Changes in anterior chamber angle morphology and diurnal intraocular pressure fluctuation following Argon Laser Peripheral Iridoplasty for angle closure, measured with Swept-source Ocular Coherence Tomography: the IMPACT Study (NIHR ID: CCRN 8955)

Abstract

Purpose : To evaluate temporal change in anterior chamber angle anatomy following argon laser peripheral iridoplasty (ALPI) in eyes with gonioscopically occludable angles post laser peripheral iridotomy compared to eyes receiving no further treatment. Additionally, the effect of ALPI treatment on diurnal intraocular pressure (DIOP) fluctuations (maximum-minimum IOP) was investigated.

Methods : Twenty-two patients newly diagnosed with bilateral primary angle closure (PAC) or as primary angle closure suspects (PACS) whose anterior chamber angles remained gonioscopically occludable following a superiorly sited laser peripheral iridotomy (LPI) were recruited and randomised to receive ALPI (n=11) or no further treatment (n=11). Angle opening distance (AOD), trabecular–iris angle (TIA), angle recess area (ARA), and trabecular–iris space area (TISA) were measured over 8 sections with swept source anterior segment optical coherence tomography (AS-OCT) at pre-determined intervals and DIOP was measured at baseline pre-LPI and repeated at 3 months after ALPI (hourly measures during office hours).

Results : There was an increase in all angle parameters following ALPI. This change was maintained for 7 of the 8 sections (e.g. temporal segment AOD500 increased by 0.063 mm, p=0.004 at 1 day; 0.051mm, p=0.029 at 1 week; 0.059 mm, p=0.006 at 6 weeks; and 0.056mm, p=0.011 at 12 weeks). The only exception was observed in the inferior sector, where an initial significant widening was noted which regressed by 12 weeks (e.g. AOD500 increased by 0.041 mm, p=0.025 at 1 day and by 0.029 mm, p=0.054 at 12 weeks). DIOP at 12 weeks was significantly reduced in the post ALPI group (5.04 mmHg; ±1.61 mmHg) compared to the eyes that did not receive ALPI (6.61 mmHg; ±1.63 mmHg). Peak IOP was significantly greater in the non-ALPI group (1.87 mmHg, p=0.026).

Conclusions : ALPI resulted in widening of all angle parameters in eyes that remained gonioscopically occludable post-LPI. The changes were maintained for 12 weeks, with the exception of the inferior segment where some regression in widening was observed. ALPI decreased DIOP fluctuation in the treated eyes by lowering the peak IOP value.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.