A method for age-matched OCT angiography deviation mapping in the assessment of disease- related changes to the radial peripapillary capillaries

Vascular density normative data of radial peripapillary capillary plexus in healthy Caucasian subjects

PURPOSE

To establish a normative database for vascular density (VD) of radial peripapillary capillary plexus (RPC) in healthy Caucasian subjects.

METHODS

633 healthy Caucasian subjects underwent a complete ophthalmological examination, including slit-lamp biomicroscopy, best corrected visual acuity measurement with Early Treatment Diabetic Retinopathy Study charts, intraocular pressure measurement, fundus examination, and macular and optic nerve head (ONH) structural optical coherence tomography (OCT). En-face 4.5 × 4.5 mm OCT angiography scans of the RPC plexus were recorded and VD values, automatically provided by the AngioAnalytics™ software, noted. We statistically estimated the impact of age and gender on RPC VD values using a linear mixed model.

RESULTS

560 subjects fully met inclusion criteria and, according to age, were stratified into 5 groups: 18-50 years (77), 51-60 years (160), 61-70 years (110), 71-80 years (132), and ≥ 81 years (81). Overall, mean RPC VD of the whole en-face image was 53.03 ± 4.27%. Age was significantly related to RPC VD values of whole en-face image (r = -0.454; p < 0.0001), which decreased with aging. The linear mixed model disclosed that age has a statistically significant effect on RPC VD values in whole en-face image (p = 0.0006). As age increases, RPC VD values decrease by 0.12 per year. Conversely, no significant gender-related differences were found in terms of RPC VD values of whole en-face image and each parapapillary quadrant analyzing all age group.

CONCLUSIONS

Results show that RPC VD values in healthy Caucasian subjects decrease with aging. These data may be used to create a reference normative database useful for clinical use.

KEY MESSAGES

What is known Radial peripapillary capillary (RPC) plexus, consisting of long parallel capillaries with rare bifurcations and anastomosis and extending straight along the course of the retinal nerve fiber layer to the posterior pole, may be affected early in some optic nerve head (ONH) and retinal diseases. What is new This study reports RPC vascular density (VD) values, automatically measured on optical coherence tomography angiography, in healthy Caucasian subjects, demonstrating that age is negatively related to RPC VD values. Results show that RPC VD values in healthy Caucasian subjects decrease with aging. These data may be used to create a reference normative database useful for clinical use.

Assessing the Sensitivity of OCT-A Retinal Vasculature Metrics

Purpose

The purpose of this study was to examine the sensitivity of quantitative metrics of the retinal vasculature derived from optical coherence tomography angiography (OCT-A) images.

Methods

Full retinal vascular slab OCT-A images were obtained from 94 healthy participants. Capillary loss, at 1% increments up to 50%, was simulated by randomly removing capillary segments (1000 iterations of randomized loss for each participant at each percent loss). Thirteen quantitative metrics were calculated for each image: foveal avascular zone (FAZ) area, vessel density, vessel complexity index (VCI), vessel perimeter index (VPI), fractal dimension (FD), and parafoveal intercapillary area (PICA) measurements with and without the FAZ (mean PICA, summed PICA, PICA regularity, and PICA standard deviation [PICA SD]). The sensitivity of each metric was calculated as the percent loss at which 80% of the iterations for a participant fell outside of two standard deviations from the sample's normative mean.

Results

The most used OCT-A metrics, FAZ area and vessel density, were not significantly different from normative values until 27.69% and 16.00% capillary loss, respectively. Across the remaining metrics, metric sensitivity ranged from 6.37% (PICA SD without FAZ) to 39.78% (Summed PICA without FAZ).

Conclusions

The sensitivity of vasculature metrics for detecting random capillary loss varies substantially. Further efforts simulating different patterns of capillary loss are needed for comparison. Additionally, mapping the repeatability of metrics over time in a normal population is needed to further define metric sensitivity.

