Assessing the Use of Incorrectly Scaled Optical Coherence Tomography Angiography Images in Peer-Reviewed Studies: A Systematic Review

Macular and submacular choroidal microvasculature in patients with primary open-angle glaucoma and high myopia

AIMS

To characterise the influence of primary open-angle glaucoma (POAG) and high myopia (HM) on the macular and choroidal capillary density (CD).

METHODS

Two hundred and seven eyes were enrolled, including 80 POAG without HM, 50 POAG with HM, 31 HM without POAG and 46 normal controls. A fovea-centred 6×6 mm optical coherence tomography angiography scan was performed to obtain the CD of the superficial capillary plexus (SCP), deep capillary plexus (DCP) and choriocapillaris. Macular and choroidal CDs were compared among the groups and the association of CDs with visual field mean deviation (MD) was determined using linear regression models.

RESULTS

Compared with normal eyes, SCP CD was decreased in the POAG without HM group (p<0.05), while DCP CD was significantly decreased in the HM without POAG group (p<0.05). Both SCP and DCP CDs were significantly decreased in the POAG with HM group (p<0.05). CD reduction occurred mainly in the outer rather than inner ring of the 6×6 mm scan size. In multivariate regression analysis, worse MD was associated with lower CD in the outer ring of the SCP in all the HM eyes (p<0.05).

CONCLUSIONS

POAG and HM reduced macular CD in different layers of the retinal capillary plexus and both particularly in the outer ring of the 6×6 mm scans. Furthermore, assessment of the CD in the outer ring of the SCP may facilitate the diagnosis of glaucoma in eyes with HM.

Longitudinal Macular Retinal and Choroidal Microvasculature Changes in High Myopia

Purpose

The purpose of this study was to determine the longitudinal changes in macular retinal and choroidal microvasculature in normal healthy and highly myopic eyes.

Methods

Seventy-one eyes, including 32 eyes with high myopia and 39 healthy control eyes, followed for at least 12 months and examined using optical coherence tomography angiography imaging in at least 3 visits, were included in this study. Fovea-centered 6 × 6 mm scans were performed to measure capillary density (CD) of the superficial capillary plexus (SCP), deep capillary plexus (DCP), and choriocapillaris (CC). The rates of CD changes in both groups were estimated using a linear mixed model.

Results

Over a mean 14-month follow-up period, highly myopic eyes exhibited a faster rate of whole image CD (wiCD) loss (−1.44%/year vs. −0.11%/year, P = 0.001) and CD loss in the outer ring of the DCP (−1.67%/year vs. –0.14%/year, P < 0.001) than healthy eyes. In multivariate regression analysis, baseline axial length (AL) was negatively correlated with the rate of wiCD loss (estimate = −0.27, 95% confidence interval [CI] = −0.48 to −0.06, P = 0.012) and CD loss in the outer ring (estimate = −0.33, 95% CI = −0.56 to −0.11, P = 0.005), of the DCP. The CD reduction rates in the SCP and CC were comparable in both groups (all P values > 0.05).

Conclusions

The rate of CD loss in the DCP is significantly faster in highly myopic eyes than in healthy eyes and is related to baseline AL. The CD in the outer ring reduces faster in eyes with longer baseline AL.

Choroidal Changes in Eyes With Polypoidal Choroidal Vasculopathy After Anti-VEGF Therapy Imaged With Swept-Source OCT Angiography

Purpose

Swept-source optical coherence tomography angiography was used to investigate choroidal changes and their association with pigment epithelial detachments (PEDs) in eyes with polypoidal choroidal vasculopathy (PCV) after treatment with vascular endothelial growth factor (VEGF) inhibitors.

Methods

Patients with treatment-naïve PCV were included and underwent anti-VEGF therapy. Mean choroidal thickness (MCT), choroidal vascularity index (CVI), and PED volume measurements were obtained before and after treatment.

Results

Thirty-four treatment-naïve PCV eyes from 33 patients were included. The PED volume decreased after treatment (P < 0.05). The MCT decreased from 223.0 ± 79.6 µm at baseline to 210.9 ± 76.2 µm after treatment (P < 0.001). The CVI at baseline was 0.599 ± 0.024, and the CVI after treatment was 0.602 ± 0.023 (P = 0.16). There was a correlation between the decreased PED volumes and the decreased MCT measurements (r = 0.47; P = 0.006). Also, there was a correlation between the decreased PED volumes and the increased CVI measurements (r = −0.63; P < 0.001).

Conclusions

In treatment-naïve eyes with PCV, the decreases in PED volumes were correlated with the decrease in MCT and the increase in CVI measurements. We propose that, at baseline, the PCV lesions serve as high-volume arteriovenous shunts between choroidal arterial and venous circulation, causing transudation into the choroidal stroma. We propose that, after treatment, the blood flow through the vascular shunt is reduced, the excess stromal transudation is resorbed, and the exudation from the neovascular lesion is reduced, resulting in thinning of the choroid, resolution of the PEDs, and an increase in the CVI due to the resorption of excess choroidal transudation.

Role of Optical Coherence Tomography Angiography Imaging in Patients with Diabetes

PURPOSE OF REVIEW

Ocular manifestations in patients with diabetes mellitus (DM) can present as microvascular changes. These microvascular changes can be challenging to identify on exams, and imaging technologies have commonly aided in the diagnosis and management of patients with DM. Optical coherence tomography angiography (OCTA) provides noninvasive image segmentation of various layers of the retina and choroid. Also, post-processing of images and associated quantitative measurements offer potential clinical enhancements. Our aim is to review the current evidence on the utility of OCTA for patients with DM.

RECENT FINDINGS

Research suggests OCTA to potentially provide potential clinical enhancements and alternative methods in detecting subclinical manifestation of diabetic retinopathy, staging diabetic retinopathy, management of diabetic macular edema, and monitoring of systemic markers in patients with diabetes mellitus. OCTA is a promising but relatively new modality, and differences in terminology, research designs, and image processing techniques provide a difficult landscape to navigate. Standardization within further validation is needed to determine the extent of OCTA's clinical utility, but the current literature suggests the potential for earlier detection of ocular manifestations in patients with DM, additional objective measurements for grading and management, and opportunity for additional biomarkers for treatment outcomes.

