Validity of the Monocular Trial of Intraocular Pressure-Lowering at Different Time Points in Patients Starting Topical Glaucoma Medication

IMPORTANCE Establishing the true therapeutic effect of eyedrops when initiating glaucoma therapy is important. Accurate prediction of the intraocular pressure (IOP)-lowering response in the fellow eye when using a monocular trial eliminates the need for additional office visits to confirm the therapeutic effect. OBJECTIVE To investigate the validity of the monocular trial in patients commencing topical glaucoma treatment at different time points. DESIGN, SETTING, AND PARTICIPANTS Prospective cohort study of untreated patients with open-angle glaucoma or ocular hypertension at a hospital-based glaucoma service among treatment-naive individuals. The study dates were October 1, 2008, to November 30, 2009. INTERVENTIONS Participants had 8 visits. After the recruitment visit, IOP was measured in both eyes by masked applanation tonometry at 8 AM, 11 AM, and 4 PM for 7 consecutive weeks. Treatment with travoprost, 0.004%, was commenced at week 3 in the trial eye and at week 4 in the fellow eye. MAIN OUTCOMES AND MEASURES Three IOP outcomes were measured for the trial eye, including unadjusted IOP-lowering effect, adjusted IOP-lowering effect, and true therapeutic effect. RESULTS Of 30 topical glaucoma treatment-naive individuals (11 male and 19 female), 16 had ocular hypertension and 14 had primary open-angle glaucoma. Their mean (SD) age was 64.4 (12.6) years (age range, 42-88 years). The unadjusted IOP-lowering effect overestimated the true therapeutic effect by mean (SD) 2.5 (4.8), 3.1 (3.8), and 4.9 (4.4) mm Hg at 8 AM, 11 AM, and 4 PM, respectively, and the mean (SD) adjusted IOP-lowering effect was almost identical to the true therapeutic effect at each of the 3 time points (0.43 [3.87], 0.02 [2.82], and -0.40 [3.90]), respectively. The correlation between the unadjusted effect of treatment and the true therapeutic effect was 0.55 (95% CI, 0.23-0.76), and the effect when adjusted by the monocular trial was 0.72 (95% CI, 0.49-0.86). Fellow eye responses to treatment were correlated at all time points (r range, 0.78-0.86). Treatment did not demonstrate any effect on the diurnal pattern of IOP. CONCLUSIONS AND RELEVANCE The monocular trial of therapy is effective in accurately predicting the response of an untreated eye to monotherapy with a prostaglandin analogue at all daytime time points measured. There is no requirement for patients to be seen at the same time of day after treatment has commenced. The effect in the first eye predicts both the likelihood and magnitude of an effect in the second eye at all time points during office hours and negates the requirement for an additional visit to check the therapeutic effect when commencing therapy in the second eye.