Clinical validation of the RTVue optical coherence tomography angiography image quality indicators

Towards standardising retinal OCT angiography image analysis with open-source toolbox OCTAVA

Quantitative assessment of retinal microvasculature in optical coherence tomography angiography (OCTA) images is important for studying, diagnosing, monitoring, and guiding the treatment of ocular and systemic diseases. However, the OCTA user community lacks universal and transparent image analysis tools that can be applied to images from a range of OCTA instruments and provide reliable and consistent microvascular metrics from diverse datasets. We present a retinal extension to the OCTA Vascular Analyser (OCTAVA) that addresses the challenges of providing robust, easy-to-use, and transparent analysis of retinal OCTA images. OCTAVA is a user-friendly, open-source toolbox that can analyse retinal OCTA images from various instruments. The toolbox delivers seven microvascular metrics for the whole image or subregions and six metrics characterising the foveal avascular zone. We validate OCTAVA using images collected by four commercial OCTA instruments demonstrating robust performance across datasets from different instruments acquired at different sites from different study cohorts. We show that OCTAVA delivers values for retinal microvascular metrics comparable to the literature and reduces their variation between studies compared to their commercial equivalents. By making OCTAVA publicly available, we aim to expand standardised research and thereby improve the reproducibility of quantitative analysis of retinal microvascular imaging. Such improvements will help to better identify more reliable and sensitive biomarkers of ocular and systemic diseases.

Peripapillary and macular microvasculature in neovascular age-related macular degeneration in long-term and recently started anti-VEGF therapy versus healthy controls

Aim

To investigate the peripapillary and macular microvasculature in neovascular age-related macular degeneration (nAMD) in recently started versus long-term anti-vascular endothelial growth factor (VEGF) therapy and healthy controls.

Methods

Eyes with nAMD treated in a treat-and-extend regimen were assigned to group 1 (<5 injections) or 2 (≥20 injections) whereas group 3 constituted the healthy age-matched controls. Blood flow signals were acquired using PLEX^® Elite 9000 swept-source optical coherence tomography angiography (OCTA) of the macular and peripapillary regions. Mean ganglion cell complex (GCC) thickness values were quantified using spectral-domain optical coherence tomography (SD-OCT).

Results

Including 80 eyes whereof 40 controls, macular superficial perfusion density was significantly reduced in group 1 and 2 compared to controls (p < 0.001; p = 0.010) without a difference between groups 1 and 2. Peripapillary perfusion parameters did not correlate with post-operative intraocular pressure (IOP) or number of anti-VEGF injections. Mean peripapillary flux index was significantly lower in group 2 than in controls (p = 0.023) and significantly decreased in the nasal quadrants for both AMD groups compared to group 3 (p = 0.013; p < 0.001). Mean peripapillary perfusion density was significantly reduced in both AMD groups compared to controls (0.515 ± 0.02 versus 0.556 ± 0.03, p < 0.0001).

Conclusion

Frequency of anti-VEGF treatment in nAMD and post-operative IOP showed no correlation with peripapillary perfusion parameters, but anti-VEGF treated nAMD patients exhibited partly altered peripapillary perfusion compared to healthy controls. Reduced macular perfusion density of the inner retina in anti-VEGF treated nAMD compared to healthy controls might be discussed as an anti-VEGF treatment effect or a characteristic of nAMD.

The Importance of Signal Strength Index in Optical Coherence Tomography Angiography: A Study of Eyes with Pseudoexfoliation Syndrome

PURPOSE

To evaluate the effect of the signal strength index (SSI) on a comparison of the vascular and structural OCT measurements between eyes with pseudoexfoliation syndrome (PXF) and healthy controls of Asian-Indian origin.

METHODS

In this cross-sectional study, 33 eyes of 33 PXF patients and 40 healthy eyes of 40 controls underwent OCT and OCT angiography (OCTA). Eyes with intraocular pressure (IOP) >21mmHg, glaucomatous disc changes, or any other ocular pathology were excluded. Peripapillary vessel density (VD) and retinal nerve fiber layer (RNFL) thickness were determined from the optic disc scans. Parafoveal VD and ganglion cell complex (GCC) thickness were measured from the macular scans. These parameters were compared between the groups using mixed effect models after adjusting for clinical confounders such as IOP, as well as SSI of the scans.

RESULTS

The 2 groups were demographically similar. Average RNFL (94µm vs 100µm, p = 0.01) and GCC (91µm vs 95µm, p = 0.03) were thinner in the PXF group compared to controls. The average peripapillary VD appeared lower in the PXF groups compared to controls (58.2% vs 58.8%, p = 0.04), but after adjusting for IOP and SSI, no difference was noted (p = 0.39). After accounting for confounders, parafoveal VD in the PXF group was significantly lower compared to controls (44.3% vs 46.8%, p = 0.008).

CONCLUSION

Peripapillary RNFL thickness, parafoveal GCC thickness and parafoveal VD were decreased in eyes with PXF when compared to controls. VD measurements are associated with the SSI and, therefore, clinicians and researchers evaluating OCTA scans quantitatively must consider the SSI value during analysis and interpretation.