Effect of axial length on peripapillary microvasculature: An optical coherence tomography angiography study

OBJECTIVE

To investigate the effects of axial length (AL) on the peripapillary microvascular density acquired from optical coherence tomography angiography (OCTA).

METHODS

Retrospective observational study. A total of 111 eyes from 111 normal healthy subjects were examined. The subjects were divided into three groups according to the AL: Group 1 (AL: < 24.0 mm; 35 eyes), Group 2 (AL: 24.0-25.99 mm; 37 eyes), and Group 3 (AL: ≥ 26 mm; 39 eyes). Peripapillary OCTA images were acquired using 6× 6 mm angiography scans, and vessel density (VD) and perfusion density (PD) of the superficial capillary plexus were calculated automatically. VD and PD were compared among the three groups according to the distance from the optic disc (inner and outer rings). Linear regression analyses were also performed to identify clinical factors associated with average VD.

RESULTS

The average ALs of Groups 1-3 were 23.33± 0.57, 25.05± 0.60, and 27.42± 0.82, respectively. Average VD (P = 0.009) and PD (P = 0.029) in the inner ring increased with increasing AL. However, average VD (P < 0.001) and PD (P < 0.001) in the outer ring decreased with AL increased; the same trends were found for the full areas (VD, p<0.001; PD, p = 0.001). Average VDs in the inner and outer rings were not associated (P = 0.938).

CONCLUSIONS

Peripapillary VD and PD were significantly associated with AL. Depending on the distance from the disc, peripapillary VDs and PDs of the inner and outer rings were differentially affected by AL. Physicians should therefore consider the effects of AL in the analyses of peripapillary microvasculature.

Challenges Associated With Ellipsoid Zone Intensity Measurements Using Optical Coherence Tomography

Translational Relevance

Qualitative evaluation of the ellipsoid zone band on optical coherence tomography is a valuable clinical tool for assessing photoreceptor structure, though more quantitative metrics are emerging. Awareness of the challenges involved in interpreting quantitative metrics is important for their clinical translation.

Induced Refractive Error Changes the Optical Coherence Tomography Angiography Transverse Magnification and Vascular Indices

PURPOSE

To assess the effect of changing anterior eye refractive power with contact lenses on the transverse magnification of en face images and associated vascular indices from optical coherence tomographic angiography (OCT-A).

DESIGN

Prospective crossover study.

METHODS

Spherical soft contact lenses (-6 diopter [D] to +6 D in 2 D steps) were used to induce anterior eye refractive power changes in 11 healthy young adults and 3 × 3-mm macular scans were captured using OCT-A (Zeiss AngioPlex, software version 11.0; Cirrus HD-OCT 5000, Carl Zeiss Meditec Inc). Image transverse magnification was predicted based on refraction and biometry measurements and compared with empirical changes in the en face images measured with image analysis. Linear regression analysis was performed to assess the relationship between induced refractive ametropia and foveal avascular zone (FAZ) area, perimeter, circularity, and vessel density and perfusion density.

RESULTS

The predicted transverse magnification was linearly related to induced refractive ametropia and to the empirical transverse magnification changes (average slope: 1.02, 95% CI: 0.90-1.34). All the OCT-A indices showed linear relationships with induced refractive ametropia (P < .05) with the 12 D tested range altering the indices by 7% to 12%. After correcting for transverse magnification, all OCT-A indices except FAZ area were linearly related to induced refractive ametropia (P < .05) and were reduced to 1% to 9%.

CONCLUSIONS

This study is the first to show that induced refractive ametropia can affect OCT-A image magnification and indices. These changes are clinically important and need to be considered along with biometry effects when interpreting OCT-A indices. Transverse magnification changes can affect the ability of OCT-A to precisely measure linear dimensions of blood vessels.

Macrophage-Like Cell Density Is Increased in Proliferative Diabetic Retinopathy Characterized by Optical Coherence Tomography Angiography

Purpose

To quantitatively characterize macrophage-like cells (MLCs) at the vitreoretinal interface in different severity stages of diabetic retinopathy (DR) using optical coherence tomography angiography (OCTA).

Methods

The study included 72 eyes of 72 subjects: 18 healthy controls, 22 diabetes mellitus (DM) without DR, 17 nonproliferative DR (NPDR), and 15 proliferative DR (PDR). We obtained repeated (average, 6.5; range, 3-10) macular OCTA scans for each eye. We registered and averaged the 3-µm OCT slab above the vitreoretinal interface to visualize MLCs. Using a semiautomated method, we binarized and quantified MLCs and compared MLC densities among groups. We also evaluated MLC distribution relative to underlying superficial capillary plexus vasculature and quantified MLCs overlying blood vessels within the perivascular 30-µm watershed region and within ischemic zones (defined as >30 µm from the nearest vessel).

Results

MLC density was 2.8- to 3.8-fold higher in PDR compared with all other groups (P < 0.05 for all). MLC density in PDR was most increased in perivascular areas (3.3- to 4.2-fold; P < 0.05 vs. all) and on blood vessels (3.0- to 4.0-fold; P < 0.05 vs. all), and elevated to a lesser extent in ischemic areas (2.3- to 3.4-fold; P < 0.05 vs. all). MLCs were more likely to localize on blood vessels in DM without DR, NPDR, and PDR (P < 0.05 for all), but not healthy eyes.

Conclusions

MLC density was significantly increased in PDR. MLCs clustered on blood vessels in diabetic but not in healthy eyes. Further studies are needed to confirm the origin, identity, and function of MLCs during DR.

