Evaluation of blebs after glaucoma filtering surgery with en face anterior segment optical coherence tomography

Abstract

Purpose: To compare bleb characteristics following filtering surgery in functioning blebs (FB) and non functioning blebs (NFB) with en face optical coherence tomography (OCT).

Methods: In this observational case series, we retrospectively evaluated 34 filtering blebs of 28 patients after at least 1 month of a first-time trabeculectomy. Patients who underwent needling or combined surgery were excluded. All blebs were evaluated with en face anterior segment spectral OCT (OCT RTVue®, Corneal Adaptator Module, Optovue Inc, Fremont, CA, USA). Preoperative, intraoperative and postoperative medical records were collected including slit-lamp examination, applanation tonometry, an evaluation of glaucoma severity, and the number, type and duration of antiglaucoma medications). Eyes were classified into 2 groups: FB [18 eyes, intraocular pressure (IOP) < 21 mmHg without glaucoma medication], and NFB (16 eyes, IOP> 21mmHg or IOP< 21mmHg with glaucoma medications). En face OCT images were analyzed for the number of intraepithelial microcysts and were graded semi-quantitatively from 0 (no microcyst) to 3 (numerous microcysts). Blood vessels, internal fluid filled cavity, conjunctival fibrosis and visualization of the scleral flap were also analyzed. Correlations between en face OCT features and clinical data were assessed.

Results: FB presented more intraepithelial microcysts than NFB: 17% were graded 3, 39% were graded 2, and 44% were graded 1. NFB were graded 0 in 82% and 1 in 18% of cases. None of the FB were rated 0 and none of the NFB were rated 2 or 3. A higher mean IOP was associated with a lower number of intraepithelial microcysts: 25 mmHg, 17 mmHg, 13.4 mmHg, 13.3 mmHg for grading 0, 1, 2 and 3 respectively. The frequent and long-term administration of antiglaucoma eyedrops before surgery was associated with fewer intraepithelial microcysts. Mean duration of treatment before surgery was 9, 6.6, 4.8 and 3.8 years for rating 0, 1, 2, and 3 respectively.

Conclusions: FB were associated with a higher number of intraepithelial microcysts on en face OCT images. A higher density of microcysts was associated with a lower IOP and lower duration of antiglaucoma topical treatment before surgery. By providing a simple, non invasive and reproducible method to analyze blebs and their density of microcysts, en face OCT constitutes a promising way to characterize blebs after filtering surgery.

Keywords: 550 imaging/image analysis: clinical • 474 conjunctiva • 421 anterior segment