Anterior segment OCT (AS-OCT) bleb imaging after Trabeculectomy and PreserFlo^TM MicroShunt: a prospective, multicentre, masked, quantitative interobserver analysis on bleb scarring.

Abstract

Purpose : Scarring is the leading cause of glaucoma surgery failure. Clinicians suspect bleb scarring with a postoperative rise in intraocular pressure. Current bleb grading systems show indirect signs of scarring but omit internal bleb evaluation. Our hypothesis is that bleb measurement by AS-OCT can help predict the risk of developing scarring.

Methods : 200 blebs (120 trabeculectomies, 80 PreserFlo, MMC 0.4 mg/ml) from 200 patients with primary open angle glaucoma were analysed by AS-OCT (Spectralis®, Heidelberg) at 4.1 ± 0.1 months post-surgery in 7 tertiary hospitals following a standardised protocol: sclera mode, ART 9 frames, 20x10°, 278 µm each, obtaining 21 scans starting at the limbus. One scan per eye with the highest bleb height was measured by two analysts masked from the clinical data, obtaining 7 measurements: maximum bleb height (BH), maximum wall height (WH), maximum cavity height (CH), maximum cavity length (CL), total bleb area (BA), total wall area (WA) and total cavity area (CA)(Fig 1). A Cox proportional hazards model tested the association of these measurements with the risk of bleb scarring during the first year, adjusting for ethnicity, gender and type of surgery.

Results : 39.5% of eyes developed bleb scarring during follow-up. A bleb with a CL<600 µm was associated with 2.9 times the risk of developing scarring during the first 12 months post-surgery (HR=2.92, 95%CI=0.20-0.56, p<0.0001) compared with CL≥600 µm, after adjusting for covariates. CA<60x10⁴ (HR=2.6, 95%CI=1.68-4.27, p=0.0001) and BA<80x10⁵ (HR=2.17, 95%CI=1.37-3.46, p=0.0007) were associated with 2 times the risk of scarring when compared with their counterparts, after adjusting. When CA was <20% of the BA, the risk of scarring doubled in contrast to CA≥20% of the BA (HR=2.16, 95%CI=0.26-0.80, p=0.027). Height measurements (BH, WH, CH) and WA were not associated with the occurrence of bleb scarring. Among covariates, only African ethnicity was associated with a higher risk of scarring (HR=2.4, 95%CI=0.45-1.37, p=0.001).

Conclusions : Bleb assessment by AS-OCT is a non-invasive and rapid clinical exam that can predict the risk of scarring during the first year post-surgery. It can be included in routine bleb assessment to evaluate its inner structure and inform patients on the risk of scarring and subsequent need for interventions.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.