Peripapillary Retinal Nerve Fiber Layer and Microvasculature in Prolonged Type 2 Diabetes Patients Without Clinical Diabetic Retinopathy

Purpose

The purpose of this study to identify the effects of prolonged type 2 diabetes (T2DM) on the peripapillary retinal nerve fiber layer (pRNFL) and peripapillary microvasculature in patients with prolonged T2DM without clinical diabetic retinopathy (DR).

Methods

Subjects were divided into 3 groups: controls (control group; 153 eyes), patients with T2DM < 10 years (DM group 1; 136 eyes), and patients with T2DM ≥ 10 years (DM group 2; 74 eyes). The pRNFL thickness and peripapillary superficial vessel density (VD) were compared. Linear regression analyses were performed to identify factors associated with peripapillary VD in patients with T2DM.

Results

The mean pRNFL thicknesses of the control group, DM group 1, and DM group 2 were 96.0 ± 7.9, 94.5 ± 0.9, and 92.2 ± 8.2 µm, respectively (P < 0.001). The VDs were 18.24 ± 0.62, 17.60 ± 1.47, and 17.15 ± 1.38 mm⁻¹ in the control group, DM group 1, and DM group 2, respectively (P < 0.001). In multivariate linear regression analyses, visual acuity (B = −2.460, P = 0.001), axial length (B = −0.169, P = 0.008), T2DM duration (B = −0.056, P < 0.001), and pRNFL (B = 0.024, P = 0.001) were significant factors affecting the peripapillary VD in patients with T2DM.

Conclusions

Patients with T2DM without clinical DR showed thinner pRNFL and lower peripapillary VD and perfusion density (PD) compared with normal controls, and such damage was more severe in patients with T2DM ≥ 10 years. Additionally, peripapillary VD was significantly associated with best-corrected visual acuity (BCVA), axial length, T2DM duration, and pRNFL thickness in patients with T2DM.

Early Postnatal Oxygen Exposure Predicts Choroidal Thinning in Neonates

Purpose

To evaluate whether choroidal thickness (CT) using arm-mounted optical coherence tomography (OCT) in infants screened for retinopathy of prematurity (ROP) correlates with oxygen exposure in neonates.

Methods

OCT images were obtained in infants screened for ROP in a single level IV neonatal intensive care unit. CT was measured at three different locations: the subfoveal center and 1.5 mm from the fovea center in each direction. Correlation and regression analyses were performed to determine the relationship between clinical factors and CT. Clinical factors included gestational age, birth weight, presence of bronchopulmonary dysplasia (BPD), and fraction of inspired oxygen (FiO₂) at defined time points: 30 weeks postmenstrual age (PMA), 36 weeks PMA, and on day of imaging.

Results

Mean subfoveal, nasal, and temporal choroidal thicknesses CT (SFCT, NCT, and TCT, respectively) were 228.0 ± 51.4 µm, 179.7 ± 50.3 µm, and 186.4 ± 43.8 µm, respectively. SFCT was found to be significantly thicker than NCT and TCT (P < 0.0001 and P = 0.0002, respectively), but no significant difference was found between NCT and TCT (P = 0.547). Compared with infants without BPD, infants with BPD had thinner SFCT and NCT (P = 0.01 and P = 0.0008, respectively). Birth weight was positively correlated with SFCT (r = 0.39, P = 0.01) and NCT (r = 0.33, P = 0.045) but not TCT. Gestational age and ROP stage were not significantly associated with CT. SFCT was found to be significantly thinner with higher average FiO₂ supplementation levels at 30 weeks PMA (r = –0.51, P = 0.01) but not at 36 weeks PMA. Regression analysis revealed that FiO₂ at 30 weeks PMA was an independent predictor of SFCT in infants screened for ROP (P = 0.01).

Conclusions

Early postnatal exposure (<32 weeks PMA) to higher oxygen supplementation in premature neonates statistically predicts choroidal thinning.

Optical Coherence Tomography Angiography in the Thirteen-Lined Ground Squirrel

Purpose

To assess the performance of two spectral-domain optical coherence tomography-angiography systems in a natural model of hypoperfusion: the hibernating thirteen-lined ground squirrel (13-LGS).

Methods

Using a high-speed (130 kHz) OCT-A system (HS-OCT-A) and a commercial OCT (36 kHz; Bioptigen Envisu; BE-OCT-A), we imaged the 13-LGS retina throughout its hibernation cycle. Custom software was used to extract the superior, middle, and deep capillary plexus (SCP, MCP, and DCP, respectively). The retinal vasculature was also imaged with adaptive optics scanning light ophthalmoscopy (AOSLO) during torpor to visualize individual blood cells. Finally, correlative histology with immunolabeled or DiI-stained vasculature was performed.

Results

During euthermia, vessel density was similar between devices for the SCP and MCP (P = 0.88, 0.72, respectively), with a small difference in the DCP (−1.63 ± 1.54%, P = 0.036). Apparent capillary dropout was observed during torpor, but recovered after forced arousal, and this effect was exaggerated in high-speed OCT-A imaging. Based on cell flux measurements with AOSLO, increasing OCT-A scan duration by ∼1000× would avoid the apparent capillary dropout artifact. High correspondence between OCT-A (during euthermia) and histology enabled lateral scale calibration.

Conclusions

While the HS-OCT-A system provides a more efficient workflow, the shorter interscan interval may render it more susceptible to the apparent capillary dropout artifact. Disambiguation between capillary dropout and transient ischemia can have important implications in the management of retinal disease and warrants additional diagnostics.

Translational Relevance

The 13-LGS provides a natural model of hypoperfusion that may prove valuable in modeling the utility of OCT-A in human pathologies associated with altered blood flow.

