Development of fundus camera for spectral imaging using liquid crystal tunable filter.

Abstract

Abstract: : Purpose: To develop a new fundus camera that measures ocular fundus spectral images over a wide wavelength range with low illumination to monitor retinal neuronal activity in vivo. Methods:The spectral imaging apparatus consists of a mydriasis type fundus camera (TRC–50LX, Topcon), liquid crystal visible and infrared wavelength tunable filters (VariSpec, CRI), a CCD camera (C8484, Hamamatsu Photonics), and a liquid crystal VGA resolution projector display that delivers visual stimuli. Images can be grabbed at a frame rate of 30 Hz for 10nm wavelength steps from 450–1000nm. A program which uses the affine transformation to arrange multiple spatially distorted images was developed for spectral or temporal sequential image comparison. Three normal eyes were measured to test the apparatus. Visible light region images were taken, and oxygen saturation levels were analyzed for 586nm and 605nm. The ratios of the optical densities of the artery and vein were measured at 700, 800, 900, and 1000nm and compared to the absorption spectra of deoxy– and oxyhemoglobin. Optical densities before and during flicker stimulation were measured for 730–780nm. Results: The program successfully arranged sequential images. Illumination levels were lower than that of conventional fundus camera measurements. Color–coded fundus images had lower oxygen saturation ratios near the fovea than in the periphery, suggesting more oxygen was consumed near the fovea. The ratios of the optical densities of the artery and vein were1.13, 1.10, 1.04, 0.98 and 0.95 for wavelengths 700, 800, 900 and 1000nm, corresponding to oxy– and deoxyhemoglobin absorption properties. Retinal response results before and during visual stimulation were inconclusive. Conclusions: The new fundus camera can analyze static oxygen consumption in the retina, possibly replacing some part of florescent angiography. Further investigation is needed to analyze dynamic neuronal activity in the retina using this apparatus.

Keywords: imaging/image analysis: non–clinical • retina • blood supply