Accuracy of intraocular pressure (IOP) measurement depends on the biomechanical properties of the cornea, including its thickness central corneal thickness (CCT) and keratometry (K). Fifty-six eyes of 56 patients with primary open angle glaucoma (POAG) who had a history of refractive corneal surgery (RCS) were included in this retrospective observations study over a period of six years. Intraocular pressure was measured with Goldmann Applanation tonometry (GAT) and this measurement (uncorrected) was corrected by using two formulas (Kohlhaas and Elhers). Glaucoma progression was determined by optic disc photographs and visual field tests. Thirty-four percent of eyes with previous history of RCS showed progression during a mean follow-up period of 4.3 years. Incidence of glaucoma progression was higher in the group with IOP of 15mmHg or higher, compared to ‘low-teen’ IOP. Many eyes in the low-teen group before IOP correction for RCS moved to the high-teen group after correction. The authors conclude that there is a possibility of underestimating true IOP (and therefore inadequately treating patients) if monitoring relies on uncorrected IOP. Furthermore, for glaucomatous eyes with prior history of RCS, more intensive IOP-lowering treatment would be required in eyes with IOP in the high teens.