Past, present and future role of retinal imaging in neurodegenerative disease

Retinal imaging technology is rapidly advancing and can provide ever-increasing amounts of information about the structure, function and molecular composition of retinal tissue in humans in vivo. Most importantly, this information can be obtained rapidly, non-invasively and in many cases using Food and Drug Administration-approved devices that are commercially available. Technologies such as optical coherence tomography have dramatically changed our understanding of retinal disease and in many cases have significantly improved their clinical management. Since the retina is an extension of the brain and shares a common embryological origin with the central nervous system, there has also been intense interest in leveraging the expanding armamentarium of retinal imaging technology to understand, diagnose and monitor neurological diseases. This is particularly appealing because of the high spatial resolution, relatively low-cost and wide availability of retinal imaging modalities such as fundus photography or OCT compared to brain imaging modalities such as magnetic resonance imaging or positron emission tomography. The purpose of this article is to review and synthesize current research about retinal imaging in neurodegenerative disease by providing examples from the literature and elaborating on limitations, challenges and future directions. We begin by providing a general background of the most relevant retinal imaging modalities to ensure that the reader has a foundation on which to understand the clinical studies that are subsequently discussed. We then review the application and results of retinal imaging methodologies to several prevalent neurodegenerative diseases where extensive work has been done including sporadic late onset Alzheimer's Disease, Parkinson's Disease and Huntington's Disease. We also discuss Autosomal Dominant Alzheimer's Disease and cerebrovascular small vessel disease, where the application of retinal imaging holds promise but data is currently scarce. Although cerebrovascular disease is not generally considered a neurodegenerative process, it is both a confounder and contributor to neurodegenerative disease processes that requires more attention. Finally, we discuss ongoing efforts to overcome the limitations in the field and unmet clinical and scientific needs.

Longitudinal Changes in Macular Optical Coherence Tomography Angiography Metrics in Primary Open-Angle Glaucoma With High Myopia: A Prospective Study

Purpose

To characterize longitudinal changes in macular microvasculature as quantified from optical coherence tomography angiography (OCTA) metrics in primary open-angle glaucoma (POAG) eyes with and without high myopia.

Methods

In total, 63 and 61 POAG eyes with and without high myopia, respectively, underwent swept-source OCTA imaging in at least four follow-up visits at an ophthalmic center, with a scanning protocol of 3- × 3-mm centered at the fovea. The foveal avascular zone (FAZ) area, FAZ circularity, and vessel density (VD) in both the superficial (SCP) and deep capillary plexuses (DCP) were measured. The rate of change in macular OCTA metrics over time was estimated using linear mixed-effects models in both groups of POAG eyes.

Results

The mean follow-up time and number of visits were 27.72 ± 8.57 months and 8.5 (8 to 13) times, and 30.95 ± 10.19 months and 10 (8‒13) times in POAG eyes with and without high myopia, respectively. VD in the DCP reduced significantly more quickly in POAG eyes with high myopia than in those without high myopia (−5.14%/year vs. −3.71%/year, P = 0.008). Moreover, lower baseline VD in the DCP was significantly associated with faster VD reduction in POAG with high myopia eyes (P < 0.001). Conversely, the VD reduction rate in the SCP, FAZ area, and FAZ circularity in both the SCP and DCP were similar in both groups (all Ps > 0.05).

Conclusions

VD in DCP reduced significantly more quickly in POAG eyes with high myopia over time. Density in the DCP reduced more quickly when baseline VD was low.

Fixation stability and deviation in optical coherence tomography angiography using soft contact lens correction in myopes

To compare fixation deviation and stability with soft contact lens correction and device built-in auto-focus system during optical coherence tomography angiography (OCTA). This observational study measured OCTA metrics first with contact lens correction, followed by removal of contact lenses, using the device auto-focus system at a University Optometry Clinic, Hong Kong. All participants were habitual soft contact lens wearers with either low or high myopia. OCTA measurements were obtained using a spectral domain OCTA. Fixation deviation was distance (in pixels) of the fovea to the center of the OCTA measurement grid. Fixation stability was test–retest repeatability (TRR) and coefficient of variation (CV) of fixation deviation from three consecutive OCTA measurements. OCTA metrics included vessel length density (VD), perfusion density (PD), and foveal avascular zone (FAZ) area. Averaged OCTA metrics were calculated from three measurements and compared between the two correction methods. The mean ± SD spherical equivalent of 74 eyes from 74 myopes measured was − 1.94D ± 0.75D in low myopes (n = 37) and − 7.97D ± 1.31D in high myopes (n = 37). When corrected with contact lenses, visual acuities of high myopes (median [IQR], − 0.06 [0.08] logMAR) and low myopes (− 0.02 ± 0.08 logMAR) were similar (P = 0.060), and with similar fixation deviation (5.0 ± 2.2 pixels vs 5.3 [3.6] pixels; P = 0.689). High myopes had poorer fixation stability than low myopes (TRR: 10.2 pixels vs 7.5 pixels; CV: 65% vs 54%, respectively). The worst fixation stability occurred when high myopes were corrected using the auto-focus system (TRR: 12.5 pixels, CV: 72%). The difference in VD and PD was within 1 mm⁻¹ and 1%, respectively. The FAZ area was similar. Difference in OCTA metrics was small in each refractive group (< 1 mm⁻¹ in VD, and < 2% in PD). High myopes had more stable fixation when corrected when wearing contact lenses. Subjects with good contact lens corrected visual acuity should wear their contact lenses during OCTA measurements.

Relationship Between Optical Coherence Tomography Parameter and Visual Function in Eyes With Epiretinal Membrane

Purpose

To investigate the associations between visual function and the optical coherence tomography (OCT) parameters in eyes with idiopathic epiretinal membrane (ERM).

Methods

Thirty-nine consecutive eyes with ERM were enrolled. In addition to OCT parameters, such as central retinal thickness (CRT), the area of gap between the ERM and the retinal surface (SUKIMA) was newly defined and calculated from the vertical and horizontal OCT images (SUKIMAv and SUKIMAh). The average of SUKIMAv and SUKIMAh (SUKIMAave) was used for the statistical analysis. The vertical and horizontal metamorphopsia scores (MV, MH) and the average of MV and MH (Mave) were also used for the analysis.

