Maria Parker

Structure-Function Modeling of Optical Coherence Tomography and Standard Automated Perimetry in the Retina of Patients with Autosomal Dominant Retinitis Pigmentosa

Purpose To assess relationships between structural and functional biomarkers, including new topographic measures of visual field sensitivity, in patients with autosomal dominant retinitis pigmentosa. Methods Spectral domain optical coherence tomography line scans and hill of vision (HOV) sensitivity surfaces from full-field standard automated perimetry were semi-automatically aligned for 60 eyes of 35 patients. Structural biomarkers were extracted from outer retina b-scans along horizontal and vertical midlines. Functional biomarkers were extracted from local sensitivity profiles along the b-scans and from the full visual field. These included topographic measures of functional transition such as the contour of most rapid sensitivity decline around the HOV, herein called HOV slope for convenience. Biomarker relationships were assessed pairwise by coefficients of determination (R2) from mixed-effects analysis with automatic model selection. Results Structure-function relationships were accurately modeled (conditional R2>0.8 in most cases). The best-fit relationship models and correlation patterns for horizontally oriented biomarkers were different than vertically oriented ones. The structural biomarker with the largest number of significant functional correlates was the ellipsoid zone (EZ) width, followed by the total photoreceptor layer thickness. The strongest correlation observed was between EZ width and HOV slope distance (marginal R2 = 0.85, p<10−10). The mean sensitivity defect at the EZ edge was 7.6 dB. Among all functional biomarkers, the HOV slope mean value, HOV slope mean distance, and maximum sensitivity along the b-scan had the largest number of significant structural correlates. Conclusions Topographic slope metrics show promise as functional biomarkers relevant to the transition zone. EZ width is strongly associated with the location of most rapid HOV decline.

Test–Retest Variability of Functional and Structural Parameters in Patients with Stargardt Disease Participating in the SAR422459 Gene Therapy Trial

Purpose The goal of this analysis was to determine the test–retest variability of functional and structural measures from a cohort of patients with advanced forms of Stargardt Disease (STGD) participating in the SAR422459 (NCT01367444) gene therapy clinical trial. Methods Twenty-two participants, aged 24 to 66, diagnosed with advanced forms of STGD, with at least one pathogenic ABCA4 mutation on each chromosome participating in the SAR422459 (NCT01367444) gene therapy clinical trial, were screened over three visits within 3 weeks or less. Functional visual evaluations included: best-corrected visual acuity (BCVA) Early Treatment Diabetic Retinopathy Study (ETDRS) letter score, semiautomated kinetic perimetry (SKP) using isopters I4e, III4e, and V4e, hill of vision (HOV) calculated from static visual fields (SVF) by using a 184n point centrally condensed grid with the stimulus size V test target. Retinal structural changes such as central macular thickness and macular volume were assessed by spectral-domain optical coherence tomography (SD-OCT). Repeatability coefficients (RC) and 95% confidential intervals (CI) were calculated for each parameter using a hierarchical mixed-effects model and bootstrapping. Results Criteria for statistically significant changes for various parameters were found to be the following: BCVA letter score (8 letters), SKP isopters I4e, III4e, and V4e (3478.85; 2488.02 and 2622.46 deg2, respectively), SVF full volume HOV (VTOT, 14.62 dB-sr), central macular thickness, and macular volume (4.27 μm and 0.15 mm3, respectively). Conclusions This analysis provides important information necessary to determine if significant changes are occurring in structural and functional assessments commonly used to measure disease progression in this cohort of patients with STGD. Moreover, this information is useful for future trials assessing safety and efficacy of treatments in STGD. Translational Relevance Determination of variability of functional and structural measures in participants with advanced stages of the STGD is necessary to assess efficacy and safety in treatment trials involving STGD patients.

REPEATABILITY AND LONGITUDINAL ASSESSMENT OF FOVEAL CONE STRUCTURE IN CNGB3-ASSOCIATED ACHROMATOPSIA.

Purpose: Congenital achromatopsia is an autosomal recessive disease causing substantial reduction or complete absence of cone function. Although believed to be a relatively stationary disorder, questions remain regarding the stability of cone structure over time. In this study, the authors sought to assess the repeatability of and examine longitudinal changes in measurements of central cone structure in patients with achromatopsia. Methods: Forty-one subjects with CNGB3-associated achromatopsia were imaged over a period of between 6 and 26 months using optical coherence tomography and adaptive optics scanning light ophthalmoscopy. Outer nuclear layer (ONL) thickness, ellipsoid zone (EZ) disruption, and peak foveal cone density were assessed. Results: ONL thickness increased slightly compared with baseline (0.184 &mgr;m/month, P = 0.02). The EZ grade remained unchanged for 34/41 subjects. Peak foveal cone density did not significantly change over time (mean change 1% per 6 months, P = 0.126). Conclusion: Foveal cone structure showed little or no change in this group of subjects with CNGB3-associated achromatopsia. Over the time scales investigated (6–26 months), achromatopsia seems to be a structurally stable condition, although longer-term follow-up is needed. These data will be useful in assessing foveal cone structure after therapeutic intervention.

