Diurnal variation of Intraocular pressure in suspected normal-tension glaucoma

Purpose: To assess diurnal variations of intraocular pressure (IOP) in suspected normal-tension glaucoma (NTG) patients with subsequent long-term observation to detect changes that may lead to a new diagnosis. Methods: Diurnal variation of IOP was measured in a sitting position at 2-h intervals for 24h in a total of 569 subjects with suspected NTG. Results: Thirty of the 569 subjects (5.3%) showed IOP values exceeding 20mmHg during the 24-h monitoring and were diagnosed as having primary open-angle glaucoma (POAG). In subjects in whom NTG was definitely diagnosed based on the results of the 24-h monitoring, the average maximum, minimum, and mean IOP was 16.1, 11.7, and 13.9 mmHg, respectively, and the mean diurnal variation in IOP was 4.4 mmHg. The peak time was observed outside clinic hours (1800-0800) in 41.4% of patients, and the trough time was observed during clinic hours (1000-1600) in 15.9%. In 2.9% of NTG subjects, the diagnosis was eventually changed to POAG during follow-up. Conclusion: Assessment of diurnal variations of IOP in suspected NTG patients is useful for the differential diagnosis of POAG from NTG and for establishment of a baseline, which may affect the management plan.