Translational Relevance

Quantitative metrics vary in their ability to detect vascular abnormalities in OCT-A images. Metric choice in screening studies will need to balance expected capillary abnormalities and the quality of the OCT-A images being used.

Age-related assessment of foveal avascular zone and surrounding capillary networks with swept source optical coherence tomography angiography in healthy eyes

AIM

To assess the macular capillary networks and foveal avascular zone (FAZ) with swept-source optical coherence tomography angiography in healthy eyes.

METHODS

This cross-sectional, prospective, observational study enrolled 222 eyes of 116 healthy participants with no ocular or systemic disease. SS-OCTA images were captured using the PLEX Elite 9000 (Carl Zeiss Meditec Inc., Dublin, CA, USA) with a 6 × 6 mm pattern centered on the foveal center. Vessel length density (VLD), perfusion density (PD), and FAZ parameters were analyzed using the manufacturer's automated software.

RESULTS

A significant negative correlation was observed between age and average VLD in the superficial plexus, and average PD in both the superficial plexus and the whole retina. A significant positive correlation between age and foveal avascular zone perimeter and area was also noted. Age-wise comparisons showed a trend for an increase in VLD and PD until 40 years of age, with a subsequent decrease in the older age in the macular region. The central subfield showed a decrease in the vessel density measurements in the 21-40 age group. FAZ area and perimeter were the mirror inverse of the central subfield vessel density measurements with a numerically greater area and perimeter in the 21-40 age group compared to the 0-20 and 41-60 age groups. FAZ circularity was significantly reduced after 40 years of age.

CONCLUSION

Age-related changes in the vessel density and FAZ parameters in the healthy macula are complex and vary with the macular location. These results carry significance when interpreting the data from diseased eyes.

A Pilot Study of Subclinical Non-Capillary Peripapillary Perfusion Changes in Thyroid-Related Orbitopathy Detected Using Optical Coherence Tomography Angiography

Purpose

Hemodynamic changes surrounding the optic nerve head are known to occur in thyroid-related orbitopathy (TRO). This pilot study explores the capillary and non-capillary peripapillary perfusion changes of the retina in TRO eyes without dysthyroid optic neuropathy (DON) using optical coherence tomography angiography (OCT-A).

Methods

Non-capillary and capillary peripapillary perfusion densities were calculated using single 4.5 × 4.5mm en face “RPC layer” OCT-A scans of 8 TRO patients without DON (8 eyes, mean age 40.6 years, range 23–69 years). Results were compared to a previously published dataset of 133 healthy controls (133 eyes, mean 41.5 years, range 11–83 years). The strength of association was measured between OCT-A perfusion densities and clinical measures of TRO.

Results

Non-capillary peripapillary perfusion density in TRO eyes was found to be significantly decreased compared to healthy controls (TRO group 15.4 ± 2.9% vs controls 21.5 ± 3.1%; p < 0.0001). Capillary peripapillary perfusion densities showed no significant difference (TRO group 42.5 ± 1.8% vs controls 42.5 ± 1.5%; p = 1.0). Clinical measures of disease did not correlate well with OCT-A perfusion densities (p>0.05).

Conclusion

These findings may represent decreased blood flow and subclinical ischemia to the optic nerve. We discuss possible pathogenic mechanisms of thyroid-related vasculopathy, including vessel wall thickening due to immunologically-induced media enlargement.

Combined wide-field optical coherence tomography angiography density map for high myopic glaucoma detection

