Laser peripheral iridotomy (LPI) increases the angle opening and flattens the iris in patients suspected of having primary angle closure, according to a China-based study published in Frontiers in Medicine.

In China, the prevalence of primary angle-closure suspicion is significantly higher than primary angle-closure or primary angle-closure glaucoma. LPI is a treatment option for primary angle-closure suspect patients because it can increase the width of the anterior chamber by establishing a channel, relieving the pupil block, and flattening the iris plane, according to researchers. However, LPI is controversial, and the treatment’s ability to induce an angle opening is not consistent, the report explains. 

Researchers investigated the changes in anterior segment parameters after LPI using ultrasound biomicroscopy (UBM). The study included 100 primary angle-closure suspects. Anterior segment UBM parameters were measured, and AOD750 was used to indicate the width of the angle associated with gonioscopic angle closure. Investigators found that all angle parameters increased after LPI, including the mean angle opening distance at 750 µm (AOD750), mean angle opening distance at 500 µm from the scleral spur (AOD500), mean angle opening distance at 750 µm from the scleral spur (AOD750), and mean angle recess area at 750 µm from the scleral spur (ARA750).


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Among iris parameters and ciliary body parameters, the iris thickness at 2000 µm (IT2000), iris curvature (IC), and trabecular-ciliary process distance (ICPD) were reduced after LPI. Researchers developed an equation to predict the width of the angle after LPI. The equation consisted of four parameters: anterior chamber depth (ACD), iris thickness at 750 µm from the scleral spur (IT750), AOD750, and lens vault (LV). This equation explained 42.7% of the variability in the angle opening indicator AOD750 after LPI. According to the findings, in the plateau iris configuration subgroup, the accuracy of the prediction equation reached the highest maximum of 68.6%.

Researchers note several limitations to their study, including using AOD750 as the standard, inter-observer variability regarding gonioscopy, basing the equation on univariable and multivariable linear regression equations, and that nonstandardized UBM gain parameters may affect the accuracy, reproducibility, and further analysis of the results.

Reference

Gao X, Zhou Y, Zuo C, et al. Predictive equation for angle opening distance at 750 µm after laser peripheral iridotomy in primary angle closure suspects. Front Med. Published online August 12, 2021. doi:10.3389/fmed.2021.715747