Multi-Functional OCT Enables Longitudinal Study of Retinal Changes in a VLDLR Knockout Mouse Model

Quantification of microvascular change of retinal degeneration in Royal College of Surgeons rats using high-resolution spectral domain optical coherence tomography angiography

Significance

For research on retinitis pigmentosa in humans, the Royal College of Surgeons (RCS) rat is commonly used as the primary animal model since the disease process is similar. Therefore, it is necessary to understand how the disease develops and determine whether the treatment is effective.

Aim

In this study, structural and microvascular change of retinal degeneration in RCS rats was assessed non-invasively on specific dates over 3.5 months.

Approach

Using a high-resolution spectral domain (SD) optical coherence tomography angiography (OCTA), the retinal degeneration in RCS rats, from day 14 until day 126, was qualitatively and quantitatively analyzed.

Results

Aside from the thinning of the retina thickness starting from 2 weeks of age, blood vessels in the deep layer of the retina also began to degenerate at about 4 weeks of age. Hole structures appeared at the inner nuclear layer and the inner plexiform layer by the age of 10 weeks. Observations of abnormal angiogenesis in the choroid began by 12 weeks of age.

Conclusions

We conducted a longitudinal study of retina degeneration structure and vascular changes in an RCS rat model using a supercontinuum laser based high-resolution SD-OCTA. Combined with OCTA, OCT leads to a better understanding of photoreceptor pathology as retinal degeneration by identifying tissue and vessel loss.

Synthesizing the degree of polarization uniformity from non-polarization-sensitive optical coherence tomography signals using a neural network

Degree of polarization uniformity (DOPU) imaging obtained by polarization-sensitive optical coherence tomography (PS-OCT) has the potential to provide biomarkers for retinal diseases. It highlights abnormalities in the retinal pigment epithelium that are not always clear in the OCT intensity images. However, a PS-OCT system is more complicated than conventional OCT. We present a neural-network-based approach to estimate the DOPU from standard OCT images. DOPU images were used to train a neural network to synthesize the DOPU from single-polarization-component OCT intensity images. DOPU images were then synthesized by the neural network, and the clinical findings from ground truth DOPU and synthesized DOPU were compared. There is a good agreement in the findings for RPE abnormalities: recall was 0.869 and precision was 0.920 for 20 cases with retinal diseases. In five cases of healthy volunteers, no abnormalities were found in either the synthesized or ground truth DOPU images. The proposed neural-network-based DOPU synthesis method demonstrates the potential of extending the features of retinal non-PS OCT.

Degeneration of Melanin-Containing Structures Observed Longitudinally in the Eyes of SOD1-/- Mice Using Intensity, Polarization, and Spectroscopic OCT

Purpose

Melanin plays an important function in maintaining eye health, however there are few metrics that can be used to study retinal melanin content in vivo.

Methods

The slope of the spectral coefficient of variation (SSCoV) is a novel biomarker that measures chromophore concentration by analyzing the local divergence of spectral intensities using optical coherence tomography (OCT). This metric was validated in a phantom and applied in a longitudinal study of superoxide dismutase 1 knockout (SOD1^−/−) mice, a model for wet and dry age-related macular degeneration. We also examined a new feature of interest in standard OCT image data, the ratio of maximum intensity in the retinal pigment epithelium to that of the choroid (RC ratio). These new biomarkers were supported by polarization-sensitive OCT and histological analysis.

Results

SSCoV correlated well with depolarization metrics both in phantom and in vivo with both metrics decreasing more rapidly in SOD1^−/− mice with age (P < 0.05). This finding is correlated with reduced melanin pigmentation in the choroid over time. The RC ratio clearly differentiated the SOD1^−/− and control groups (P < 0.0005) irrespective of time and may indicate lower retinal pigment epithelium melanin in the SOD1^−/− mice. Histological analysis showed decreased melanin content and potential differences in melanin granule shape in SOD1^−/− mice.

Conclusions

SSCoV and RC ratio biomarkers provided insights into the changes of retinal melanin in the SOD1^−/− model longitudinally and noninvasively.

