Multimodal imaging in a case of presumed secondary vitreoretinal lymphoma presenting with inner retina and optic nerve head infiltration.

Purpose: To report the findings supported by multimodal imaging in a case of secondary vitreoretinal lymphoma presenting with inner retina and optic nerve head infiltration. Observations: A 64-year-old man with systemic diffuse large B-cell lymphoma presented with reduced visual acuity. Moderate anterior chamber and vitreous cell were present. Fundus exam showed bilateral disc edema and diffuse opaque macular infiltrates with a pseudo cherry-red spot in the left eye. Optical coherence tomography showed inner retinal infiltration and loss of normal architecture. Surgery for tissue biopsy was discussed and declined due to risk. Instead, multimodal imaging and anterior chamber fluid sampling were used as a surrogate for tissue biopsy and helped rule out infectious uveitis and retinal vascular disease. The patient was empirically treated with intravitreal methotrexate with rapid improvement in vision, exam, and quality of life. Conclusions and importance: Multimodal imaging can support a presumed diagnosis of secondary vitreoretinal lymphoma in order to proceed with intravitreal methotrexate treatment, which can result in rapid clinical and visual improvement.

Disability-Adjusted Life Years Resulting from Ocular Injury among Deployed Service Members, 2001-2020.

PURPOSE: To quantify the burden of ocular injuries on deployed US service members by calculating disability-adjusted life years (DALYs). DESIGN: Retrospective, observational cohort study. PARTICIPANTS: US service members with ocular injuries sustained in combat zones from January 1, 2001 to May 19, 2020. METHODS: Health states and duration of injuries were identified using data from the Defense and Veterans Eye Injury and Vision Registry. These health states were mapped to disability weights from the Global Burden of Disease (GBD) study. Average duration of injury or illness was calculated until remission or death. For the latter, life expectancy at age of sustaining injury, as identified from US Life Tables from the National Vital Statistics Reports 2020, was used. Using Defense Manpower Data Center reports capturing number of service members deployed per year, incidence rates were calculated for ocular injury and DALYs. MAIN OUTCOME MEASURES: Disability-adjusted life years of ocular injury. RESULTS: Seventeen thousand five hundred fifty-five patients sustained ocular injury that incurred DALYs. In total, these injuries resulted in 11 214 DALYs (average, 0.64 DALYs per included patient and 20.6 DALYs per 10 000 US service members per year). Severe impairment of distance vision (77.9%) and blindness (10.6%) were the primary contributors of DALYs. Although only 9.3% of patients sustained a permanent ocular injury, permanent disability accounted for 99.5% of total DALYs. The average yearly incidence rate of ocular injury was 32.0 cases per 10 000 US service members. Foreign body was the most frequent injury type (2754 occurrences), followed by abrasion (2419 occurrences) and multiple injury types (1429 occurrences). The most DALYs occurred in patients with multiple injury types (2485 DALYs), followed by abrasion (accounting for 725 DALYs) and foreign body (accounting for 461 DALYs). DISCUSSION: We report higher average DALYs per case ratio among US service members compared with the general population studied by the GBD study, highlighting the differences in probabilities of permanent injury between the two studies. Our study provides understanding of the impact of ocular injuries on active-duty service members and lays the groundwork for further research and interventions to mitigate their burden. FINANCIAL DISCLOSURE(S): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Persistent diabetic macular edema: Definition, incidence, biomarkers, and treatment methods.

Intravitreal antivascular endothelial growth factor (anti-VEGF) treatment has drastically improved the visual and anatomical outcomes in patients with diabetic macular edema (DME); however, success is not always guaranteed, and a proportion of these eyes demonstrate persistent DME (pDME) despite intensive treatment. While standardized criteria to define these treatment-resistant eyes have not yet been established, many studies refer to eyes with no clinical response or an unsatisfactory partial response as having pDME. A patient is considered to have pDME if the retinal thickness improves less than 10-25% after 6 months of treatment. A range of treatment options have been recommended for eyes with pDME, including switching anti-VEGF agents, using corticosteroids and/or antioxidant drugs in adjunct with anti-VEGF therapy, and vitrectomy. In addition, multimodal imaging of DME eyes may be advantageous in predicting the responsiveness to treatment; this is beneficial when initiating alternative therapies. We explore the literature on persistent DME regarding its defining criteria, incidence, the baseline biological markers that may be useful in anticipating the response to treatment, and the available treatment options.

