Generalized 3D registration algorithm for enhancing retinal optical coherence tomography images

Significance

Optical coherence tomography (OCT) has emerged as the standard of care for diagnosing and monitoring the treatment of various ocular disorders due to its noninvasive nature and in vivo volumetric acquisition capability. Despite its widespread applications in ophthalmology, motion artifacts remain a challenge in OCT imaging, adversely impacting image quality. While several multivolume registration algorithms have been developed to address this issue, they are often designed to cater to one specific OCT system or acquisition protocol.

Aim

We aim to generate an OCT volume free of motion artifacts using a system-agnostic registration algorithm that is independent of system specifications or protocol.

Approach

We developed a B-scan registration algorithm that removes motion and corrects for both translational eye movements and rotational angle differences between volumes. Tests were carried out on various datasets obtained from two different types of custom-built OCT systems and one commercially available system to determine the reliability of the proposed algorithm. Additionally, different system specifications were used, with variations in axial resolution, lateral resolution, signal-to-noise ratio, and real-time motion tracking. The accuracy of this method has further been evaluated through mean squared error (MSE) and multiscale structural similarity index measure (MS-SSIM).

Results

The results demonstrate improvements in the overall contrast of the images, facilitating detailed visualization of retinal vasculatures in both superficial and deep vasculature plexus. Finer features of the inner and outer retina, such as photoreceptors and other pathology-specific features, are discernible after multivolume registration and averaging. Quantitative analyses affirm that increasing the number of averaged registered volumes will decrease MSE and increase MS-SSIM as compared to the reference volume.

Conclusions

The multivolume registered data obtained from this algorithm offers significantly improved visualization of the retinal microvascular network as well as retinal morphological features. Furthermore, we have validated that the versatility of our methodology extends beyond specific OCT modalities, thereby enhancing the clinical utility of OCT for the diagnosis and monitoring of ocular pathologies.

Mechanisms of cone sensitivity loss in retinitis pigmentosa

PURPOSE

To explore the mechanisms of cone sensitivity loss in retinitis pigmentosa by combining two-colour perimetry with threshold versus intensity (tvi) testing.

METHODS

Seven subjects with autosomal recessive retinitis pigmentosa and 10 normal subjects were recruited and underwent perimetric testing of one eye using 480- and 640-nm Goldman size V targets presented under scotopic conditions (no background illumination) and against a white background ranging in luminance from -1.5 to 2 log cd m-2 in 0.5 log cd m-2 steps. Data were fitted with tvi functions of the form logT = logT0 + log ((A + A0)/A0)n, where T is the threshold, T0 is the absolute threshold, A is the background intensity, A0 is the 'dark-light' constant and n is a gain constant.

RESULTS

Reliable tvi functions could not be obtained within the region of the visual field corresponding to loss of the ellipsoid zone on optical coherence tomography. At fixation, changes in both T0 and A0 were observed, consistent with a d1 mechanism loss, which resulted in an upwards and rightwards shift of the tvi function. Losses at [±3°, ±3°] demonstrated changes in T0, consistent with a d3 mechanism loss, resulting in an upwards translation of the tvi curve.

CONCLUSIONS

Although the absolute cone threshold was elevated at each location, shifts in the tvi function (so-called d1 mechanism loss) at fixation minimise threshold elevation in the presence of white adapting backgrounds, such as those typically employed in standard two-colour perimetry. At more peripheral testing locations, changes in threshold occurred independent of background luminance (so-called d3 mechanism loss). These findings suggest that backgrounds which selectively adapt rods while maintaining cones at, or near, absolute threshold may be preferable to conventional two-colour perimetry for assessing loss of cone sensitivity, especially at the point of fixation.

Outcomes of Scleral Buckling After Failed Pneumatic Retinopexy

Purpose: To assess the visual and anatomic outcomes of eyes that had secondary scleral buckle (SB) surgery after unsuccessful pneumatic retinopexy (PR) for rhegmatogenous retinal detachment (RRD). Methods: A retrospective study, performed over a 12-year period, comprised patients who had secondary SB procedures after failed primary PR. Clinical parameters (eg, best-corrected visual acuity [BCVA], lens status, macula status, details of RRD and subretinal fluid) were assessed at presentation, before additional procedures, and at follow-up (6 months, 1 year, and last visit). Statistical comparisons were made using Brown-Forsythe and Welch analysis-of-variance tests, with significance levels set at P < .05. Results: Fifty-four eyes with adequate follow-up were included. Forty-four (81.5%) of 54 eyes had successful retinal reattachment with secondary SB alone. The remaining eyes had subsequent pars plana vitrectomy (PPV). Patients presenting with macula-on RRD who had successful secondary SB had no statistically significant change in BCVA from baseline (mean final, 0.23 ± 0.25 logMAR [Snellen 20/34]; P = .999). There was a statistically significant improvement in BCVA in patients presenting with macula-off RRD who had successful secondary SB (mean final, 0.32 ± 0.36 logMAR [20/42]; P < .001 and mean change, -1.06 ± 0.85 logMAR). Ten patients presenting with macula-off RRD who had failed secondary SB had a significant improvement in the final BCVA (mean final, 0.22 ± 0.28 logMAR [20/33]; P = .044), despite the need for an additional PPV to achieve reattachment. Conclusions: Secondary SB remains a good option for RRD repair after unsuccessful PR and may avoid the need for PPV.