Results

The Mave was not significantly associated with logMAR visual acuity (VA) (P = 0.57, linear regression analysis). Analysis using second-order bias-corrected Akaike information criterion model selection identified the age, CRT, and SUKIMAave as being associated with logMAR VA. On the other hand, among the OCT parameters, SUKIMAave and CRT were associated with the Mave. In addition, there was a significant relationship between SUKIMAh and MV (P = 0.011) and between SUKIMAv and MH (P = 0.0014).

Conclusions

We identified SUKIMA as a novel OCT parameter that is useful to predict both VA and metamorphopsia in patients with ERM.

Repeatability of Peripapillary Optical Coherence Tomography Angiography Parameters in Older Adults

Purpose:

This work assesses the intrasession repeatability of capillary perfusion density (CPD) and capillary flux index (CFI) measurements on peripapillary optical coherence tomography angiography (OCTA) in healthy eyes of older adults.

Methods:

In this cross-sectional study, healthy volunteers aged 50 years or older underwent 4.5 × 4.5 mm OCTA imaging centered on the optic nerve head using Zeiss Cirrus HD-5000 AngioPlex (Carl Zeiss Meditec). Two consecutive images were acquired in the same eye during a single study session. CPD and CFI were assessed using AngioPlex Software (version 11.0.0.29946) for the radial peripapillary capillary plexus (average over whole scan area) and 4 quadrants (superior, inferior, temporal, and nasal). CPD and CFI repeatability was assessed by intraclass correlation (ICC), mean interocular differences using 2-tailed t test, and association with age using generalized estimating equations.

Results:

A total of 150 images were acquired from 75 eyes of 47 patients. For CPD, ICC results ranged from 0.7160 (nasal CPD) to 0.9218 (average CPD). For CFI, ICC results ranged from 0.6167 (temporal CFI) to 0.8976 (inferior CFI). Temporal CFI was significantly different between right and left eyes of the same patient ( P = .03). CPD and CFI decreased with age in all analyses (average CPD β coefficient –0.00172, P < .001; average CFI β coefficient −0.00278, P < .001).

Conclusions:

Moderate to good repeatability was observed for most peripapillary OCTA metrics; temporal measurements were least repeatable for CPD and CFI. Peripapillary CPD and CFI decrease with age even beyond the fifth decade in healthy older adults.

Macular Microvasculature and Associated Retinal Layer Thickness in Pediatric Amblyopia: Magnification-Corrected Analyses

Purpose

The purpose of this study was to characterize macular microvasculature and structural retinal layers using magnification-corrected optical coherence tomography angiography (OCTA) images in children with amblyopia.

Methods

This prospective cross-sectional study included 22 children with unilateral amblyopia (4–11 years of age) receiving spectral-domain OCTA. Vessel densities in foveal and parafoveal regions of the superficial capillary plexus (SCP) and deep capillary plexus (DCP) were measured in amblyopic and fellow eyes using a customized image analysis program correcting the scale of retinal image with axial length. Iowa Reference Algorithms (Iowa Institute for Biomedical Imaging) were used to measure mean thickness values of 10 intra-retinal layers rescaled for image size correction.

Results

Foveal and parafoveal vessel densities in amblyopic eyes were lower than that of the fellow eyes in the SCP (fovea: P = 0.006 and parafovea: P = 0.003) and the DCP (P = 0.024 and P = 0.025, respectively). Amblyopic eyes had significantly smaller foveal avascular zone (FAZ) area than fellow eyes (P < 0.001). There were significant differences in retinal layer thickness between paired eyes, particularly in the inner retina in both foveal and parafoveal regions; retinal nerve fiber layer (RNFL) (P = 0.024 and P = 0.095, respectively), ganglion cell layer (P < 0.001 and P = 0.008), inner plexiform layer (IPL; P = 0.12 and P = 0.037), inner nuclear layer (P = 0.005 and P = 0.005), and outer plexiform layer (OPL; P = 0.02 and P = 0.057), except in the foveal IPL, the parafoveal RNFL, and OPL.

Conclusions

Unilateral amblyopic eyes demonstrate reduced macular vessel density and thicker inner retinal layers compared with fellow eyes even after correcting for image magnification. Changes in macular microvasculature and structural layers may offer valuable insights in the development of amblyopia.

Interaction Between the Distribution of Diabetic Retinopathy Lesions and the Association of Optical Coherence Tomography Angiography Scans With Diabetic Retinopathy Severity

Importance

Studies have not yet determined whether the distribution of lesions in the retinal periphery alters the association between the severity of diabetic retinopathy (DR) and macular vessel density.

Objective

To evaluate the association of DR lesion distribution with optical coherence tomography angiography (OCTA) metrics and DR severity.

Design, Setting, and Participants

This cross-sectional observational study was conducted at a tertiary care center for diabetic eye disease among 225 patients with type 1 or 2 diabetes who had undergone imaging between February 15, 2016, and December 31, 2019.

Exposures

Optical coherence tomography angiography 3 × 3-mm macular scans and ultra-widefield color imaging.

Main Outcomes and Measures

Optical coherence tomography angiography vessel density in the superficial capillary plexus, intermediate capillary plexus, and deep capillary plexus and choriocapillaris flow density. The severity of DR and the predominantly peripheral lesions (PPL) were evaluated from ultra-widefield color imaging.

