Corneal Pachymetry: A Prerequisite for Applanation Tonometry?

Herndon et al¹ found increased corneal thickness in patients with ocular hypertension; the authors concluded that such patients have only apparent, as opposed to true, elevated intraocular pressure. Conversely, decreased corneal thickness has been measured in patients with normal-tension glaucoma.^2- 3 The implication of these and other studies is that corneal thickness cannot be ignored in the diagnosis and management of glaucoma or even perhaps with any given applanation reading. Goldmann applanation tonometry is an imperfect method for measuring intraocular pressure. Indeed, pachymetry adds another dimension to the spectrum of intraocular pressure abnormalities (Figure 1). Thus, we have "thick cornea pseudo-ocular hypertension" vs "normal cornea ocular hypertension" and "thin cornea pseudonormal-tension glaucoma" vs "normal cornea normal-tension glaucoma." Hopefully, these terms will never find their way into the already confusing glaucoma nomenclature. Rather, clinicians will use applanation tonometry values corrected for central corneal thickness to obtain a better estimate of the true intraocular pressure.