Abstract

We have developed a device for projecting psychophysical stimuli onto precise retinal locations while the fundus is being viewed. The device consists of a fundus camera, modified by removing the ocular and 35-mm camera mount and replacing them with an infrared-sensitive video camera and a stimulus port. Any stimulus configuration can be used, as long as the stimulus image plane is conjugate with the retina (e.g., in the plane of the 35-mm film). Light for viewing the fundus is reduced to scotopic levels by insertion of a red cutoff filter in front of the background light. The image of the fundus is intensified using the video camera, whose output is displayed on a high-resolution video monitor. The x,y position of the stimulus is recorded using linear potentiometers and is marked by cursor on the image of the fundus displayed on the monitor. Each experimental session is videotaped. Because the deep-red viewing light reduces the resolution of fundus features, we obtain a fundus photo of each patient using standard clinical techniques, and register the fundus photo with the fundus image from one frame of a videotape obtained prior to testing, using the IS-2000 image processing system (PAR Microsystems, Inc.). In this manner, retinal locations corresponding to experimentally pertinent fundus features can be identified and electronically marked on the video monitor for later testing. If necessary, the image enhancement capabilities of the IS-2000 can be used to delineate low-contrast fundus features. Results from psychophysical measurements on clinical patients using the fundus camera stimulator are described.

© 1985 Optical Society of America