Abstract
Purpose: :
The one–eye drug trial for intraocular pressure (IOP) lowering medications assumes the concordant fluctuation of the IOP between the eyes. Our objective was to determine the diurnal variation and concordance of IOP in normal tension glaucoma (NTG) patients.
Methods: :
A retrospective review was performed on 273 NTG patients with diurnal curves performed at the University of Iowa. NTG was defined as glaucomatous nerve or visual field changes with IOP ≤ 21 mmHg. Subjects were excluded with: glaucoma surgery, trauma, use of anti–glaucoma or steroid medications, uveitis or secondary glaucoma. The IOPs were measured using Goldmann applanation tonometry at 10:00, 13:00, 16:00, 19:00, 22:00 and 07:00. The linear association of OD and OS IOP over the 6 time points was estimated using the average Pearson correlation coefficient (r). Linear mixed model analysis for repeated measures, with Eye and Time as the within subject fixed effects, was used to test if the mean change in the IOP over time differs between OD and OS. For the analysis of concordance, the diurnal period was divided into seven time intervals of 3, 6, 9, 12, 15, 18 and 21 hours and the probability that the difference in the change in IOP between OD and OS over a given time interval was no more than 2 mm Hg was calculated.
Results: :
95 subjects (32 males and 63 females; average age 62.2±14.9) with NTG were included in the analysis (mean pooled IOP 15.5 mmHg). The minimum IOP occurred at 22:00 (OD 14.19±0.28; OS 14.29±0.26) and the maximum at 7:00 (OD 16.02±0.29; OS 16.22±0.27). The average correlation of OD and OS IOP was r=0.81 (95% CI: 0.76, 0.84). There was no significant Eye*Time interaction (p=0.20) implying that the diurnal curves of the OD and OS are parallel. The probabilities (95% CI) that the difference in the change in IOP between OD and OS was within 2 mmHg over 3, 6, 9, 12, 15, 18 and 21 hour intervals were 87 (83–90), 81 (75–86), 86 (81–89), 84 (78–89), 83 (74–89), 84 (75–90) and 77% (68–85) respectively.
Conclusions: :
The probability of < 2 mmHg difference in the change in IOP between OD and OS during a diurnal cycle is approximately 80% in NTG. The diurnal variation in IOP between the two eyes in NTG is largely concordant. The results support the use of one–eye trial for determining the efficacy of IOP–lowering medications in NTG.
Keywords: intraocular pressure