Long-term Follow-up of a Phase 1/2a Clinical Trial of a Stem Cell-Derived Bioengineered Retinal Pigment Epithelium Implant for Geographic Atrophy.

PURPOSE: To report long-term results from a phase 1/2a clinical trial assessment of a scaffold-based human embryonic stem cell-derived retinal pigmented epithelium (RPE) implant in patients with advanced geographic atrophy (GA). DESIGN: A single-arm, open-label phase 1/2a clinical trial approved by the United States Food and Drug Administration. PARTICIPANTS: Patients were 69-85 years of age at the time of enrollment and were legally blind in the treated eye (best-corrected visual acuity [BCVA], ≤ 20/200) as a result of GA involving the fovea. METHODS: The clinical trial enrolled 16 patients, 15 of whom underwent implantation successfully. The implant was administered to the worse-seeing eye with the use of a custom subretinal insertion device. The companion nonimplanted eye served as the control. The primary endpoint was at 1 year; thereafter, patients were followed up at least yearly. MAIN OUTCOME MEASURES: Safety was the primary endpoint of the study. The occurrence and frequency of adverse events (AEs) were determined by scheduled eye examinations, including measurement of BCVA and intraocular pressure and multimodal imaging. Serum antibody titers were collected to monitor systemic humoral immune responses to the implanted cells. RESULTS: At a median follow-up of 3 years, fundus photography revealed no migration of the implant. No unanticipated, severe, implant-related AEs occurred, and the most common anticipated severe AE (severe retinal hemorrhage) was eliminated in the second cohort (9 patients) through improved intraoperative hemostasis. Nonsevere, transient retinal hemorrhages were noted either during or after surgery in all patients as anticipated for a subretinal surgical procedure. Throughout the median 3-year follow-up, results show that implanted eyes were more likely to improve by > 5 letters of BCVA and were less likely to worsen by > 5 letters compared with nonimplanted eyes. CONCLUSIONS: This report details the long-term follow-up of patients with GA to receive a scaffold-based stem cell-derived bioengineered RPE implant. Results show that the implant, at a median 3-year follow-up, is safe and well tolerated in patients with advanced dry age-related macular degeneration. The safety profile, along with the early indication of efficacy, warrants further clinical evaluation of this novel approach for the treatment of GA. FINANCIAL DISCLOSURE(S): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Retinal perfusion is linked to cognition and brain MRI biomarkers in Black Americans.

INTRODUCTION: We investigated whether retinal capillary perfusion is a biomarker of cerebral small vessel disease and impaired cognition among Black Americans, an understudied group at higher risk for dementia. METHODS: We enrolled 96 Black Americans without known cognitive impairment. Four retinal perfusion measures were derived using optical coherence tomography angiography. Neurocognitive assessment and brain magnetic resonance imaging (MRI) were performed. Multiple linear regression analyses were performed. RESULTS: Lower retinal capillary perfusion was correlated with worse Oral Symbol Digit Test (P < = 0.005) and Fluid Cognition Composite scores (P < = 0.02), but not with the Crystallized Cognition Composite score (P > = 0.41). Lower retinal perfusion was also correlated with higher free water and peak width of skeletonized mean diffusivity, and lower fractional anisotropy (all P < 0.05) on MRI (N = 35). DISCUSSION: Lower retinal capillary perfusion is associated with worse information processing, fluid cognition, and MRI biomarkers of cerebral small vessel disease, but is not related to crystallized cognition.

Retinotopic degeneration of the retina and optic tracts in autosomal dominant Alzheimer's disease.

INTRODUCTION: We investigated the correlation between retinal thickness and optic tract integrity in subjects with autosomal dominant Alzheimer's disease (ADAD) causing mutations. METHODS: Retinal thicknesses and diffusion tensor images (DTI) were obtained using optical coherence tomography and magnetic resonance imaging, respectively. The association between retinal thickness and DTI measures was adjusted for age, sex, retinotopy, and correlation between eyes. RESULTS: Optic tract mean diffusivity and axial diffusivity were negatively correlated with retinotopically defined ganglion cell inner plexiform thickness (GCIPL). Fractional anisotropy was negatively correlated with retinotopically defined retinal nerve fiber layer thickness. There was no correlation between outer nuclear layer (ONL) thickness and any DTI measure. DISCUSSION: In ADAD, GCIPL thickness is significantly associated with retinotopic optic tract DTI measures even in minimally symptomatic subjects. Similar associations were not present with ONL thickness or when ignoring retinotopy. We provide in vivo evidence for optic tract changes resulting from ganglion cell pathology in ADAD.

