Retinal temperature increase during transpupillary thermotherapy: effects of pigmentation, subretinal blood, and choroidal blood flow.

PURPOSE: To study the risk of adverse events in transpupillary thermotherapy (TTT) for age-related macular degeneration by measuring how laser-induced retinal temperature increase is affected experimentally by subretinal blood, choroidal blood flow, and chorioretinal pigmentation. METHODS: An ultrafine thermocouple technique was developed to measure retinal temperature increase during TTT in albino and pigmented rabbit eyes. TTT was performed with 60-second, 0.78-mm spot size, 810-nm infrared diode laser exposures with power settings ranging from 50 to 950 mW. Intraretinal and subretinal temperature increases were measured in pigmented and albino rabbits, with or without subretinal blood and choroidal blood flow. RESULTS: Threshold power settings for visible lesions in albino and pigmented rabbits were 950 and 90 mW, respectively, corresponding to retinal temperature increases of 11.8 degrees C and 5.28 degrees C, respectively. Power settings required to produce threshold lesions in albino rabbits caused retinal temperature increases in pigmented rabbits that were five times higher than in the albino rabbits. Temperature increases in albino rabbits were 1.5 times higher with subretinal blood than without it. Choroidal blood flow generally did not affect measured retinal temperature increases. CONCLUSIONS: The results confirm prior theoretical recommendations that clinicians should consider decreasing TTT power settings in darkly pigmented eyes and proceed with caution in those with subretinal hemorrhage or pigment clumping.

Monitoring retinal function during transpupillary thermotherapy for occult choroidal neovascularization in age-related macular degeneration.

PURPOSE: To use focal electroretinography to evaluate changes in retinal function during transpupillary thermotherapy (TTT) for neovascular age-related macular degeneration (ARMD). METHODS: Sixteen eyes of 16 patients with ARMD with occult choroidal neovascularization (CNV) were studied. A 630-nm photocoagulator aiming beam was modified for use as a 41-Hz square-wave focal electroretinogram (fERG) stimulus. The stimulus was presented on a light-adapting background by a Goldmann-type lens (visual angle, 18 degrees; mean luminance, 50 cd/m(2)). fERGs were continuously monitored before, during, and after TTT for occult CNV. The amplitude and phase of the fERG's fundamental harmonic were measured. RESULTS: No suprathreshold or adverse clinical events occurred during the course of the study. fERG amplitude decreased transiently during TTT (23% +/- 9% [SE]; P < 0.05). The decrease in amplitude was greatest 16 to 20 seconds and 32 to 40 seconds after the onset of TTT. It was followed by a recovery to baseline amplitude during TTT (48 to 60 seconds after TTT was begun). Within 60 seconds after TTT was completed, fERG amplitude was within the range of baseline. TTT did not alter the fERG phase. Mean fERG amplitudes and phases recorded 1 week and 1 month after TTT were comparable to mean pretreatment levels. CONCLUSIONS: fERG amplitude decreases transiently during TTT, despite the absence of ophthalmoscopically apparent lesions. Intraoperative amplitude depression may result from an adaptation effect to laser light energy and/or hyperthermia, resulting in desensitization of cone photoreceptors and bipolar cells. Treatment sites are electrophysiologically functional 1 month after TTT. Detailed parametric study of a larger patient group is needed to determine whether fERG testing is potentially useful for monitoring and perhaps for controlling and optimizing TTT for choroidal neovascularization.

A wide-field, high-resolution ophthalmoscopic contact lens.

A new inverted-image ophthalmoscopic contact lens provides 2X laser spot magnification and a 117 degrees degree instantaneous field of view. It has three times the resolution of very wide-field, inverted-image ophthalmoscopic contact lenses to permit effective use of higher slit-lamp magnifications. The lens was designed for transpupillary thermotherapy with large lesions and panretinal photocoagulation with hazy ocular media.