas: Thinner corneas offer less resistance to applanation and can produce falsely low IOP readings. This is common after refractive surgery and in congenitally thin corneas. A patient may appear to have a normal IOP while still carrying higher glaucoma risk based on optic nerve findings or progression.
Thick corneas: Thicker corneas often require more force to flatten and can yield falsely elevated IOP readings, which is a common reason patients are labeled with ocular hypertension. CCT is also a risk marker. Thinner CCT is associated with higher risk in major glaucoma studies, while thicker CCT is relatively protective. Use both the measured IOP and the clinical context before starting or withholding therapy.
Use nomograms as a guide, not a verdict
Nomograms and correction tables provide a rough framework, but they assume a simple relationship between corneal thickness and stiffness. That assumption can fail in eyes with altered biomechanics such as corneal edema (thick but soft), keratoconus, post-LASIK ectasia, or significant surface disease. In these settings, any corrected IOP should be treated as an estimate. When available, additional information such as corneal hysteresis, serial OCT and optic nerve assessment, and visual fields often guide long-term decisions more reliably than a single adjusted IOP value.