Stem cell-derived retinal pigment epithelium transplantation in age-related macular degeneration: recent advances and challenges.

PURPOSE OF REVIEW: Age-related macular degeneration (AMD) is one of the leading causes of irreversible vision loss in the world with more than 80% of the prevalence accounted for by the nonneovascular (NNAMD) or 'dry' form of the disease. NNAMD does not have any definitive treatment once vision loss has ensued and presents a major unmet medical need. This review will highlight stem cell-based therapies that are a promising form of treatment for advanced NNAMD. RECENT FINDINGS: In the past decade, clinical trials utilizing both induced pluripotent stem cell-derived RPE and human embryonic stem cell-derived RPE have been aggressively pursued as potential treatments of RPE loss and prevention of overlying neurosensory atrophy. While promising preliminary results demonstrating safety and potential efficacy have been published, new challenges have also been identified. These include selecting the most appropriate cell-based therapy, identifying and managing potential immune response as well as characterizing anatomic and functional efficacy. In this review, we will discuss some of these challenges in light of the available data from several early phase clinical trials and discuss the strategies that are being considered to further advance the field. SUMMARY: Cell-based therapies demonstrate promising potential to treat advanced stages of NNAMD. Several early phase clinical trials using both induced pluripotent stem cells (iPSC) and human embryonic stem cell derived (hESC) have demonstrated safety and preliminary signs of efficacy and highlighted remaining challenges which appear surmountable. These challenges include development of selection criteria for use of cell suspensions versus RPE sheets, especially in light of immunological properties of RPE that are intrinsic to the status of RPE differentiation in each of these cell formulations.

MarkVCID cerebral small vessel consortium: II. Neuroimaging protocols.