Results

The study evaluated 352 eyes (225 patients; 125 men [55.6%]; mean [SD] age, 52.1 [15.1] years), of which 183 eyes (52.0%) had mild nonproliferative diabetic retinopathy (NPDR), 71 eyes (20.2%) had moderate NPDR, and 98 eyes (27.8%) had severe NPDR or proliferative diabetic retinopathy (PDR). In eyes with no PPL (209 [59.4%]), the mean (SD) vessel density in the superficial capillary plexus (mild NPDR, 38.1% [4.7%]; moderate NPDR, 36.4% [4.6%]; severe NPDR or PDR, 34.1% [4.1%]; P < .001) and the deep capillary plexus (mild NPDR, 45.8% [3.0%]; moderate NPDR, 45.8% [2.2%]; severe NPDR or PDR, 44.5% [1.9%]; P = .002), as well as the mean (SD) choriocapillaris flow density (mild NPDR, 69.7% [6.2%]; moderate NPDR, 67.6% [5.6%]; severe NPDR or PDR, 67.1% [5.6%]; P = .01), decreased with increasing DR severity. These associations remained statistically significant even after correcting for age, signal strength index, spherical equivalent, duration of diabetes, type of diabetes, and correlation between eyes of the same patient. In eyes with PPL (143 [40.6%]), mean (SD) vessel density in the superficial capillary plexus (mild NPDR, 34.1% [4.1%]; moderate NPDR, 35.2% [4.1%]; severe NPDR or PDR, 36.0% [4.3%]; P = .42) and the deep capillary plexus (mild NPDR, 44.5% [1.7%]; moderate NPDR, 45.4% [1.4%]; severe NPDR or PDR, 44.9% [1.5%]; P = .81), as well as the mean (SD) choriocapillaris flow density (mild NPDR, 67.1% [5.6%]; moderate NPDR, 69.3% [4.6%]; severe NPDR or PDR, 68.3% [5.6%]; P = .49), did not appear to change with increasing DR severity.

Conclusions and Relevance

These results suggest that central retinal vessel density is associated with DR severity in eyes without, but not with, PPL. These findings suggest a potential need to stratify future optical coherence tomography angiography studies of eyes with DR by the presence or absence of PPL. If DR onset and worsening are associated with the location of retinal nonperfusion, assessment of global retinal nonperfusion using widefield angiography may improve the ability to evaluate DR severity and risk of DR worsening over time.

Diabetic Macular Ischemia: Influence of Optical Coherence Tomography Angiography Parameters on Changes in Functional Outcomes Over One Year

Purpose

To prospectively evaluate whether diabetic macular ischemia detected with coherence tomography angiography (OCTA) is associated with change in functional outcomes over a period of one year.

Methods

This is a one-year prospective, observational study that included 56 eyes with varying levels of diabetic retinopathy. All participants underwent best corrected visual acuity evaluation, swept-source OCTA and microperimetry at baseline and repeated at one year. Parafoveal vessel densities (VD) and foveal avascular zone (FAZ) areas were generated from OCTA in the superficial and deep vascular plexuses. The influence of baseline and change in OCTA parameters on change in visual acuity and retinal sensitivity over one year was evaluated.

Results

Over the one-year follow-up period, 16% (9) of eyes had at least one line worsening in BCVA and 7% (4) of eyes had at least 5% decrease in retinal sensitivity compared to baseline. Diabetic retinopathy progressed in 12.5%. Mean superficial vascular plexus (SVP) FAZ area increased (0.32 ± 0.15 to 0.39 ± 0.18 mm2, P = 0.003) and parafoveal VD in deep vascular plexus (DVP) decreased (49.8 ± 3.7% to 48.8 ± 2.9%, P = 0.040) at one year compared to baseline. In the multivariate regression analysis, larger baseline DVP FAZ area was associated with worsening of BCVA over one year (β = 0.16 logMAR per mm2, 95% CI 0.02 to 0.31, P = 0.032). In addition, larger decreases in SVP VD (β = -4.18 db per 10% decrease, 95% CI -6.55 to -1.80, P = 0.002) was associated with worsening of retinal sensitivity over one year.

Conclusions

Progression of parafoveal microvasculature changes over one year can be detected using OCTA. Larger baseline DVP FAZ area on OCTA is predictive of worsening in visual outcomes, and larger decreases in SVP VD were associated with worsening of retinal sensitivity over a course of one year in diabetic individuals.

The Influence of Axial Length Upon the Retinal Ganglion Cell Layer of the Human Eye

Purpose

Variation in retinal thickness with eye size complicates efforts to estimate retinal ganglion cell number from optical coherence tomography (OCT) measures. We examined the relationship among axial length, the thickness and volume of the ganglion cell layer (GCL), and the size of the optic chiasm.

Methods

We used OCT to measure GCL thickness over 50 degrees of the horizontal meridian in 50 healthy participants with a wide range of axial lengths. Using a model eye informed by individual biometry, we converted GCL thickness to tissue volume per square degree. We also measured the volume of the optic chiasm for 40 participants using magnetic resonance imaging (MRI).

Results

There is a positive relationship between GCL tissue volume and axial length. Given prior psychophysical results, we conclude that increased axial length is associated with increased retinal ganglion cell size, decreased cell packing, or both. We characterize how retinal ganglion cell tissue varies systematically in volume and spatial distribution as a function of axial length. This model allows us to remove the effect of axial length from individual difference measures of GCL volume. We find that variation in this adjusted GCL volume correlates well with the size of the optic chiasm.

Conclusions

Our results provide the volume of ganglion cell tissue in the retina, adjusted for the presumed effects of axial length upon ganglion cell size and/or packing. The resulting volume measure accounts for individual differences in the size of the optic chiasm, supporting its use to characterize the post-retinal visual pathway.

Translational Relevance

Variations in ametropia can confound clinical measures of retinal features. We present a framework within which the thickness and volume of retinal structures can be measured and corrected for the effects of axial length.

Carotid Disease and Retinal Optical Coherence Tomography Angiography Parameters in Type 2 Diabetes: The Fremantle Diabetes Study Phase II

OBJECTIVE

To use optical coherence tomography angiography (OCTA) to determine whether retinal microvascular parameters are associated with carotid arterial disease in people with type 2 diabetes.

RESEARCH DESIGN AND METHODS

Participants (community-based) underwent detailed assessments including carotid ultrasonography and OCTA. Ultrasound images were assessed for mean intima-media thickness (IMT) and the presence of stenosis. OCTA image analysis provided measures of vessel density, foveal avascular zone (FAZ) area, blood flow areas, and retinal thickness. For each OCTA variable, the most parsimonious model was generated using generalized estimating equations, then ipsilateral and contralateral carotid disease-related variables were added to determine their significance.