Translational Relevance

These biomarkers were designed with the potential for rapid adoption by existing clinical OCT systems without requiring new hardware.

Pulsatile tissue deformation dynamics of the murine retina and choroid mapped by 4D optical coherence tomography

Irregular ocular pulsatility and altered mechanical tissue properties are associated with some of the most sight-threatening eye diseases. Here we present 4D optical coherence tomography (OCT) for the quantitative assessment and depth-resolved mapping of pulsatile dynamics in the murine retina and choroid. Through a pixel-wise analysis of phase changes of the complex OCT signal, we reveal spatiotemporal displacement characteristics across repeated frame acquisitions. We demonstrate in vivo fundus elastography (FUEL) imaging in wildtype mouse retinas and in a mouse model of retinal neovascularization and uncover subtle structural deformations related to ocular pulsation. Our data in mouse eyes hold promise for a powerful retinal elastography technique that may enable a new paradigm of OCT-based measurements and image contrast.

Morphometric and Microstructural Changes During Murine Retinal Development Characterized Using In Vivo Optical Coherence Tomography

Purpose

The purpose of this study was to develop an in vivo optical coherence tomography (OCT) system capable of imaging the developing mouse retina and its associated morphometric and microstructural changes.

Methods

Thirty-four wild-type mice (129S1/SvlmJ) were anesthetized and imaged between postnatal (P) day 7 and P21. OCT instrumentation was developed to optimize signal intensity and image quality. Semi-automatic segmentation tools were developed to quantify the retinal thickness of the nerve fiber layer (NFL), inner plexiform layer (IPL), inner nuclear layer (INL), and the outer retinal layers (ORL), in addition to the total retina. The retinal maturation was characterized by comparing layer thicknesses between consecutive time points.

Results

From P7 to P10, the IPL increased significantly, consistent with retinal synaptogenesis. From P10 to P12, the IPL and ORL also increased, which is coherent with synaptic connectivity and photoreceptor maturation. In contrast, during these periods, the INL decreased significantly, consistent with cellular densification and selective apoptotic “pruning” of the tissue during nuclear migration. Thereafter from P12 to P21, the INL continued to thin (significantly from P17 to P21) whereas the other layers remained unchanged. No time-dependent changes were observed in the NFL. Overall, changes in the total retina were attributed to those in the IPL, INL, and ORL. Regions of the retina adjacent to the optic nerve head were thinner than distal regions during maturation.

Conclusions

Changes in retinal layer thickness are consistent with retinal developmental mechanisms. Accordingly, this report opens new horizons in using our system in the mouse to characterize longitudinally developmental digressions in models of human diseases.

High-resolution, depth-resolved vascular leakage measurements using contrast-enhanced, correlation-gated optical coherence tomography in mice

Vascular leakage plays a key role in vision-threatening retinal diseases such as diabetic retinopathy and age-related macular degeneration. Fluorescence angiography is the current gold standard for identification of leaky vasculature in vivo, however it lacks depth resolution, providing only 2D images that complicate precise identification and localization of pathological vessels. Optical coherence tomography (OCT) has been widely adopted for clinical ophthalmology due to its high, micron-scale resolution and rapid volumetric scanning capabilities. Nevertheless, OCT cannot currently identify leaky blood vessels. To address this need, we have developed a new method called exogenous contrast-enhanced leakage OCT (ExCEL-OCT) which identifies the diffusion of tracer particles around leaky vasculature following injection of a contrast agent. We apply this method to a mouse model of retinal neovascularization and demonstrate high-resolution 3D vascular leakage measurements in vivo for the first time.

