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Editors Selection IGR 12-3
Surgical treatment: Snuff-out
Comment by Paul Palmberg on:
13053 Risk of sudden visual loss following filtration surgery in end-stage glaucoma, Topouzis F; Tranos P; Koskosas A et al., American Journal of Ophthalmology, 2005; 140: 661-666
Topouzis et al. (1085) have performed a small (21 eyes), but prospective study of the risk of 'snuff-out' of the central vision in patients with advanced visual field loss (mean deviation -27 &plm; 3 dB). They did not observe any cases of snuff-out. This paper adds further support to the current consensus that the risk of snuff out after filtering surgery is quite small, and that it is wiser to operate such cases than to continue medical therapy when IOP control is not optimal. A generation ago, concern over the risk of snuff out was based upon individual, tragic cases, but represented numerators without denominators. Even when percentages of cases suffering snuff out were given, inadequate attention was given to the wide 95% confidence limits of small series. Kolker's classic paper cited a risk of 14% (in a series of cataract as well as filtering surgeries), but the 95% confidence limits of that study were 3-36%, and he had no additional cases of snuff out in his next 50 cases. Costa et al. reviewed over 500 filtering operations from Spaeth's group, and found a risk of snuff out of 1% overall, and 2.6% in a sub-group of patients with split fixation, and no cases in those without split fixation. Large studies from San Francisco, Ann Arbor and Miami also found a risk of 0-1% of snuff out. As discussant of the Costa paper at the AAO, I presented a meta-analysis of five studies, and found that the 95% confidence limits were 1-3%. What would be the result of not operating sub-optimally controlled eyes for fear of snuff out? Kolker's classic paper reported that the risk of losing fixation was even higher (22% in 4 years) with continued medical therapy in such eyes, and others have had the same experience.
Are there ways to further reduce the risk of snuff out? It has been reported that either pressure spikes or hypotony increase the risk of snuff out. Therefore, it would seem judicious in eyes with split fixation to adjust the scleral flap resistance intraoperatively to yield, at equilibrium flow, an IOP that is neither too high nor too low, and to monitor the IOP in the first few hours after surgery so that pressure spikes could be blunted.
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