Intrinsic Signal Optical Imaging of Retinal Responses to Patterned Stimuli

Abstract

Abstract: : Purpose: To permit the non-invasive study of the response of the retina to spatially patterned stimuli, we have developed an optical imaging apparatus that can deliver a video-based visual stimulus to the retina while imaging the functionally correlated intrinsic signal response in the near-infrared (IR). Methods: A commercially available fundus camera (Topcon) was modified to permit collection of retinal images with a cooled CCD camera in the near IR, while delivering a visible patterned stimulus generated by a computer-driven LCD. The patterns of visual stimuli tested included counterflickering checkerboards of differing spatial extent, designed systematically map the imaged field. Recordings were conducted in 20-30 sec blocks, with a 3 sec stimulus period. The IR illumination wavelengths ranged from 750 to 860nm. The studies were primarily conducted in the cat. Results: The spatial distribution of the recorded response was tightly correlated with the spatially patterned stimuli. With increasing activation area, laterally suppressive effects decreased the response amplitude, particularly within the central regions of stimulated retina. Multiple intrinsic signals were observed, depending on wavelength, differing in amplitude and sign. Signal amplitudes were in the range of .1-.5% at 750nm and significantly smaller at 855nm (0.05-0.1%). Time to peak of the signals was typically 1-3 secs with a decay time of 3-5 sec. Conclusions: Non-invasive intrinsic signal functional imaging of the retina in vivo represents a new and promising tool for the assessment and visualization of retinal function for both basic science studies and for clinical applications. The technique can yield spatially precise recordings of retinal activation and, in combination with patterned stimuli, permit the study of spatial patterns of response. Although further investigations are required to determine the various signal sources present, these retinal signals mirror many of the same properties of those found in the mammalian neocortex.  

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, S • pattern vision • retina