Polarization-Diversity Optical Coherence Tomography Assessment of Choroidal Nevi

Purpose

The purpose of this study was to demonstrate the utility of polarization-diversity optical coherence tomography (PD-OCT), a noninvasive imaging technique with melanin-specific contrast, in the quantitative and qualitative assessment of choroidal nevi.

Methods

Nevi were imaged with a custom-built 55-degree field-of-view (FOV) 400 kHz PD-OCT system. Imaging features on PD-OCT were compared to those on fundus photography, auto-fluorescence, ultrasound, and non-PD-OCT images. Lesions were manually segmented for size measurement and metrics for objective assessment of melanin distributions were calculated, including degree of polarization uniformity (DOPU), attenuation coefficient, and melanin occupancy rate (MOR).

Results

We imaged 17 patients (mean age = 69.5 years, range = 37-90) with 11 pigmented, 3 non-pigmented, and 3 mixed pigmentation nevi. Nevi with full margin acquisition had an average longest basal diameter of 5.1 mm (range = 2.99-8.72 mm) and average height of 0.72 mm (range = 0.37 mm-2.09 mm). PD-OCT provided clear contrast of choroidal melanin content, distribution, and delineation of nevus margins for melanotic nevi. Pigmented nevi were found to have lower DOPU, higher attenuation coefficient, and higher MOR than non-pigmented lesions. Melanin content on PD-OCT was consistent with pigmentation on fundus in 15 of 17 nevi (88%).

Conclusions

PD-OCT allows objective assessment of choroidal nevi melanin content and distribution. In addition, melanin-specific contrast by PD-OCT enables clear nevus margin delineation and may improve serial growth surveillance. Further investigation is needed to determine the clinical significance and prognostic value of melanin characterization by PD-OCT in the evaluation of choroidal nevi.

RetINal Toxicity And HydroxyChloroquine Therapy (INTACT): protocol for a prospective population-based cohort study

PURPOSE

Hydroxychloroquine (HCQ) is an important medication for patients with systemic lupus erythematosus (SLE), rheumatoid arthritis (RA) and other rheumatic diseases. Although it is well-tolerated and cost-effective, the risk of HCQ retinal toxicity is of increasing concern. The aim of this study is to re-examine the HCQ retinal toxicity incidence rate, risk factors and clinical course after discontinuation.

METHODS

We designed a prospective population-based cohort study in adult patients with SLE or RA, currently receiving HCQ for five or more years, who are residents of British Columbia (BC), Canada. Based on administrative data, we identified 5508 eligible participants (1346 SLE and 4162 RA). They will participate in annual or biannual retinal screening over 5 years in alignment with the recently revised American Academy of Ophthalmology guidelines. To standardise procedures for retinal screening, imaging, diagnostic criteria, severity staging and data transfer, a consensus meeting was convened in December 2019 with participation of BC retinal specialists and the research team. Agreement was attained on: use of spectral domain-optical coherence tomography as the primary objective screening modality; classification of images into categories of normal, equivocal or abnormal; and transferring the equivocal and abnormal images plus corresponding subjective test results via cloud-based server from each clinic to a reading centre. Confirmation of HCQ retinal toxicity diagnoses and severity staging will be performed by three independent and masked reviewers. The incidence of HCQ retinal toxicity will be calculated, accounting for the competing risk of death. Hazard ratios for each risk factor will be calculated for the risk of HCQ retinopathy, after adjusting for confounders. We will also estimate the risk of HCQ retinal toxicity progression over 5 years.

ETHICS AND DISSEMINATION

This study has received approval from the University of British Columbia Clinical Research Ethics Board (H20-00736) and the Vancouver Coastal Health Research Institute.

SURGICAL RETINAL EXPLANTS AS A SOURCE OF RETINAL PROGENITOR CELLS

PURPOSE

To describe the novel observation of spontaneously migrating retinal cells from living donor surgical retinal explants that express progenitor cell markers in the absence of exogenous growth factors.

METHODS

Surgical retinal explants were harvested from 5 consecutive patients undergoing 23 G pars plana vitrectomy for the management of rhegmatogenous detachment. During surgery, equatorial flap tears were trimmed with the vitreous cutter and aspirated. Excised tissue was then regurgitated into a syringe containing balanced salt solution and immediately transferred to tissue culture. Migrating cells subsequently underwent immunohistochemical staining and their characteristics were compared with those of a spontaneously immortalized Müller stem cell line.