MULTISCALE CORRELATION OF MICROVASCULAR CHANGES ON OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY WITH RETINAL SENSITIVITY IN DIABETIC RETINOPATHY.

PURPOSE: To assess global, zonal, and local correlations between vessel density changes measured by optical coherence tomography angiography and retinal sensitivity measured by microperimetry across diabetic retinopathy severity. METHODS: Diabetic patients and nondiabetic controls underwent optical coherence tomography angiography imaging and microperimetry testing. Pearson's correlation was used to assess associations between average sensitivity and skeletonized vessel density (SVD) or foveal avascular zone area centrally. Linear mixed effects modeling was used to assess relationships between local SVD measurements and their spatially corresponding retinal sensitivity measurements. RESULTS: Thirty-nine eyes from 39 participants were imaged. In all slabs, there was a statistically significant positive correlation between retinal sensitivities and SVDs on both global and zonal scales. No statistically significant correlation was found between central retinal sensitivities and the foveal avascular zone areas. Assessment of 1,136 spatially paired retinal sensitivity and SVD measurements revealed a statistically significant local relationship; this seemed to be driven by eyes with proliferative diabetic retinopathy that had reduced retinal sensitivities. CONCLUSION: This study supports positive correlations between SVD and retinal sensitivity at global and zonal spatial scales in diabetic eyes. However, our analysis did not find evidence of statistically significant correlations between retinal sensitivity and SVD on a local scale until advanced diabetic retinopathy.

Modeling the impact of COVID-19 on Retina Clinic Performance.

BACKGROUND: COVID-19, a highly contagious respiratory virus, presents unique challenges to ophthalmology practice as a high-volume, office-based specialty. In response to the COVID-19 pandemic, many operational changes were adopted in our ophthalmology clinic to enhance patient and provider safety while maintaining necessary clinical operations. The aim of this study was to evaluate how measures adopted during the pandemic period affected retina clinic performance and patient satisfaction, and to model future clinic flow to predict operational performance under conditions of increasing patient and provider volumes. METHODS: Clinic event timestamps and demographics were extracted from the electronic medical records of in-person retina encounters from March 15 to May 15, 2020 and compared with the same period in 2019 to assess patient flow through the clinical encounter. Patient satisfaction was evaluated by Press Ganey patient experience surveys obtained from randomly selected outpatient encounters. A discrete-events simulation was designed to model the clinic with COVID-era restrictions to assess operational performance under conditions of increasing patient and provider volumes. RESULTS: Retina clinic volume declined by 62 % during the COVID-19 health emergency. Average check-in-to-technician time declined 79 %, total visit length declined by 46 %, and time in the provider phase of care declined 53 %. Patient satisfaction regarding access nearly doubled during the COVID-period compared with the prior year (p < 0.0001), while satisfaction with overall care and safety remained high during both periods. A model incorporating COVID-related changes demonstrated that wait time before rooming reached levels similar to the pre-COVID era by 30 patients-per-provider in a 1-provider model and 25 patients-per-provider in a 2-provider model (p < 0.001). Capacity to maintain distancing between patients was exceeded only in the two 2-provider model above 25 patients-per-provider. CONCLUSIONS: Clinic throughput was optimized in response to the COVID-19 health emergency. Modeling these clinic changes can help plan for eventual volume increases in the setting of limits imposed in the COVID-era.

Macular Vessel Density in Diabetic Retinopathy Patients: How Can We Accurately Measure and What Can It Tell Us?

