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Chen D Lu, Woo Jhon Choi, Zhao Wang, Martin F Kraus, Joachim Hornegger, Jay S Duker, James G Fujimoto; Photoreceptor Lengthening During Dark Adaptation Detected With Ultra-High Resolution Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5978.
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© ARVO (1962-2015); The Authors (2016-present)
Delayed rod-based dark adaptation is one of the signs of a variety of ocular diseases including age-related macular degeneration (AMD). Ultra-high resolution optical coherence tomography (UHR-OCT) allows for better resolution of outer retinal layers compared to commercial systems. The objective of this study is to use an UHR-OCT system to analyze the thickness changes of the photoreceptor layers in normal subjects to identify morphological changes that occur after photobleaching and during dark adaptation.
11 normal subjects of age 29.7±4.9 were imaged on a 91 kHz UHR-OCT system with ~3 µm axial resolution and 0.5 µm pixel resolution in tissue. The subjects were exposed to a reflected white Xenon flash with a luminance of 2.58x105 cd/m2 for 1 ms. Each subject was OCT imaged immediately after the flash and then every 4 minutes up to 20 minutes. Two orthogonal 6x6 mm OCT volumes of 400x400 A-scans centered at the fovea were taken at each time point. The two volumes were dispersion compensated, motion-corrected, and merged. Each volume was flattened to the IS/OS ellipsoid layer and downsampled to an 80x80 A-scan volume. The thicknesses from the IS/OS ellipsoid layer to the top of the RPE and of the outer segment indicated in Figure 1 were measured per A-scan. The average thickness values of the A-scans in a ring of 1.5 mm to 5.5 mm diameter about the fovea were recorded per time point.
Statistical analysis was completed using a one-sample t-test with a null hypothesis of 0 µm thickness difference between the time point and immediately after flash. Shown in Figure 2A, the IS/OS ellipsoid to the top of the RPE thickness significantly lengthens by 0.244 µm (95% confidence interval [CI], 0.087 to 0.402 µm), 0.362 µm (95% CI, 0.164 to 0.561 µm), 0.402 µm (95% CI, 0.183 to 0.622 µm), and 0.391 µm (95% CI, 0.171 to 0.611 µm) at time points 8, 12, 16, and 20 minutes, respectively. For the outer segment thickness difference in Figure 2B, there were no significant thickness differences.
UHR-OCT allows for resolution of photoreceptor thickness changes that occur due to photobleaching and dark adaptation. The lengthening occurs on a similar time scale to rod-based dark adaptation. These detected changes could be used as a marker to detect early signs of AMD and other diseases.
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