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Editors Selection IGR 7-1

(Laser) Surgical treatment: Laser iridotomy and temperature

Comment by Robert Ritch & Yaniv Barkana on:

20102 Using pharmacy claims data to study adherence to glaucoma medications: methodology and findings of the Glaucoma Adherence and Persistency Study (GAPS), Friedman DS; Quigley HA; Gelb L et al., Investigative Ophthalmology and Visual Science, 2007; 48: 5052-5057

See also comment(s) by Kenji Kashiwagi •

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Kataoka et al. (1466) evaluated the rise in anterior chamber temperature and effects on the cornea when ALI was performed in ten rabbits. ALI was performed in one eye in the regular fashion, and in the fellow eye through a contact lens attached to a cooling system. A thermometer probe at the top of the anterior chamber measured a temperature rise to 44.60°C in the first eye, whereas it was maintained at 11-16°C in the fellow eye. Significant focal corneal haze was seen during a few days in the area of ALI in all eyes that were treated without cooling, whereas light haze was seen in only one of the cooled eyes. Staining of endothelial cells showed an area of non-viable cells only in the eyes treated without cooling. These results are intriguing and remind us that ALI works by photocoagulation, i.e., raising the temperature in iris tissue enough for protein denaturation and disintegration to occur. However, they do not have immediate clinical implications.

A cooled iris will be more resistant to the photocoagulating effect of the argon laser

The anterior segment is different in rabbits and humans,  regarding depth, volume, and iris pigment and structure. Anterior chamber depth and iris color were not reported by the authors. The implications of corneal cooling on its health and patient comfort are yet to be evaluated. Interestingly, a uniform protocol was used of 10 shots of 200 mW/200 um/0.2s and then 500 shots/1000mW/50 um/0.05s. However, the authors did not report in how many eyes this resulted in a patent iridotomy. It seems that a cooled iris will be more resistant to the photocoagulating effect of the argonlaser.

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