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Vimal Prabhu Pandiyan, Aiden Maloney Bertelli, James A Kuchenbecker, B. Hyle Park, Daniel V Palanker, Austin Roorda, Ramkumar Sabesan; Optoretinogram: stimulus-induced optical changes in photoreceptors observed with phase-resolved line-scan OCT. Invest. Ophthalmol. Vis. Sci. 2019;60(9):1426. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
In photoreceptors, the transduction of photons to electrical signals is accompanied by nanometer-scale optical path length changes. These changes can be reliably detected using interferometric imaging of photoreceptors. Here, we characterize such light-induced changes using phase-resolved line-scan OCT.
A line-field spectral domain OCT was used to image human retina at 4 deg eccentricity through an artificial 4 mm pupil at the eye. A custom-built spectrometer with a high-speed 2D sensor enabled rapid OCT volume acquisitions at the rate of 120 - 228 Hz (8400 - 15900 B-scans/sec). Defocus was optimized using a Badal optometer. OCT volumes were acquired for 1-2 seconds after 3 mins of dark adaptation. After the 10th volume, a 660±10 nm LED flash illuminated the retina in Maxwellian view for durations between 5 and 30 ms. The acquired OCT volumes were reconstructed, registered and segmented to retrieve complex valued images corresponding to the cone inner/outer segment and outer segment tips. The averaged phase difference between them yielded optical path length change in the outer segment and this measure was inspected for its repeatability and dependence on time, stimulus intensity and stimulus size.
The photoreceptors showed an exceptionally reproducible light-driven response - a 5-10 nm reduction in path length 10-20 ms after stimulus onset, followed by a continuous increase in path length saturating 300-500 ms post-stimulus. Over six repeat trials with stimulus energy of 13.7 µJ/deg2, the magnitude of maximum reduction and expansion in path length was very repeatable: 10.2 ± 3.3 nm and 152 ± 8.8 nm respectively, on average. The response saturation level scaled linearly with stimulus energy, increasing at the rate of 12.8 nm per 1 µJ/deg2. The mean amplitude and time-course of this response did not change with the stimulus area, tested in the range between 0.07 deg2 (encompassing ~12-15 cones) and 0.27 deg2.
Line-scan OCT offers sufficient phase stability for detecting minute stimulus-induced functional changes in outer segments of cone photoreceptors. This specific component of the optoretinogram - generally defined here as light-induced optical signals from the retina - offers a robust and sensitive biomarker for cone function in health and disease.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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