RESULTS

Spontaneously migrating cells were observed from samples taken from all 5 patients from Day 2 to 10 after transfer to culture. These cells were found to express embryonic cell markers, including paired box 6 (Pax6), sex-determining region Y-box 2 (Sox-2), nestin, cone-rod homeobox, and cyclin-dependent kinase inhibitor 1B (p27Kip1) as well as proteins consistent with early or retained differentiation down the Müller cell lineage, including glial fibrillary acidic protein and glutamine synthetase.

CONCLUSION

After injury, the human equatorial retina is capable of spontaneously producing cells that demonstrate migration and that express progenitor cell markers. In addition, these cells express proteins consistent with Müller cell lineage. These initial observations support the assertion that the human retina may possess the potential for regeneration and that surgical retinal explants could also act as a ready source of retinal progenitor cells.

Investigation of the Peripapillary Choriocapillaris in Normal Tension Glaucoma, Primary Open-angle Glaucoma, and Control Eyes

PRECIS

The peripapillary choriocapillaris (CC) was observed to be significantly impaired in normal tension glaucoma (NTG) subjects compared with normal controls using optical coherence tomography angiography (OCTA).

PURPOSE

The aim was to quantitatively evaluate the peripapillary CC in NTG, primary open-angle glaucoma (POAG), and control eyes using OCTA.

MATERIALS AND METHODS

Ninety eyes (30 controls, 30 NTG, and 30 POAG) from 73 patients were imaged using the Zeiss Plex Elite 9000. Five repeat 3×3 mm OCTA scans were acquired both nasally and temporally to the optic disc and subsequently averaged. Four CC flow deficit (FD) measures were calculated using the fuzzy C-means approach: FD density (FDD), mean FD size (MFDS), FD number (FDN), and FD area (FDA).

RESULTS

Temporal NTG CC parameters were associated with visual field index and mean deviation (P<0.05). The control group showed a significantly lower nasal FDD (nasal: 3.79±1.26%, temporal: 4.48±1.73%, P=0.03), FDN (nasal: 156.43±38.44, temporal: 178.40±45.68, P=0.02), and FDA (nasal: 0.22±0.08, temporal: 0.26±0.10, P=0.03) when compared with temporal optic disc. The NTG group showed a significantly higher FDD (NTG: 5.04±2.38%, control: 3.79±1.26%, P=0.03), FDN (NTG: 185.90±56.66, control: 156.43±38.44, P=0.04), and FDA (NTG: 0.30±0.14 mm2, control: 0.22±0.08 mm2, P=0.03) nasal to the optic disc compared with controls.

CONCLUSIONS

Association between CC parameters and glaucoma severity in NTG, but not POAG subjects, suggests vascular abnormalities may be a potential factor in the multifactorial process of glaucoma damage in NTG patients.

Intravitreal anti-vascular endothelial growth factor versus panretinal LASER photocoagulation for proliferative diabetic retinopathy: a systematic review and meta-analysis

OBJECTIVE

To systematically review and perform a meta-analysis on the available evidence for anti-vascular endothelial growth factor (anti-VEGF) monotherapy versus panretinal photocoagulation (PRP) for proliferative diabetic retinopathy (PDR).

DESIGN

Systematic review and meta-analysis PARTICIPANTS: Randomized clinical trials included participants ≥18 years old with clinical or angiographic evidence of PDR. Interventions included were anti-VEGF monotherapy and PRP. Excluded studies were those with potentially biased treatment allocation and those offering combination therapies.

METHODS

The primary outcome was mean change in best-corrected visual acuity. Secondary outcomes were the proportion of patients developing severe (<6/60) or moderate (6/24-6/60) vision loss, rates of vitrectomy or vitreous hemorrhage, worsening macula edema, and reduced visual field indices.

RESULTS

Five studies of varying quality met the inclusion criteria (n = 632). The anti-VEGF intervention arm had a mean difference of -0.08 logMAR or 4 Early Treatment Diabetic Retinopathy Study (EDTRS) letters gained (p = 0.02) when compared with PRP at 12 months. The difference in rates of vitrectomy and vitreous hemorrhage favoured anti-VEGF over PRP (risk difference [RD] -0.10, p = < 0.001 and RD -0.10, p = 0.003 respectively).

CONCLUSIONS

This meta-analysis of the available evidence in patients with early PDR demonstrates a potential benefit for anti-VEGF over PRP alone. However, these benefits must be weighed against the relative costs of treatment and the potential risks of loss to follow-up.

Swept Source Optical Coherence Tomography Compared to Ultrasound and Biomicroscopy for Diagnosis of Posterior Vitreous Detachment

Background

Biomicroscopy, B-scan ultrasound imaging, and SD-OCT are all modalities used to characterize a posterior vitreous detachment (PVD). Our objective is to assess the precision of the diagnosis of PVD by SS-OCT.

