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V. J. Srinivasan, I. Gorczynska, J. J. Liu, J. S. Duker, J. G. Fujimoto; In vivo Functional Imaging of the Human Retina With Optical Coherence Tomography (OCT). Invest. Ophthalmol. Vis. Sci. 2008;49(13):3196. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies demonstrated the use of optical coherence tomography (OCT) for optophysiology, the measurement of functional changes, in excised retinas. Recent work has begun to adapt these measurement techniques to in vivo retinal measurements in animal models and human subjects. Using the signal averaging capabilities of high-speed OCT with "spectral/Fourier domain" detection, we investigate in vivo imaging of functional changes in the human retina.
The measurement apparatus used a white light stimulus and near-infrared observation light. Spectral / Fourier domain OCT at ~870 nm and 50,000 axial scans per second was used to monitor the retina for intrinsic reflectance changes. The axial resolution in the retina was approximately 3 microns. A 0.3 mm2 portion of the retina was focally stimulated with white light. Individual layers of the retina were segmented and monitored for reflectance changes. Reflectance measured in the stimulated region was normalized to reflectance of a nearby, unstimulated region of the retina. Repeated trials were used to determine confidence intervals for the stimulus-induced changes. The stimulus location was randomized to prevent systematic errors.
A repeatable backscattering change in the photoreceptors is observed that correlates spatially with the stimulus location. The rise time of the signal is rapid (100-200 milliseconds). In the parafovea, the change in photoreceptor amplitude reflectance induced by the stimulus was 2-4% under dark-adapted conditions. In addition, a delayed backscattering change from the inner plexiform layer (IPL) was observed. The rise time of the IPL signal was relatively slower (0.5-1 second).
Optophysiology is demonstrated using OCT in the human retina in vivo. A repeatable backscattering change in the photoreceptor outer segments is observed in response to a white light stimulus. The photoreceptor response shows evidence of both rod and cone contributions with different properties. The backscattering change in the inner retina may be related to blood volume changes. Further work will characterize the properties of the functional response under different stimuli and background illumination conditions.
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