Effect of Tartrazine Dye on Corneoscleral Rim Clarity: An Ab Externo Visualization of Cannulated Schlemm's Canal

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• Picked for Histology (top studies of the week, 18 October 2026): Tartrazine improves corneoscleral clarity for visualization

Abstract

The intrinsic opacity of the sclera limits ab externo visualization of deeper structures such as Schlemm's canal, thereby constraining angle-based glaucoma surgery. Tartrazine, a US FDA-approved azo dye, transiently enhances tissue optical transparency and may improve intraoperative visualization. This study evaluated whether tartrazine improves the optical clarity of human corneoscleral rim segments (CSRS) and the ab externo visibility of Schlemm's canal cannulation. In this ex vivo feasibility (proof-of-concept) study, five human corneoscleral rims from donors unsuitable for corneal transplantation were obtained from Ramayamma International Eye Bank. Two rims were each divided into four quadrants (eight segments in total) and allocated to four groups (n = 2 independent segments per group): 0.25 or 0.50 M tartrazine, each without (CSRS-1) and with 6-0 Prolene suture cannulation of Schlemm's canal (CSRS-2), for 5 min. Segments were examined microscopically at 2.5× magnification, and scleral transparency was compared before and after treatment. Scleral clarity and suture visibility were graded by four independent evaluators on a 0-10 scale, with 10 representing maximum clarity, giving eight scored observations per group from two independent segments. Three further rims (CSRS 5, 6, and 7) underwent histopathological evaluation, comparing tartrazine-treated rims (0.25 and 0.50 M) with untreated rims to assess tissue integrity. Tartrazine at both concentrations increased corneoscleral clarity from an untreated baseline (score 0), with mean clarity scores above 6 in all groups. In non-cannulated segments (CSRS-1), scores were 6.13 at both 0.25 and 0.50 M. In cannulated segments (CSRS-2), suture visibility improved to 6.63 at 0.25 M and 8.00 at 0.50 M, the latter significantly higher than the reference group (p = 0.008), although the difference between the two concentrations was not significant (interaction p = 0.168). Histopathology showed preserved histological structure with no gross structural damage on light microscopy at either concentration. In this small preliminary series, tartrazine rapidly enhanced scleral translucency and ab externo visualization of underlying structures, suggesting potential clinical utility in ophthalmic surgery pending in vivo validation. Larger studies with more independent specimens and objective optical measurements are required to confirm these findings.

Abstract as published, via PubMed.