Methods

This prospective observational study examines ninety-five eyes of forty-nine patients with biomicroscopy, B-scan ultrasound, and SS-OCT for the presence or absence of a complete PVD. All SS-OCT images were reviewed by two retina specialists (RWSC, ZM). All three diagnostic methods were evaluated for agreement by Cohen’s kappa statistic.

Results

The inter-rater reliability between retina specialists reading the SS-OCT images was 97.9% (κ = 0.957). Agreement on PVD status between SS-OCT and biomicroscopy was 85.3% (κ = 0.711). Agreement between SS-OCT and B-scan ultrasound was 83.2% (κ = 0.667). Agreement between B-scan ultrasound and biomicroscopy was 87.4% (κ = 0.743).

Conclusion

For the diagnosis of complete PVD, SS-OCT allows for high accuracy and agreement between graders.

Threshold versus intensity functions in two-colour automated perimetry

PURPOSE

Two-colour computerised perimetry is a technique developed for assessing cone- and rod-function at fixed background luminances in retinal disease. However, the state of adaptation during testing is unknown but crucial in the interpretation of results. We therefore aimed to determine the adaptational state of rod- and cone-mechanisms in two-colour perimetry.

METHODS

Sensitivity to 480 nm (blue) and 640 nm (red) Goldmann size V targets was determined for 10 normal subjects aged 16 to 46 years at 17 locations in the central 60 degrees of the visual field under scotopic conditions and then from -1.5 log cd m^-2 to 2 log cd m^-2 (white background) in 0.5 log unit steps. Data were fitted with threshold versus intensity (tvi) functions of the form logT = logT₀ + log ((A + A₀ )/A₀ )ⁿ .

RESULTS

No clear rod-cone break was observed for 640 nm stimuli. For 480 nm stimuli, transition from rod-detection to cone-detection occurred at mesopic illumination levels, where rod adaptation approached Weber behaviour. Cone detection mechanisms did not display Weber-like adaptation until the background luminance approached 1 log cd.m^-2 . Diseases resulting in a "filter effect" - including disorders of the photoreceptors - are therefore predicted to affect sensitivity when rod function is probed with short-wavelength targets under scotopic conditions, but less so under mesopic conditions. Filter effects are similarly anticipated to affect cone function measured using long-wavelength targets under mesopic conditions (e.g., during microperimetry), but less so under photopic conditions.

CONCLUSIONS

Asymmetries in adaptation in automated two-colour perimetry are predicted to artefactually favour the detection of losses in rod sensitivity under scotopic conditions and cones under mesopic conditions.

Semi-supervised deep learning based 3D analysis of the peripapillary region

Optical coherence tomography (OCT) has become an essential tool in the evaluation of glaucoma, typically through analyzing retinal nerve fiber layer changes in circumpapillary scans. Three-dimensional OCT volumes enable a much more thorough analysis of the optic nerve head (ONH) region, which may be the site of initial glaucomatous optic nerve damage. Automated analysis of this region is of great interest, though large anatomical variations and the termination of layers make the requisite peripapillary layer and Bruch's membrane opening (BMO) segmentation a challenging task. Several machine learning-based segmentation methods have been proposed for retinal layer segmentation, and a few for the ONH region, but they typically depend on either heavily averaged or pre-processed B-scans or a large amount of annotated data, which is a tedious task and resource-intensive. We evaluated a semi-supervised adversarial deep learning method for segmenting peripapillary retinal layers in OCT B-scans to take advantage of unlabeled data. We show that the use of a generative adversarial network and unlabeled data can improve the performance of segmentation. Additionally, we use a Faster R-CNN architecture to automatically segment the BMO. The proposed methods are then used for the 3D morphometric analysis of both control and glaucomatous ONH volumes to demonstrate the potential for clinical utility.

Ensemble Deep Learning for Diabetic Retinopathy Detection Using Optical Coherence Tomography Angiography

Purpose

To evaluate the role of ensemble learning techniques with deep learning in classifying diabetic retinopathy (DR) in optical coherence tomography angiography (OCTA) images and their corresponding co-registered structural images.

Methods

A total of 463 volumes from 380 eyes were acquired using the 3 × 3-mm OCTA protocol on the Zeiss Plex Elite system. Enface images of the superficial and deep capillary plexus were exported from both the optical coherence tomography and OCTA data. Component neural networks were constructed using single data-types and fine-tuned using VGG19, ResNet50, and DenseNet architectures pretrained on ImageNet weights. These networks were then ensembled using majority soft voting and stacking techniques. Results were compared with a classifier using manually engineered features. Class activation maps (CAMs) were created using the original CAM algorithm and Grad-CAM.

Results

The networks trained with the VGG19 architecture outperformed the networks trained on deeper architectures. Ensemble networks constructed using the four fine-tuned VGG19 architectures achieved accuracies of 0.92 and 0.90 for the majority soft voting and stacking methods respectively. Both ensemble methods outperformed the highest single data-type network and the network trained on hand-crafted features. Grad-CAM was shown to more accurately highlight areas of disease.

