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V.J. Srinivasan, M.D. Wojtkowski, J.J. Liu, J.S. Duker, A. Clermont, S.E. Bursell, J.G. Fujimoto; Non–Invasive in vivo Measurement of Retinal Physiology Using High–Speed, Ultrahigh Resolution Optical Coherence Tomography . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4758.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies demonstrated the feasibility of using optical coherence tomography (OCT) for optophysiology, the measurement of functional changes, in excised rabbit and frog retinas. Using the signal averaging capabilities of high–speed OCT with "spectral/Fourier domain" detection, we investigate in vivo imaging of functional changes in the intact rat retina.
Measurements were performed using a high–speed, ultrahigh resolution OCT system. A transient white light stimulus is delivered to the retinas of healthy, anesthetized rats and the OCT reflectance is recorded as a function of time. Rats are immobilized in a stereotaxic mount to minimize motion during the recordings. The baseline recording is performed identically to the functional recording, with the exception that the stimulus remains off. The spectrum of wavelengths used in the OCT measurements was from ∼820 to 960 nm, well outside the sensitivity range of the rat retina. While scattering changes due to neural activation have been observed in this wavelength range in functional experiments in brain and retina, changes in oxygenation may also play a small role in observed scattering or absorption changes.
A baseline recording established the noise level at ∼2%. The functional recording showed that a white light stimulus induced a 10–15% increase in the average amplitude reflectance from the photoreceptor outer segments. The spatial distribution of the reflectance change showed a clear maximum in the photoreceptor outer segments, and was localized to the region between the photoreceptor inner and outer segment junction and the retinal pigment epithelium. The response was significantly reduced by photobleaching prior to the measurement, and was restored after photopigment regeneration. Spectroscopic analysis of the response showed that the reflectance change showed little or no wavelength dependence within the OCT measurement bandwidth.
Optophysiology is demonstrated using OCT in the intact rat retina in vivo. A repeatable backscattering change in the photoreceptor outer segments is observed in response to a white light stimulus. To our knowledge, this is the first demonstration of in vivo optophysiology using OCT in the intact retina, and may be an important step toward developing optophysiology for human studies.
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