Effect of surgical intraocular pressure lowering on retinal structures - nerve fibre layer, foveal avascular zone, peripapillary and macular vessel density: 1 year results

Abstract

Objectives: To determine the effect of surgical intraocular pressure (IOP) lowering on peripapillary retinal nerve fibre layer thickness (RNFL), fovea avascular zone (FAZ), peripapillary and macular vessel density (VD) in glaucoma using with optical coherence tomography angiography (OCT-A).

Methods: This was a prospective observational study performed at the Glaucoma Research Centre, Montchoisi Clinic, Lausanne. In total 40 eyes with open-angle glaucoma were included. OCT-A scans were performed before glaucoma surgery, and at 1-month, 3-month, 6-month, and 12-month post-operatively. AngioVue AngioAnalytic (Optovue Inc, Fremont, CA) software was used to analyse the RNFL, FAZ, peripapillary and macular VD. Changes were analysed using analysis of variance (ANOVA) models.

Results: Mean IOP dropped from 19.4 (±7.0) mmHg pre-surgery and stabilized at 13.0 (±3.1) mmHg at 12 months (p < 0.001). The number of topical medications reduced from 2.2 (±1.2) preoperatively to 0.4 (±0.8) at 1 year (p < 0.001). Peripapillary RNFL thickness was transiently increased at 1-month postoperatively (p = 0.03). Peripapillary VD fluctuated throughout the follow-up. Foveal VD showed increased perfusion at 3 and 6 months post-operatively with minimal changes at 1 month (p < 0.01). Glaucoma surgery had a significant effect initially on FAZ area (p = 0.03), FAZ perimeter (p = 0.02) and Acircularity Index (AI) (p = 0.04). By 12-months FAZ measurements had reversed to baseline values.

Conclusions: Peripapillary and macular microcirculations responded differently to surgically induced IOP reduction. Peripapillary microcirculation was IOP-independent within the studied range of surgically-controlled IOP. Macular microcirculation, however, exhibited a "delayed response" followed by near-normal reperfusion after glaucoma surgery. FAZ parameters could be potentially useful modalities to assess vascular reperfusion after glaucoma surgery as, amongst all studied parameters, the area was the most sensitive to surgically induced IOP changes.

Fig. 1

Shows the delimitation of scan regions for peripapillary retinal nerve fibre layer (RNFL, top), peripapillary vessel density (VD, middle) and macular vessel density (VD, bottom) scans

Fig. 2

A flowchart of the excluded eyes following study enrolment

Fig. 3

a shows the mean intraocular pressures preoperatively and at 1 month, 3 months, 6 months and 12 months after surgery. b shows the mean number of topical anti-glaucoma medications per patient, preoperatively and at 1 month, 3 months, 6 months, and 12 months after surgery. c shows mean retinal nerve fibre layer (RNFL) thickness preoperatively and at 1 month, 3 months, 6 months, and 12 months after surgery. d shows peripapillary vessel density (VD) preoperatively and at 1 month, 3 months, 6 months, and 12 months after surgery. e shows foveal VD preoperatively and at 1 month, 3 months, 6 months, and 12 months after surgery. f shows the parafoveal vessel density (VD) preoperatively and at 1 month, 3 months, 6 months, and 12 months after surgery. g shows the perifoveal vessel density (VD) preoperatively and at 1 month, 3 months, 6 months, and 12 months after surgery. h shows the fovea avascular zone (FAZ) surface preoperatively and at 1 month, 3 months, 6 months, and 12 months after surgery. Vertical dotted lines represent standard error of means. Asterisks represent statistically significant inter-visit differences (p < 0.05). ANOVA showed no statistically significant variations of the parameters where no asterisks are present