Diabetic retinopathy is one of the leading causes of blindness worldwide. Optical coherence tomography angiography (OCTA) is a non-invasive technology that provides depth-resolved images of the chorioretinal vasculature and allows for the understanding of the changes in vasculature with diabetic retinopathy. Not only can it provide qualitative information, but OCTA can also provide quantitative information about the vasculature in patients with diabetic retinopathy. Macular vessel density is one of the quantitative metrics that can be obtained from OCTA images. This is a repeatable and non-subjective measurement that can provide valuable insight into the pathophysiology of diabetic retinopathy. In this non-systematic review, the measurement of macular vessel density in diabetic retinopathy and the reasons for its importance in the diagnosis and management of patients with diabetes and varying severities of diabetic retinopathy is discussed.

SWEPT-SOURCE OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY IN SMALL CHOROIDAL MELANOMAS AND CHOROIDAL NEVI.

PURPOSE: To evaluate the use of swept-source optical coherence tomography angiography to detect distinct vascular features in small choroidal melanomas and choroidal nevi. METHODS: Patients with a choroidal nevus or a treatment-naïve choroidal melanoma were imaged with color fundus photography, ultrasound, and swept-source optical coherence tomography angiography (12 × 12 mm). High-risk features including overlying fluid, orange pigment, shaggy photoreceptors, acoustic hollowness, depth >2 mm, and basal diameter >5 mm were assessed. Optical coherence tomography angiography vascular markers included: choroidal vessel visualization, choroidal vessel depth, and choriocapillaris flow signal, assessed qualitatively by comparison with surrounding, unaffected choriocapillaris. RESULTS: Twenty-nine lesions were included in this study, seven flat choroidal nevi, 17 elevated choroidal nevi, and 5 choroidal melanomas. Distinct vascular patterns were noted between flat nevi, elevated nevi, and small choroidal melanomas. Choroidal melanomas displayed two types of vasculature: "nevus-like" vasculature with straight parallel vessels and complex vasculature with vascular loops and crosslinking. Visualized choroidal vessels were significantly deeper in melanomas (110 µm) than elevated (84 µm) or flat nevi (70 µm). In a size-matched subanalysis of 5 elevated choroidal nevi and 5 choroidal melanomas, choroidal melanomas had increased mean choroidal vessel depth (P = 0.015), deepest choroidal vessel visualized (P = 0.034), and presence of a deep choroidal vessel >155 µm (P = 0.048). CONCLUSION: Swept-source optical coherence tomography angiography may detect distinct vascular features in choroidal nevi and small choroidal melanomas.

Retinal Imaging Using a Confocal Scanning Laser Ophthalmoscope-Based High-Magnification Module.

PURPOSE: To evaluate the usefulness of a high-magnification module (HMM) lens to visualize retinal photoreceptors, retinal nerve fiber layer (RNFL), and superficial retinal vasculature in physiologic and pathologic retinal conditions. DESIGN: Observational descriptive study. PARTICIPANTS: Thirty-two participants with normal and pathologic retina examination results. METHODS: Normal and pathologic maculae were imaged in vivo using still and video HMM lens modes, with fixation and contrast adjustments to enhance visualization. The HMM images were classified qualitatively based on structures identified as either good (photoreceptors seen), average (photoreceptor mosaic cannot be visualized clearly, retinal vessels and other retinal changes can be seen), or poor (no identifiable structures). Selected eyes were imaged with fundus photography, OCT, OCT angiography, indocyanine green angiography, and fluorescein angiography for comparison with the pathologic maculae. MAIN OUTCOMES MEASURES: Description of HMM module-obtained macula images. RESULTS: From 32 eyes imaged (16 normal and 16 pathologic retinas), 12 of 16 normal and 11 of 16 pathologic retinas demonstrated at least average image quality, in which retinal vasculature and landmarks could be visualized. The mosaic pattern of hexagonal shapes representing photoreceptors could not be resolved in most pathologic retinas. For the retinas in which the photoreceptor mosaics were visualized (12 of 16 normal and 2 of 16 pathologic retinas), parafoveal mosaic patterns appeared denser with better image quality for all participants compared with foveal photoreceptors. Difficulty in resolving the photoreceptors in the umbo, fovea, and perifovea was encountered, similar to what has been reported with adaptive optics devices. The RNFL was seen as arcuate hyperreflective bundles. Flow was observed in the macular microvasculature. Poorly resolved photoreceptors and scattered hyperreflective foci were correlated with changes in the retinal pigment epithelium in eyes with age-related macular degeneration or central serous chorioretinopathy. Macular striae were seen in eyes with epiretinal membrane. CONCLUSIONS: In most eyes, regardless of whether retinal pathologic features were present, it was challenging to obtain average quality (or better) images. In the few participants with good-quality imaging, the parafoveal photoreceptor mosaic, vascular flow, and various features of pathologic eyes could be visualized.

