Acute primary angle closure (APAC) can cause rapid, severe vision loss and even glaucoma-related blindness, yet there’s uncertainty over why some eyes with narrow angles are more susceptible to APAC than others despite similar triggers. Closing this gap, a recent study found that pharmacological pupil dilation worsened angle closure in half of untreated APAC patients with narrow angles.

This cross-sectional cohort study evaluated 106 patients over the age of 50—of which 93.4% were Chinese and 79.2% were female—with a diagnosis of APAC. Swept-source OCT captured 360-degree scans of the angles before and one hour after dilation. A team analyzed the angle scans to calculate the change in iris-trabecular contact index.

The researchers reported an overall mean pre-dilation index of 45.3% and post-dilation index of 46.1%, with a mean change of 0.78%. They noted that half the study eyes showed an increase in iris-trabecular contact index after dilation, adding that this angle narrowing was associated with a shallower anterior chamber and a bigger lens vault.

“Further research is needed to understand the pathophysiology of APAC and to help unravel why APAC occurs in some PAC suspects after pupil dilation,” the study authors concluded in their paper.