AB026.Ocular rigidity is correlated with glaucomatous structural damage

Background:The rigidity of the corneoscleral shell is an important biomechanical property which could be relevant in the pathophysiology of open-angle glaucoma(OAG).This study aims to evaluate the relationship between ocular rigidity(OR)and glaucomatous damage as represented by structural optical coherence tomography(OCT)-based parameters such as retinal nerve fiber layer(RNFL)and ganglion cell layer+inner plexiform layer(GCL+IPL)thicknesses.These parameters characterize the retinal layers that contain neuronal structures that form the optic nerve.Methods:Sixty-six subjects(37 with early OAG,11 with moderate to advanced OAG,16 healthy)were recruited in this study.OR measurements were carried out using a non-invasive clinical method developed by our group.As described in Beaton et al.(2015),this method,which is based on Friedenwald’s equation,involves video-rate OCT imaging and automated choroidal segmentation,as well as dynamic contour tonometry to calculate the OR coefficient.RNFL and macular GCL thicknesses were acquired using the Cirrus SD-OCT(Carl-Zeiss Meditec,Dublin,CA,USA).Correlations between OR and structural parameters in all 66 eyes were assessed using SPSS.Results:Significant correlations were found between OR and the average GCL+IPL thickness(r=0.355,P=0.004)as well as the minimum GCL+IPL thickness(r=0.340,P=0.006).Direct correlations were also found between OR and RNFL thickness in the inferior quadrant(r=0.258,P=0.036)and inferior clock hour(r=0.313,P=0.011).Conclusions:In this study,we found a positive correlation between structural OCT-based parameters and OR,perhaps indicating more structural damage in less rigid eyes.These findings could provide insight unto the pathophysiology of OAG.Further investigation is warranted to confirm the role of OR in glaucoma and elucidate whether there is a subgroup of patients for which OR plays a greater role.

AB036. Pulsatile choroidal blood flow (PCBF) in the glaucoma spectrum-preliminary results obtained with a novel optical method

Background:Decrease of ocular blood flow has been linked to the pathogenesis of ocular diseases such as glaucoma and age-related macular degeneration.Current methods that measure the pulsatile blood flow have major limitations,including the assumption that ocular rigidity is the same in all eyes.Our group has recently developed a new method to measure the pulsatile choroidal volume change by direct visualization of the choroid with OCT imaging and automated segmentation.Our goal in this study is to describe the distribution of PCBF in a healthy Caucasian population.Methods:Fifty-one subjects were recruited from the Maisonneuve-Rosemont Hospital Ophthalmology Clinic and underwent PCBF measurement in one eye.The distribution of PCBF in healthy eyes was assessed.Results:The distribution of PCBF among the healthy eyes was found to be 3.94±1.70µL with this technique.Conclusions:This study demonstrates the normal range of PCBF values obtained in a healthy Caucasian population.This technique could be used for further investigation of choroid pulsatility and to study glaucoma pathophysiology.

AB091.A novel method for the measurement of pulsatile choroidal blood flow based on video-rate OCT imaging and automated segmentation of the choroid:description and reproducibility

Background:Over the years,a variety of non-invasive techniques have been developed to allow the measurement of blood flow in living human eyes.However,none of the existing techniques has yet been adopted in clinical practice due to their limitations and lack of standardization.Moreover,no reliable technique is currently available to measure the pulsatile choroidal blood flow(PCBF).We propose a novel method based on video-rate optical coherence tomography(OCT)imaging and automated segmentation to measure the pulsatile component of choroidal blood flow in vivo,and demonstrate its repeatability.Methods:Adapted from our earlier work(Beaton et al.),this method uses video-rate OCT with enhanced depth imaging and automated segmentation of the choroid to measure the pulsatile choroidal volume change.Imaging is carried out at the fundus for less than a minute at 7 Hz.In each frame,choroidal thickness(CT)is measured by a segmentation algorithm based on graph cuts using an edge-probability weighting scheme.The algorithm computes the CT change corresponding to choroidal filling over the time-series and subsequently derives the pulsatile choroidal volume change through an approximate model of the eye.Fifty-eight subjects were recruited from the Maisonneuve-Rosemont Hospital and PCBF was measured twice in one eye within the same session and by a single examiner.Repeatability was assessed using the Bland-Altman plot and Intraclass correlation coefficient as calculated with SPSS.Results:Two measurements of PCBF were successfully obtained for each eye using our technique.The average measures ICC for choroidal volume change was 0.929(95%CI,0.881,0.958),showing good to excellent repeatability.The Bland-Altman plot and Pearson coefficient(r=0.840,P<0.001)showed agreement and a strong correlation respectively between intra-session measurement of OR in all examined eyes.Conclusions:This study confirms the high repeatability of pulsatile choroidal blood flow measurements obtained with our optical method,allowing further investigation of blood flow in ocular diseases such as glaucoma and AMD.

