Lateral Resolution of a Commercial Optical Coherence Tomography Instrument

Abstract

Purpose The lateral resolution of an optical coherence tomography (OCT) instrument was considered to be equal to the illumination spot size on the retina. To evaluate the potential lateral resolution of the Spectralis OCT, an instrument calculated to have a 14 µm resolution. Methods The lateral point spread function (PSF) was evaluated using diamond abrasive powder 0 to 1 µm in diameter in silicone elastomer and a validated target with 800 nm FeO particles in urethane. The amplitude transfer function was calculated from human OCT images. Finally, resolution was measured using the 1951 USAF target. Results Measurement of the lateral PSF from 1215 diamond particle images yielded a full-width half maximum (FWHM) to be 5.11 µm and for 732 FeO particles, 4.9 µm. From the amplitude transfer function, the FWHM of the diffraction limited PSF was calculated to be 5.0 µm. The USAF target imaging showed a lateral resolution of 4.6 µm. Conclusions Although a calculation of the spot size of the illumination beam was reported in the past as the lateral resolution of the OCT instrument, the actual lateral resolution is better by a factor of at least 2.5 times. The clinically used A-scan spacing was derived from the calculated, and not the true resolution, and results in under sampling. This set of findings likely apply to all commercial clinical instruments. Translational Relevance The scan density parameters of past and present commercial OCT instruments were based on earlier translational concepts, which now appear to have been incorrect.

Spatio-temporal optical coherence tomography provides full thickness imaging of the chorioretinal complex

“…To show that the STOC-T system improves penetration depth into the choroid, we compared the relative changes in OCT signal against two commercially available scanning OCT devices with nominal values of lateral resolution of 15 μm and 20 μm, respectively, which correspond theoretically to values of the confocal parameter of 450 μm and 650 μm, respectively ( Figure 4 A). 50 Because of differences in exposure times, number of averages, and scan densities, the signals were normalized with respect to the reflectance values from the IS/OS layer and the hypo-reflective signal corresponding to the outer parts of the photoreceptors. The graphs are shown on a logarithmic scale in Figure 4 B.…”

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“…The discrepancy between the dots seen in AO and their more diffuse, appearance on SD-OCT may be explained by the larger point spread function of the SD-OCT, which would blur many individual points into one hyperreflective region along the scan line. 6,8 Retinal crystalline deposits may arise as a sign of different entities such as Niemann-Pick disease, Bietti crystalline dystrophy, hyperoxaluria, cystinosis, and Sjögren-Larsson syndrome. 9 However, these pathologies include ocular and systemic manifestations not present in our patient.…”

“…The discrepancy between the dots seen in AO and their more diffuse, appearance on SD-OCT may be explained by the larger point spread function of the SD-OCT, which would blur many individual points into one hyperreflective region along the scan line. 6,8…”

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