The present study aimed to evaluate the diagnostic ability of wide-field optical coherence tomography angiography (OCTA) density map for detection of glaucomatous damage in high myopic (HM) eyes and to further compare the diagnostic ability of OCTA with that of conventional imaging approaches including red-free photography and swept-source OCT (SS-OCT) wide-field maps. A total of 77 healthy HM eyes and 72 HM eyes with open angle glaucoma (OAG) participated in this retrospective observational study. Patients underwent a comprehensive ocular examination, including wide-field SS-OCT scan and peripapillary area and macular OCTA scans. An integrated OCTA density map thereafter was merged by vascular landmark-guided superimposition of peripapillary and macular superficial vascular density maps onto the red-free photography (resulting in the OCTA-PanoMap). Glaucoma specialists then determined the presence of glaucomatous damage in HM eyes by reading the OCTA-PanoMap and compared its sensitivity and specificity with those of conventional images. Sensitivity and specificity of OCTA-PanoMap for HM-OAG diagnosis was 94.4% and 96.1%, respectively. Compared with other imaging methods, the sensitivity of OCTA-PanoMap was significantly higher than that of red-free photography (P = 0.022) and comparable to that of wide-field SS-OCT maps. Specificity of OCTA-PanoMap was significantly higher than those of other conventional imaging methods (except for wide-field thickness map). The OCTA-PanoMap showed good diagnostic ability for discrimination of HM-OAG eyes from healthy HM eyes. As a complementary method of an alternative imaging modality, OCTA-PanoMap can be a useful tool for detection of HM-OAG.

Age and signal strength-related changes in vessel density in the choroid and the retina: an OCT angiography study of the macula and optic disc

PURPOSE

To investigate the effects of ageing and signal strength index (SSI) on vessel density (VD) measurements of the radial peripapillary capillaries (RPC) in the optic disc, the retinal superficial (SCP) and deep (DCP) capillary plexi and the choriocapillaris (CC) of the macular area using optical coherence tomography angiography (OCT-A) imaging.

METHODS

This cross-sectional study included 138 eyes from 77 healthy participants. High-definition (HD) disc Angio scan (4.5X4.5 mm) and HD Angio retina scan (6X6 mm) were acquired. Whole image (WI) VDs, inside disc (ID) VD and global and hemifield peripapillary RPC VDs were evaluated from the Angio Disc scans. Global and hemifield VD for the SCP, DCP and CC slab in the macula area were also recorded across different age groups.

RESULTS

Mean age was 48.2 ± 15.0 years (range 25-82 years). Signal strength index (SSI) was 71.6 ± 7.6 in the macula and 74.6 ± 9.2 in the disc OCT-A image. VD for both SCP and DCP decreased by 0.084% and 0.188%/year (both p < 0.001). WI VD and ID VD also decreased by 0.037%/year (p = 0.005) and 0.092%/year (p < 0.001). Peripapillary RPC VD did not change with age or SSI. The effect of SSI was significant in SCP, DCP, WI RPC, ID RPC and CC VD. In the generalized estimating equation model testing for both SSI and age, SSI remained significant against SCP, DCP and ID RPC.

CONCLUSION

With ageing, a decrease in VD in the SCP, DCP, WI and ID RPC, as well as in SSI, is seen. SSI and age are associated with VD changes, but only SSI is the significant variable that explains the variation in the retina microvasculature in the macula and the optic disc in multivariate analysis. In the CC, a larger SSI was associated with a lower VD. These findings underscore the importance of controlling for SSI in future studies using OCT-A.

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

Importance

Individual differences in axial length affect the lateral magnification of in vivo retinal images and as a result can affect the accuracy of quantitative measurements made from these images. As measurements from optical coherence tomography angiography (OCTA) images are becoming increasingly used in the diagnosis and monitoring of a wide range of diseases, evaluating which studies use correctly scaled images is crucial to their interpretation.

Objective

To perform a systematic literature review to assess the percentage of articles that report correcting the scale of their OCTA images for individual differences in retinal magnification.

Evidence Review

A PubMed (MEDLINE) search was conducted for articles on OCTA retinal imaging published between June 1, 2015, and June 1, 2018. Initial results included 7552 articles. Initial exclusion criteria removed studies of animal models, as well as reviews, letters, replies, comments, and image-based or photographic essays. Articles not written in English and those that required purchase from non-English language websites were excluded. Articles that did not use OCTA for imaging the retina were also excluded. Remaining articles were reviewed in detail to assess whether the OCTA measurements required correct lateral scaling, and if so, whether axial length was reported or used to scale the images. We also determined the number of articles that mentioned the lack of correct lateral scaling as a limitation of the study.

