DOES THE CORNEAL CONFIGURATION OF THE EYES WITH NORMAL TENSION GLAUCOMA LEAD TO UNDERESTIMATION OF INTRAOCULAR PRESSURE ?

Abstract

[Purpose] The intraocular pressure (IOP) is the only parameter that distinguishes normal tension glaucoma (NTG) from primary open angle glaucoma (POAG). NTG may be misdiagnosed as a result of underestimation of IOP due to corneal configuration. Whether the corneal configuration of the eye with NTG can cause underes- timation of IOP was investigated. [Methods] The corneal thickness and curvature were measured in 57 eyes of 38 NTG patients, and the IOP measurements were corrected for corneal configuration using Ehlers' formula. The incidence of disc hemorrhage (DH) was compared between eyes with a high corrected IOP and those with a normal corrected IOP. [Results] Measurements of the corneal thickness and curvature in NTG eyes were similar to those in normal eyes. The corrected IOP was above the normal range (≧20 mmHg) for 12 eyes and remained normal (＜20 mmHg) for 45 eyes. DH did not develop in any of the eyes with a high corrected IOP, but did develop in 15 eyes with a normal corrected IOP (p ＜0.05). [Conclusions] Some cases of NTG can be misdiagnosed as a result of underestimation of IOP. The incidence of DH in eyes with an underestimation IOP suggests that the correct diagnosis may be POAG in some eyes.