Purchase this article with an account.
Tingwei Zhang, Shau Poh Poh Chong, Aaron Michael Kho, Marcel Bernucci, Alfredo Dubra, Vivek Jay Srinivasan; Achromatized visible light OCT for ultrahigh resolution retinal imaging. Invest. Ophthalmol. Vis. Sci. 2018;59(9):299.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Visible light OCT theoretically provides better resolution than near-infrared OCT and enables spectroscopic imaging of chromophores such as hemoglobin. However, achievable spectral bandwidth and axial resolution are limited by chromatic aberrations. In particular, longitudinal chromatic aberration (LCA) of the human eye is significantly greater for visible light than for near-infrared light. To achieve ultrahigh resolution and high efficiency visible light OCT, correction of LCA is needed.
Starting with our visible light spectral / Fourier domain OCT ophthalmoscope, we incorporated a reflective collimator and a custom zero-power triplet achromatizing lens (AL) in the sample arm, to compensate population-averaged LCA of the human eye. In the spectrometer, a reflective collimator and focusing lens were chosen to generate a linear chromatic focal shift, to minimize the sensitivity rolloff. To minimize light exposure, 0.03 mW at the cornea was used to align the subject, and 0.15 mW was used for image acquisition. The axial scan rate ranged from 10 kHz-70 kHz. Two volumetric scan protocols were investigated: 1) 4096 axial scans with a 6.5 mm FOV along the fast axis; and 2) 168 axial scans with a 0.16 mm FOV along the fast axis. The improvement in detected spectral bandwidth with achromatization was assessed by analyzing complex speckles in retinal images.
In vivo human retinal images from protocol 1 are shown in Fig. 1. Bruch’s membrane (BM) and the retinal pigment epithelium (RPE) can be clearly distinguished across the entire 6.5 mm FOV. Retinal images from protocol 2, generated by motion correction, speckle reduction, and maximum intensity projection along the slow axis, are shown in Fig. 2. Distinct textures in inner retinal layers are evident. Finally, achromatization improved the achievable axial resolution by ~20% (~1.7 µm).
Chromatic aberrations are important to consider in visible light OCT. With compensation of the population-averaged LCA of the human eye, achievable axial resolution and image quality improved. Further improvements are achievable by compensating monochromatic and transverse chromatic aberrations.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
(A) Ultrahigh resolution visible light OCT imaging of the macula. (B) Zoom of white box in panel A, showing six outer retinal bands.
(A) Inner retinal imaging with visible light OCT at ~2° nasal to the fovea. (B-D) The inner retinal layers show a texture suggestive of neurites.
This PDF is available to Subscribers Only