Vascular morphology and blood flow signatures for differential artery-vein analysis in optical coherence tomography of the retina

Differential artery-vein (AV) analysis is essential for retinal study, disease detection, and treatment assessment. This study is to characterize vascular reflectance profiles and blood flow patterns of retinal artery and vein systems in optical coherence tomography (OCT) and OCT angiography (OCTA), and establish them as robust signatures for objective AV classification. A custom designed OCT was employed for three-dimensional (3D) imaging of mouse retina, and corresponding OCTA was reconstructed. Radially resliced OCT B-scans revealed two, i.e. top and bottom, hyperreflective wall boundaries in retinal arteries, while these wall boundaries were absent in OCT of retinal veins. Additional OCTA analysis consistently displayed a layered speckle distribution in the vein, which may indicate the venous laminar flow. These OCT and OCTA differences offer unique signatures for objective AV classification in OCT and OCTA.

Quantitative multi-contrast in vivo mouse imaging with polarization diversity optical coherence tomography and angiography

Retinal microvasculature and the retinal pigment epithelium (RPE) play vital roles in maintaining the health and metabolic activity of the eye. Visualization of these retina structures is essential for pre-clinical studies of vision-robbing diseases, such as age-related macular degeneration (AMD). We have developed a quantitative multi-contrast polarization diversity OCT and angiography (QMC-PD-OCTA) system for imaging and visualizing pigment in the RPE using degree of polarization uniformity (DOPU), along with flow in the retinal capillaries using OCT angiography (OCTA). An adaptive DOPU averaging kernel was developed to increase quantifiable values from visual data, and QMC en face images permit simultaneous visualization of vessel location, depth, melanin region thickness, and mean DOPU values, allowing rapid identification and differentiation of disease symptoms. The retina of five different mice strains were measured in vivo, with results demonstrating potential for pre-clinical studies of retinal disorders.

Indocyanine green provides absorption and spectral contrast for optical coherence tomography at 840 nm in vivo

In recent years, there has been growing interest in the application of exogenous contrast agents to supplement the traditional strengths of optical coherence tomography (OCT) and provide additional biological information. In this Letter, we present how indocyanine green, a common fluorescent contrast agent approved by the United States Food and Drug Administration, can provide absorption and spectral contrast for OCT imaging in the mouse eye in vivo. We further demonstrate high stability of spectral contrast measurements for the long-term monitoring of contrast agents in spite of fluctuations in intensity.

Optical Coherence Tomography Findings in the Retinas of SOD1 Knockout Mice

Purpose

The retinal phenotype of popular mouse models mimicking ophthalmic diseases, such as the superoxide dismutase 1 (SOD1) knockout (KO) mouse model, has mainly been assessed by ex vivo histology and in vivo fundus photography. We used multifunctional optical coherence tomography (OCT) to characterize the retinas of SOD1 KO mice in vivo.

Methods

The custom-made ophthalmoscope featured a combination of conventional OCT, polarization-sensitive OCT, and OCT angiography. Seven SOD1 KO mice and nine age-matched controls were imaged between 6 and 17 months of age. A postprocessing framework was used to analyze total and outer retinal thickness changes. Drusenlike lesions were segmented, and their sizes and the number of lesions were assessed quantitatively. Their appearance in the conventional reflectivity images, as well as in the corresponding polarization-sensitive images, was characterized qualitatively.

Results

Drusenlike lesions increased in size and number with age for SOD1 KO mice. Exploiting the multiple contrast channels, the appearance of the lesions was found to resemble pseudodrusen observed in eyes of patients suffering from dry age-related macular degeneration. The total and outer retinal thicknesses were lower on average after 11 months and 7 months in SOD1 KO mice compared with age-matched controls. Neovascularizations were found in one out of seven KO animals.

Conclusions

OCT imaging proved beneficial for a detailed in vivo characterization of the pathological changes in SOD1 KO mice.

Translational Relevance

Phenotyping of animal models using modern imaging concepts can be conducted with more precision and might also ease the translation of conclusions between clinical and preclinical research.