Findings

A total of 989 articles were included in the detailed review. Of these, 509 were determined to require correct image scaling for their analyses, but only 41 (8.0%) report measuring and using axial length to correct the lateral scale of their OCTA images. Furthermore, of the 468 articles that did not correctly scale their images, only 18 (3.8%) mentioned this as a limitation to their study.

Conclusions and Relevance

These findings suggest that most peer-reviewed articles in PubMed that use quantitative OCTA measurements use incorrectly scaled images. This could call into question the conclusions of such studies and warrants consideration by OCTA manufacturers, physicians, authors, journal reviewers, and journal editors.

Retinal alterations in patients with Lafora disease

Purpose

Lafora disease is a genetic neurodegenerative metabolic disorder caused by insoluble polyglucosan aggregate accumulation throughout the central nervous system and body. The retina is an accessible neural tissue, which may offer alternative methods to assess neurological diseases quickly and noninvasively. In this way, noninvasive imaging may provide a means to characterize neurodegenerative disease, which enables earlier identification and diagnosis of disease and the ability to monitor disease progression. In this study, we sought to characterize the retina of individuals with Lafora disease using non-invasive retinal imaging.

Methods

One eye of three individuals with genetically confirmed Lafora disease were imaged with optical coherence tomography (OCT) and adaptive optics scanning light ophthalmoscopy (AOSLO). When possible, OCT volume and line scans were acquired to assess total retinal thickness, ganglion cell-inner plexiform layer thickness, and outer nuclear layer + Henle fiber layer thickness. OCT angiography (OCTA) scans were acquired in one subject at the macula and optic nerve head (ONH). AOSLO was used to characterize the photoreceptor mosaic and examine the retinal nerve fiber layer (RNFL).

Results

Two subjects with previous seizure activity demonstrated reduced retinal thickness, while one subject with no apparent symptoms had normal retinal thickness. All other clinical measures, as well as parafoveal cone density, were within normal range. Nummular reflectivity at the level of the RNFL was observed using AOSLO in the macula and near the ONH in all three subjects.

Conclusions

This multimodal retinal imaging approach allowed us to observe a number of retinal structural features in all three individuals. Most notably, AOSLO revealed nummular reflectivity within the inner retina of each subject. This phenotype has not been reported previously and may represent a characteristic change produced by the neurodegenerative process.

Optic disc and peripapillary vessel density measured with optical coherence tomography angiography and its associations in Chinese adults: a large population-based study

PURPOSE

To investigate the optic disc and peripapillary vessel density, as well as its ocular and systemic associations, in healthy eyes among adult Chinese population.

METHODS

A population-based cross-sectional eye survey was conducted on Chinese adults residing in Hong Kong. 1891 eyes from 1891 participants who completed 4.5×4.5 mm optical coherence tomography angiography scans were recruited. Among the 1891 eyes, 404 were excluded due to low scan quality, optic disc or retinal disorders and non-Chinese ethnicity. The vessel densities (VDs) at nerve fibre layer plexus (NFLP) at both optic disc and peripapillary were collected for analysis. Multiple linear regression analysis was performed to determine the ocular and systemic associations of NFLP VD.

RESULTS

The study included 1487 participants (men: 41.2%) with a mean age of 48.8±15.4 years. The mean NFLP VD of the whole en face image, inside disc and peripapillary region was 53.8%, 42.7% and 60.3%, respectively. In the multivariable model, decreased NFLP VDs were significantly associated with older age, male gender, longer axial length (AL) and lower Signal Strength Index.

CONCLUSIONS

This large population-based cross-sectional study provided quantitative data of optic disc and peripapillary NFLP VD which may serve as a normative reference for clinical use. Apart from age, gender and AL, the scan signal strength also should be taken into consideration during the assessment of NFLP VD.

