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Xiao Shu, Hao Li, Biqin Dong, Hao F Zhang; Quantifying melanin concentration and light-induced melanin loss in retinal pigment epithelium by photoacoustic microscopy. Invest. Ophthalmol. Vis. Sci. 2016;57(12):4946.
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© ARVO (1962-2015); The Authors (2016-present)
There is currently no effective way to quantify the melanin concentration in the retinal pigment epithelium (RPE) noninvasively, though its loss is believed to be both a cause and a sign of age-related macular degeneration (AMD). Recently, photoacoustic microscopy (PAM) has become an emerging imaging technology capable of quantifying endogenous chromophores in biological tissues, such as hemoglobin and epidermal melanin. We hypothesize that RPE melanin concentration and its loss can be monitored by PAM.
Phantoms were made by mixing purified squid melanin granules with agarose and then solidified in 12-µm deep cavity to mimic RPE layer. The melanin concentration in the phantom was controlled by reagent weight and confirmed by optical density (OD) measurement. The PAM system was calibrated by relating photoacoustic (PA) signal amplitudes generated by the RPE phantoms to their known melanin concentration. Porcine and human RPE samples were peeled off from formalin-fixed eyeballs and tested on the calibrated system. Broadband micro-ring ultrasonic transducer was used in PA detection to ensure sufficient axial resolution to locate the 10-µm cell monolayer and minimize influence from the choroidal melanin, which is of little pathological interest. We measured the melanin concentration in pig and human RPE and monitored light-induced melanin loss in pig RPE.
While the RPE melanin concentrations are comparable between pig and human, more melanin is found in the pig choroid. The RPE melanin loss can be caused by light illumination and the loss rate increases with higher power.
PAM is capable of quantifying the RPE melanin concentration and its variation noninvasively with the help of broadband micro-ring transducer.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
Measurement of the RPE melanin concentration by PAM. (a)-(d) PAM images of pig RPE, pig choroid, human RPE and human choroid. (e) Comparison of ocular melanin distribution between pig and human. (f) Quantification of light-induced melanin loss.
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