Conclusions

Ensemble learning increases the predictive accuracy of CNNs for classifying referable DR on OCTA datasets.

Translational Relevance

Because the diagnostic accuracy of OCTA images is shown to be greater than the manually extracted features currently used in the literature, the proposed methods may be beneficial toward developing clinically valuable solutions for DR diagnoses.

Comparison of United States and International Ophthalmic Drug Pricing

PURPOSE

To compare United States and international drug pricing for commonly prescribed intravitreal and topical ophthalmic medications.

DESIGN

Cross-sectional observational study.

METHODS

For 25 commonly used ophthalmic medications (3 intravitreal, 22 topical), we obtained 2017 third quarter United States average wholesale price (AWP), drug acquisition cost, or consumer pricing through United States government health insurance plans (Veterans Affairs [VA], Medicaid, Medicare Part B, and Medicare Part D) and commercial drug plans (CVS Caremark and Navitus Health Solutions), online pricing without insurance through a large United States warehouse retailer (Costco), and international drug pricing through government-sponsored health plans in Italy, Spain, Turkey, Canada, and Japan.

MAIN OUTCOME MEASURES

Drug acquisition costs and consumer pricing of ophthalmic drugs through various payment systems. All prices were converted to United States dollars.

RESULTS

For intravitreal medications in the United States, aflibercept and ranibizumab were priced similarly to each other and were more expensive than dexamethasone implants. Pricing of aflibercept and ranibizumab through government health insurance plans in Italy, Spain, Turkey, Canada, and Japan were less expensive by as much as 84.3% compared with the United States. For topical medications in the United States, pricing varied significantly both across different classes of medications and also between nonbranded and branded medications. Drug acquisition costs through the VA and Medicaid were inexpensive on average, but pricing through a hospital-employee drug insurance plan offered the smallest range (between $2.35 and $60.00). In all 5 non-United States countries studied, each topical medication with the exceptions of cyclosporine emulsion and difluprednate was less than $100, and 94.4% of topical medications in these countries had a nonbranded or branded option that was less than $50.

CONCLUSIONS

In the United States, for topical more than intravitreal medications, significant price variation exists across both different drug pricing systems and different medications. Price differentials between nonbranded and branded medications can be significant. Internationally, topical medications exhibited a more limited and lower price range compared with drug pricing in the United States.

Quantitative Study of the Macular Microvasculature in Human Donor Eyes

Purpose

To precisely quantify the macular microvasculature density using microperfusion and labeling techniques in human donor eyes. Such information may be useful in understanding the role of the macular microvasculature in coping with the metabolic requirements of the neurons in this densely packed region, and provide a reference point for clinical studies using recently developed optical imaging techniques.

Methods

The macular microvasculature was perfusion-labeled in 18 human donor eyes and optical stacks collected from regions superior, temporal, inferior, and nasal to the foveola using confocal microscopy. The optical slices were separated into the deep macula vascular layer (DL), and the superficial layer (SL) in which all the vessels superficial to the deep macular vessel layer were included. The DL and SL images were analyzed and vessel density measured according to their orientation from the foveola and in foveal and parafoveal regions. Vessel densities were compared across regions and age groups.

Results

Both the SL and DL showed an increase in vessel density with increasing eccentricity from the foveal to parafoveal regions. Vessel density was found to rank in the order of inferior > superior > temporal > nasal in both SL and DL layers. The SL vascular density was approximately 31%, whereas DL was approximately 17%. The DL was planar in nature and density not affected by age. Age-related increase in vessel density was observed in the SL.

Conclusions

Microperfusion and labeling techniques in combination with confocal microscopy has enabled collection of reliable data on vascular density in the macula region. Regional differences may reflect well-matched vascular supply and neuronal demands. Age-related changes might indicate the importance of stable blood supply for the human macula.

Normal Variation of Photoreceptor Outer Segment Volume With Age, Gender, Refractive Error, and Vitreomacular Adhesion

BACKGROUND AND OBJECTIVE

Thickness and volume changes of the photoreceptor outer segment (PROS) layer on spectral-domain optical coherence tomography (SD-OCT) images are associated with various disease states. However, there are limited data on normal anatomical variation. This study evaluates the correlation of PROS volume with age, gender, refractive error, and presence of vitreomacular adhesion (VMA) in healthy subjects.

PATIENTS AND METHODS

SD-OCT scans of 68 normal eyes were analyzed. The ellipsoid zone and the apical retinal pigment epithelium boundary were segmented using an automated algorithm. The PROS volume was calculated as the region bounded by these two layers within a 6-mm diameter circle centered at the fovea. A general linear model was used for statistical analysis.

RESULTS

PROS volume increased with age to a significant degree (P = .013). Gender, refractive error, and presence of VMA were insignificant factors.