Can the Onset of Neovascular Age-Related Macular Degeneration Be an Acceptable Endpoint for Prophylactic Clinical Trials?

Many studies over the past 20 years have pursued the goal of preventing or deferring progression from early and intermediate age-related macular degeneration (AMD) to advanced AMD. The onset of neovascular AMD has been used as a primary endpoint in some prophylactic clinical trials because it is easy to assess and relatively well-defined. Nevertheless, the use of this endpoint for assessing progression of AMD lacks validation. The aims of this paper are to review the current practice of clinical trials investigating the prevention of progression of early or intermediate AMD to neovascular AMD, so-called prophylactic trials, as well as identify ongoing efforts to standardize endpoints and select the ideal population for such studies.

Choroidal nonperfusion on optical coherence tomography angiography in a case of unilateral posterior segment ocular sarcoidosis misdiagnosed as MEWDS.

PURPOSE: To report a case of presumed ocular sarcoidosis initially presenting with features of multiple evanescent white dot syndrome (MEWDS) with atypical optical coherence tomography angiography (OCTA) findings. OBSERVATIONS: A 23 year-old woman presented with a unilateral central scotoma, photophobia, and decreased visual acuity after a viral illness. Examination of the right eye revealed multiple round white macular spots and stippled granularity at the fovea. Multimodal imaging with fluorescein angiography (FA), indocyanine green angiography (ICG), fundus autofluorescence (FAF), and optical coherence tomography (OCT) was consistent with a diagnosis of MEWDS. However, OCTA demonstrated choriocapillaris (CC) flow deficits, which is not typical for MEWDS. The clinical course was initially consistent with MEWDS, with spontaneous recovery of symptoms over ensuing months. The patient presented five months later with floaters and a central scotoma. Examination showed panuveitis, and systemic evaluation revealed an elevated angiotensin converting enzyme (ACE) and hilar lymphadenopathy on chest x-ray consistent with presumed sarcoidosis. CONCLUSIONS AND IMPORTANCE: A case of MEWDS atypically demonstrated CC flow deficits on OCTA and subsequently presented as uveitis secondary to presumed sarcoidosis. Atypical features in MEWDS may be a sign of another disorder masquerading early on as MEWDS and ought to prompt further investigation.

The long-term effects of anti-vascular endothelial growth factor therapy on the optical coherence tomography angiographic appearance of neovascularization in age-related macular degeneration.