RESULTS

A total of 474 eyes from 261 participants (mean ± SD age 72.0 ± 9.3 years, 57.1% males, median diabetes duration 15.4 years [interquartile range 11.1-22.4]) were analyzed. When carotid variables were added to the most parsimonious models, the ipsilateral natural logarithm of common carotid artery IMT (coefficient -2.56 [95% CI -4.76, -0.35], P = 0.023) and presence of any ipsilateral stenosis (-0.82 [-1.48, -0.17], P = 0.014) were statistically significantly associated with a lower parafoveal density in the deep capillary plexus. A mean bifurcation IMT ≥1 mm was associated with a decreased vessel density in the 300-μm ring surrounding the FAZ (coefficient -0.79 [-1.50, -0.08], P = 0.030)). Contralateral carotid disease-related variables were also significantly associated with retinal microvascular parameters.

CONCLUSIONS

This is the first study to show that carotid disease is an independent associate of retinal microvascular disease assessed by OCTA in type 2 diabetes. Appropriately intensive management of carotid disease may improve the retinal microcirculation.

Repeatability and Reproducibility of Axial and Lateral Measurements on Handheld Optical Coherence Tomography Systems Compared with Tabletop System

Purpose

To compare the repeatability and reproducibility of axial and lateral retinal measurements using handheld optical coherence tomography (OCT) systems and a tabletop OCT system.

Methods

Graders measured central foveal thickness (CFT), optic nerve-to-fovea distance (OFD), and retinal nerve fiber layer (RNFL) thickness on OCT scans of the right eye of 10 healthy adults. Three OCT systems were used: handheld Leica Envisu, investigational handheld swept-source OCT (UC3), and Heidelberg Spectralis tabletop system. All eyes were imaged five times with each OCT system by each of two imagers. A components of variance analysis provided estimates of repeatability (variation due to random error) and reproducibility (variation due to imager, grader, and random error) expressed as standard deviation and (coefficient of variation %).

Results

Repeatability of CFT (µm) for Envisu, UC3, and Spectralis was 5.9 (2.6%), 6.9 (2.9%), and 4.7 (2.1%), and the reproducibility was 6.1 (2.7%), 7.3 (3.1%), and 4.7 (2.1%), respectively. The repeatability of OFD (mm) was 0.13 (2.9%), 0.10 (2.3%), and 0.07 (1.6%), and the reproducibility was 0.13 (3.0%), 0.10 (2.3%), and 0.07 (1.6%,) respectively. The repeatability for RNFL thickness (µm) for Envisu, UC3, and Spectralis was 4.3 (7.8%), 2.7 (5.4%), and 2.9 (4.9%), and the reproducibility was 4.5 (8.3%), 2.9 (5.8%), and 2.9 (4.9%), respectively.

Conclusions

All three OCT systems had good repeatability and reproducibility with coefficients of variation of less than 3.5% for CFT and OFD measurements, and less than 8.5% for RNFL thickness.

Translational Relevance

Our findings inform the repeatability and reproducibility of retinal axial and lateral measurements on handheld OCT and are useful for both clinical research and patient care.

Assessing the Influence of OCT-A Device and Scan Size on Retinal Vascular Metrics

Purpose

The purpose of this study was to investigate the effect of device and scan size on quantitative optical coherence tomography angiography (OCT-A) metrics.

Methods

The 3 × 3 mm scans from Optovue AngioVue and Zeiss AngioPlex systems were included for 18 eyes of 18 subjects without ocular pathology. The foveal avascular zone (FAZ) was segmented manually by two observers, from which estimates of FAZ area (using both the nominal image scale and the axial length corrected image scale) and acircularity were derived. Three scan sizes (3 mm, 6 mm HD, and 8 mm) from the AngioVue system were included for 15 eyes of 15 subjects without ocular pathology. For each subject, larger image sizes were resized to the same resolution as 3 × 3 mm scans, aligned, then cropped to a common area. FAZ area, FAZ acircularity, average and total parafoveal intercapillary area, vessel density, and vessel end points were computed.

Results

Between the devices used here, there were no significant differences in FAZ acircularity (P = 0.88) or FAZ area using scaled (P = 0.11) or unscaled images (P = 0.069). Although there was no significant difference in FAZ area across scan sizes (P = 0.30), vessel morphometry metrics were all significantly influenced by scan size.

Conclusions

The scan devices and sizes used here do not affect FAZ area measures derived from manual segmentations. In contrast, vessel morphometry metrics are affected by scan size. As individual differences in axial length induce differences in absolute scan size, extreme care should be taken when interpreting metrics of vessel morphometry, both between and within OCT-A devices.

Translational Relevance

A better characterization of the confounds surrounding OCT-A retinal vasculature metrics can lead to improved application of these metrics as biomarkers for retinal and systemic diseases.

Approaches to quantify optical coherence tomography angiography metrics

Optical coherence tomography (OCT) has revolutionized the field of ophthalmology in the last three decades. As an OCT extension, OCT angiography (OCTA) utilizes a fast OCT system to detect motion contrast in ocular tissue and provides a three-dimensional representation of the ocular vasculature in a non-invasive, dye-free manner. The first OCT machine equipped with OCTA function was approved by U.S. Food and Drug Administration in 2016 and now it is widely applied in clinics. To date, numerous methods have been developed to aid OCTA interpretation and quantification. In this review, we focused on the workflow of OCTA-based interpretation, beginning from the generation of the OCTA images using signal decorrelation, which we divided into intensity-based, phase-based and phasor-based methods. We further discussed methods used to address image artifacts that are commonly observed in clinical settings, to the algorithms for image enhancement, binarization, and OCTA metrics extraction. We believe a better grasp of these technical aspects of OCTA will enhance the understanding of the technology and its potential application in disease diagnosis and management. Moreover, future studies will also explore the use of ocular OCTA as a window to link ocular vasculature to the function of other organs such as the kidney and brain.