Vascular Patterning as Integrative Readout of Complex Molecular and Physiological Signaling by VESsel GENeration Analysis

The molecular signaling cascades that regulate angiogenesis and microvascular remodeling are fundamental to normal development, healthy physiology, and pathologies such as inflammation and cancer. Yet quantifying such complex, fractally branching vascular patterns remains difficult. We review application of NASA's globally available, freely downloadable VESsel GENeration (VESGEN) Analysis software to numerous examples of 2D vascular trees, networks, and tree-network composites. Upon input of a binary vascular image, automated output includes informative vascular maps and quantification of parameters such as tortuosity, fractal dimension, vessel diameter, area, length, number, and branch point. Previous research has demonstrated that cytokines and therapeutics such as vascular endothelial growth factor, basic fibroblast growth factor (fibroblast growth factor-2), transforming growth factor-beta-1, and steroid triamcinolone acetonide specify unique "fingerprint" or "biomarker" vascular patterns that integrate dominant signaling with physiological response. In vivo experimental examples described here include vascular response to keratinocyte growth factor, a novel vessel tortuosity factor; angiogenic inhibition in humanized tumor xenografts by the anti-angiogenesis drug leronlimab; intestinal vascular inflammation with probiotic protection by Saccharomyces boulardii, and a workflow programming of vascular architecture for 3D bioprinting of regenerative tissues from 2D images. Microvascular remodeling in the human retina is described for astronaut risks in microgravity, vessel tortuosity in diabetic retinopathy, and venous occlusive disease.

Age-related changes in macular vessels and their perfusion densities on optical coherence tomography angiography

Purpose

To evaluate age-related changes in macular vessels and their perfusion densities using optical coherence tomography angiography (OCTA).

Methods

A total of 108 eyes of 54 healthy subjects between the age group of 11 to 60 years having unaided visual acuity of 20/20 were studied on spectral domain OCTS using 3 * 3 mm macula protocol. These subjects were divided into 5 groups; Group 1: 11-20 years, Group 2: 21-30 years, Group 3: 31-40 years, Group 4: 41-50 years, and Group 5: 51-60 years. An early treatment diabetic retinopathy study (ETDRS) grid overlay at the macula was used to calculate changes in different quadrants of the superficial retinal plexus.

Results

A total of 98 eyes of 49 patients were considered for the final analysis. The vessel density values decreased from the second to the sixth decade in all four quadrants (except the third decade, where a slight increase was noted). The total vessel density decreased from 168 ± 78 mm^-1 (group 1) to 131.47 ± 18.32 mm^-1 (group 5). A similar reduction pattern in perfusion density was seen in each quadrant from the second to the sixth decade. The total perfusion density reduced from 309 ± 15.63% (group 1) to 283.05 ± 45.23% (group 5). The foveal avascular zone area was 0.18 ± 0.09 mm² in group 1, 0.33 ± 0.13 mm² in group 2, 0.30 ± 0.10 mm² in group 3, 0.38 ± 0.05 mm² in group 4, and 0.46 ± 0.06 mm² in group 5.

Conclusion

In our population, macular vessel density appears to decrease noticeably from the fourth decade onwards but a statistically significant decrease was observed only from the fifth decade onwards. However, it was not uniform along with all the quadrants. Similarly, the percentage of perfusion density dropped from the fourth decade but these values also varied among the different quadrants.

Peripapillary capillary density in acute angle closure crisis and angle closure suspect: A structure, flow and function correlation study

PURPOSE

to describe peripapillary vascular changes using Optical Coherence Tomography Angiography (OCT-A) in patients with acute angle closure crisis (AACC) and primary-angle closure-suspects (PACS) in comparison to normal controls.

METHODS

This cross-sectional/case-control/non-randomized study was conducted at Cairo University Hospitals. It included 21 eyes following AACC, 21 eyes of PACS and 32 eyes of age-matched-controls. Participants underwent visual field (VF) examination, retinal nerve fiber layer (RNFL) assessment using spectral-domain-OCT (SD-OCT), and radial peripapillary capillary density (RPC%) using OCT-A.

