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Abstract

PURPOSE: To characterize conjunctiva-scleral thickness over the Ahmed glaucoma valve tube in eyes clinically considered to be at increased risk of tube exposure based on a superficially positioned tube on anterior segment optical coherence tomography, and to explore the association between post-operative follow-up duration and conjunctiva-scleral thickness.
METHODS: This retrospective study included 22 eyes of 21 patients with 23 Ahmed glaucoma valve tubes. One patient contributed both eyes, and another had two Ahmed glaucoma valve tubes in one eye. All eyes had a minimum post-operative follow-up of 6 months and a clinically apparent superficial tube trace on slit-lamp examination. Over-the-tube conjunctiva-scleral thickness and total conjunctiva-scleral thickness were measured at corresponding locations using anterior segment optical coherence tomography. Associations between conjunctiva-scleral thickness measurements and post-operative follow-up duration were evaluated using correlation analysis and generalized estimating equation models to account for clustering.
RESULTS: The mean age was 56 ± 12 years (range, 38–80 years). Best-corrected visual acuity was 1.00 (range, 0.10–3.00) LogMAR, and intraocular pressure was 16 (range, 7–27)mmHg. The median post-operative follow-up duration was 40 months (range, 6–135 months), and the median CST overlying the tube at its most superficial location was 190 μm (range, 54–552 μm). A modest inverse correlation was observed between post-operative follow-up duration and conjunctiva-scleral thickness overlying the tube (ρ=−0.44, p=0.034). generalized estimating equation analysis showed a similar association (p=0.019). However, when eyes were categorized according to post-operative follow-up duration (≤1 year, 1–5 years, and ≥5 years), no statistically significant differences in conjunctiva-scleral thickness measurements were detected were observed among the groups: 273 (79–552), 190 (54–402), and 119 (64–227) μm, respectively (p=0.087).
CONCLUSION: In this preselected high-risk cohort, a modest inverse correlation was observed between post-operative follow-up duration and conjunctiva-scleral thickness overlying the tube; however, this association was not consistently demonstrated across analytical approaches and should therefore be considered exploratory. Anterior segment optical coherence tomography allows objective characterization of tissue coverage over the Ahmed glaucoma valve tube. Further prospective studies with larger cohorts and appropriate control groups are warranted to determine the clinical significance of these findings.

Keywords: Glaucoma; Ahmed glaucoma valve; Intraocular pressure; Anterior segment; Optical coherence tomography; Conjunctiva; Scleral thickness