BACKGROUND: The short-term effects of anti-vascular endothelial growth factor (anti-VEGF) treatment on macular neovascularization (MNV) morphology is well described, but long-term studies on morphologic changes and correlation of such changes to the type of MNV have not been conducted. This study aims to determine if different types of MNVs in neovascular AMD (nAMD) behave differently with anti-VEGF treatment as visualized on optical coherence tomography angiography (OCTA). METHODS: Treatment-naïve nAMD patients were retrospectively screened for baseline and follow-up OCTA imaging 10 or more months after initial treatment. Images were graded for MNV type, area, activity, mature versus immature vessels, vessel density, presence of atrophy, atrophy location and area. Growth rate was calculated as the percent change in lesion area from baseline over the years of follow-up. In addition, the occurrence of complete regression and the percent of lesions that grew, remained stable, and shrunk per type was also evaluated. RESULTS: Forty-three eyes from 43 patients with a mean follow-up of 2 years were evaluated. On structural OCT, 26 lesions were classified as pure type 1 MNVs, 12 MNVs had a type 2 component, and 5 MNVs had a type 3 component. Of these cases, 2 mixed-type MNVs were considered to have completely regressed. There was no significant differences in MNV area and growth rate between type 1 and type 2 lesions, but all cases of type 3 lesions shrunk in the follow-up period. There was no correlation between the number of injections per year and growth rate, endpoint MNV area or endpoint activity status for any MNV type. There was no significant association between the development of atrophy and the number of injections, baseline MNV area, baseline vessel density, or lesion growth rate. CONCLUSIONS: In nAMD, complete regression of an MNV network exposed to anti-VEGF is rare. This work emphasizes the role of anti-VEGF as anti-leakage rather than vascular regression agents in nAMD.

Macular and Peripapillary Optical Coherence Tomography Angiography Metrics Predict Progression in Diabetic Retinopathy: A Sub-analysis of TIME-2b Study Data.

PURPOSE: To identify optical coherence tomography angiography (OCTA)-derived vessel metrics of the macula and optic nerve head (ONH) that predict diabetic retinopathy (DR) disease progression. DESIGN: Secondary analysis of clinical trial data. METHODS: This was a sub-analysis of prospectively collected data from 73 subjects that participated in the TIME-2b study (Aerpio Pharmaceuticals), a multicenter clinical trial for patients with moderate-to-severe DR treated with AKB-9778 and followed over a 12-month period. Eligible subjects were tested every 3 months with color fundus photography, spectral-domain OCT, and slit-lamp biomicroscopy. OCTA of the macula and ONH was obtained for a subset of patients enrolled at participating sites. En face, full-depth retinal projections centered at the macula were analyzed for multiple metrics including foveal avascular zone (FAZ) area and perimeter, nonperfusion area, vessel density (VD), and presence of intraretinal microvascular abnormalities (IRMA). VD of the radial peripapillary capillaries was evaluated in 4 quadrants surrounding the optic disc for ONH images. Progression was defined as a ≥2-step increase in DR severity scale score or development of diabetic macular edema. RESULTS: Over a follow-up period of 12 months, 15 of 73 (20.5%) subjects progressed. At pretreatment baseline, larger FAZ area, presence of IRMA, and reduced peripapillary VD in the superior temporal and inferior temporal regions were significantly associated with increased odds of progression. CONCLUSIONS: FAZ area and temporal peripapillary VD are predictors of DR progression. OCTA metrics may improve progression risk assessment in DR when compared to established risk factors alone.

Repeatability and reproducibility of vessel density measurements on optical coherence tomography angiography in diabetic retinopathy.

PURPOSE: Understanding the precision of measurements on and across optical coherence tomography angiography (OCTA) devices is critical for tracking meaningful change in disease. The purpose of this study is to investigate the repeatability and reproducibility of vessel area density and vessel skeleton density measurements from various commercial OCTA devices in diabetic eyes. METHODS: Patients were imaged three consecutive times each on three different OCTA devices. En face OCTA images of the superficial capillary plexus, deep capillary plexus, and full retinal layer were exported for analysis. Vessel area density and vessel skeleton density were calculated. The coefficient of repeatability (CoR) was calculated to assess the repeatability of these measurements, and linear mixed models were utilized to assess the reproducibility of these measurements. RESULTS: Forty-four eyes from 27 diabetic patients were imaged. Normalized CoR values ranged between 3.44 and 6.65% when calculated for vessel area density and between 1.35 and 23.39% when calculated for vessel skeleton density. When stratified by disease severity, the swept-source OCTA device consistently produced the smallest CoR values for vessel area density in the full retinal layer. Vessel area density measurements were repeatable across the two spectral-domain devices in the full retinal layer when all severities were combined, as well as in diabetic patients without retinopathy, mild nonproliferative diabetic retinopathy (NPDR), and moderate NPDR. CONCLUSION: Vessel area density measured in the full retinal layer may be a more precise measure than vessel skeleton density to follow diabetic retinopathy patients both on the same device and across devices.

