ANGIOSCOTOMETRY WITH THE SCANNING LASER OPHTHALMOSCOPE - COMPARISON OF THE EFFECT OF DIFFERENT WAVELENGTHS

Purpose. Angioscotomas are scotomata caused by vessel shadows. Their e xtent may be influenced by physiological and pharmacologic conditions and disease. In this study, the authors quantified angioscotomas in no rmal subjects using a fundus perimetry technique with a scanning laser ophthalmoscope. They further investigated the influence of two differ ent wavelengths on scotoma depth. Methods. For blue-on-yellow perimetr y, the authors used two different lasers--an argon laser (lambda = 458 nm) for stimuli and a low background and a HeNE (lambda = 594 nm) for a superimposed yellow background. For redon-red perimetry, the author s used another HeNe laser (lambda = 633 nm). Fundus illumination was p rovided by an infrared light. Five healthy subjects were examined. Twe nty-one to 24 stimuli (200 msec duration, 0.4 degrees X 0.4 degrees) w ere presented at different intensities in randomized order in a 5 degr ees X 2.5 degrees retinal test field, directly inferior and adjacent t o the disk. Results. The depth of scotomas caused by major vessels var ied in all subjects and depended on perimetry condition. To quantify t he influence of vessels on sensitivity, the authors analyzed psychomet ric functions for stimuli projected on the vessels and for those far f rom the vessels. The authors found a significant difference for target s on the vessel compared to those far, which was more pronounced for t he blue-on-yellow condition. Conclusions. Angioscotomas are detected b etter with blue targets on a yellow background than with red-on-red pe rimetry. The greater light absorption by hemoglobin and oxyhemoglobin at short wavelengths compared to longer wavelengths is not compensated for by visual mechanisms.