Intrinsic optical imaging of the retina in awake humans

Abstract

Abstract: : Purpose: Intrinsic optical imaging of the retina in anesthetized animal preparation has been reported [Ts'o, et al., IOVS [ARVO abstract], (43) 4, 2003]. In this study we attempted to detect similar intrinsic optical signal in the retina in awake, alert humans in response to patterned visual stimuli. Methods: Images of the retinal reflectance of near infrared light (780nm ±20nm) were collected before, during and after presentation of patterned visual stimuli (550nm±20nm), using a modified fundus camera with a cooled CCD camera. The fundus camera was modified in such a way that the stimulus light was seen by the human subject but not by the CCD camera, while the near infrared light was seen by both the human subject and the CCD camera, using appropriate light filters. Stimuli consisted of 4 Hz counterflickering checkerboards, at a spatial frequency of 0.5c/degree. The stimulus was a horizontal, vertical, or combination (L–shaped) bar, which was projected within the central 20º of the visual field. The collected images were registered using a Mutual Information–based algorithm. The time course of the intrinsic optical signal was determined by dividing the average infrared reflectance from the stimulated area of the retina by that of the opposite non–stimulated area. Eight normal subjects were examined. Results: A reproducible change in retinal reflectance of 0.15% (99% CI: 0.12–0.17%) was found in response to all 3 visual stimuli. The peak of the intrinsic optical signal was approximately at 2s after the stimulus onset. The spatial pattern of the optical signal was found to correspond in size, location and orientation to the visual stimulus pattern. Conclusions: It is possible to detect the intrinsic optical signal associated with patterned visual stimulus in awake, alert humans. We infer the measured signal reflects the functional state of the visually stimulated retina.

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