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Francesco LaRocca, Derek Nankivil, Al-Hafeez Dhalla, Ryan McNabb, Cynthia Toth, Sina Farsiu, Joseph Izatt; Handheld Combined SLO/OCT System. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1488. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Scanning laser ophthalmoscopy (SLO) and optical coherence tomography (OCT) are widely used retinal imaging modalities that can assist in the diagnosis of retinal pathologies. Portable, handheld SLO/OCT systems would be useful in imaging patients that are supine, under anesthesia, or unable to position. While handheld SLO systems and handheld OCT systems have been described in the literature, no combined, handheld SLO/OCT system has yet been described. In consideration of optical and mechanical design constraints, we present an optimized SLO/OCT design that is handheld while maintaining high imaging speed, throughput, and resolution.
The combined handheld system contains independently controlled SLO and OCT systems with separate scanners and wavelengths (770 ± 8 nm and 840 ± 25 nm, respectively). The SLO and OCT paths combine at a dichroic mirror directly behind the final objective lens, which provides up to ± 8D of refractive correction via linear rack-and-pinion motion activation. In the optical design, near diffraction-limited resolutions of 7 µm (SLO) and 7.5 µm (OCT) were obtained over a common 20° FOV in a model eye with gradient index lens.
The handheld SLO/OCT system was fabricated and tested on normal subjects. Single-frame SLO and OCT images were acquired separately spanning a 20° FOV at 16 and 20 frames per second (fps), respectively. Representative images are shown in Figure 1. SLO and OCT image pixel resolutions were 500 x 625 and 1000 x 1024, respectively. The incident powers on the eye for the SLO and OCT were under the ANSI limit at 300 µW each, which comprised 56% and 41% of the thermal hazard MPE limit. The SNR of the OCT system was 104 dB.
We have demonstrated a compact, handheld SLO/OCT design with diffraction-limited illumination on the retina. High image quality was observed with a combined power under the ANSI limit.
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