Assessing total retinal blood flow in diabetic retinopathy using multiplane en face Doppler optical coherence tomography

Aim To assess total retinal blood flow (TRBF) in diabetic retinopathy (DR) using multiplane en face Doppler optical coherence tomography (OCT). Methods A 70 kHz spectral-domain OCT system scanned a 2×2 mm area centred at the optic disc of the eyes with DR and healthy participants. The multiplane en face Doppler OCT algorithm generated a three-dimensional volumetric data set consisting of 195 en face planes. The TRBF was calculated from the maximum flow values of each branching retinal vein at an optimised en face plane. DR severity was graded according to the international clinical classification system. The generalised linear model method was used to compare flow values between DR groups and the control group. Results A total of 71 eyes from 71 participants were included. Ten eyes were excluded due to poor image quality. The within-visit repeatability of scans was 4.1% (coefficient of variation). There was no significant difference in the TRBF between the healthy (46.7±10.2 µL/min) and mild/moderate non-proliferative DR (44.9±12.6 µL/min) groups. The TRBF in severe non-proliferative DR (39.1±12.6 µL/min) and proliferative DR (28.9±8.85 µL/min) groups were significantly lower (p=0.04 and p<0.0001, respectively) than that of the healthy group. TRBF was correlated with DR disease severity (p<0.0001, linear trend test). Conclusion The novel multiplane en face Doppler OCT method provided reliable measurements of TRBF in DR eyes. This may be a useful tool in understanding the pathophysiology of DR.

Safety and Efficacy of OXB-202, a Genetically Engineered Tissue Therapy for the Prevention of Rejection in High-Risk Corneal Transplant Patients

Due to both the avascularity of the cornea and the relatively immune-privileged status of the eye, corneal transplantation is one of the most successful clinical transplant procedures. However, in high-risk patients, which account for >20% of the 180,000 transplants carried out worldwide each year, the rejection rate is high due to vascularization of the recipient cornea. The main reason for graft failure is irreversible immunological rejection, and it is therefore unsurprising that neovascularization (NV; both pre and post grafting) is a significant risk factor for subsequent graft failure. NV is thus an attractive target to prevent corneal graft rejection. OXB-202 (previously known as EncorStat®) is a donor cornea modified prior to transplant by ex vivo genetic modification with genes encoding secretable forms of the angiostatic human proteins, endostatin and angiostatin. This is achieved using a lentiviral vector derived from the equine infectious anemia virus called pONYK1EiA, which subsequently prevents rejection by suppressing NV. Previously, it has been shown that rabbit donor corneas treated with pONYK1EiA substantially suppress corneal NV, opacity, and subsequent rejection in an aggressive rabbit model of cornea graft rejection. Here, efficacy data are presented in a second rabbit model, which more closely mirrors the clinical setting for high-risk corneal transplant patients, and safety data from a 3-month good laboratory practice toxicology and biodistribution study of pONYK1EiA-modified rabbit corneas in a rabbit corneal transplant model. It is shown that pONYK1EiA-modified rabbit corneas (OXB-202) significantly reduce corneal NV and the rate of corneal rejection in a dose-dependent fashion, and are tolerated with no adverse toxicological findings or significant biodistribution up to 13 weeks post surgery in these rabbit studies. In conclusion, angiogenesis is a valid target to prevent corneal graft rejection in a high-risk setting, and transplanted genetically modified corneas are safe and well-tolerated in an animal model. These data support the evaluation of OXB-202 in a first-in-human trial.

31. EncorStat®: A Human Donor Cornea Genetically Engineered To Resist Rejection in High Risk Patients

Corneal transplantation is one of the most successful transplant procedures because of the relatively immune-privileged status of the eye and the avascularity of the cornea. However, normal corneal immune privilege can be eroded by neovascularization by providing a route of entry for immune-mediating cells, leading to subsequent irreversible immunological rejection of the corneal graft, the most common reason for graft failure. In high risk patients, which account for >20% of the 100,000 transplants carried out worldwide each year, the rejection rate can be very high (50-90%), particularly if there is pre-existing vascularization of the recipient corneal bed. In these patients the prognosis is extremely poor, with grafts failing at an accelerating rate to the point where patients are no longer considered suitable for further transplants and are left blind, despite an otherwise healthy eye. It is therefore not surprising that neovascularization (both pre- and post-grafting) is a significant risk factor for corneal graft failure. Neovascularization is thus an attractive target to prevent corneal graft failure due to rejection.EncorStat® is a human donor cornea modified prior to transplant by the ex vivo delivery of the genes encoding secretable forms of the angiostatic human proteins, endostatin and angiostatin, by a lentiviral vector, derived from the Equine Infectious Anaemia Virus (EIAV), which prevents subsequent rejection by suppressing neovascularization.Modified rabbit corneas have been evaluated in two different models of corneal graft rejection, a highly aggressive model in which rejection is driven by the retention of thick graft sutures, and a less aggressive model in which rejection is driven by pre-vascularizing the recipient corneal bed prior to surgery. In this latter model thin sutures are used to secure the graft that are removed two weeks following surgery, which is more analogous to the clinical setting. The process to generate EncorStat® corneas has been optimized to secrete substantial and persistent levels of angiostatic proteins with very little shedding of residual vector. These corneas substantially suppress corneal neovascularization, opacity and subsequent rejection in both rabbit models of cornea graft rejection.The non-clinical data to be presented support the evaluation of EncorStat® corneas in a First-in-Man trial. With support from the UK Technology Strategy Board (Innovate UK), this trial will be conducted in 2016, following completion of non-clinical safety studies and GMP vector manufacture this year. An outline of this clinical trial design will also be presented.