INSTRUMENTS AND TECHNICS FOR THE CLINICAL TESTING OF LIGHT SENSE

Abstract

It is generally recognized that with other factors constant the intensity of light incident on the retina varies with the size of the pupil and that consequently determinations of the sensitivity of the eye to light are influenced by the size of the subject's pupil. Opinions differ, however, both as to the proper method of controlling or correcting for this variable factor and as to the practical necessity for so doing in clinical studies of light sense. Troland¹ in 1917 suggested the employment of a special unit of retinal brightness called the "photon," defined by him as "that intensity of stimulation which accompanies the use of a pupillary area of one square millimeter and an external stimulus surface brightness of one candle per square meter." In order to obtain the photon value of any given stimulus, the external brightness in millilamberts is multiplied by¹⁰ π times the area