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Hao Zhang, Shuliang Jiao, Tan Liu, Wei Song; Photoacoustic ophthalmoscopy guided by real-time fundus camera. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1493.
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We want to test the feasibility of integrating photoacoustic ophthalmoscopy (PAOM) with fundus photography for guiding and cross-modality imaging. If successful, PAOM based retinal oximetry can be compared and verified with fundus photography based retinal oximetry.
We constructed a fundus imager using a wide-spectrum, dark-field illumination, and a high-sensitivity, high-speed CCD camera. Then we combined the fundus imager with PAOM through a beam splitter, after which illumination lights for both fundus camera and PAOM merge before passing through the objective lens and entering the eye. When PAOM illumination was on, the reflected laser light from retina can be detected by the CCD in addition to fundus image. As a result, when PAOM is being aligned, its laser illumination position can be monitored in real-time by the fundus camera to better identify region of interests. The PAOM is illuminated by a tunable laser system for the next-stage multi-wavelength PAOM oximetry and the fundus camera can be achieved within both visible (VIS) and near infrared (NIR) spectral ranges.
Both albino and pigmented rat eyes were imaged in vivo. In albino rat, VIS-illumination fundus image provided very high contrast, with several choroidal vessels clearly observed, and the result was comparable to PAOM image. In comparison, NIR-illumination fundus showed much worse image contrast. In pigmented rat, the radial striation feature of retinal nerve fiber layer can be observed in the full-spectrum illumination fundus image, but are absent in narrow-band fundus images. Comparing to fundus camera, PAOM provided a higher contrast in imaging retinal vessels and the melanin distribution in the retinal pigment epithelium in pigmented eyes. However, PAOM has only limited field-of-view and cannot provide fundus imaging in real-time.
We successfully integrated PAOM with a fundus camera. The fundus camera is capable of wide-band illuminating, which sets the stage for conducting fundus photography based oximetry and comparing with PAOM based oximetry on the same subjects in vivo. Moreover, integrating with NIR fundus camera makes it is easier for PAOM to be adopted into clinics in the future.
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