Retinal analysis of a mouse model of Alzheimer's disease with multicontrast optical coherence tomography

Significance. Recent Alzheimer's disease (AD) patient studies have focused on retinal analysis, as the retina is the only part of the central nervous system that can be imaged noninvasively by optical methods. However, as this is a relatively new approach, the occurrence and role of retinal pathological features are still debated. Aim. The retina of an APP/PS1 mouse model was investigated using multicontrast optical coherence tomography (OCT) in order to provide a documentation of what was observed in both transgenic and wild-type mice. Approach. Both eyes of 24 APP/PS1 transgenic mice (age: 45 to 104 weeks) and 15 age-matched wild-type littermates were imaged by the custom-built OCT system. At the end of the experiment, retinas and brains were harvested from a subset of the mice (14 transgenic, 7 age-matched control) in order to compare the in vivo results to histological analysis and to quantify the cortical amyloid beta plaque load. Results. The system provided a combination of standard reflectivity data, polarization-sensitive data, and OCT angiograms. Qualitative and quantitative information from the resultant OCT images was extracted on retinal layer thickness and structure, presence of hyper-reflective foci, phase retardation abnormalities, and retinal vasculature. Conclusions. Although multicontrast OCT revealed abnormal structural properties and phase retardation signals in the retina of this APP/PS1 mouse model, the observations were very similar in transgenic and control mice.

Optical Coherence Tomography Angiography in Mice: Quantitative Analysis After Experimental Models of Retinal Damage

Purpose

We implemented optical coherence tomography angiography (OCT-A) in mice to: (1) develop quantitative parameters from OCT-A images, (2) measure the reproducibility of the parameters, and (3) determine the impact of experimental models of inner and outer retinal damage on OCT-A findings.

Methods

OCT-A images were acquired with a customized system (Spectralis Multiline OCT2). To assess reproducibility, imaging was performed five times over 1 month. Inner retinal damage was induced with optic nerve transection, crush, or intravitreal N-methyl-d-aspartic acid injection in transgenic mice with fluorescently labeled retinal ganglion cells (RGCs). Light-induced retinal damage was induced in albino mice. Mice were imaged at baseline and serially post injury. Perfusion density, vessel length, and branch points were computed from OCT-A images of the superficial, intermediate, and deep vascular plexuses.

Results

The range of relative differences measured between sessions across the vascular plexuses were: perfusion density (2.8%-7.0%), vessel length (1.9%-4.1%), and branch points (1.9%-5.0%). In mice with progressive RGC loss, imaged serially and culminating in around 70% loss in the fluorescence signal and 18% loss in inner retinal thickness, there were no measurable changes in any OCT-A parameter up to 4 months post injury that exceeded measurement variability. However, light-induced retinal damage elicited a progressive loss of the deep vascular plexus signal, starting as early as 3 days post injury.

Conclusions

Vessel length and branch points were generally the most reproducible among the parameters. Injury causing RGC loss in mice did not elicit an early change in the OCT-A signal.

En-Face Optical Coherence Tomography Angiography for Longitudinal Monitoring of Retinal Injury

A customized Optical Coherence Tomography Angiography (OCTA) algorithm and Orthogonal OCT (en-face and B-Scans) were used for longitudinal assessment of retina murine vascular and tissue remodeling comparing photoreceptor ablation and laser-induced Choroidal Neovascularization (CNV). In the mouse model, we utilized a combined OCTA/OCT technique to image and quantify morphological and vascular features of laser lesions over time. This approach enabled us to monitor and correlate the dynamics of retina vascular and tissue remodeling as evidenced by swelling, edema, and scarring. From the OCT B-Scans, three stages of inflammatory progression were identified: the early response occurring within hours to day 3, the transition phase from 3-7 days, and the late stage of 7-21 days entering either the resolving phase or chronic phase, respectively. For the case of CNV, en-face OCTA revealed a transient non-perfusion of inner retina capillaries, specifically Deep Vascular Plexus (DVP), which corresponded to growth in lesions of a height of 200 μm or greater. Non-perfusion first occurred at 24 hours, persisted during edema and CNV formation days 7-14. In contrast, the acute inflammation induced photoreceptor damage, but no detectable alterations to the microvasculature were observed. We demonstrated that the en-face OCTA system is capable of visualizing capillary networks (~5 μm) and the corresponding tissue remodeling and growth dynamics allowing for separating acute injury from CNV. For the first time, by using OCTA we observed the presence of the 5-10 μm capillary non-perfusion present in DVP as part of CNV formation and the associated wound healing in the retina.

