Seasonal variation in intraocular pressure

Generally speaking, physicians have the impression that intraocular pressure (IOP) in winter is higher than in summer, but it is very difficult to evaluate the difference between summer and winter IOP statistically, because the treatments of glaucoma patients are changed according to their conditions. We compared the winter and summer IOP of normal subjects and of several glaucoma patients who had no therapy or no change in therapy. The subjects were divided into four groups, i.e., 20 eyes of the normal group, 17 eyes of the ocular hypertensive group, 24 eyes of the primary open angle glaucoma group, and 52 eyes of the low tension glaucoma group. The difference in mean IOP between summer and winter were evaluated for each subject. In all groups, the mean difference in mean winter IOP was significantly higher. The ups and downs of IOP were greater in the ocular hypertensive group and the primary open angle glaucoma group than in the normal group and the low tension glaucoma group. These results suggest that the seasonal variation of IOP should be taken in consideration when treating glaucoma patients.