The MarkVCID consortium was formed under cooperative agreements with the National Institute of Neurologic Diseases and Stroke (NINDS) and National Institute on Aging (NIA) in 2016 with the goals of developing and validating biomarkers for the cerebral small vessel diseases associated with the vascular contributions to cognitive impairment and dementia (VCID). Rigorously validated biomarkers have consistently been identified as crucial for multicenter studies to identify effective strategies to prevent and treat VCID, specifically to detect increased VCID risk, diagnose the presence of small vessel disease and its subtypes, assess prognosis for disease progression or response to treatment, demonstrate target engagement or mechanism of action for candidate interventions, and monitor disease progression during treatment. The seven project sites and central coordinating center comprising MarkVCID, working with NINDS and NIA, identified a panel of 11 candidate fluid- and neuroimaging-based biomarker kits and established harmonized multicenter study protocols (see companion paper "MarkVCID cerebral small vessel consortium: I. Enrollment, clinical, fluid protocols" for full details). Here we describe the MarkVCID neuroimaging protocols with specific focus on validating their application to future multicenter trials. MarkVCID procedures for participant enrollment; clinical and cognitive evaluation; and collection, handling, and instrumental validation of fluid samples are described in detail in a companion paper. Magnetic resonance imaging (MRI) has long served as the neuroimaging modality of choice for cerebral small vessel disease and VCID because of its sensitivity to a wide range of brain properties, including small structural lesions, connectivity, and cerebrovascular physiology. Despite MRI's widespread use in the VCID field, there have been relatively scant data validating the repeatability and reproducibility of MRI-based biomarkers across raters, scanner types, and time intervals (collectively defined as instrumental validity). The MRI protocols described here address the core MRI sequences for assessing cerebral small vessel disease in future research studies, specific sequence parameters for use across various research scanner types, and rigorous procedures for determining instrumental validity. Another candidate neuroimaging modality considered by MarkVCID is optical coherence tomography angiography (OCTA), a non-invasive technique for directly visualizing retinal capillaries as a marker of the cerebral capillaries. OCTA has theoretical promise as a unique opportunity to visualize small vessels derived from the cerebral circulation, but at a considerably earlier stage of development than MRI. The additional OCTA protocols described here address procedures for determining OCTA instrumental validity, evaluating sources of variability such as pupil dilation, and handling data to maintain participant privacy. MRI protocol and instrumental validation The core sequences selected for the MarkVCID MRI protocol are three-dimensional T1-weighted multi-echo magnetization-prepared rapid-acquisition-of-gradient-echo (ME-MPRAGE), three-dimensional T2-weighted fast spin echo fluid-attenuated-inversion-recovery (FLAIR), two-dimensional diffusion-weighted spin-echo echo-planar imaging (DWI), three-dimensional T2*-weighted multi-echo gradient echo (3D-GRE), three-dimensional T2 -weighted fast spin-echo imaging (T2w), and two-dimensional T2*-weighted gradient echo echo-planar blood-oxygenation-level-dependent imaging with brief periods of CO2 inhalation (BOLD-CVR). Harmonized parameters for each of these core sequences were developed for four 3 Tesla MRI scanner models in widespread use at academic medical centers. MarkVCID project sites are trained and certified for their instantiation of the consortium MRI protocols. Sites are required to perform image quality checks every 2 months using the Alzheimer's Disease Neuroimaging Initiative phantom. Instrumental validation for MarkVCID MRI-based biomarkers is operationally defined as inter-rater reliability, test-retest repeatability, and inter-scanner reproducibility. Assessments of these instrumental properties are performed on individuals representing a range of cerebral small vessel disease from mild to severe. Inter-rater reliability is determined by distribution of an independent dataset of MRI scans to each analysis site. Test-retest repeatability is determined by repeat MRI scans performed on individual participants on a single MRI scanner after a short (1- to 14-day) interval. Inter-scanner reproducibility is determined by repeat MRI scans performed on individuals performed across four MRI scanner models. OCTA protocol and instrumental validation The MarkVCID OCTA protocol uses a commercially available, Food and Drug Administration-approved OCTA apparatus. Imaging is performed on one dilated and one undilated eye to assess the need for dilation. Scans are performed in quadruplicate. MarkVCID project sites participating in OCTA validation are trained and certified by this biomarker's lead investigator. Inter-rater reliability for OCTA is assessed by distribution of OCTA datasets to each analysis site. Test-retest repeatability is assessed by repeat OCTA imaging on individuals on the same day as their baseline OCTA and a different-day repeat session after a short (1- to 14-day) interval. Methods were developed to allow the OCTA data to be de-identified by the sites before transmission to the central data management system. The MarkVCID neuroimaging protocols, like the other MarkVCID procedures, are designed to allow translation to multicenter trials and as a template for outside groups to generate directly comparable neuroimaging data. The MarkVCID neuroimaging protocols are available to the biomedical community and intended to be shared. In addition to the instrumental validation procedures described here, each of the neuroimaging MarkVCID kits will undergo biological validation to determine its ability to measure important aspects of VCID such as cognitive function. The analytic methods for the neuroimaging-based kits and the results of these validation studies will be published separately. The results will ultimately determine the neuroimaging kits' potential usefulness for multicenter interventional trials in small vessel disease-related VCID.

Subretinal Implantation of a Human Embryonic Stem Cell-Derived Retinal Pigment Epithelium Monolayer in a Porcine Model.

The goal of this study was to quantitatively assess retinal thickness using spectral domain optical coherence tomography (SD-OCT) after subretinal implantation of human embryonic stem cell-derived retinal pigment epithelium in a porcine model. The implant is called CPCB-RPE1 for the California Project to Cure Blindness-Retinal Pigment Epithelium 1. Data were derived from previous experiments on 14 minipigs that received either subretinal implantation of CPCB-RPE1 (n = 11) or subretinal bleb formation alone (sham; n = 3) using previously described methods and procedures (Brant Fernandes et al. Ophthalmic Surg Lasers Imaging Retina 47:342-51, 2016; Martynova et al. (2016) Koss et al. Graefes Arch Clin Exp Ophthalmol 254:1553-65, 2016; Hu et al. Ophthalmic Res 48:186-91, 2016; Martynova et al. ARVO Abstract 2016. SD-OCT retinal thickness (RT) and sublayer thickness over the implant were compared with topographically similar preimplantation regions as described previously Martynova et al. ARVO Abstract 2016. Imaging results were compared to postmortem histology using hematoxylin-eosin staining. RT overlying the CPCB-RPE1 postimplantation was not significantly different from preimplantation (308 ± 72 µm vs 292 ± 41 µm; p = 0.44). RT was not significantly different before and after implantation in any retinal sublayer at 1 month. Histology demonstrated grossly normal retinal anatomy as well as photoreceptor interdigitation with RPE.