Scattering-Angle-Resolved Optical Coherence Tomography of a Hypoxic Mouse Retina Model

Several studies have noted a correlation between retinal degeneration and traumatic encephalopathy (TE) making the retina a leading candidate for detection and assessment. Scattering-angle-resolved optical coherence tomography (SAR-OCT) is a candidate imaging modality to detect sub-resolution changes in retinal microstructure. SAR-OCT images of murine retinas that experience a hypoxic insult-euthanasia by isoflurane overdose-are presented. A total of 4 SAR-OCT measurement parameters are reported in 6 longitudinal experiments: blood flow volume fraction, total retinal thickness, reflectance index, and scattering angle. As each mouse expires, blood flow volume fraction decreases, total retinal thickness increases, reflectance index decreases, and scattering angle diversity increases. Contribution of the retinal vasculature to scattering angle diversity is discussed. Results of this study suggest the utility of SAR-OCT to measure TE using scattering angle diversity contrast in the retina.

Supercontinuum source-based multi-contrast optical coherence tomography for rat retina imaging

This study proposed an ultrahigh-resolution multi-contrast optical coherence tomography system integrated with fundus photography for in vivo retinal imaging of rodents. A supercontinuum light source was used in the system, providing an axial resolution of less than 3 µm within 1.8 mm (in the tissue). Three types of tissue contrast based on backscattered intensity, phase retardation, and microvasculature at a capillary level can be simultaneously obtained using the proposed system. Pigmented Long-Evans, non-pigmented (albino) Sprague Dawley, and Royal College of Surgeons rats were imaged and compared. In vivo imaging results were validated with histology.

Polarization-sensitive optical coherence tomography imaging of the anterior mouse eye

Polarization-sensitive optical coherence tomography (PS-OCT) enables noninvasive, high-resolution imaging of tissue polarization properties. In the anterior segments of human eyes, PS-OCT allows the visualization of birefringent and depolarizing structures. We present the use of PS-OCT for imaging the murine anterior eye. Using a spectral domain PS-OCT setup operating in the 840-nm regime, we performed in vivo volumetric imaging in anesthetized C57BL/6 mice. The polarization properties of murine anterior eye structures largely replicated those known from human PS-OCT imagery, suggesting that the mouse eye may also serve as a model system under polarization contrast. However, dissimilarities were found in the depolarizing structure of the iris which, as we confirmed in postmortem histological sections, were caused by anatomical differences between both species. In addition to the imaging of tissues in the anterior chamber and the iridocorneal angle, we demonstrate longitudinal PS-OCT imaging of the murine anterior segment during mydriasis as well as birefringence imaging of corneal pathology in an aged mouse.

White light polarization sensitive optical coherence tomography for sub-micron axial resolution and spectroscopic contrast in the murine retina

A white light polarization sensitive optical coherence tomography system has been developed, using a supercontinuum laser as the light source. By detecting backscattered light from 400 - 700 nm, an axial resolution of 1.0 µm in air was achieved. The system consists of a free-space interferometer and two homemade spectrometers that detect orthogonal polarization states. Following system specifications, images of a healthy murine retina as acquired by this non-contact system are presented, showing high resolution reflectivity images as well as spectroscopic and polarization sensitive contrast. Additional images of the very-low-density-lipoprotein-receptor (VLDLR) knockout mouse model were acquired. The high resolution allows the detection of small lesions in the retina.

Isolation and Culture of Primary Mouse Retinal Pigment Epithelial (RPE) Cells with Rho-Kinase and TGFβR-1/ALK5 Inhibitor

Background

Primary RPE cells could be a reliable model for representing in vivo status of RPE compared with cell lines. We present a protocol for in vitro isolation and culture of primary RPE cells from C57BL mice.

