Intraocular pressure measurement in keratoconus: a narrative review

Accurate measurement of intraocular pressure (IOP) is essential for the diagnosis and treatment of glaucoma. Keratoconus (KC) is an ectatic corneal disease, which evolves with progressive non-inflammatory thinning and is characterized by irregular astigmatism, and alteration of corneal biomechanics. There are many doubts regarding the best method to measure IOP in patients with KC, and, as far as we know, there are no manometric studies in patients with KC. It seems that IOP measurements made by Goldmann applanation tonometry (GAT) probably underestimate the real values in patients with KC. With the aim of obtaining more accurate measurements of IOP in KC, new devices were developed such as dynamic contour tonometry (DCT), ocular response analyzer (ORA) and corneal visualization scheimpflug technology (Corvis-ST). Possibly, DCT, corneal-compensated IOP (IOPcc)-ORA, and biomechanical corrected IOP (bIOP)-Corvis-ST can reduce some inaccuracies in IOP measurements related to thinning central corneal thickness and other biomechanical changes present in these patients. The different IOP measurement methods in KC are not interchangeable. Therefore, in KC we must always monitor IOP using the same device during follow-up. Furthermore, it is necessary to carefully study possible structural and functional changes that may occur in suspected cases of glaucoma.