Normative Retinal Thicknesses in Common Animal Models of Eye Disease Using Spectral Domain Optical Coherence Tomography.

Purpose This study demonstrates a standardized approach to measuring retinal thickness (RT) using spectral domain optical coherence tomography (SD-OCT) in commonly used animal models of disease and reports a normative data set for future use. Materials and Methods Twenty normal eyes of 4 adult animal models (5 rats, 5 rabbits, 5 canines, and 5 mini-pigs) were used. Manual measurements were made on the commercially available Heidelberg Spectralis™ SD-OCT to determine the total, inner, and outer retinal thickness (RT) at fixed distances from the optic nerve head (ONH) (1, 2, 3, 4, 5, and 6 mm away) in order to control for normal variation in retinal thickness. Analysis of variance (ANOVA) with P value <0.05 indicated statistical significance. Results Total RT significantly decreased with increasing distance from the ONH for the canine, mini-pig, and rabbit vascular models. Inner RT significantly decreased for the canine, mini-pig, rabbit vascular, and rabbit avascular models; and outer RT significantly decreased for only the canine model. Among the animal models, RT at similar distances from the ONH were significantly different for total, inner, and outer RT. Conclusion There are significant differences in the total, inner, and outer RT of normal canine, mini-pig, rabbit, and rat retinas with SD-OCT using a standardized approach. These measurements provide a normative reference for future studies and illustrate a standardized method of assessing RT.

Subretinal implantation of a monolayer of human embryonic stem cell-derived retinal pigment epithelium: a feasibility and safety study in Yucatán minipigs.

PURPOSE: A subretinal implant termed CPCB-RPE1 is currently being developed to surgically replace dystrophic RPE in patients with dry age-related macular degeneration (AMD) and severe vision loss. CPCB-RPE1 is composed of a terminally differentiated, polarized human embryonic stem cell-derived RPE (hESC-RPE) monolayer pre-grown on a biocompatible, mesh-supported submicron parylene C membrane. The objective of the present delivery study was to assess the feasibility and 1-month safety of CPCB-RPE1 implantation in Yucatán minipigs, whose eyes are similar to human eyes in size and gross retinal anatomy. METHODS: This was a prospective, partially blinded, randomized study in 14 normal-sighted female Yucatán minipigs (aged 2 months, weighing 24-35 kg). Surgeons were blinded to the randomization codes and postoperative and post-mortem assessments were performed in a blinded manner. Eleven minipigs received CPCB-RPE1 while three control minipigs underwent sham surgery that generated subretinal blebs. All animals except two sham controls received combined local (Ozurdex™ dexamethasone intravitreal implant) and systemic (tacrolimus) immunosuppression or local immunosuppression alone. Correct placement of the CPCB-RPE1 implant was assessed by in vivo optical coherence tomography and post-mortem histology. hESC-RPE cells were identified using immunohistochemistry staining for TRA-1-85 (a human marker) and RPE65 (an RPE marker). As the study results of primary interest were nonnumerical no statistical analysis or tests were conducted. RESULTS: CPCB-RPE1 implants were reliably placed, without implant breakage, in the subretinal space of the minipig eye using surgical techniques similar to those that would be used in humans. Histologically, hESC-RPE cells were found to survive as an intact monolayer for 1 month based on immunohistochemistry staining for TRA-1-85 and RPE65. CONCLUSIONS: Although inconclusive regarding the necessity or benefit of systemic or local immunosuppression, our study demonstrates the feasibility and safety of CPCB-RPE1 subretinal implantation in a comparable animal model and provides an encouraging starting point for human studies.

Longitudinal optical density analysis of subretinal fluid after surgical repair of rhegmatogenous retinal detachment.

