Topographic Map of Photoreceptor Bleaching in Macaque and Human Retinas Measured by Commercial Fundus Camera

Abstract

Purpose: : The retinal densitometry technique has been used to construct two-dimensional topographic maps of photoreceptor bleaching in normal and diseased retinas from data obtained by either a fundus camera or a SLO. However, this imaging technique is not commonly used in the clinic because of the complexity of the measuring procedures. We have successfully obtained topographic maps of cone and rod photoreceptor bleaching simply by taking several consecutive photographs (duration: 1/125sec) with a commercial fundus camera system.

Methods: : After fifteen to thirty minutes of dark-adaptation, photographs of the ocular fundus of anesthetized macaque monkeys or humans illuminated by a white flash were taken by a commercial fundus camera (AFC-210, Nidek, Japan) at four seconds intervals. The luminance information given by the CMOS camera was separately analyzed based on three colors. The peak sensitivities of the CMOS camera for the blue, green, and red were 470, 530, and 620 nms, respectively. The flash-induced reflectance increases (bleaching) were calculated by dividing the reflectance of the first image into the subsequent images.

Results: : In monkeys, an increase in the light reflectance was observed both at the macula (peak: 10 to 30%) and surrounding regions indicating cone and rod-driven functions, respectively (Figure). The reflectance ratio of the central peak to the surround was highest for the red and lowest for the blue images. Similar results were obtained in human subjects

Conclusions: : The bleaching topography of the three types of cones and rods can be easily obtained by a commercial fundus camera although a separation of the three types of photoreceptors is not complete. This technique can potentially provide an acute measurement of photoreceptor function in normal and diseased retinas.

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • retina • photoreceptors