Evaluating Distribution of Foveal Avascular Zone Parameters Corrected by Lateral Magnification and Their Associations with Retinal Thickness

Purpose

To examine the distribution of foveal avascular zone (FAZ) parameters, with and without correction for lateral magnification, in a large cohort of healthy young adults.

Design

Cross-sectional, observational cohort study.

Participants

A total of 504 healthy adults, 27 to 30 years of age.

Methods

Participants underwent a comprehensive ophthalmic examination including axial length measurement and OCT angiography (OCTA) imaging of the macula. OCT angiography images of combined superficial and deep retinal vessel plexuses were processed via a custom software to extract foveal avascular zone area (FAZA) and foveal density-300 (FD-300), the vessel density in a 300-μm wide annulus surrounding the FAZ, with and without correction for lateral magnification. Bland–Altman analyses were performed to examine the effect of lateral magnification on FAZA and FD-300, as well as to evaluate the interocular agreement in both parameters. Linear mixed-effects models were used to examine the relationship between retinal thicknesses and OCTA parameters.

Main Outcome Measures

The FAZA and FD-300, corrected for lateral magnification.

Results

The mean (standard deviation [SD]) of laterally corrected FAZA and FD-300 was 0.22 mm² (0.10 mm²) and 51.9% (3.2%), respectively. Relative to uncorrected data, 55.6% of corrected FAZA showed a relative change > 5%, whereas all FD-300 changes were within 5%. There was good interocular symmetry (mean right eye–left eye difference, 95% limits of agreement [LoA]) in both FAZA (0.006 mm², -0.05 mm², to 0.07 mm²) and FD-300 (-0.05%, -5.39%, to 5.30%). There were significant negative associations between central retinal thickness and FAZA (β = -0.0029), as well as between central retinal thickness and FD-300 (β = -0.044), with the relationships driven by inner, not outer, retina.

Conclusions

We reported lateral magnification adjusted normative values for FAZA and FD-300 in a large cohort of young, healthy eyes. Clinicians should strongly consider accounting for lateral magnification when evaluating FAZA. Good interocular agreement in FAZA and FD-300 suggests the contralateral eye can be used as control data.

Towards standardizing retinal optical coherence tomography angiography: a review

The visualization and assessment of retinal microvasculature are important in the study, diagnosis, monitoring, and guidance of treatment of ocular and systemic diseases. With the introduction of optical coherence tomography angiography (OCTA), it has become possible to visualize the retinal microvasculature volumetrically and without a contrast agent. Many lab-based and commercial clinical instruments, imaging protocols and data analysis methods and metrics, have been applied, often inconsistently, resulting in a confusing picture that represents a major barrier to progress in applying OCTA to reduce the burden of disease. Open data and software sharing, and cross-comparison and pooling of data from different studies are rare. These inabilities have impeded building the large databases of annotated OCTA images of healthy and diseased retinas that are necessary to study and define characteristics of specific conditions. This paper addresses the steps needed to standardize OCTA imaging of the human retina to address these limitations. Through review of the OCTA literature, we identify issues and inconsistencies and propose minimum standards for imaging protocols, data analysis methods, metrics, reporting of findings, and clinical practice and, where this is not possible, we identify areas that require further investigation. We hope that this paper will encourage the unification of imaging protocols in OCTA, promote transparency in the process of data collection, analysis, and reporting, and facilitate increasing the impact of OCTA on retinal healthcare delivery and life science investigations.

Optical coherence tomography-signal strength index following trifocal and monofocal intraocular lens implantation

PURPOSE

To evaluate the influence of trifocal and monofocal intraocular lens implantation on the optical coherence tomography-signal strength index values obtained during macular and peripapillary scanning.

METHOD

Study group included 60 eyes of 60 patients with intraocular lens (Acriva BB UD 613 monofocal in 30 eyes and Acriva Trinova UD trifocal in 30 eyes) implantation after uneventful phacoemulsification. Thirty eyes of 30 healthy subjects without any intraocular surgery were selected as the control group. Eyes with best corrected visual acuity less than 20/20 due to any media opacity, high refractive errors excluded. Macular and retinal nerve fiber layer scans were generated by optical coherence tomography after pupillary dilation. Intergroup comparisons of signal strength index values of the macular and peripapillary scans were performed between eyes implanted with two different intraocular lenses and control group.

RESULTS

The mean signal strength index of the peripapillary and macular scans obtained in the eyes implanted with both monofocal and trifocal intraocular lenses were statistically less than the control group (p < 0.05, for all). SSI's of macular and peripapillary scans recorded from the eyes implanted with either monofocal or trifocal intraocular lenses were not statistically different from each other (p = 0.957 and p = 0.877, respectively).

CONCLUSION

In the present study despite different intraocular lenses properties, the image quality values were not found to be lower in eyes with trifocal sinusoidal intraocular lenses implantation compared to monofocal intraocular lenses during macular and peripapillary optical coherence tomography scans.