Material/Methods

We used C57BL mice ages 7 days to 4 months. The RPE layer was separated from the neural retina layer by digestion with 2% Dispase for 45 min and scraped off from the choroid after 25-min incubation in 37°C. Collected RPE sheets were gently pipetted up into smaller sheets. RPE sheets were transferred into well plates and cultured in vitro for 2 weeks. To inhibit epithelial-mesenchymal transition (EMT) of RPE cells, we used Y27632 and Repsox to treat cultured primary RPE cells.

Results

RPE cells isolated from C57BL mice maintained pigmented and hexagonal morphology in culture. However, long-term in vitro culture lead to the periphery cells of a RPE sheet becoming mesenchymal-like cells. In contrast to the control group, Y27632 and Repsox, which are inhibitors of Rho-kinase or TGFβR-1/ALK5, promoted primary RPE cells to maintain epithelial-like morphology and eventually become confluent.

Conclusions

RPE cells isolated from C57BL mice could be a powerful cell model to study the biological function of RPE. Especially, C57BL mice with different defective genetic background resulting in ocular diseases, would expand the genome type of RPE cells. The method presented here could be an efficient and applicable technique to obtain large numbers of primary RPE cells that maintain some characteristics of in vivo RPE.

Multi-directional optical coherence tomography for retinal imaging

We introduce multi-directional optical coherence tomography (OCT), a technique for investigation of the scattering properties of directionally reflective tissue samples. By combining the concepts of multi-channel and directional OCT, this approach enables simultaneous acquisition of multiple reflectivity depth-scans probing a mutual sample location from differing angular orientations. The application of multi-directional OCT in retinal imaging allows for in-depth investigations on the directional reflectivity of the retinal nerve fiber layer, Henle's fiber layer and the photoreceptor layer. Major ophthalmic diseases (such as glaucoma or age-related macular degeneration) have been reported to alter the directional reflectivity properties of these retinal layers. Hence, the concept of multi-directional OCT might help to gain improved understanding of pathology development and progression. As a first step, we demonstrate the capabilities of multi-directional OCT in the eyes of healthy human volunteers.

Multifunctional in vivo imaging for monitoring wound healing using swept-source polarization-sensitive optical coherence tomography

BACKGROUND AND OBJECTIVE

Wound healing involves a complex and dynamic biological process in response to tissue injury. Monitoring of the cascade of cellular events is useful for wound management and treatment. The aim of this study is to demonstrate the potential of multifunctional polarization-sensitive optical coherence tomography (PS-OCT) to longitudinally monitor the self-healing process in a murine cutaneous wound model.

MATERIALS AND METHODS

A multi-functional PS-OCT system based on swept source OCT configuration (1,310 nm central wavelength) was designed to obtain simultaneously microstructural, blood perfusion, and birefringent information of a biological tissue in vivo. A 1-mm-diameter wound was generated in a mouse pinna with a complete biopsy punch. Afterwards, the self-healing process of the injured tissue was observed every week over 6-week period using the multifunctional system to measure changes in the tissue birefringence. Further OCT angiography (OCTA) was used in post data processing to obtain blood perfusion information over the injured tissue.

RESULTS

Three complementary images indicating the changes in anatomical, vascular, and birefringent information of tissue around wound were simultaneously provided from a 3-dimensional (3-D) PS-OCT data set during the wound repair over 1 month. Specifically, inflammatory and proliferative phases of wound healing were characterized by thickened epidermal tissue (from OCT images) and angiogenesis (from OCT angiography images) around wound. Also, it was observed that the regenerating tissues had highly realigned birefringent structures (from PS-OCT images).

CONCLUSION

This preliminary study suggests that the proposed multi-functional imaging modality has a great potential to improve the understanding of wound healing through non-invasive, serial monitoring of vascular and tissue responses to injury. Lasers Surg. Med. 50:213-221, 2018. © 2017 Wiley Periodicals, Inc.

