The lowering of intraocular pressure (IOP) remains the only proven method to prevent the development, or slow the progression, of glaucomatous optic neuropathy.¹ Unfortunately, patients with seemingly well-controlled, office-measured IOP may still go on to develop glaucomatous visual field progression.

Several explanations exist for glaucomatous progression in the setting of well-controlled office-measured IOP. However, one must also consider the possibility that office-measured IOP may not accurately represent a given patient’s 24-hour IOP profile and that glaucomatous damage may occur during times of undetected increases in IOP. Mosaed et al² evaluated the correlations between office-hour IOP and peak nocturnal IOP in 68 nonglaucomatous eyes and 35 glaucomatous eyes. The correlation between a single office-hour sitting IOP and peak nocturnal IOP measurements was moderate in glaucomatous eyes (r = 0.557, P < .001) and even less in age-matched nonglaucomatous eyes (r = 0.351, P < .001). The majority of peak 24-hour IOP values (67.2%) in habitual body positions in glaucomatous patients occurred at night. Results of this study suggest that a single office-measured IOP may not be a sufficient indicator of a given individual’s 24-hour IOP profile. The finding that peak IOP occurs at night in the majority of glaucomatous patients is of clinical importance because peak IOP has been shown to be a strong predictor of glaucomatous progression.³