Objective: To determine the histopathologic effects of transpupillary thermotherapy (TTT) on the normal human retina.
Design: Prospective, noncomparative small case series.
Participants: Three patients with eyes scheduled for enucleation because of the presence of a malignant intraocular tumor.
Intervention: Application of TTT to the posterior pole by using an 810-nm laser and the following laser parameters: 2-mm spot size, 60-second duration, and power settings of 430, 530, and 630 mW (low, medium, and high doses, respectively). Two or three TTT treatments at varying dose levels were performed in each eye. The eyes were then enucleated within 7 days of TTT, and light microscopy of serial sections was performed.
Main outcome measures: Light microscopic histopathologic changes of the neurosensory retina, retinal pigment epithelium (RPE), and choroid in the areas of treatment compared with adjacent normal (control) tissue. Visual acuity, fundus appearance by slit-lamp biomicroscopy, and symptoms of pain, burning, or visual change were recorded before and after each TTT application. The degree of fundus pigmentation was also noted.
Results: Eight treatment spots from three eyes were analyzed. The first eye was judged to have a lightly pigmented fundus, and no histopathologic alterations were seen on light microscopy at any of the three dose levels. The second eye had a more pigmented fundus. This eye had minimal outer retinal changes in the area corresponding to the low-dose treatment, more prominent changes in the outer and middle layers in the medium-dose treatment area, and full-thickness retinal alterations, along with changes in the RPE and choroid, where the high dose was applied. The third eye was found to have an unexpected extension of pigmented choroidal melanoma under the fovea, and full-thickness retinal changes were observed in this area after a medium-dose application. No histopathologic changes were seen at the low dose in this eye.
Conclusions: TTT applications resulted in a spectrum of histopathologic effects of the retina that are related to both energy level and fundus pigmentation. Mild or no changes were observed in most low- or medium-dose applications. More extensive retinal damage occurred with applications that used energy levels higher than what have been used in the clinical setting or when the fundus was more heavily pigmented.