Clinicopathologic Correlation of Anti-Vascular Endothelial Growth Factor-Treated Type 3 Neovascularization in Age-Related Macular Degeneration

PURPOSE

To correlate histologic results with previously recorded multimodal imaging results from a patient with type 3 neovascularization secondary to age-related macular degeneration (AMD).

DESIGN

Case study, clinical imaging, laboratory imaging, and eye-tracked clinicopathologic correlation.

PARTICIPANT

An 86-year-old white woman with type 3 neovascularization secondary to AMD treated with 6 intravitreal injections of bevacizumab.

METHODS

Multimodal retinal imaging at each clinic visit was correlated with ex vivo and high-resolution histologic images of the preserved donor eye. Clinical imaging included serial near-infrared reflectance and eye-tracked spectral-domain OCT. Eye tracking, applied to the donor eye, enabled identification of histologic features corresponding to clinical OCT signatures.

MAIN OUTCOME MEASURES

Histologic correlates for clinical OCT signatures were sought, including reflectivity of the vascular complex, intraretinal hyperreflective foci and intraretinal cellularity, analysis of the topography of pathologic features, and evaluation of the sub-retinal pigment epithelium (RPE) plus basal lamina (BL) space.

RESULTS

Clinical imaging showed a deep neovascular lesion in close relationship with a mixed serous and drusenoid pigment epithelium detachment (PED), characteristic of type 3 neovascularization. Antiangiogenic therapy achieved a complete resolution of exudation. The PED progressively flattened with each treatment, leaving a persistent triangular hyperreflectivity in the outer retina. This persistent deep lesion histologically correlated with a vascular complex implanted into sub-RPE basal laminar deposit. No connection between the choriocapillaris and the sub-RPE plus BL space was observed. Both RPE-derived and lipid-filled cells were correlated with clinical intraretinal hyperreflective foci. The sub-RPE plus BL space contained macrophages, lymphocytes, Müller cell processes, and subducted RPE.

CONCLUSIONS

Clinicopathologic correlation of type 3 neovascularization showed vascular elements of retinal origin accompanied by collagenous material and Müller cell processes implanting into thick sub-RPE basal laminar deposit, which may simulate the appearance of chorioretinal anastomosis. Surrounding RPE-derived and lipid-filled cells thought to be microglia correlated with clinical intraretinal hyperreflective foci.

Ocular fundus pulsations within the posterior rat eye: Chorioscleral motion and response to elevated intraocular pressure

A multi-functional optical coherence tomography (OCT) approach is presented to determine ocular fundus pulsations as an axial displacement between the retina and the chorioscleral complex in the albino rat eye. By combining optical coherence elastography and OCT angiography (OCTA), we measure subtle deformations in the nanometer range within the eye and simultaneously map retinal and choroidal perfusion. The conventional OCT reflectivity contrast serves as a backbone to segment the retina and to define several slabs which are subsequently used for quantitative ocular pulsation measurements as well as for a qualitative exploration of the multi-functional OCT image data. The proposed concept is applied in healthy albino rats as well as in rats under acute elevation of the intraocular pressure (IOP). The evaluation of this experiment revealed an increased pulsatility and deformation between the retinal and chorioscleral complex while increasing the IOP level from 15 mmHg to 65 mmHg. At IOP levels exceeding 65 mmHg, the pulsatility decreased significantly and retinal as well as choroidal perfusion vanished in OCTA. Furthermore, the evaluation of the multi-parametric experiment revealed a spatial correlation between fundus pulsatility and choroidal blood flow. This indicates that the assessed pulsatility may be a valuable parameter describing the choroidal perfusion.

