Incidence of Occludable Angles in a High Risk Mongolian Population

Abstract

Purpose: : To determine the 6 year incidence of occludable angles in a high risk Mongolian population from a nested cohort study, and to ascertain ocular risk factors at baseline associated with the development of occludable angles.

Methods: : In 1999, 644 participants aged ≥50 years with a central anterior chamber depth (ACD) of <2.53mm underwent full slit lamp examination including Goldmann intraocular pressure (IOP), gonioscopy and optic disc assessment. Evidence of glaucoma had been excluded in all subjects. A cut–off point of 2.53mm yielded a sensitivity of 77% and a specificity of 83% for the detection of occludable angles.160 participants with occludable angles(ISGEO classification for use in epidemiological studies) were excluded from further analysis, leaving 484 for follow up. Six years later, 95/484 (19.6%) had died. 201/389 participants traced (51.7%) were re–examined using the same equipment. Differences in baseline cup–disc ratio (CDR) between subjects who did and did not attend for re–examination were analysed to assess the effect of bias on the results. The effect of age, gender, limbal chamber depth (LCD) grade, baseline ACD, change in ACD, baseline IOP, and baseline angle width on the development of an occludable angle was assessed using chi squared test, t–test or the Wilcoxon rank sum test.

Results: : At follow up, 41 participants (20.2%, 95% CI: 14.6–25.8) were diagnosed with occludable angles without evidence of raised IOP or peripheral anterior synechiae. There was no difference in median CDR between those attending and not attending for re–examination (0.3, IQR: 0.2–0.4 in both groups, p=0.49). Narrower angles, identified by grading of LCD and gonioscopy at baseline, were strongly associated with incident occludable angles (p=0.01 and p<0.01 respectively). There was weak evidence of an association with change in ACD (p=0.05), and no evidence of an association with age, gender, and baseline ACD for the development of occludable angles.

Conclusions: : 20.2% of subjects with an ACD<2.53mm developed occludable angles over 6 years. The similarities in baseline CDR mitigates the effect of bias due to the loss to follow up. The finding of narrower angles as determined by LCD grading and gonioscopy at baseline was the main risk factor identified for the development of occludable angles.

Keywords: clinical (human) or epidemiologic studies: prevalence/incidence • clinical (human) or epidemiologic studies: natural history • clinical (human) or epidemiologic studies: risk factor assessment