CONCLUSION

PROS volume, as measured on routine SD-OCT, increases with age in healthy subjects, after adjusting for gender, refractive error, and VMA. [Ophthalmic Surg Lasers Imaging Retina. 2018;49:523-527.].

INCIDENCE OF ACUTE EXUDATIVE MACULOPATHY AFTER REDUCED-FLUENCE PHOTODYNAMIC THERAPY

PURPOSE

To describe the incidence and features of acute exudative maculopathy (AEM) after half-fluence photodynamic therapy (PDT) and/or very minimal fluence PDT.

METHODS

Retrospective chart review of all patients treated over a 7-year period.

RESULTS

A total of 52 patients (58 eyes, 140 treatments) were treated with half-fluence PDT and/or very minimal fluence PDT. Patients were diagnosed with either central serous chorioretinopathy (CSCR) or neovascular age-related macular degeneration (nAMD). Two patients (1 CSCR and 1 nAMD) returned to the clinic with acute vision loss after treatment and were identified as having developed AEM. In the CSCR case, resolution occurred after intravitreal bevacizumab treatment. The nAMD case resolved with topical difluprednate treatment. We were unable to identify any risk factors for the development of AEM.

CONCLUSION

AEM seems to be a rare (incidence 1.4% per treatment) and unpredictable reaction related to the proinflammatory effects of half-fluence PDT and very minimal fluence PDT. Because of the inherent limitations of this study, the true incidence of AEM after reduced-fluence PDT may be higher.

SURGICAL EMBOLECTOMY FOR FOVEA-THREATENING ACUTE RETINAL ARTERY OCCLUSION

Supplemental Digital Content is Available in the Text.

The authors describe a surgical technique to facilitate the exposure and retrieval of embolus in cases of fovea-threatening retinal artery occlusion without a patent cilioretinal artery. The authors include a number of surgical pearls based on our experience that may facilitate intraocular emboli retrieval and minimize the common complication of vitreous hemorrhage associated with retinal embolectomy.

To describe a technique of surgical intraocular embolectomy in patients with acute fovea-threatening branch retinal artery occlusion.

Strip-based registration of serially acquired optical coherence tomography angiography

The visibility of retinal microvasculature in optical coherence tomography angiography (OCT-A) images is negatively affected by the small dimension of the capillaries, pulsatile blood flow, and motion artifacts. Serial acquisition and time-averaging of multiple OCT-A images can enhance the definition of the capillaries and result in repeatable and consistent visualization. We demonstrate an automated method for registration and averaging of serially acquired OCT-A images. Ten OCT-A volumes from six normal control subjects were acquired using our prototype 1060-nm swept source OCT system. The volumes were divided into microsaccade-free en face angiogram strips, which were affine registered using scale-invariant feature transform keypoints, followed by nonrigid registration by pixel-wise local neighborhood matching. The resulting averaged images were presented of all the retinal layers combined, as well as in the superficial and deep plexus layers separately. The contrast-to-noise ratio and signal-to-noise ratio of the angiograms with all retinal layers (reported as average ± standard deviation ) increased from 0.52 ± 0.22 and 19.58 ± 4.04 ?? dB for a single image to 0.77 ± 0.25 and 25.05 ± 4.73 ?? dB , respectively, for the serially acquired images after registration and averaging. The improved visualization of the capillaries can enable robust quantification and study of minute changes in retinal microvasculature.

Quantitative Optical Coherence Tomography Angiography of Radial Peripapillary Capillaries in Glaucoma, Glaucoma Suspect, and Normal Eyes

PURPOSE

To evaluate the quantitative characteristics of the radial peripapillary capillary (RPC) network in glaucoma, glaucoma suspect, and normal eyes using speckle variance optical coherence tomography angiography (OCT-A). To determine correlations between RPC density, nerve fiber layer (NFL) thickness, and visual field indices.

DESIGN

Cross-sectional study.

METHODS

OCT-A images of RPCs were acquired at a single institution using a custom-built 1060 nm system from 3 groups: unilateral glaucoma (10 eyes from 5 subjects), glaucoma suspects (6 eyes from 3 subjects), and normal control eyes (16 eyes from 9 normal subjects). Peripapillary NFL thickness measurements were determined using spectral-domain optical coherence tomography. Glaucoma and glaucoma suspects also underwent automated 30-2 Humphrey visual field analysis. Manual tracing techniques were used to quantify RPC density in the OCT-A images. Data were analyzed using a linear mixed model with 1 fixed-effect covariate. Correlations between main outcome measures (RPC density, NFL thickness, and visual field index) were determined.

RESULTS

Mean age was not significantly different between the 3 groups (P = .25). The density of RPCs was significantly lower in glaucomatous eyes compared with matched-peripapillary regions in the fellow eye, glaucoma suspect group, and normal group (all P < .001). RPC density was strongly correlated with NFL thickness (P < .001) and visual field index (P < .001).