PURPOSE: To investigate optical coherence tomography-derived reflectivity and optical density (OD) characteristics of persistent subretinal fluid (SRF) in eyes after surgical repair of macula-off rhegmatogenous retinal detachment. METHODS: Retrospective case series of nine eyes with macula-off rhegmatogenous retinal detachment that underwent surgical repair with either scleral buckling or vitrectomy with or without scleral buckling. Major inclusion criteria included 1) availability of high-quality optical coherence tomography scans at 2 or more time points, and 2) sufficient SRF for optical coherence tomography sampling without including tissue edges. Demographic, clinical, and optical coherence tomography imaging data were collected on all eyes. Optical density and SRF height measurements were obtained using a manual image segmentation method with ImageJ. Optical density measurements were standardized by conversion to optical density ratios to facilitate comparison between different visits and eyes. Correlations were assessed for significance through both univariate and multivariate regression analyses. RESULTS: Optical density ratio measurements increased with time after surgery, and this was statistically significant (P = 0.001, R = 0.331). Subretinal fluid height measurements decreased in all eyes. There was a significant correlation between optical density ratios and log of SRF height (P ≤ 0.001, R = 0.485). In multivariate analysis, neither optical density ratios nor SRF height was a statistically significant predictor of visual acuity. CONCLUSION: Changes in optical density ratios of the residual SRF after retinal detachment repair may be representative of changes in the SRF composition over time. This is in agreement with previous biochemical studies and may serve as a noninvasive method of assessing SRF content in vivo.

OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY OF RETINAL VENOUS OCCLUSION.

PURPOSE: To noninvasively evaluate the retinal microvasculature in human subjects with retinal venous occlusions using optical coherence tomography angiography and assess potential clinical applications. METHODS: This was a prospective, observational study of adult human subjects with clinical and imaging findings demonstrating retinal venous occlusion. Subjects underwent complete ophthalmic examination and fluorescein angiography as appropriate for their standard of care. Optical coherence tomography angiography was performed on a prototype spectral domain-OCTA system in 3 mm × 3 mm and 6 mm × 6 mm regions centered on the fovea and parafoveal areas. Retinal vasculature was assessed within three horizontal slabs consisting of the superficial, middle, and deep retina. The vasculature within each slab was reconstructed using intensity contrast-based algorithms and visualized as en-face images. Optical coherence tomography angiograms were manually segmented to verify the accuracy of the automated segmentation algorithms. RESULTS: Optical coherence tomography angiography was able to demonstrate almost all of the clinically relevant findings in 25 subjects with acute and chronic retinal venous occlusion. These findings were consistent with clinical, anatomic, and fluorescein angiographic findings including areas of impaired vascular perfusion, retinal atrophy, vascular dilation, shunt vessels, and some forms of intraretinal edema. CONCLUSION: Optical coherence tomography angiography is an investigational method that generates high-resolution, noninvasive angiograms that qualitatively illustrate most of clinically relevant findings in retinal venous occlusion. Optical coherence tomography angiography corresponds well with fluorescein angiograms and in many cases provides more detailed anatomic and blood flow information. Optical coherence tomography angiography, in conjunction with standard spectral domain-OCT, is at least equally as effective as fluorescein angiography for evaluation and management of the macular complications of retinal venous occlusions.

High prevalence of peripheral retinal vascular anomalies in family members of patients with familial exudative vitreoretinopathy.

OBJECTIVE: To describe the prevalence and severity of familial exudative vitreoretinopathy (FEVR) in asymptomatic relatives of known symptomatic FEVR patients. DESIGN: Uncontrolled and retrospective case series at a single tertiary referral vitreoretinal practice. PARTICIPANTS: A total of 148 eyes of 74 subjects were studied. METHODS: A retrospective chart review was conducted of patients with a diagnosis of FEVR between January 2011 and January 2013 at a single tertiary care retina practice. Data were collected from patient charts, including sex, gestational age at birth, age at presentation, referring diagnosis, family history, prior ocular surgery, clinical presentation, and diagnostic imaging in each eye. Inclusion criteria included confirmed clinical diagnosis of FEVR in patients referred to our clinic for evaluation of decreased vision. Patients were excluded if a definitive diagnosis of FEVR could not be made. MAIN OUTCOME MEASURES: Clinical and angiographic findings. RESULTS: A total of 74 subjects from 17 separate families met the inclusion criteria for this study. There were an average of 4.4 subjects per family included in this study. The cohort was 55% male and included 17 patients and 57 family members who agreed to undergo genotyping, examination, and diagnostic imaging. Forty-three percent of FEVR patients had detectable mutations in FZD4, NDP, or TSPAN12. Only 8% of the cohort reported a positive family history of FEVR in a first-degree relative. Among the index patients, 76% had clinical stage 3, 4, or 5 FEVR and 24% had stage 1 or 2 FEVR. Among the asymptomatic family members screened, 58% demonstrated clinical or angiographic findings consistent with stage 1 or 2 FEVR and 21% demonstrated clinical or angiographic findings consistent with stage 3, 4, or 5 FEVR. CONCLUSIONS: Asymptomatic family members of FEVR patients frequently have early manifestations of FEVR (stage 1 or 2). Early-stage FEVR may progress to more advanced stages, which can result in vision loss. These data support the use of angiographic screening and clinical examination in immediate relatives of patients with symptomatic FEVR.

