Sir,

We read with great interest the article by AC Hogan and DJ Kilmartin1 on ‘Low power transpupillary thermotherapy’ in patients with choroidal neovascularisation (CNV) secondary to age-related macular degeneration (AMD) with great interest. Firstly, we would like to congratulate the authors for highlighting the efficacy of TTT in treatment of patients with CNV who are ineligible for photodynamic therapy while stabilising vision. However, there are a few issues that we would like them to clarify pertaining to their article.

In the materials and methods, they have not mentioned the time interval between fluorescein angiogram and time of treatment. In the low power group of patients, it has not been mentioned as to how they arrived at the required power. Was there any use of a test spot? If so, where was the preferred site of the test spot? In our practice, we generally fire a test shot outside the vascular arcades with the end point being a very faint greying of the retina. If there is any whitening of the retina noted before the end of 1 min, the power is lowered in steps of 100 MW till there is no reaction or a very faint greying. This is in accordance with the method described by Reichel et al2 and Newsom et al3 in their previous studies. Did they treat patients at a subthreshold level such that no end reaction was noted at all? If so, how did they arrive at this end point? What was the difference in the end points between standard power and low power transpupillary thermotherapy? Did the presence of serous elevation and subretinal haemorrhage need increase in power? In our practice, we have noted that there is a need to slightly increase the power when there is increased serous elevation and subretinal haemorrhage. Was the power/retinal diameter coefficient the same for all the patients treated in each group?

In our practice in the Indian eyes, we have noted that titration of the required laser power is dependent on the pigmentation of the choroidal layer which is more in the Asian eyes while compared to the Caucasian eyes. More the pigment, lesser the power required. We generally use power in the range 200–600 MW for almost all of our patients with the end point being a very faint greying of the retina at the end of treatment duration of 1 min. The importance of ocular pigmentation in this modality of treatment has been stressed by Auer et al.4 They reported choroidal atrophy in five of 32 eyes that underwent TTT in pigmented individuals. Similar effects have been shown in animal models.5 We feel that titration of power is dependant on the level of pigmentation of the choroid and that determines whether an individual has a low power or a standard power TTT as defined by the authors.