CONCLUSIONS

Significant reductions in RPC density were correlated with sites of NFL decrease and visual field loss in glaucoma. Speckle variance OCT-A allows visualization and quantification of RPCs and may therefore be a useful tool for indirectly quantifying and monitoring retinal ganglion cell axonal injury in glaucoma.

Oral Bisphosphonates and Risk of Wet Age-Related Macular Degeneration

PURPOSE

To examine the risk of age-related macular degeneration (AMD) with oral bisphosphonates.

DESIGN

Three study designs were used: (1) disproportionality analysis; (2) case-control study; (3) self-controlled case series (SCCS).

METHODS

setting: (1) Food and Drug Administration (FDA) Adverse Event Reporting System (FAERS) Database; (2) 2 patient cohorts from British Columbia, Canada.

STUDY POPULATION

(1) All reports of AMD to the FDA with oral bisphosphoantes; (2) patients with wet AMD in British Columbia (2009-2013) and 1 million controls (2000-2007).

INTERVENTION

Oral bisphosphonates.

MAIN OUTCOME MEASURES

(1) Reports of AMD to the FDA; (2) first diagnosis of wet AMD verified by a retina specialist in British Columbia.

RESULTS

In the disproportionality analysis there were 133 cases of AMD reported with alendronate, 20 with ibandronate, and 14 with risedronate. The reported odds ratios (RORs) for alendronate, ibandronate, and risedronate were 3.82 (95% CI: 2.94-4.96), 2.40 (95% CI: 1.49-3.86), and 2.87 (95% CI: 1.58-5.19), respectively. In the case-control analysis there were 6367 cases and 6370 corresponding controls. The adjusted OR for wet AMD among regular users of bisphosphonates in the 1, 2, and 3 years prior to the index date were 1.24 (1.12-1.38), 1.38 (1.22-1.56), and 1.59 (1.38-1.82), respectively. In the SCCS analysis there were 198 cases of wet AMD on continuous bisphosphonate therapy. The rate ratio for wet AMD for continuous bisphosphonate use was 1.99 (95% CI: 1.41-2.79). We did not have information on intravenous bisphosphonates.

CONCLUSIONS

Continuous users of oral bisphosphonates are at a higher risk of developing wet AMD. Given the observational nature of this study and limitation of the data, future studies are needed to confirm these findings.

Segmentation of the foveal microvasculature using deep learning networks

Accurate segmentation of the retinal microvasculature is a critical step in the quantitative analysis of the retinal circulation, which can be an important marker in evaluating the severity of retinal diseases. As manual segmentation remains the gold standard for segmentation of optical coherence tomography angiography (OCT-A) images, we present a method for automating the segmentation of OCT-A images using deep neural networks (DNNs). Eighty OCT-A images of the foveal region in 12 eyes from 6 healthy volunteers were acquired using a prototype OCT-A system and subsequently manually segmented. The automated segmentation of the blood vessels in the OCT-A images was then performed by classifying each pixel into vessel or nonvessel class using deep convolutional neural networks. When the automated results were compared against the manual segmentation results, a maximum mean accuracy of 0.83 was obtained. When the automated results were compared with inter and intrarater accuracies, the automated results were shown to be comparable to the human raters suggesting that segmentation using DNNs is comparable to a second manual rater. As manually segmenting the retinal microvasculature is a tedious task, having a reliable automated output such as automated segmentation by DNNs, is an important step in creating an automated output.

Comparison of ophthalmic training in 6 English-speaking countries

OBJECTIVE

To compare key characteristics of ophthalmology training programs in 6 different English-speaking countries: Australia, New Zealand, Canada, Ireland, the United Kingdom, and the United States.

PARTICIPANTS

Seven ophthalmologists with personal knowledge of all 6 systems contributed.

METHODS

The main features examined were career pathway, duration of training, surgical training, governing bodies, and examination structure. Data were collected from the literature, online resources, and personal experience.

RESULTS

Several differences were highlighted, including length of training (ranging from 4 to 9 years after medical school), number of surgical procedures such as cataracts (ranging from minimum 86 to approximately 600), and structure of fellowship training.

CONCLUSIONS

As trainees increasingly seek international experience to enhance their knowledge and skills, the similarities and differences between training programs in different countries have become more relevant. Some of these differences may reflect differing needs of different patient populations and different healthcare delivery systems across the globe. However, these differences should also prompt educators to more carefully scrutinize their own training system and search for potential improvements.

Vascular endothelial growth factor inhibitor use and treatment approach for choroidal neovascularization secondary to pathologic myopia

INTRODUCTION

Myopic choroidal neovascularization (CNV) is the most common cause of CNV in those under 50 years of age. It is a significant cause of visual loss in those with pathologic myopia. The current standard of care involves therapy with intravitreal inhibitors of vascular endothelial growth factor (VEGF).

