Monte Carlo investigation on quantifying the retinal pigment epithelium melanin concentration by photoacoustic ophthalmoscopy

Abstract

Abstract. The retinal pigment epithelium (RPE) melanin plays an important role in maintaining normal visual functions. A decrease in the RPE melanin concentration with aging is believed to be associated with several blinding diseases, including age-related macular degeneration. Quantifying the RPE melanin noninvasively is therefore important in evaluating the retinal health and aging conditions. Photoacoustic ophthalmoscopy (PAOM), as an optical absorption-based imaging technology, can potentially be applied to measure variations in the RPE melanin if the relationship between the detected photoacoustic (PA) signal amplitudes and the RPE melanin concentrations can be established. In this work, we tested the feasibility of using PA signals from retinal blood vessels as references to measure RPE melanin variation using Monte Carlo (MC) simulation. The influences from PAOM axial resolution, the depth and diameter of the retinal blood vessel, and the RPE thickness were examined. We proposed a calibration scheme by relating detected PA signals to the RPE melanin concentrations, and we found that the scheme is robust to these tested parameters. This study suggests that PAOM has the capability of quantitatively measuring the RPE melanin in vivo.

Dual-band optical coherence tomography using a single supercontinuum laser source

“…Such a feature has the potential to facilitate RPE pathognomonic evaluation. 24 Other discrepancies also existed, which were largely due to the distinctive absorption and scattering properties within the two bands. First, visible light attenuated and dissipated quickly along the depth, so it could barely image structures beneath the RPE layer.…”

Single all-fiber-based nanosecond-pulsed supercontinuum source for multispectral photoacoustic microscopy and optical coherence tomography

“…We acquired PA A-lines of the sample repeatedly without scanning the illumination beam laterally and recorded the averaged PA signal from 32 acquisitions for each wavelength narrow band to reconstruct the absorption spectrum. Eumelanin, the dominant optical absorber in RPE, and hemoglobin in blood, are the two major contrast sources in PAM [14]. We measured their absorption spectra through optical transmission to compare them with multispectral PAM measurements.…”

Quantifying melanin concentration in retinal pigment epithelium using broadband photoacoustic microscopy

“…In ex vivo examination, melanin is the dominant optical absorber in both layers since choroidal blood is removed from tissue preparation [5,14,29,30]. The absorption coefficient can be related to the concentration of the melanin M C by mass extinction coefficient M ε , as…”

“…Though feasible, accurate quantification of the RPE melanin concentration by either OA or ESR method remained practically challenging. The RPE is only around tenmicrometer-thick and is tightly attached to choroid, a hundreds-of-micrometer-thick connective tissue layer containing large amount of melanin and blood vessels [14]. The choroidal melanin carries little pathological information and is considered of less interest [15].…”

“…Photoacoustic ophthalmoscopy (PAOM) was developed to visualize RPE melanin in vivo, demonstrating distinct difference of RPE PA generation between normal and albino mice [25]. However, quantitative RPE melanin measurement using PAM has not been performed, due to the lack of calculation model to transform the PA signal to RPE melanin concentration, as well as insufficient axial resolution (23 µm) [25] to separate RPE from choroid using piezoelectric detectors [14].…”