A DEVICE FOR PHOTOTESTING PATIENTS BEFORE PUVA THERAPY

A device is described and validated for rapid and easy phototesting of patients at the start of a course of PUVA therapy. The phototesting template consists of metal foil with four apertures of 10 mm diameter, mounted in pliable polyurethane. One aperture is open, and the other three each incorporate a grid of hexagonal holes of differing size which attenuate the radiation, resulting in relative intensities at the skin surface of 1, 2, 4 and 8. Thus, a single exposure through the foil of, for example, 8J/cm2, would allow the minimal phototoxic dose to be determined as either 1, 2, 4, 8, or > 8J/cm2. The device was validated by comparison with a metal foil with four open apertures, but otherwise identical construction, in which the dose was controlled by varying the exposure time. In 11 subjects, tested with one device on each arm, the minimal phototoxic dose, judged visually, was identical. Reflectance measurements of erythema at each of the test sites showed no systematic difference between the two methods. The device has no moving parts, requires no source of electrical power, will not change its optical transmission with age, and it robust and easy to use. It should, therefore, allow much wider application of the useful technique of minimal phototoxic dose determination before PUVA therapy.