TTT and CNV

Editor,—The article by Newsomet al1 on transpupillary thermotherapy (TTT) raises more questions than it is able to answer. Although TTT is definitely a method which seems to show a certain efficacy in occult choroidal neovascularisation (CNV) and thus warrants further investigation, we must take issue with the authors' conclusions concerning its use in classic CNV.

The authors state that 78% of the predominantly occult membranes and 75% of the predominantly classic membranes closed as a result of TTT. This seems hard to believe, in particular because only 24 of 44 patients had angiographic follow up, which is the criterion for determining CNV closure. Furthermore, how is the irradiance used to be understood? On the one hand, the authors state—without providing any evidence—that smaller lesions need a higher irradiance, but on the other hand larger lesions—which are presumably requiring only lower irradiance—received confluent treatment with several overlapping spots of TTT, which implies that the amount of irradiance necessary on a cumulative basis might be similar to the irradiance needed to treat smaller lesions!

The authors also state that TTT compared well with the results of the TAP study group for predominantly classic CNV.2 They imply that the 75% of their cases which showed stabilised vision (nine eyes with a visual loss of less than 3 lines) can be compared with the TAP results at 1 year (246 eyes with a visual loss of less than 3 lines). Firstly, the TAP study was a masked and placebo controlled multicentre study performed on 609 patients which, without doubt, has a much higher statistical value than the present study with 12 predominantly classic membranes.

Secondly, Newsom et al cannot compare their visual results adequately as the TAP study used a standardised testing procedure employing Early Treatment for Diabetic Retinopathy charts as well as masked and certified vision examiners in comparison to the Snellen values mentioned in the above study, which were obtained by unmasked, and therefore biased, examiners. Furthermore, on closer examination of the results, not one of the 12 patients showed any improvement for visual acuity at 12 months after TTT; in comparison, in the TAP study 5.7% of all verteporfin treated patients showed an improvement of more than 15 letters (approximately 3 lines) at the 12 months visit.

While we recognise the potential of the TTT method, we would like to warn against extrapolating the data of this study in a relatively small patient cohort to make conclusions on the efficacy in treating classic CNV.