Monocular trial of intraocular pressure-lowering medication: a prospective study

Abstract

Objective: To investigate the validity of the monocular therapeutic trial of therapy in patients commencing topical glaucoma treatment.

Design: Prospective intention-to-treat cohort study of untreated patients presenting with open-angle glaucoma or ocular hypertension.

Participants: We included 30 treatment-naïve subjects.

Intervention: All subjects had 8 visits at which intraocular pressure (IOP) was measured by masked Goldmann tonometry. After the recruitment visit, IOP was measured in both eyes at 11 am for 7 consecutive weeks. At week 3, travaprost (0.001%) was commenced in the eye with the higher IOP and at week 4 travaprost was also commenced in the fellow eye.

Main outcome measures: Three IOP outcomes were measured for the trial eye: (1) Unadjusted IOP-lowering effect (difference between recruitment IOP and first IOP on treatment); (2) adjusted IOP-lowering effect (unadjusted effect - [difference between IOPs at the same visits in the fellow eye]); and (3) true therapeutic effect (mean difference between 3 baseline pretreatment IOPs and 3 IOPs on treatment).

Results: Mean recruitment IOPs were 28.2 and 26.0 mmHg in the trial and fellow eyes, respectively. The mean baseline IOPs were 25.8 and 22.7 mmHg in the trial and fellow eyes, respectively, indicating that regression to the mean was responsible for 2.4 and 3.3 mmHg, respectively, in the trial and fellow eyes. The unadjusted treatment effect (11.7 mmHg) overestimated the true effect (8.6 mmHg) by a mean of 3.1 mmHg, whereas the mean adjusted IOP was almost identical to the true effect. The correlation between the unadjusted effect of treatment and the true effect was 0.55, whereas the effect when adjusted by the monocular trial was 0.72.

Conclusions: In our cohort of patients with bilateral IOPs >21 mmHg at baseline, the monocular trial provides a significantly more accurate estimate of the therapeutic response when initiating prostaglandin monotherapy in untreated eyes. It is particularly helpful in avoiding overestimation of effectiveness and so reducing the number of patients on inadequate treatment.

Financial disclosure(s): The authors have no proprietary or commercial interest in any of the materials discussed in this article.