Re: Transpupillary thermotherapy in choroidal neovascularization

, Surgeon,

Other Contributors:

August 13, 2001

Dear Editor

We thank Dr Ergun and Dr Stur [1] for their interest in our paper and agree with their comments that it is not possible to directly compare a pilot study with the results of a randomized controlled study. We also pointed out in our conclusion that studies such as this one cannot prove efficacy of a treatment but only indicate fruitful areas of further research. We also pointed out that the angiographic follow-up data were not complete, as once membrane closure was obtained the patients were followed up clinically.

The issue of the laser spot size in Transpupillary thermotherapy (TTT) is confusing, however it is known that more irradiance (W/cm2) is needed for smaller laser spots because heat conduction from choroidal blood flow cools smaller spots more efficiently than larger spots. This physiological phenomenon was established in experiements [2], theoretical [3], and clinical [4] studies. Furthermore, it is true that overlapping zones occur when multiple spots are used for very large treatment areas. Nonetheless, these zones experience the same temperature rise as every other treated area and no clinical abnormalities have been noted in the small overlapping zones. Although TTT is mainly used for occult membranes our results indicate that it may have a place in classic membranes and in this study stabilization of vision was obtained in the majority of these patients and in a minority an improved vision was noted.

References

(1) Ergun, E. and Stur, M. Transpupillary thermotherapy in choroidal neovascularization (letter). Brit J Ophthalmol 2001;85: 1014.
(2) Mainster, MA and Reichel E. Transpupillary thermotherapy for age-related macular degeneration: long-pulse photocoagulation, apoptosis, and heat shock proteins. Ophthalmic Surg Lasers 2000;31(5):359-73.
(3) Mainster, MA, White, TJ, et al. Spectral dependence of retinal damage produced by intense light sources. J Opt Soc Am 1970;60(6):848-55.
(4) Reichel E, Berrocal, AM, et al. Transpupillary thermotherapy of occult subfoveal choroidal neovascularization in patients with age-related macular degeneration. Ophthalmology 1999;106(10):1908-14.
(5) Wolbarsht, ML. Safety with Lasers and Other Optical Sources: A Comprehensive Handbook. New York, Plenum Press 1980; pp. 130-1.

Conflict of Interest

None declared