RESULTS

There was a statistically significant difference in MD and PSD among the three groups (p ⩽ 0.001). There was a significant difference in mean RNFL among the three groups (p ⩽ 0.001), this decrease was still present when comparing the AACC group to controls p = 0.032. There was a significant decrease in the peripapillary RPC% in all groups p ⩽ 0.001. The correlation between structure, function and flow was studied for all groups. Peripapillary RPC% in AACC was positively correlated to MD and peripapillary RNFL (p ⩽ 0.001). In PACS, RPC% was positively correlated to RNFL (p = 0.012). In controls, RPC% was positively correlated to PSD and peripapillary RNFL (p ⩽ 0.001). AUC was 0.8 for the MD, 0.56 for the RPC and 0.38 for the RNFL.

CONCLUSIONS

Peripapillary vessel density was lower in AACC eyes than in suspects and control eyes. OCT-A parameters could be a more sensitive marker than OCT parameters after an AACC attack as evident on ROC analysis. PACS remains a clinical diagnosis as we could not find any significant differences in OCT or OCT-A parameters between suspects and normal healthy controls.

Interocular asymmetry of foveal avascular zone morphology and parafoveal capillary density in sickle cell retinopathy

OBJECTIVES

To examine interocular asymmetry of foveal avascular zone (FAZ) and parafoveal capillary density metrics in sickle cell retinopathy (SCR) using optical coherence tomography angiography (OCT-A).

METHODS

This cross-sectional, retrospective study evaluated SCR patients and unaffected controls who underwent 3x3mm macular OCT-A imaging using a spectral domain-OCT system. FAZ (area, perimeter, and acircularity index) and parafoveal capillary density metrics were computed for both eyes of each participant. In unaffected controls, interocular difference in FAZ and parafoveal capillary density metrics were evaluated using Bland-Altman plots. SCR patients with interocular difference outside the upper 97.5% and lower 2.5% limits of agreement from controls were defined as having interocular asymmetry. Area under receiver operating characteristic curve (AROC) was also performed to determine the ability of the absolute interocular difference to differentiate between subjects with SCR-including non-proliferative SCR (NP-SCR) and proliferative SCR (P-SCR)-and unaffected controls.

RESULTS

Thirty-one patients with SCR (21 NP-SCR and 10 P-SCR) and 14 race-matched and age-matched controls were included for analysis. Interocular asymmetry was seen for all FAZ and parafoveal capillary density metrics in NP-SCR and P-SCR subjects. SCR subjects showed greater disease severity in the left-eye for FAZ and parafoveal capillary density metrics.

CONCLUSIONS

NP-SCR and P-SCR patients demonstrated quantifiable interocular asymmetry in FAZ and parafoveal capillary density metrics compared to unaffected subjects, with left-eye predominance in disease severity.

Normative Database of Peripapillary Vessel Density Measured by Optical Coherence Tomography Angiography and Correlation Study

Purpose: To provide a normative data set of swept-source optical coherence tomography angiography (SS-OCTA) peripapillary vessel density (VD) measurements and assess correlations with age, gender, disc area and axial length (AL). Material and Methods: This was an observational cross-sectional study conducted on 346 right eyes of healthy subjects. Peripapillary SS-OCTA VD measurements were obtained in the retinal superficial capillary plexus (SCP), deep capillary plexus (DCP), and choriocapillaris (CC) in all four quadrants using the Triton device (Topcon, Nagoya, Japan). AL measurements were made by optical biometry. Results: Mean participant age was 37.7 ± 19.8 years (range 5- 83), AL was 23.9 ± 1.3 mm (21-27), and 59% were women. Mean VDs for all quadrants were 57.2 ± 5.7% for SCP (52.4 ± 4.0% - 62.1 ± 4.2%), 46.3 ± 6.5% for DCP (41.9 ± 5.8% - 49.7 ± 4.8%) and 60.8 ± 7.4% for CC (53.4 ± 5.8% - 65.7 ± 5.5%). Negative correlation was detected between SCP VD and age (R = -0.264; P < .001), while correlation between DCP densities and age was positive (R = 0.202; P = .002). No associations were detected between peripapillary VD and gender (P ≥ 0.087) and negative correlation was found with AL and disc area only in the CC (P ≤ 0.004). In a subgroup analysis of 33 individuals, we noted no differences in VD between fellow eyes (P ≥ 0.139). Conclusion: Peripapillary VD showed wide individual variation when measured with the Triton SS-OCTA in the different retinal plexuses and CC. While correlations were observed with age, no relationships emerged with gender and only CC showed negative correlation with AL and disc area.

