Importance of intraocular pressure measurement at 6:00 a.m. in bed and in darkness in suspected and glaucomatous patients.

PURPOSE To assess the importance of intraocular pressure measurement obtained at 6:00 a.m. in bed and darkness for the diagnosis and intraocular pressure control of primary open-angle glaucoma. METHODS Retrospective analysis of the daily curve of intraocular pressure of suspects and glaucomatous patients under treatment. Suspects were classified as intraocular pressure values ranging from 19 to 24 mmHg in isolated measurements and/or cup/disc ratio > 0.7 in one or both eyes and/or asymmetry of cup/disc ratio > 0.3 and a normal visual field. Each daily curve of intraocular pressure comprised five to seven IOP measurements with Goldmann applanation tonometer at 9:00 a.m., 12:00 p.m., 3:00 and/or 6:00 and 10:00 p.m. and/or 12:00 a.m. and in the following day morning at 6:00 a.m. in supine position in bed and in darkness with Perkins tonometer before the patient had stood up. Only the daily curves of intraocular pressure that presented an intraocular pressure peak (difference between the higher and the lesser intraocular pressure value) >6 mmHg were analyzed. In these daily curves, the average intraocular pressure and the standard deviation were calculated. The average intraocular pressure and standard deviation values were compared with the normal superior limits: average + two standard deviation of average intraocular pressure and standard deviation of intraocular pressure daily curve from normal patients of the same age group. Daily curves were considered abnormal when their average intraocular pressure and standard deviation values were above the normal superior limits. Secondary and congenital glaucoma were excluded. RESULTS Daily curves of intraocular pressure of 565 eyes were analyzed; 361 suspected eyes and 204 eyes with primary open-angle glaucoma. In suspects, 64.3% presented an intraocular pressure peak at 6:00 a.m. in bed. In primary open-angle glaucoma, 68.6% presented an intraocular pressure peak at 6:00 a.m. in bed. In 5.3% of the suspects and in 5.9% of primary open-angle glaucoma patients, the daily curve of intraocular pressure profile was inverted (lesser intraocular pressure at 6:00 a.m.). CONCLUSION Intraocular pressure peaks at 6:00 a.m. were responsible for the diagnosis of preperimetric glaucoma in 64.3% of suspects and revealed inadequate intraocular pressure control in 68.6% of eyes with primary open-angle glaucoma. The daily curve of intraocular pressure including the intraocular pressure measurement at 6:00 a.m. in bed and in darkness is of vital importance in doubtful cases in order to confirm the diagnosis of preperimetric glaucoma in suspects as well as for the adequate intraocular pressure evaluation of antiglaucomatous treatment.