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Editors Selection IGR 9-4
Surgical treatment: Trypan Blue
Comment by Paul Palmberg on:
13078 Trypan blue identifies antimetabolite treatment area in trabeculectomy, Healey PR; Crowston JG, British Journal of Ophthalmology, 2005; 89: 1152-1156
Healey and Crowston (1110) have shown convincingly that the clever addition of Trypan Blue to the antimetabolites 5-FU or MMC allows one to visualize areas of treatment, whether applied by sponge or injected. They also provide some evidence that the addition of Trypan Blue does not affect the cytotoxic effects of the drugs on fibroblasts in vitro, nor surgical results in a small group of patients. The authors suggest that this off label use of Trypan Blue with antimetabolites has potential benefits in clinical practice, including the teaching of surgery, and in research.
Wendy Franks, in an accompanying BJO Editorial, reviewed the role of antimetabolite filtering surgery in achieving lower target pressures, the evidence that lower target pressures are associated with better visual field outcomes in eyes with advanced damage, and her view that the use of Trypan Blue to stain the tissues treated with antimetabolites could be useful.
Before glaucoma surgeons rush out to do this, however, they need to think analytically about what the use of Trypan Blue would actually accomplish. In cataract surgery it is obvious that using Trypan Blue to stain lens capsules facilitates continuous tear capsulorrhexis in eyes in which the capsule is difficult to visualize, and its use in the eye, when the excess dye is rinsed away, is safe. However, how likely is it that visualizing the area of treatment will be helpful in glaucoma surgery? Do we really have trouble adequately identifying where MMC is being applied with the large, thin sponges currently in favor, or seeing the sponges to remove them? Not really. Is it really important to avoid having a MMC sponge touch the anterior edge of a fornix-based conjunctival flap? Probably not, when the conjunctiva is anchored to the sclera with sutures that are sufficiently perpendicular to the surface and deep enough that they do not claw through and become loose.
If further studies were to show some benefit in surgical outcomes, we would still have to consider that Trypan Blue is not cheap, and that the safety of its use in the conjunctiva (especially when injected) would have to be studied more extensively before its widespread use is adopted.
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