Retinal/choroidal imaging with transcranial back-illumination

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ABSTRACT Human retinal imaging is conventionally performed with a fundus camera, which sends light into the subject’s eye and records images of the light reflected from the retina. Our goal is to develop an alternative imaging strategy based on light delivered transcranially through the subject’s temple. The light diffuses through the bone and illuminates the retina not from the front, as in a standard fundus camera, but rather mostly from the back. As such, we image light transmitted through the retina rather than reflected from the retina. In addition to being glare-free and allowing deeper image penetration well into the choroid, we hypothesize that transmitted-light imaging reveals qualitatively different tissue structure than reflected-light imaging. Our strategy will be compatible with existing fundus cameras, enabling transmission and reflection modalities to be operated quasi-simultaneously, allowing a direct comparison of the two modalities and a potential fusion of the information they provide. Specifically, we propose to equip our device with eight different LED illumination wavelengths, any two of which can be operated simultaneously, from which we propose to identify a variety of chromophore distributions such as oxy- and deoxy-hemoglobin and melanin. We hypothesize that such chromophore mapping over extended depths will provide valuable information useful for the potential diagnosis and study of macular degeneration, and for the real-time monitoring of hemodynamics. To gauge the performance of our device and its potential utility in the clinic, we have enlisted the help of Dr. Elias Reichel at the Tufts Medical Center, who has clinical experience with both fundus and OCT imaging.