Progressive Choriocapillaris Impairment in ABCA4 Maculopathy Is Secondary to Retinal Pigment Epithelium Atrophy

Purpose

To analyze the progression of choriocapillaris (CC) impairment in recessive Stargardt disease (STGD) and compare it to the progression of retinal pigment epithelium (RPE) atrophy.

Methods

Fifty-five patients with a clinical diagnosis of STGD and genetic confirmation of pathogenic biallelic variants in ABCA4 were imaged with short-wavelength fundus autofluorescence (SW-AF) and optical coherence tomography angiography (OCTA) at a single clinic visit, whereas a subset of 12 patients were imaged with the same modalities at two different clinic visits.

Results

We observed three stages of CC impairment: an area of bright yet intact macular CC (11 patients), regions of vascular rarefaction and incomplete CC atrophy within an area of bright CC (10 patients), and areas of extensive CC atrophy (26 patients). These changes correlated to the degree of RPE atrophy observed in SW-AF imaging. Furthermore, 8 patients presented with early changes on SW-AF, but healthy CC. Quantitative analyses of the atrophic changes revealed that the area of RPE atrophy is larger (9.6 ± 1.7 mm2 vs. 6.9 ± 1.3 mm2, P < 0.001) and that it progresses at a faster rate (1.1 ± 0.1 mm2/year vs. 0.8 ± 0.2 mm2/year, P = 0.004) than the corresponding area of CC atrophy.

Conclusions

CC impairment is progressive and OCTA imaging can be used to demonstrate the stages, which culminate in extensive CC atrophy. Furthermore, CC impairment is secondary to RPE atrophy in STGD. We further advocate the use of SW-AF and OCTA imaging in monitoring the progression of STGD.

Impact of Axial Eye Size on Retinal Microvasculature Density in the Macular Region

Mechanical tissue stresses are important contributors to the increased risk of sight-threatening pathology in larger, more myopic eyes. The contribution of altered ocular vasculature to the development of this pathology is less well defined. The current study investigated the impact of eye size on the superficial vasculature of the macula. Subjects (n = 104) aged 18–50, with no history of ocular or vascular disease, or myopia control, were recruited from university staff and student populations in Australia and Hong Kong. Refractive error, ocular size, retinal morphology and vascular morphology were quantified through open field autorefraction, ocular biometry and ocular coherence tomography angiography. Morphology of the superficial retinal capillary plexus was assessed over a 3 × 3 mm fovea-centred area. Perfusion area and vessel length densities were analysed relative to axial eye length and retinal thickness. A significant inverse association was found between axial length and vascular density measures (perfusion area density r² = 0.186, p < 0.001; and vessel length density r² = 0.102, p = 0.001). Perfusion area and vessel length densities were reduced by 5.8% (p = 0.001) in the longest, relative to the shortest, eyes. The aggregated ganglion cell layer inner plexiform layer thickness was also inversely associated with eye size (r² = 0.083, p = 0.003), and reduced, by 8.1% (p < 0.001), in the longest eyes. An inverse association of eye size and superficial retinal vasculature density, that is not simply explained by retinal expansion or image magnification factors, was confirmed. These data support the hypothesis that ongoing metabolic challenges may underlie the development of myopia-related and -associated pathology in larger eyes.

Retinal Microvasculature Changes After Repair of Macula-off Retinal Detachment Assessed with Optical Coherence Tomography Angiography

Objective

To characterize the microvascular retinal changes after repair of macula-off rhegmatogenous retinal detachment (RRD) using optical coherence tomography angiography (OCT-A).

Patients and Methods

A retrospective review of patients who underwent repair of macula-off RRD. Fellow unaffected eyes were used as controls. Post-operative OCT-A allowed comparison of vessel density (VD) and foveal avascular zone (FAZ) area in the superficial and deep retinal capillary plexus (DCP) as well as VD in the choriocapillaris layer.

Results

Seventeen eyes of 17 RRD patients were included in the final analysis. There was a reduction in VD of the deep retinal capillary plexus in affected eyes compared to fellow eyes (p = 0.046). RRD eyes with reduced VD in DCP compared with their fellow control eyes had worse visual acuity after repair compared to those without (p = 0.032). No significant microvasculature changes were detected in the FAZ area and VD in the superficial capillary plexus and choriocapillaris compared to fellow eyes.

Conclusion

In macula-off RRD eyes, significant microvascular changes were detected in the DCP using OCT-A even after successful anatomical repair. Decreased VD in the DCP compared to the fellow healthy eyes was correlated with worse visual acuity.

Optical Coherence Tomography Angiography in Diabetes and Diabetic Retinopathy

Diabetic retinopathy (DR) is a common complication of diabetes mellitus that disrupts the retinal microvasculature and is a leading cause of vision loss globally. Recently, optical coherence tomography angiography (OCTA) has been developed to image the retinal microvasculature, by generating 3-dimensional images based on the motion contrast of circulating blood cells. OCTA offers numerous benefits over traditional fluorescein angiography in visualizing the retinal vasculature in that it is non-invasive and safer; while its depth-resolved ability makes it possible to visualize the finer capillaries of the retinal capillary plexuses and choriocapillaris. High-quality OCTA images have also enabled the visualization of features associated with DR, including microaneurysms and neovascularization and the quantification of alterations in retinal capillary and choriocapillaris, thereby suggesting a promising role for OCTA as an objective technology for accurate DR classification. Of interest is the potential of OCTA to examine the effect of DR on individual retinal layers, and to detect DR even before it is clinically detectable on fundus examination. We will focus the review on the clinical applicability of OCTA derived quantitative metrics that appear to be clinically relevant to the diagnosis, classification, and management of patients with diabetes or DR. Future studies with longitudinal design of multiethnic multicenter populations, as well as the inclusion of pertinent systemic information that may affect vascular changes, will improve our understanding on the benefit of OCTA biomarkers in the detection and progression of DR.