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Editors Selection IGR 7-2

Intraocular Pressure: Modified dark room provocative test

Comment by Paul Foster on:

28093 Modified dark room provocative test for primary angle closure, Li D; Wang N; Wang B et al., Journal of Glaucoma, 2011; Epub ahead of print

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This cross-sectional study by Li et al. (227) reports on the use of anterior segment OCT imaging (after three minutes of dark adaptation) in eyes of Chinese people known to have narrow angles, to identify those that experience a rise in IOP ≥ 8 mmHg after 1.5 hours of darkness. The end point from imaging was any contact between iris and and angle wall anterior to the scleral spur. Participants in the study were enrolled if aged > 40 years, a van Herick grade of ≤ 1/4 corneal thickness and either anterior trabecular meshwork alone or no trabecular meshwork visible on gonioscopy in the dark. Synechial angle closure was an exclusion criterion. The study included data on 76 eyes of 76 people aged 56 to 78 years, two thirds of who were women. In 30% of the AS-OCT images, the exact location of the scleral spur could not be determined. This underlines one significant limitation of AS OCT in quantifying extent of angle closure.

With a positive test result defined as one in which there was a rise in intraocular pressure by ≥ 8 mmHg after 1.5 hours of dark adaptation, the question which remains unanswered by this study is how useful is that rise in IOP in the dark as a marker of angle-closure disease. Without a control group with 'open' angles, this question remains tantalizingly unclear. In the 1960's, Ron Lowe expressed the opinion that provocative tests using intraocular pressure as an end point were time-consuming, frequently misleading, and potentially dangerous. Without a control group to demonstrate the validity of using an IOP rise in the dark to define significant, pathological angle closure, it is uncertain what the results of this current study mean.

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