To evaluate critically visual field (VF) improvement in participants in the Collaborative Initial Glaucoma Treatment Study (CIGTS).

Prospective, comparative case series from a randomized clinical trial comparing trabeculectomy and topical medications in treating open-angle glaucoma (OAG).

A total of 607 subjects with newly diagnosed OAG were identified for study. Baseline and follow-up VF tests were obtained and mean deviation (MD) change from baseline over follow-up was analyzed. Clinically substantial change (loss or improvement) was defined as change from baseline of ≥3 decibels in MD. Baseline factors were inspected to determine their association with VF improvement in repeated measures regression models.

The percentage of participants showing substantial VF improvement over time was similar to that showing VF loss through 5 years after initial treatment, after which VF loss became more frequent. Measures of better intraocular pressure (IOP) control during treatment were significantly predictive of VF improvement, including a lower mean IOP, a lower minimum IOP, and lower sustained levels of IOP over follow-up. Other predictive factors included female sex (odds ratio [OR] = 1.73), visits 1 year prior to cataract extraction (OR = 0.11), and an interaction between treatment and baseline MD wherein surgically treated subjects with worse baseline VF loss were more likely to show VF improvement.

In the CIGTS, substantial VF loss and improvement were comparable through 5 years of follow-up, after which VF loss became more frequent. Predictive factors for VF improvement included several indicators of better IOP control, which supports the postulate that VF improvement was real.