Ocular coherence tomography-measured changes over time in anterior chamber angle and diurnal intraocular pressure after laser iridotomy: IMPACT study

Importance: The change in the anatomical dimensions over time and the effect on diurnal intraocular pressure following laser peripheral iridotomy is poorly understood. Background: To evaluate change over time in anterior chamber angle anatomy following laser peripheral iridotomy (LPI) in patients with primary angle closure compared to control eyes. Additionally, the effect of LPI on diurnal intraocular pressure (DIOP) fluctuation was investigated. Design: Longitudinal, prospective, double-randomised research study. Participants: Adults with suspected angle closure or angle closure diagnosis referred to hospital services in the United Kingdom. Methods: Thirty-nine patients newly diagnosed with bilateral primary angle closure/suspects (PAC/PACS) received LPI to one eye and changes in angle morphology were measured over 8 sections with swept source AS-OCT. The other eye acted as control with intraocular pressure (IOP) measured hourly. Main outcome measures: Angle opening distance (AOD), trabecular–iris angle (TIA), angle recess area (ARA), and trabecular–iris space area (TISA) at 500 m and 750 m from scleral spur Results: There was an increase in all angle parameters following LPI, which was maintained for 6 months (e.g inferotemporal segment AOD500 0.041mm (p=0.008) at 1 week and 0.039mm (p=0.003) at 6 months) following LPI. Greatest effect at 6 months post-LPI was observed opposite the iridotomy site in the inferior/inferotemporal sections (AOD500 0.039mm, p=0.003 and AOD750 0.075mm, p=0.002). There were no statistically significant differences for the overall DIOP fluctuation values in the treated group at 6 months post-LPI compared to baseline. Conclusions and Relevance: LPI widened all angle sections with maximum effect observed in the site opposite the iridotomy. Angle changes were maintained up to 6 months after LPI treatment without any statistically significant change in DIOP fluctuation.