Diversity of retinal vascular anomalies in patients with familial exudative vitreoretinopathy.

PURPOSE: To describe the diversity of clinical findings associated with familial exudative vitreoretinopathy (FEVR) using wide-field angiography and to update the current classification system. DESIGN: Retrospective case series at a single tertiary referral vitreoretinal practice. PARTICIPANTS: A total of 174 eyes of 87 subjects were studied. METHODS: A retrospective chart review was conducted of patients with a diagnosis of FEVR between January 2011 and January 2013 at a single tertiary care retina practice. Data were collected from patient charts, including sex, gestational age at birth, age at presentation, referring diagnosis, family history, prior ocular surgery, clinical presentation, and diagnostic imaging in each eye. Inclusion criteria included clinical diagnosis of FEVR in patients referred to our clinic for evaluation of decreased vision. Patients were excluded if a diagnosis of FEVR could not be made. MAIN OUTCOME MEASURES: Clinical and angiographic findings. RESULTS: A total of 87 subjects met the inclusion criteria for this study. A broad spectrum of previously undescribed clinical and angiographic findings were associated with FEVR on wide-field angiography. These findings can be grossly divided into anatomic and functional changes. Anatomic changes include aberrant circumferential peripheral vessels, venous and arterial tortuosity, late-phase disc leakage, central and peripheral telangiectasias, capillary anomalies, and capillary agenesis. Functional changes include venous-venous shunting, delayed arteriovenous transit, and delayed or absent choroidal perfusion on fluorescein angiography. CONCLUSIONS: Familial exudative vitreoretinopathy has a wide range of unrecognized or under-recognized clinical and angiographic findings that are easily identified using wide-field fluorescein angiography. These novel findings have led to an update of the original FEVR classification scheme and more complete characterization of early stages of FEVR.

Noninvasive assessment of retinal vascular oxygen content among normal and diabetic human subjects: a study using hyperspectral computed tomographic imaging spectroscopy.

PURPOSE: This pilot study was aimed to demonstrate the clinical feasibility of using hyperspectral computed tomographic spectroscopy to measure blood oxygen content in human retinal vessels. METHODS: All procedures were performed under a University of Southern California Institutional Review Board-approved protocol and after obtaining informed consent. Fifty-seven subjects with and without diabetic retinopathy were dilated for standard fundus photography. Fundus photographs and retinal vascular oxygen measurements (oximetry) were made using a custom-made hyperspectral computed tomographic imaging spectrometer coupled to a standard fundus camera. Oximetry measurements were made along arteries (Aox) and veins (Vox) within vessel segments that were 1 to 2 disk diameters from the optic disk. RESULTS: For all control subjects (n = 45), mean Aox and Vox were 93 ± 7% and 65 ± 5% (P = 0.001), respectively. For all diabetic subjects (n = 12), mean Aox and Vox were 90 ± 7% and 68 ± 5% (P = 0.001), respectively. In subjects with proliferative diabetic retinopathy, Aox was significantly lower, and Vox was significantly higher than other groups (85 ± 4% and 71 ± 4%, respectively; P = 0.04, analysis of variance). There was a highly significant difference in the arteriovenous difference between subjects with proliferative diabetic retinopathy and those in the control group (14 vs. 26%, P = 0.003). CONCLUSION: Hyperspectral computed tomographic spectroscopy is a clinically feasible method for measurement and analysis of vascular oxygen content in retinal health and disease. This study uses the techniques relevant to oximetry; however, the breadth of spectral data available through this method may be applicable to study other anatomical and functional features of the retina in health and disease.

Rigid alignment method for secondary analyses of optical coherence tomography volumes.

Optical coherence tomography (OCT) provides micron level resolution of retinal tissue and is widely used in ophthalmology. Millions of pre-existing OCT images are available from research and clinical databases. Analysis of this data often requires or can benefit significantly from image registration and reduction of speckle noise. One method of reducing noise is to align and average multiple OCT scans together. We propose to use surface feature information and whole volume information to create a novel and simple pipeline that can rigidly align, and average multiple previously acquired 3D OCT volumes from a commercially available OCT device. This pipeline significantly improves both image quality and visualization of clinically relevant image features over single, unaligned volumes from the commercial scanner.