AB025.Machine learning applied to the oxygen induced retinopathy model

Background:The oxygen induced retinopathy rodent model is widely used,notably for the assessment of developmental dystrophies in preclinical studies of vascular retinal diseases.Typically,the quantification of vessel tufts and avascular regions is computed manually from flat mounted retinas imaged using fluorescent probes that highlight the vascular network.However,such manual measurements are time-consuming and hampered by user variability and bias,thus a rapid and objective alternative is required.Methods:We employ a machine learning approach to segment and characterize vascular tufts.The proposed quantitative retinal vascular assessment(QuRVA)technique uses quadratic discrimination analysis and morphological techniques to provide reliable measurements of vascular density and pathological vascular tuft regions,devoid of user intervention within seconds.Our algorithms allow also delineating the whole vasculature network,and identifying and analyzing avascular regions.Results:Our first experiment shows the high degree of error and variability of manual segmentations.In consequence,we developed a set of algorithms to perform this task automatically.We benchmark and validate the results of our analysis pipeline using the consensus of several manually curated segmentations using commonly used computer tools.We describe the method,provide details for reproducing the algorithm,and validate all aspects of the analysis.Conclusions:Manual and semi-automated procedures for tuft detection present strong fluctuations among users,demonstrating the need for fast and unbiased tools in this highly active research field with tremendous implications for basic research and industry.

AB034. In vivo laser-mediated retinal ganglion cell optoporation using Kv1.1 conjugated gold nanoparticles

Background:There is a current void in efficient,cell-specific,retinal drug delivery systems,thus developing a safe,effective,selective drug delivery system would open novel therapeutic avenues.We previously demonstrated that femtosecond(fs)laser irradiation can transfect DNA plasmids into cultured cells in the presence of gold nanoparticles(AuNPs).These AuNPs locally amplify laser energy at a submicron range creating transient pores allowing exogenous genetic material or cell impermeable dyes to enter the cell.Here,we sought out to selectively optoporate retinal cells in vivo with functionalized AuNPs and a 800 nm femtosecond(fs)laser.Methods:The cell-surface Kv1.1 voltage-gated channel was chosen to selectively target retinal ganglion cells(RGC)in the rat retina.Citrate-capped spherical 100 nm AuNPs functionalized with orthopyridyl-disulfide-poly(ethylene glycol)(5 kDa)-N-hydroxysuccinimide(OPSS-PEG-NHS)conjugated to a Kv1.1 monoclonal antibody were injected intravitreally in Sprague Dawley rats 3 hours prior to irradiation,concomitantly to a FITC-dextran dye to detect optoporation.The eyes of anesthetized rats were placed in the beam path of a laser system consisting of an 800 nm,100 fs laser and a Heidelberg Spectralis HRA ophthalmoscope for fundus visualization.The rat retina was irradiated at powers ranging from 20-750 mW,the eyes fixed in 4%paraformaldehyde,dissected,rinsed,mounted and imaged by confocal microscopy.Results:Our novel laser system coupled to a Heidelberg ophthalmoscope allowed for a clear visualisation of the rat ocular fundus.A timecourse of AuNP intravitreal injections revealed that optimal nanoparticle dispersion on the retinal surface occurred at 3 hours post injection.Following Kv1.1-AuNP and FITC-dextran intravitreal injection and incubation,irradiation at 120-750 mW resulted in FITC uptake by retinal cells.Conclusions:Since living biological tissues absorb energy very weakly at 800 nm,this non-invasive tool may provide a safe,cost effective clinically relevant approach to selectively target retinal cells and limit complications associated with surgical interventions,and potential biological hazards associated with viral-based gene therapy.