Abstract
Cone phototransduction is a cornerstone of visual process and defects in phototransduction underlie many ocular diseases. We describe an optical method for direct in vivo observation of physiological processes accompanying phototransduction. The method takes advantage of interference among multiple reflections that straddle the cone outer segment, where phototransduction is known to begin. This self-interference is highly sensitive to phase changes within the outer segment such as those caused by changes in its refractive index, scattering properties, and size. A high-speed flood-illumination retina camera equipped with adaptive optics was used to observe changes in reflectance of individual cones following delivery of varying levels of visible stimulation. This pattern of changing reflectance, termed “scintillation”, was analyzed in terms of its amplitude, onset, and frequency, and their varying dependence upon stimulus energy. Measurements were taken on four subjects. Amplitude of scintillation was determined to be uncorrelated with stimulus energy (p[[gt]]0.1), onset of scintillation occurred within 10 ms after stimulus, and scintillation frequency was found to depend upon stimulus energy. Repeatability tests and quantitative comparison between subjects were conducted. Possible physiological origins for the phase changes underlying scintillation are discussed and a simple mathematical model is presented.