Optical coherence tomography angiography-derived flow density: a review of the influencing factors

Research interest in the possibility of quantifying macular and optic nerve head perfusion through optical coherence tomography angiography (OCTA) is rapidly advancing. Numerous scientific trials have furthered our understanding of the capabilities and the limitations of this novel technology, while applying OCTA to various ocular pathologies. In recent years, different parameters such as age, gender, intraocular pressure, spherical equivalent, physical activity, systemic diseases, and medication have been shown to have a significant impact on quantitative OCTA metrics. Since OCTA is likely to remain a "hot topic" in the near future, it is crucial to be aware of influencing factors in order to ensure correct interpretation of imaging results. This article reviews the factors currently known to influence flow density (FD) as measured by OCTA in healthy eyes.

The vascular densities of the macula and optic disc in normal eyes from children by optical coherence tomography angiography

PURPOSE

This study aims to describe the variation and characteristics of vessel density (VD) of the macula and optic disc in the normal eyes of children.

METHODS

This was a retrospective study where subjects aged 5-18 years with normal eyes were enrolled. The macula and optic disc were scanned by optical coherence tomography angiography (OCTA). The influences of age, gender, and axial length (AL) on VD were analyzed.

RESULTS

A total of 71 normal eyes from 71 subjects were enrolled. For the macula, the mean VD of fovea, parafovea, and perifovea at superficial retina and deep retina were 20.1%, 50.2%, 49.4%, 36.1%, 53.9%, and 48.1%, respectively. The mean foveal avascular zone (FAZ) was 0.277 mm². For optic disc, the mean VD of radial peripapillary capillary (RPC) and inside-disc areas were 51.8% and 51.7%, respectively. Significant differences were found between the superior-hemi and inferior-hemi VD of the superficial retinal parafovea, deep retinal perifovea, and perifovea. The fovea VD of the superficial and deep retina and FAZ areas were different between genders. The inside-disc VD was positively correlated with AL, while other VDs had no significant correlation with age and AL.

CONCLUSIONS

The parafovea VD of the superficial retina, parafovea, and perifovea of the deep retina had superior-hemi VD; boys had a higher fovea VD and smaller FAZ area than those of girls, the macular VD and peripapillary RPC density were steady for 5-18 year-olds. This study provided useful information for furthering the understanding of the development mode of vessel in children and the OCTA clinical applications in children.

Systemic Determinants of Peripapillary Vessel Density in Healthy African Americans: The African American Eye Disease Study

PURPOSE

To determine the relationship between systemic factors and radial peripapillary capillary (RPC) vessel density (VD) in healthy African American (AA) participants of the African American Eye Disease Study.

DESIGN

A population-based, cross-sectional study.

METHODS

A total of 4135 eyes from 2127 AA participants aged 40 years and older in Inglewood, California, were imaged for 6×6-mm optic disc scans on a spectral-domain optical coherence tomography angiography (OCTA) device. Of these, 1029 eyes from 1029 participants who met the inclusion and exclusion criteria were analyzed, including only 1 eye per participant. Custom software was used to quantify RPC VD. Multivariate linear regression was used to identify systemic factors associated with RPC VD with a significance level set at 0.05. The contribution of each variable to the final model was estimated with the magnitude of standardized regression coefficients (SRCs). The fit of the final model was measured by R².