Test-retest variability of microperimetry in geographic atrophy.

PURPOSE: Microperimetry (MP) allows for measurement of retinal sensitivity at precise locations and is now commonly employed as a clinical trial endpoint. Test-retest reliability is important when evaluating treatment effects in patients with geographic atrophy (GA). This study aimed to determine the test-retest variability of MP in patients with moderate to severe GA using the MAIA MP device. METHODS: In this prospective study, patients with a confirmed diagnosis of foveal-involving GA were enrolled. Participants performed three MP assessments of a selected eye over two visits with the Macular Integrity Assessment (MAIA) 2 instrument (Centervue, Padova, Italy) utilizing a wide 30° grid, consisting of 93 stimuli (Goldmann III) using a 4-2 representation strategy, encompassing the entire area of GA and beyond. Mean retinal sensitivity (MS) was expressed as an average threshold value (dB) for the entire field tested. Coefficients of Repeatability at a 95% level (CoR95) were calculated for Point Wise Sensitivity (PWS). Fixation stability (FS) was assessed by evaluating the area of an elliptical representation encompassing 95% of the cloud of fixation points (CFP) dataset generated by the MAIA MP, known as the bivariate contour ellipse area (BCEA). RESULTS: A total of 8 subjects were enrolled (21 tests), with six subjects completing 3 MP assessments. BCVA in these patients ranged from 20/100 to 20/800. The mean area of GA was 18.7 ± 12.3 mm2. The average time to complete one MP assessment was 13 min 9 s and mean BCEA@95% was 38.5 ± 19.3°2. The MS was 14.3 ± 4.5 dB. No significant increase in MS was noted between testing pairs 1&2 and 2&3. The preferred retinal locus was maintained in the same quadrant on successive tests. The mean CoR95 for PWS were similar for testing pairs 1&2 (± 3.50 dB) and 2&3 (± 3.40). CONCLUSION: Microperimetry using a wide grid can be reliably performed in a reasonable amount of time in patients with moderate and severe vision loss secondary to GA. There was no learning effect seen between sequential assessments when analyzing MS or PWS. A change of approximately 4 dB in PWS provides a threshold for considering a true change in this patient cohort.

Topographic analysis of macular choriocapillaris flow deficits in diabetic retinopathy using swept-source optical coherence tomography angiography.

BACKGROUND: The purpose of this study was to investigate the association between diabetic retinopathy (DR) severity and macular choriocapillaris (CC) flow deficit percentage (FD %) in different macular regions using swept-source optical coherence tomography angiography (SS-OCTA). METHODS: Diabetic patients with SS-OCTA images were graded by severity and retrospectively assessed. CC FD % was calculated in four different regions of the OCTA image: inner, middle, outer, and full-field region. The generalized estimating equations (GEE) approach for clustered eye data was used to determine effect size and significance of age and disease severity on FD % for each region. RESULTS: 160 eyes from 90 total diabetic patients met inclusion criteria. Out of 90 patients, 33 had no DR, 17 had mild nonproliferative DR (NPDR), 8 had moderate NPDR, 10 had severe NPDR and 22 had proliferative DR. Age and DR severity had a significant positive association with FD % for each region studied with a greater effect in the two centermost regions. The increase in flow deficit percentage per year of age by region was: inner 0.12 (p < 0.001), middle 0.09 (p < 0.001), outer 0.05 (p < 0.001, full-field 0.06 (p < 0.001). The increase in flow deficit percentage per increase in diabetic retinopathy severity stage by region was: inner 0.65 (p < 0.0087), middle 0.56 (p < 0.0012), outer 0.33 (p < 0.045), full-field 0.36 (p < 0.018). CONCLUSIONS: Topographic analysis of the CC FD % in diabetic eyes suggests that CC flow impairment corresponds to DR severity, with all studied regions of the CC significantly affected. There was greater regional impairment due to age and disease severity in the inner and middle regions.

