Imaging Of Rod And Cone Photoreceptor Activities Using Functional Optical Coherence Tomography (fOCT) In The Macaque Retina

Abstract

Purpose: : OCT signals in the photoreceptor layers significantly change after application of light stimulation to the posterior retina. Since these signal changes are dependent on the stimulus intensity and observed only in the stimulated region, OCT can be used to evaluate the stimulus-evoked retinal activities (fOCT). In this study, we have measured fOCT signals by the stimuli with different wavelengths of light from the macaque retina in order to map the photoreceptors responses originating from cones and rods.

Methods: : We have developed a fOCT system based on spectral domain OCT (SLD, 840 nm; band width 50 nm; Galvano Scanning mirror, 30 Hz). Following dark-adaptation, the fundus of the anesthetized macaque retina was continuously illuminated with light from a halogen lamp filtered through a green (_max = 500 ± 15 nm) filter for rods or a yellow (_max = 590 ± 15 nm) filter for M/L cones. The evoked signals were calculated by dividing the consecutive images for 16 seconds by those obtained during the initial 0.5 second, pixel by pixel, after spatial alignment of the images.

Results: : Continuous light stimulation through either green or yellow filter gradually decreased the OCT signals in the inner and outer segment (IS/OS) junction of the photoreceptor layer (up to 50% during 16 seconds’ stimulation). When the light through green filter was applied, the fOCT signals at the peri-macular region (10 degrees temporal from the fovea) were twice more intense than those at the fovea. On the other hand, when the light through yellow filter was applied, the fOCT signals at the fovea were three times more intense than those at the peri-macular region.

Conclusions: : Light through green or yellow filter evoked fOCT signals in the IS/OS junction of the photoreceptor layer, and the response distributions correlated well with the distribution of rod or cone photoreceptors, respectively.

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