AREAS COVERED

The epidemiology of myopia, high myopia, pathologic myopia, and myopic CNV is reviewed, along with a brief discussion of historical treatments. The pharmacology of the three most commonly used anti-VEGF agents is discussed, with an emphasis on the licensed drugs, ranibizumab and aflibercept. A comprehensive clinical approach to diagnosis and treatment of myopic CNV is presented.

EXPERT OPINION

The current standard of care for myopic CNV is intravitreal inhibition of VEGF, with ranibizumab and aflibercept licensed for intraocular use. The diagnosis, OCT features of disease activity and retreatment algorithm for myopic CNV is different from wet age-related macular degeneration. In the long-term, myopic CNV may be associated with gradual, irreversible visual loss due to progressive chorioretinal atrophy, for which there is currently no treatment.

Label-Free Density Measurements of Radial Peripapillary Capillaries in the Human Retina

Radial peripapillary capillaries (RPCs) comprise a unique network of capillary beds within the retinal nerve fibre layer (RNFL) and play a critical role in satisfying the nutritional requirements of retinal ganglion cell (RGC) axons. Understanding the topographical and morphological characteristics of these networks through in vivo techniques may improve our understanding about the role of RPCs in RGC axonal health and disease. This study utilizes a novel, non-invasive and label-free optical imaging technique, speckle variance optical coherence tomography (svOCT), for quantitatively studying RPC networks in the human retina. Six different retinal eccentricities from 16 healthy eyes were imaged using svOCT. The same eccentricities were histologically imaged in 9 healthy donor eyes with a confocal scanning laser microscope. Donor eyes were subject to perfusion-based labeling techniques prior to retinal dissection, flat mounting and visualization with the microscope. Capillary density and diameter measurements from each eccentricity in svOCT and histological images were compared. Data from svOCT images were also analysed to determine if there was a correlation between RNFL thickness and RPC density. The results are as follows: (1) The morphological characteristics of RPC networks on svOCT images are comparable to histological images; (2) With the exception of the nasal peripapillary region, there were no significant differences in RPC density measurements between svOCT and histological images; (3) Capillary diameter measurements were significantly greater in svOCT images compared to histology; (4) There is a positive correlation between RPC density and RNFL thickness. The findings in this study suggest that svOCT is a reliable modality for analyzing RPC networks in the human retina. It may therefore be a valuable tool for aiding our understanding about vasculogenic mechanisms that are involved in RGC axonopathies. Further work is required to explore the reason for some of the quantitative differences between svOCT and histology.

Retinal angiography with real-time speckle variance optical coherence tomography

This report describes a novel, non-invasive and label-free optical imaging technique, speckle variance optical coherence tomography (svOCT), for visualising blood flow within human retinal capillary networks. This imaging system uses a custom-built swept source OCT system operating at a line rate of 100 kHz. Real-time processing and visualisation is implemented on a consumer grade graphics processing unit. To investigate the quality of microvascular detail acquired with this device we compared images of human capillary networks acquired with svOCT and fluorescein angiography. We found that the density of capillary microvasculature acquired with this svOCT device was visibly greater than fluorescein angiography. We also found that this svOCT device had the capacity to generate en face images of distinct capillary networks that are morphologically comparable with previously published histological studies. Finally, we found that this svOCT device has the ability to non-invasively illustrate the common manifestations of diabetic retinopathy and retinal vascular occlusion. The results of this study suggest that graphics processing unit accelerated svOCT has the potential to non-invasively provide useful quantitative information about human retinal capillary networks. Therefore svOCT may have clinical and research applications for the management of retinal microvascular diseases, which are a major cause of visual morbidity worldwide.

Academic screencasting: internet-based dissemination of ophthalmology grand rounds

OBJECTIVE

To evaluate and compare the preferences and attitudes of Ontario ophthalmologists and ophthalmology residents toward screencasting as an educational tool with potential use for continuing medical education (CME) events.

DESIGN

Cross-sectional study.

PARTICIPANTS

Eighty of 256 participants completed the survey.

METHODS

The surveys were sent to participants by email, with follow-up via telephone. Study participants were urban and rural Ontario ophthalmologists, registered with the Canadian Ophthalmological Society, and University of Toronto ophthalmology residents. Pre-recorded online presentations-screencasts-were used as the main intervention. Online surveys were used to measure multiple variables evaluating the attitudes of the participants toward screencasting. This data was then used for further quantitative and qualitative analysis.

RESULTS

Over 95% of participants replied favourably to the introduction and future utilization of screencasting for educational purposes. Rural ophthalmologists were the most enthusiastic about future events. Practising in rural Ontario was associated with a higher interest in live broadcasts than practising in urban centres (p < 0.02), an association supported by qualitative data. Qualitative analysis revealed geographic isolation, busy schedules, ease of use/access, and convenience to be the key factors contributing to interest in screencasting.

CONCLUSIONS

Practising ophthalmologists and residents in Ontario are interested in academic online screencasting. Rural ophthalmologists were more interested in live lectures than their urban colleagues. More research is required to assess the potential of screencasting as a CME tool.