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Y. Zhang, J. Rha, R.S. Jonnal, W. Gao, D.T. Miller; Retinal Imaging With Parallel AO Spectral OCT . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1112.
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© ARVO (1962-2015); The Authors (2016-present)
Abstract Purpose:Current clinical instruments fail to detect individual cells in the living retina owing to their small size and poor reflectivity as well as eye motion artifacts. To this end we have developed a retina camera that achieves the necessary resolution, sensitivity, and speed by incorporating adaptive optics (AO) with parallel spectral optical coherence tomography (OCT). Methods: A parallel AO spectral OCT system was constructed that is based on a free–space Michelson interferometer design. The OCT sub–system consisted of a broadband superluminescent diode ( = 843 nm) whose beam passes through an astigmatic lens to form a line illumination pattern on the retina, which is oriented parallel to the spectrometer slit; voice coil translator for controlling the optical path length of the reference channel; and an imaging spectrometer that was cascaded with a scientific–grade 12–bit area CCD array. To confirm the axial position of the focal plane in the tissue, the instrument included an incoherent flood–illuminated sub–system that captured images of the cone mosaic and retinal capillary bed. The AO sub–system consisted of a 37–actuator Xinetics mirror and a Shack–Hartmann wavefront sensor that operated at closed loop up to 22 Hz and corrected the most significant aberrations of the eye across 6mm pupil. A bite bar and forehead rest stabilized the subject’s head. Individual B–scans were collected at a single shot fashion. B–scan consisted of at least 100 A–scans (100 µm) and was acquired at short burst rates up to 500 Hz. Results: Single shot B–scans of the living retina were successfully captured with a transverse and axial resolution of <3 µm and <5 µm, respectively. The 3D resolution of these images is the highest reported to date in the living human eye. Sensitivity was sufficient for observing the major layers in the retina. High contrast speckle was present and contaminated the microscopic view. Multiple short–burst images were captured at rates exceeding 50,000 A–scans/sec. Averaging of three short–burst images reduced speckle while increasing the dynamic range by 4.5 dB. With the instrument well focused at the specific layer in the retina, early results suggest that correction of the eye’s higher–order aberrations increases OCT sensitivity. Conclusions: A parallel AO spectral OCT camera was developed and provided the highest resolution images to date of the living human retina. Initial results demonstrate an OCT system with acquisition speed more than 50,000 A–scan/sec with improved dynamic range and reduced speckle achieved by averaging multiple images of the same patch of retinal tissue.
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