Monocyte infiltration rather than microglia proliferation dominates the early immune response to rapid photoreceptor degeneration.

BACKGROUND: Activation of resident microglia accompanies every known form of neurodegeneration, but the involvement of peripheral monocytes that extravasate and rapidly transform into microglia-like macrophages within the central nervous system during degeneration is far less clear. METHODS: Using a combination of in vivo ocular imaging, flow cytometry, and immunohistochemistry, we investigated the response of infiltrating cells in a light-inducible mouse model of photoreceptor degeneration. RESULTS: Within 24 h, resident microglia became activated and began migrating to the site of degeneration. Retinal expression of CCL2 increased just prior to a transient period of CCR2+ cell extravasation from the retinal vasculature. Proliferation of microglia and monocytes occurred concurrently; however, there was no indication of proliferation in either population until 72-96 h after neurodegeneration began. Eliminating CCL2-CCR2 signaling blocked monocyte recruitment, but did not alter the extent of retinal degeneration. CONCLUSIONS: These results demonstrate that the immune response to photoreceptor degeneration includes both resident microglia and monocytes, even at very early times. Surprisingly, preventing monocyte infiltration did not block neurodegeneration, suggesting that in this model, degeneration is limited by cell clearance from other phagocytes or by the timing of intrinsic cell death programs. These results show monocyte involvement is not limited to disease states that overwhelm or deplete the resident microglial population and that interventions focused on modulating the peripheral immune system are not universally beneficial for staving off degeneration.

New Developments in Murine Imaging for Assessing Photoreceptor Degeneration In Vivo.

Optical Coherence Tomography (OCT) is a powerful clinical tool that measures near infrared light backscattered from the eye and other tissues. OCT is used for assessing changes in retinal structure, including layer thicknesses, detachments and the presence of drusen in patient populations. Our custom-built OCT system for the mouse eye quantitatively images all layers of the neural retinal, the RPE, Bruchs' membrane and the choroid. Longitudinal assessment of the same retinal region reveals that the relative intensities of retinal layers are highly stable in healthy tissue, but show progressive increases in intensity in a model of retinal degeneration. The observed changes in OCT signal have been correlated with ultrastructural disruptions that were most dramatic in the inner segments and nuclei of the rods. These early changes in photoreceptor structure coincided with activation of retinal microglia, which migrated vertically from the inner to the outer retina to phagocytose photoreceptor cell bodies (Levine et al., Vis Res 102:71-79, 2014). We conclude that quantitative analysis of OCT light scattering signals may be a useful tool for early detection and subcellular localization of cell stress prior to cell death, and for assessing the progression of degenerative disease over time. Future efforts to develop sensitive approaches for monitoring microglial dynamics in vivo may likewise elucidate earlier signs of cellular stress during retinal degeneration.

Rapid light-induced activation of retinal microglia in mice lacking Arrestin-1.

Microglia dynamically prune synaptic contacts during development, and digest waste that accumulates in degeneration and aging. In many neurodegenerative diseases, microglial activation and phagocytosis gradually increase over months or years, with poorly defined initial triggering events. Here, we describe rapid retinal microglial activation in response to physiological light levels in a mouse model of photoreceptor degeneration that arises from defective rhodopsin deactivation and prolonged signaling. Activation, migration and proliferation of microglia proceeded along a well-defined time course apparent within 12 h of light onset. Retinal imaging in vivo with optical coherence tomography revealed dramatic increases in light-scattering from photoreceptors prior to the outer nuclear layer thinning classically used as a measure of retinal neurodegeneration. This model is valuable for mechanistic studies of microglial activation in a well-defined and optically accessible neural circuit, and for the development of novel methods for detecting early signs of pending neurodegeneration in vivo.