Temporal ocular coherence tomography-measured changes in anterior chamber angle and diurnal intraocular pressure after laser iridoplasty: IMPACT study

Abstract

Aims: To evaluate temporal change in anterior chamber angle anatomy following argon laser peripheral iridoplasty (ALPI) in eyes with occludable angles postlaser peripheral iridotomy (LPI) compared with control eyes. Additionally, the effect on diurnal intraocular pressure (DIOP) fluctuation (maximum-minimum IOP) was investigated.

Methods: Twenty-two patients with bilateral primary angle closure/suspects with gonioscopically occludable anterior chamber angles following LPI were randomised to receive ALPI (n=11) or no further treatment (n=11). Angle opening distance (AOD), trabecular-iris angle, angle recess area and trabecular-iris space area were measured over eight sections with swept-source anterior segment optical coherence tomography and DIOP was measured pre-LPI and repeated at 3 months after ALPI (hourly measures).

Results: All angle parameters increased following ALPI. This change was maintained for 3 months in seven of the eight sections (eg, inferotemporal AOD500 increased by 0.063 mm, p=0.004 at 1 day; 0.051 mm, p=0.029 at 1 week; 0.059 mm, p=0.006 at 6 weeks and 0.056 mm, p=0.011 at 3 months). The only exception was in the inferior sector (eg, AOD500 increased by 0.041 mm, p=0.025 at 1 day and by 0.029 mm, p=0.054 at 3 months). DIOP at 3 months was significantly reduced (5.04 mm Hg; ±1.61 mm Hg) compared with controls (6.61 mm Hg; ±1.63 mm Hg). Maximum IOP was significantly greater in the non-ALPI group (1.87 mm Hg, p=0.026).

Conclusions: ALPI widened all angle sections in eyes that remained occludable post-LPI. Changes were maintained for 3 months. ALPI decreased DIOP fluctuation in the treated eyes by lowering the maximum IOP value.

Keywords: Anterior chamber; Clinical Trial; Glaucoma; Imaging; Treatment Lasers.

Figure 1

Schematic of IMPACT study pathway. AC, Anterior Chamber, PAC, primary angle closure, PACS, primary angle closure suspects, LPI, laser peripheral iridotomy, ALPI, argon laser peripheral iridoplasty. Patients with angles no longer judged as occludable on gonioscopy following LPI (red outline) were excluded from further analysis of effect of ALPI from time of treatment.

Figure 2

Schematic representation of the eight iridotrabecular angle sections under study. Iridotrabecular angle parameters as measured with the Casia AS-OCT analysis software. AOD, angle opening distance, ARA, angle recess area, TISA, trabecular-iris space area, TIA, trabecular-iris angle at 500 and 750 μm are highlighted in bright green.

Figure 3

Changes in angle opening distance at 500 μm from scleral spur in all eight sections of the anterior chamber angle (11 eyes) in argon laser peripheral iridoplasty-treated eyes measured with swept-source optical coherence tomography in dark conditions.

Figure 4

Changes in angle opening distance at 750 μm from scleral spur in all eight sections of the anterior chamber angle (11 eyes) in argon laser peripheral iridoplasty-treated eyes measured with swept-source optical coherence tomography in dark conditions.

Figure 5

Temporal changes in angle parameters as visualised by SS-OCT. (A) Prior to argon laser peripheral iridoplasty (ALPI) treatment, (B) 1 month after ALPI treatment, (C) 3 months after ALPI treatment.

Figure 6

Intraocular pressure (IOP) measurements in treated (argon laser peripheral iridoplasty) and untreated eyes over 6 months, displayed as diurnal IOP (maximum-minimum IOP) and maximal and minimal IOP separately, y error bars indicate SE.