Evaluation of intraretinal migration of retinal pigment epithelial cells in age-related macular degeneration using polarimetric imaging

The purpose of the present study was to evaluate the intraretinal migration of the retinal pigment epithelium (RPE) cells in age-related macular degeneration (AMD) using polarimetry. We evaluated 155 eyes at various AMD stages. Depolarized light images were computed using a polarization-sensitive scanning laser ophthalmoscope (PS-SLO), and the degree of polarization uniformity was calculated using polarization-sensitive optical coherence tomography (OCT). Each polarimetry image was compared with the corresponding autofluorescence (AF) images at 488 nm (SW-AF) and at 787 nm (NIR-AF). Intraretinal RPE migration was defined by the presence of depolarization at intraretinal hyperreflective foci on PS-SLO and PS-OCT images, and by the presence of hyper-AF on both NIR-AF and SW-AF images. RPE migration was detected in 52 of 155 eyes (33.5%) and was observed in drusenoid pigment epithelial detachment (PED) and serous PED with significantly higher frequencies than in other groups (P = 0.015). The volume of the migrated RPE cluster in serous PED was significantly correlated with the volume of the PED (R² = 0.26; P = 0.011). Overall, our results showed that intraretinal RPE migrations occurred in various AMD stages, and that they occurred more commonly in eyes with serous and drusenoid PED.

Simultaneous Fluorescein Angiography and Spectral Domain Optical Coherence Tomography Correlate Retinal Thickness Changes to Vascular Abnormalities in an In Vivo Mouse Model of Retinopathy of Prematurity

Background

Retinopathy of prematurity (ROP) is a condition of abnormal retinal vascular development (RVD) in premature infants. Fluorescein angiography (FA) has depicted phases (early, mid, late, and mature) of RVD in oxygen-induced retinopathy (OIR) mice. We sought to establish the relationship between retinal structural and vascular changes using simultaneous FA and spectral domain optical coherence tomography (SD-OCT).

Method

63 mice were exposed to 77% oxygen at postnatal day 7 (P7) for 5 days, while 63 mice remained in room air (RA). Total retinal thickness (TRT), inner retinal thickness (IRT), and outer retinal thickness (ORT) were calculated at early (P19), mid (P24), late (P32), and mature (P47) phases of RVD.

Results

TRT was reduced in OIR (162.66 ± 17.75 μm, n = 13) compared to RA mice at P19 (197.57 ± 3.49 μm, n = 14), P24, P32, and P49 (P < 0.0001). ORT was similar in RA and OIR mice at all ages (P > 0.05). IRT was reduced in OIR (71.60 ± 17.14 μm) compared to RA (103.07 ± 3.47 μm) mice at P19 and all ages (P < 0.0001).

Conclusion

We have shown the spatial and temporal relationship between retinal structure and vascular development in OIR. Significant inner retinal thinning in OIR mice persisted despite revascularization of the capillary network; further studies will elucidate its functional implications in ROP.

Polarization sensitive optical coherence tomography - a review [Invited]

Optical coherence tomography (OCT) is now a well-established modality for high-resolution cross-sectional and three-dimensional imaging of transparent and translucent samples and tissues. Conventional, intensity based OCT, however, does not provide a tissue-specific contrast, causing an ambiguity with image interpretation in several cases. Polarization sensitive (PS) OCT draws advantage from the fact that several materials and tissues can change the light's polarization state, adding an additional contrast channel and providing quantitative information. In this paper, we review basic and advanced methods of PS-OCT and demonstrate its use in selected biomedical applications.

Posterior rat eye during acute intraocular pressure elevation studied using polarization sensitive optical coherence tomography

Polarization sensitive optical coherence tomography (PS-OCT) operating at 840 nm with axial resolution of 3.8 µm in tissue was used for investigating the posterior rat eye during an acute intraocular pressure (IOP) increase experiment. IOP was elevated in the eyes of anesthetized Sprague Dawley rats by cannulation of the anterior chamber. Three dimensional PS-OCT data sets were acquired at IOP levels between 14 mmHg and 105 mmHg. Maps of scleral birefringence, retinal nerve fiber layer (RNFL) retardation and relative RNFL/retina reflectivity were generated in the peripapillary area and quantitatively analyzed. All investigated parameters showed a substantial correlation with IOP. In the low IOP range of 14-45 mmHg only scleral birefringence showed statistically significant correlation. The polarization changes observed in the PS-OCT imaging study presented in this work suggest that birefringence of the sclera may be a promising IOP-related parameter to investigate.