Melanin Pigmentation in Rat Eyes: In Vivo Imaging by Polarization-Sensitive Optical Coherence Tomography and Comparison to Histology

Estimation of polarimetric parameters has been a fundamental issue to assess biological tissues that have form birefringence or polarization scrambling in polarizationsensitive optical coherence tomography (PS-OCT). We present a mathematical framework to provide a maximum likelihood estimation of the target covariance matrix and its incoherent target decomposition to estimate a Jones matrix of a dominant scattering mechanism, called Cloude-Pottier decomposition, thereby deriving the phase retardation and the optic axis of the sample. In addition, we introduce entropy that shows the randomness of the polarization property. Underestimation of the entropy at a low sampling number is mitigated by asymptotic quasi maximum likelihood estimator. A bias of the entropy from random noises is corrected to show only the polarization property inherent in the sample. The theory is validated with experimental measurements of a glass plate and waveplates, and applied to the imaging of a healthy human eye anterior segment as an image filter.

Section: Discussionmentioning

confidence: 99%

“…6(g) showed moderately high entropy as indicated by the light-green arrows. This result is because of melanin in the pigmented tissues, which is common in the retinal pigment epithelium (RPE) [21,[54][55][56][57][58][59]. High entropy of the cornea indicated by red arrows in Fig.…”

Section: Estimation Of H Noise At a Single Depthmentioning

confidence: 99%

Estimation of Jones matrix, birefringence and entropy using Cloude-Pottier decomposition in polarization-sensitive optical coherence tomography

Yamanari¹,

Tsuda²,

Kokubun³

et al. 2016

“…In a recent study, we used a PS-OCT system with lower resolution of 7.6 µm in air (5.6 µm in tissue) to study birefringence in the peripapillary rat sclera in vivo [33]. Very recently, we used the same system for quantifying depolarization in the posterior rat eye [60]. While that study did provide a correlation of in vivo PS-OCT images with ex vivo quantification of melanin density, the resolution was not sufficient to distinguish the RPE from the choroid.…”

Section: Discussionmentioning

confidence: 99%

“…Melanin in RPE and choroid causes depolarization of backscattered light [15]. In our previous study on the depolarizing properties of these structures in rat eyes, our analysis was limited to measurements of the combined depolarizing effect of the RPE/choroid complex [60]. In this article, the improvement of axial resolution enabled us to use smaller DOPU evaluation kernels and, thus, to discriminate the depolarizing contributions of RPE and choroid.…”

Section: Discussionmentioning

confidence: 99%

Polarization properties of single layers in the posterior eyes of mice and rats investigated using high resolution polarization sensitive optical coherence tomography

Fialová¹,

Augustin²,

Glösmann³

et al. 2016

Self Cite

Abstract:We present a high resolution polarization sensitive optical coherence tomography (PS-OCT) system for ocular imaging in rodents. The system operates at 840 nm and uses a broadband superluminescent diode providing an axial resolution of 5.1 µm in air. PS-OCT data was acquired at 83 kHz A-scan rate by two identical custom-made spectrometers for orthogonal polarization states. Pigmented (Brown Norway, Long Evans) and non-pigmented (Sprague Dawley) rats as well as pigmented mice (C57BL/6) were imaged. Melanin pigment related depolarization was analyzed in the retinal pigment epithelium (RPE) and choroid of these animals using the degree of polarization uniformity (DOPU). For all rat strains, significant differences between RPE and choroidal depolarization were observed. In contrast, DOPU characteristics of RPE and choroid were similar for C57BL/6 mice. Moreover, the depolarization within the same tissue type varied significantly between different rodent strains. Retinal nerve fiber layer thickness, phase retardation, and birefringence were mapped and quantitatively measured in Long Evans rats in vivo for the first time. In a circumpapillary annulus, retinal nerve fiber layer birefringence amounted to 0.16°/µm ± 0.02°/µm and 0.17°/µm ± 0.01°/µm for the left and right eyes, respectively. 934-936 (1997). ©2016 Optical Society of America

“…To overcome the inherent limitation of 2D imaging, Baumann, et al related the depolarization contrast from 3D polarization-sensitive optical coherence tomography (PS-OCT) to RPE melanin concentration and demonstrated detecting RPE melanin difference in normal and albino human subjects. However, quantitatively measuring RPE melanin concentration has yet to be demonstrated [18,19].…”

Section: Introductionmentioning

confidence: 99%

Quantifying melanin concentration in retinal pigment epithelium using broadband photoacoustic microscopy

Xiao¹,

Li²,

Dong³

et al. 2017

Abstract:Melanin is the dominant light absorber in retinal pigment epithelium (RPE). The loss of RPE melanin is a sign of ocular senescence and is both a risk factor and a symptom of age-related macular degeneration (AMD). Quantifying the RPE melanin concentration provides insight into the pathological role of RPE in ocular aging and the onset and progression of AMD. The main challenge in accurate quantification of RPE melanin concentration is to distinguish this ten-micrometer-thick cell monolayer from the underlying choroid, which also contains melanin but carries different pathognomonic information. In this work, we investigated a three-dimensional photoacoustic microscopic (PAM) method with high axial resolution, empowered by broad acoustic detection bandwidth, to distinguish RPE from choroid and quantify melanin concentrations in the RPE ex vivo. We first conducted numerical simulation on photoacoustic generation in the RPE, which suggested that a PAM system with at least 100-MHz detection bandwidth provided sufficient axial resolution to distinguish the melanin in RPE from that in choroid. Based on simulation results, we integrated a transparent broadband micro-ring resonator (MRR) based detector in a homebuilt PAM system. We imaged ex vivo RPE-choroid complexes (RCCs) from both porcine and human eyes and quantified the absolute melanin concentrations in the RPE and choroid, respectively. In our study, the measured melanin concentrations were 14.7 mg/mL and 17.0 mg/mL in human and porcine RPE, and 12 mg/mL and 61 mg/mL in human and porcine choroid, respectively. This study suggests that broadband PAM is capable of quantifying the RPE melanin concentration from RCCs ex vivo. 164-170 (1978). 34. S. Jacques, Optical Absorption of Melanin (Oregon Medical Laser Center, 1998). 35. T. Sarna and R. C. Sealy, "Photoinduced oxygen consumption in melanin systems. Action spectra and quantum yields for eumelanin and synthetic melanin," Photochem. Photobiol. 39(1), 69-74 (1984). 36. T. Berer, E. Leiss-Holzinger, A. Hochreiner, J. Bauer-Marschallinger, and A. Buchsbaum, "Multimodal noncontact photoacoustic and optical coherence tomography imaging using wavelength-division multiplexing," J. Biomed. Opt. 20(4), 46013 (2015). 37. M. O. Culjat, D. Goldenberg, P. Tewari, and R. S. Singh, "A review of tissue substitutes for ultrasound imaging," Ultrasound Med. Biol. 36(6), 861-873 (2010).