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Editors Selection IGR 9-4

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Comment by Keith Barton on:

26370 Transscleral diode laser cycloablation in patients with good vision, Rotchford AP; Jayasawal R; Madhusudhan S et al., British Journal of Ophthalmology, 2010; 94: 1180-1183

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Rotchford et al. report a retrospective study of 49 eyes of 43 patients who had transscleral diode laser cyclophotocoagulation (cyclodiode) for uncontrolled glaucoma and snellen Acuity of 20/60 or better before treatment.The aim of the study was to identify the risk of visual loss after cyclodiode in eyes that had reasonably good visual acuity before the procedure.

 The eligilibity criteria included only that a cyclodiode was performed between 1994 and 2006, and that the preoperative Snellen visual acuity was 20/60 or better on at least two consecutive occasions before treatment and included patients represent approximately 13% of the total number of cyclodiode treatments performed in that department during the study period. Median pretreatment BCVA was 20/30, range 20/16-20/60.

It is odd that the authors chose to include both eyes of some patients, as these are clearly not independent in their behaviour. Overall, 30% of patients experienced a two line loss of visual acuity which is not dissimilar to that reported for aqueous shunts e.g. 27% in the TVT study at three years of follow-up. The authors make the plea that cyclodiode is a safe and effective alternative to shunts in patients with recalcitrant glaucoma. It is clearly difficult to make that comparison from a retrospective study with different case selection criteria and case mix. Unlike the Tube versus Trabeculectomy (TVT) study, visual field parameters such as mean deviation, are not given.

The apparent assumption of similar hypotensive efficacy to aqueous shunts is not borne out, at least in comparison to TVT in the manner they have used to compare visual acuity

The stated limitations of the study are its retrospective and noncomparative design. It is true that case mix biases in a study of this restricts comparison with studies such as TVT to very crude statements. Nevertheless the authors' main assertion, that visual acuity results are no worse than TVT, appears true. However, it is worth noting that both mean IOP and numbers of glaucoma medications are higher at five years than in either arm of TVT at three years. The authors assumption that the barrier to wider uptake of cyclodiode is a high rate of acuity loss, when in fact there are also efficacy concerns. The apparent assumption of similar hypotensive efficacy to aqueous shunts is not borne out, at least in comparison to TVT in the manner they have used to compare visual acuity, though their call for a randomised controlled trial comparing the two is not unreasonable.

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