Variability of Vascular Reactivity in the Retina and Choriocapillaris to Oxygen and Carbon Dioxide Using Optical Coherence Tomography Angiography.

Purpose: To investigate the regional and layer-specific vascular reactivity of the healthy human retina and choriocapillaris to changes in systemic carbon dioxide or oxygen. Methods: High-resolution 3 × 3-mm2 optical coherence tomography angiography (OCTA) images were acquired from the central macula, temporal macula, and peripapillary retina while participants were exposed to three gas breathing conditions-room air, 5%CO2, and 100% O2. OCTA from all three regions were extracted and the apparent skeletonized vessel density (VSD) was assessed. The mean flow deficit sizes (MFDSs) of the choriocapillaris were also assessed. Repeated-measures analysis of variance was used to compare the ratio of intrasubject VSD change induced by the gas conditions from baseline in the superficial retinal layer (SRL) and deep retinal layer (DRL) for each retinal region independently, as well as the MFDS of the choriocapillaris. We also compared the vessel reactivity between the retinal capillaries and the choriocapillaris. Results: The cumulative intrasubject response to the gas conditions differed significantly among regions of the SRL (F(2, 7) = 28.22, P < 0.001), with the temporal macula showing the largest response (15%) compared to the macula (8%) and radial peripapillary capillaries (7%). A similar trend was found in the DRL. The choriocapillaris reactivity was similar between the macula (5.8%) and temporal macula (5.6%). There was also a significant heterogeneity in the layer-specific gas responses, with the DRL showing the largest response (28.2%) and the choriocapillaris showing the smallest response (2.8%). Conclusions: Capillary reactivity to changes in inhaled O2 and CO2 is spatially heterogeneous across the retina but not choriocapillaris.

Ocular and systemic determinants of perifoveal and macular vessel parameters in healthy African Americans.

PURPOSE: To determine the relationship of various systemic and ocular characteristics with perifoveal and macular vessel density in healthy African American eyes. DESIGN: A population-based cross-sectional study of prospectively recruited African Americans ≥40 years of age. Participants underwent 3×3 mm and 6×6 mm macula scans using spectral-domain optical coherence tomography angiography (OCTA), clinical examinations and clinical questionnaires. Participants with glaucoma, severe non-proliferative diabetic retinopathy, proliferative diabetic retinopathy and macular oedema were excluded. Custom MATLAB based software quantified vessel area density (VAD) and vessel skeleton density (VSD) in the superficial retinal layer of the macula. Multivariable regression analysis, controlling for inter-eye correlation, was performed to determine systemic and ocular determinants of macular vessel metrics using stepwise selection. Candidate variables included: age, gender, body mass index, history of smoking, history of diabetes, diabetes duration, history of stroke or brain haemorrhage, systolic blood pressure, diastolic blood pressure (DBP), pulse pressure, mean arterial pressure, central subfield thickness (CSFT), visual field mean deviation, intraocular pressure, axial length (AL), mean ocular perfusion pressure and signal strength (SS). RESULTS: A total of 2221 OCTA imaged eyes from 1472 participants were included in this study. Reduced perifoveal and macular VAD and VSD were independently associated with longer AL, reduced SS, reduced CSFT and older age. Male gender and lower DBP were also associated with reduced perifoveal and macular VSD. CONCLUSIONS: When interpreting OCTA images in a clinical setting, it is important to consider the effects ocular and systemic characteristics may have on the macular microcirculation.

Characterization of spastic paraplegia in a family with a novel PSEN1 mutation.

