Randomised Controlled Trial of Screening for Primary Angle Closure Glaucoma in Mongolia

Abstract

Purpose: : To determine if screening for angle closure and treatment with prophylactic laser iridotomy reduces the incidence of primary angle closure glaucoma (PACG).

Methods: : 4597 Mongolian adults aged ≥50 with no evidence of glaucomatous optic neuropathy (GON) were randomized to screening with ultrasound anterior chamber depth measurement (<2.53 mm = test positive) or no intervention (control arm). All had baseline optic disc photographs. Subjects testing positive underwent full slit lamp examination and those found to have iridotrabecular contact in ≥270° of the angle on gonioscopy were offered bilateral iridotomies. At 6 yr follow up participants were traced and examined to determine incident cases of PACG in each arm of the study. GON was identified by clinical examination of the optic disc, grading of disc photographs by masked graders and threshold visual field testing using the levels of evidence (structural + functional, structural only) for glaucoma diagnosis according to the ISGEO classification. Sensitivity analysis using multiple imputation was used to examine the effects of missing data.

Results: : At baseline 156 subjects in the intervention arm were treated with iridotomies. Six years later, 801 participants (17.4%) were known to have died, 2047 (53.9% of those believed still alive) were traced and examined at follow up. Numbers of cases of PACG identified for each level of evidence and identification method are shown in the table. Overall incidence of PACG was 1.9%. There was no statistically significant difference in the number of PACG cases identified for each arm of the trial. Analysis using imputed data also demonstrated a null effect.

Conclusions: : We could not identify any benefit of screening for angle-closure using ACD measurement and prophylactic laser iridotomy in this study. Limited response to follow-up was a concern.

Clinical Trial: : www.ISRCTN.org 20194450

Keywords: clinical (human) or epidemiologic studies: treatment/prevention assessment/controlled clinical trials • laser • anterior chamber