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Choroidal melanoma is the most common primary malignant ocular tumor, yet none of the several available treatments is wholly successful. One therapy recently tried in humans was transpupillary thermotherapy. In this procedure, an 810 nm wavelength laser beam passes through the cornea, aqueous, lens, and vitreous to be absorbed by the tumor in the back of the eye. The results of transpupillary thermotherapy were encouraging, but in some patients only the anterior portion of the tumor was necrosed while the center and posterior portions remained viable. The new treatment modality proposed in this study is similar in concept to transpupillary thermotherapy, but we propose to apply the laser energy through the sclera onto the posterior portion of the tumor, known as the tumor bed. At infrared wavelengths, sclera has excellent transmission characteristics, while most ocular tumors are mildly absorbing. Some of the laser energy is absorbed in the posterior portion of the tumor, but some transmission of the energy through the tumor allows the anterior portion of the tumor to be heated as well. In qualitative terms, this scheme sounds appealing, but it is not yet known whether it will fulfill the quantitative requirements required to achieve the appropriate biological response -- that is, raising the temperature of the tumor to the level which causes cell necrosis (greater than or equal to 43 degrees Celsius) for the appropriate amount of time, without causing photocoagulation of the tumor (approximately equal to 60 degrees Celsius) or damage to the sclera (approximately equal to 55 degrees Celsius). The calculation of temperature distribution is a complicated matter, however, because the actual result of a rise in temperature happens only after the applied laser light has undergone several physical processes.
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