Patients who present with evidence of previous or current primary angle-closure (PAC) need a prompt laser peripheral iridotomy (LPI) to avoid sight-threatening outcomes. But what about patients with narrow angles but no other symptoms? A new study suggests patients with a “triple hump” sign on anterior-segment optical coherence tomography (AS-OCT) may achieve significantly lower intraocular pressure (IOP) with an LPI.

Researchers in Korea used AS-OCT and IOP measurements to study 84 eyes of 84 PAC suspects before LPI. They defined the positive-triple hump group as those with “the characteristic configuration formed by the angulations between the crystalline lens’s central anterior surface and both sides of the iris pigment epithelium,” the study says. Two glaucoma specialists, masked to any other clinical data, separated AS-OCT images into positive and a negative triple hump groups.

The one-month post-LPI assessment revealed the positive triple hump group had significantly decreased IOP, an average of 1.19mm Hg, compared with the negative triple hump group, which had no statistically significant change in IOP.

The researchers speculate that, for the positive triple hump group, the “significant IOP reduction after one month indicated that the pressure gradient of the anterior and posterior chambers was eliminated, and pupil block resolved, by LPI.” The negative triple hump group, however, had no change in IOP post-op, suggesting pupil block didn’t play a role in the angle closure and “a pushing mechanism might be the key contributing factor” that may warrant lens extraction rather than LPI.

The triple hump sign was “a useful screening tool for discriminating ‘LPI responder’ cases from ‘LPI non-responder’ cases in PAC suspect eyes,” the researchers conclude. They further speculate the new AS-OCT sign may be a beneficial screening method for discriminating pupil block and phacomorphic angle-closure in PAC suspect eyes.

KI Na, A Ha, SU Baek, et al. Predicting the therapeutic efficacy of laser peripheral iridotomy for individuals with asymptomatic narrow angle: the triple hump sign. J Glaucoma. December 10, 2018. [Epub ahead of print].