Spastic paraparesis has been described to occur in 13.7% of PSEN1 mutations and can be the presenting feature in 7.5%. In this paper, we describe a family with a particularly young onset of spastic paraparesis due to a novel mutation in PSEN1 (F388S). Three affected brothers underwent comprehensive imaging protocols, two underwent ophthalmological evaluations and one underwent neuropathological examination after his death at age 29. Age of onset was consistently at age 23 with spastic paraparesis, dysarthria and bradyphrenia. Pseudobulbar affect followed with progressive gait problems leading to loss of ambulation in the late 20s. Cerebrospinal fluid levels of amyloid-ß, tau and phosphorylated tau and florbetaben PET were consistent with Alzheimer's disease. Flortaucipir PET showed an uptake pattern atypical for Alzheimer's disease, with disproportionate signal in posterior brain areas. Diffusion tensor imaging showed decreased mean diffusivity in widespread areas of white matter but particularly in areas underlying the peri-Rolandic cortex and in the corticospinal tracts. These changes were more severe than those found in carriers of another PSEN1 mutation, which can cause spastic paraparesis at a later age (A431E), which were in turn more severe than among persons carrying autosomal dominant Alzheimer's disease mutations not causing spastic paraparesis. Neuropathological examination confirmed the presence of cotton wool plaques previously described in association with spastic parapresis and pallor and microgliosis in the corticospinal tract with severe amyloid-ß pathology in motor cortex but without unequivocal disproportionate neuronal loss or tau pathology. In vitro modelling of the effects of the mutation demonstrated increased production of longer length amyloid-ß peptides relative to shorter that predicted the young age of onset. In this paper, we provide imaging and neuropathological characterization of an extreme form of spastic paraparesis occurring in association with autosomal dominant Alzheimer's disease, demonstrating robust diffusion and pathological abnormalities in white matter. That the amyloid-ß profiles produced predicted the young age of onset suggests an amyloid-driven aetiology though the link between this and the white matter pathology remains undefined.

Alterations in Retinal Vascular and Oxygen Metrics in Treated and Untreated Proliferative Diabetic Retinopathy: A Case Report.

Proliferative diabetic retinopathy (PDR) is a vision-threatening complication of diabetes. Panretinal photocoagulation (PRP) and anti-vascular endothelial growth factor (anti-VEGF) are approved treatment modalities aimed at regressing neovascularization. Data are lacking about abnormalities in retinal vascular and oxygen metrics before and after combination treatments. A 32-year-old Caucasian male diagnosed with PDR in the right eye was treated by a combination of PRP and multiple anti-VEGF treatments over a 12-month period. The subject underwent optical coherence tomography (OCT) angiography, Doppler OCT, and retinal oximetry before treatment and at 12 months, which was 6 months following the last treatment. Measurements of vascular metrics (vessel density [VD] and mean arterial and venous diameters [DA, DV]) and oxygen metrics (total retinal blood flow [TRBF], inner retinal oxygen delivery [DO2], metabolism [MO2], and extraction fraction [OEF]) were obtained. Both before and after treatments, VD, TRBF, MO2, and DO2 were below the normal lower confidence limits. Additionally, DV and OEF were decreased after treatments. Alterations in retinal vascular and oxygen metrics were reported for the first time in untreated and treated PDR. Future studies are warranted to evaluate the clinical value of these metrics in PDR.

OCTA Derived Vessel Skeleton Density Versus Flux and Their Associations With Systemic Determinants of Health.

Purpose: To examine the associations of optical coherence tomography angiography (OCTA)-derived retinal capillary flux with systemic determinants of health. Methods: This is a cross-sectional study of subjects recruited from the African American Eye Disease Study. A commercially available swept-source (SS)-OCTA device was used to image the central 3 × 3 mm macular region. Retinal capillary perfusion was assessed using vessel skeleton density (VSD) and flux. Flux approximates the number of red blood cells moving through vessel segments and is a novel metric, whereas VSD is a previously validated measure commonly used to quantify capillary density. The associations of OCTA derived measures with systemic determinants of health were evaluated using multivariate generalized linear mixed-effects models. Results: A total of 154 eyes from 83 participants were enrolled. Mean VSD and flux were 0.148 ± 0.009 and 0.156 ± 0.016, respectively. In a model containing age, systolic blood pressure, diabetes status, hematocrit, and presence of retinopathy as covariates, there was a negative correlation between VSD and age (P < 0.001) and retinopathy (P = 0.02), but not with hematocrit (P = 0.85) or other factors. There was a positive correlation between flux and hematocrit (P = 0.02), as well as a negative correlation for flux with age (P < 0.001), systolic blood pressure (P = 0.04), and diabetes status (P = 0.02). A 1% decrease in hematocrit was associated with the same magnitude change in flux as ∼1.24 years of aging. Signal strength was associated with flux (P < 0.001), but not VSD (P = 0.51). Conclusions: SS-OCTA derived flux provides additional information about retinal perfusion distinct from that obtained with skeleton density-based measures. Flux is appropriate for detecting subclinical changes in perfusion in the absence of clinical retinopathy.