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 t emplate consists of metal foil with four apertures of 10 mm diameter, mounted in pliable polyurethane. One aperture is open, and the other t hree each incorporate a grid of hexagonal holes of differing size whic h attenuate the radiation, resulting in relative intensities at the sk in 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 validate d by comparison with a metal foil with four open apertures, but otherw ise identical construction, in which the dose was controlled by varyin g the exposure time. In 11 subjects, tested with one device on each ar m, the minimal phototoxic dose, judged visually, was identical. Reflec tance measurements of erythema at each of the test sites showed no sys tematic difference between the two methods. The device has no moving p arts, requires no source of electrical power, will not change its opti cal transmission with age, and it robust and easy to use. It should, t herefore, allow much wider application of the useful technique of mini mal phototoxic dose determination before PUVA therapy.