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Editors Selection IGR 20-4

Surgical Treatment: Filtering Surgery with Drainage Devices

Comment by Arshram Sheybani on:

82692 Novel approaches to model effects of subconjunctival blebs on flow pressure to improve clinical grading systems after glaucoma drainage surgery, Bouremel Y; Lee RMH; Eames I et al., PLoS ONE, 2019; 14: e0221715

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Bouremel and colleagues address an important issue in their study. Bleb grading systems are fraught with error by nature of their subjectivity. The presence or absence of a bleb leak or microcysts may be concrete depending on examination technique but bleb height, vascularity, and encapsulation grading are completely subjective. The authors present a system that factors bleb pressure into bleb characterization.

Bleb grading systems are fraught with error by nature of their subjectivity

The purpose of having a reproducible bleb grading system is to identify blebs that may carry risk of complications and also to identify blebs that function optimally. While there is some correlation to bleb shape and functionality, this paper studies an ex-vivo and in-vitro system to model blebs. Unfortunately, so much of bleb porosity, shape, and functionality is dependent on the wound healing response. In live rabbits, a single passage of balanced salt solution through a bleb (without aqueous flowing through it) resulted in a 75-80% reduction in bleb porosity over 72 hours.¹ Coupled with the fact that infusion pressures in these experimental blebs was at 5 ul/min, it is difficult to translate the results of Bouremel's paper to clinical practice.

This paper should encourage additional studies looking to identify objective variables in grading filtering blebs. OCT imaging or metrics to measure bleb porosity may be possible targets of future study. Despite recent studies, there is still a need for a clinically applicable and objective grading system for blebs.

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