Asymmetry of habitual 24-hour intraocular pressure rhythm in glaucoma patients

To examine the strength of association between 24-hour rhythms of habitual IOP in the paired eyes of healthy individuals and glaucoma patients.

Laboratory records of 24-hour habitual IOP from 38 younger healthy individuals, 53 older healthy individuals, and 41 untreated older primary open-angle glaucoma patients were examined. Intraocular pressure was measured every 2 hours sitting during the day and supine at night using a pneumatonometer. Rhythms of 24-hour IOP in the right eye and in the left eye were estimated separately using cosinor rhythmometry. Estimated 24-hour IOP peak timing (acrophase) and estimated 24-hour IOP variation (amplitude) were compared between the paired eyes for each subject group. Strength of association was determined by the absolute time interval between paired 24-hour IOP peak timings and by the coefficient of determination (r(2)) between paired 24-hour IOP variations.

Mean absolute time intervals between the paired IOP peak timings were 1 hour and 33 minutes in the younger healthy group and 1 hour and 37 minutes in the older healthy group. In the older glaucoma group, the mean absolute time interval was 2 hours and 30 minutes. Coefficient of determination for the paired 24-hour IOP variations in the older glaucoma group was 0.343, significantly lower than the coefficients of determination in the younger healthy group (0.571) and the older healthy group (0.646).

The strength of association between the paired 24-hour rhythms of habitual IOP is significantly weaker in glaucoma patients than in healthy individuals.