The nitroglycerin-flicker test.

The nitroglycerin-flicker test, as suggested and modified by Krasno and Ivy, has been used to test normal individuals and patients with a variety of cardiovascular diseases. The hypothesis that this test would serve as an index of the presence of vascular disease or spasm elsewhere in the body than the retina was explored. These studies have failed to justify the drawing of conclusions based on the results of this test regarding the presence or absence of generalized vascular disease or of localized vascular disease or spasm elsewhere than the retinal vessels. It is concluded that the use of this test in mass surveys to detect cardiovascular disease is not justified. F LICKER may be defined as the visual sensation produced by intermittent flashes of light. At a certain rate of such flashes a sensation of continuous brightness is experienced and this rate is called the critical fusion frequency (C. F. F.) or flicker fusion threshold (F. F. T.). These values can be obtained with a flicker photometer. Duke-Elder' has established flicker photometry as a sound method of obtaining quantitative values for this basic physiologic function. The method of flicker photometry had its beginning in the rotating tops first mentioned by \Iusischenbrock.2 More recently, flicker fusion has usually been studied by sectored disks which rotate between a constant light source and the subject to be tested. The speed of rotation of such disks can be recorded and the number of flickers per second at which the subject sees fusion of the flickering light can be obtained. Various investigators have shown that fatigue3'4 hypoxia,5 advancing age6 and lower relative intelligence' cause a decrease in the flicker fusion threshold. It has been generally found that similar testing conditions are necessary to achieve reproducible results on successive days. Krasno and Ivy8 have recently reported the effect of nitroglycerin on the flicker fusion threshold. Using their less complicated instrument , they have studied 421 subjects by a procedure which will be described later. They postulate that after sublingual nitroglycerin Hyde Foundation. 350 administration patients having spasm of their retinal arterioles will show a significant increase in their flicker fusion threshold over their initial threshold, while normal subjects not having such spasm will show a decrease in their threshold under similar experimental conditions. This hypothesis is based on the premise that nitroglycerin can relieve vaso-spasm of the retinal arterioles resulting in a more adequate blood and …