Translational photoacoustic ophthalmoscopy for RPE melanin concentration quantification

Melanin in retina absorbs the majority of extra incident light and protects photoreceptor cells from photo induced oxidation. It plays an important role in formation of age-related macular degeneration (AMD). Quantitative investigation of melanin will benefit both fundamental research and early diagnosis of AMD. However, non-invasive in vivo melanin quantification is challenging because the strong absorption minimized reflected light from melanin for ophthalmoscopic. Photoacoustic ophthalmoscopy (PAOM) is the only method that can directly measure absorption contrast and is suitable for melanin imaging, however, in current PAOM, piezoelectric ultrasound transducers in contact with eyelid are normally used for ultrasound detection. The bulky, opaque features of the transducers and their limited bandwidth restrict the performance of PAOM. Here we propose to develop an optically transparent, ultra-broadband contact-lens-style ultrasound detector incorporated with PAOM to achieve quantitative imaging of retinal melanin. We recently developed a polymer micro-ring optical resonator (MRR) ultrasound detector, achieving highly sensitive, ultra-broadband ultrasound detection. MRR is an optical oscillating circuit similar to LC circuit in electronics but is formed by optically transparent material in micron-scale and oscillate photons. The optical resonance of MRR is highly sensitive to surrounding pressure and the response is normally in nanosecond, supporting GHz ultrasound detection. Thus, MRR can be potentially integrated with contact lens to achieve a broadband, sensitive and easy-wear PAOM ultrasound detector for in vivo non-invasive quantitative melanin imaging.