RESULTS

The average RPC VD was 0.346±0.045. Controlling for signal strength, the systemic variables in the final multivariate model associated with reduced RPC VD were older age (β = -0.0123 per decade; SRC = -0.2733; P < .0001), male sex (β = -0.0067; SRC = -0.0716; P = .0060), and longer diabetes duration (β = -0.0022 per 5 years; SRC = -0.0527; P = .0427). The model R² was 0.3689.

CONCLUSIONS

Age, sex, and systemic influences, such as diabetes duration, need to be considered when assessing changes in RPC VD in glaucoma and other ocular diseases. Longitudinal studies are needed to investigate whether reduced RPC VD and the factors that affect it are associated with an increased risk of developing glaucomatous nerve damage.

Ocular Determinants of Peripapillary Vessel Density in Healthy African Americans: The African American Eye Disease Study

Purpose

The African American (AA) population has unique ocular anatomic characteristics and a disproportionately high incidence of glaucoma, which is associated with lower peripapillary vessel density (VD). This study aimed to identify ocular determinants of peripapillary VD in healthy AAs.

Methods

This was a cross-sectional, population-based study of 1029 AAs, ages 40 and older. Participants underwent examination to obtain axial length (AL), IOP, central corneal thickness (CCT), mean retinal nerve fiber layer (RNFL) thickness, visual field mean deviation (MD), and 6 × 6-mm optical coherence tomography angiography scans of the optic nerve. Participants with glaucoma, vision-threatening diabetic retinopathy, or other relevant ocular disease were excluded. Prototype software was used to quantify VD. A multivariable regression model, controlling for age and signal strength, identified the ocular variables that predicted peripapillary VD. The contribution of each variable was assessed with the magnitude of standardized regression coefficients (SRC).

Results

Based on univariate regressions, AL, RNFL thickness, and MD had significant associations with peripapillary VD (all P < 0.001). In the final multivariate model, lower mean RNFL thickness (β = 0.0022, P < 0.001, SRC = 0.542) and longer AL (β = -0.0055, P < 0.001, SRC = -0.118) were associated with lower peripapillary VD, controlling for age and signal strength, with model R2 of 0.69.

Conclusions

Thinner RNFL and longer AL were the most influential ocular determinants of lower peripapillary perfusion in healthy AA eyes. Additional research is needed to clarify whether longer AL increases risk of glaucoma by affecting capillary perfusion.

Foveal avascular zone morphology and parafoveal capillary perfusion in sickle cell retinopathy

Background/aims

To assess foveal avascular zone (FAZ) morphology and parafoveal capillary perfusion in patients with various stages of sickle cell retinopathy (SCR) using optical coherence tomography angiography (OCT-A).

Methods

This is a multi-institutional retrospective study of patients with various stages of SCR compared with healthy controls. Parafoveal OCT-A images obtained using a commercial spectral domain-OCT system were reviewed. Foveal-centred 3×3 mm full vascular slab OCT-As were used for image processing and data analysis. FAZ area, perimeter, and acircularity index were determined on the OCT-A image after manual delineation of the FAZ border. Quadrant-based parafoveal capillary density and per cent area deviating from normal distribution were also measured.

Results

Fifty-two patients with SCR (33 non-proliferative and 19 proliferative) and 20 age and race-matched healthy controls were included. One randomly selected eye per study participant was analysed. FAZ perimeter and acircularity index were significantly greater in SCR eyes when compared with the controls. While parafoveal capillary density was significantly lower, per cent area deviated from normal distribution was significantly higher in SCR eyes than that of the control. However, no statistically significant difference between the two SCR stages was observed. In quadrant-based analysis, the temporal quadrant showed greater parafoveal capillary dropout due to SCR, with the most profound effect in patients with proliferative SCR.

Conclusions

Abnormal FAZ morphology and altered parafoveal capillary perfusion were found in patients with SCR. Our customised OCT-A image analysis method uniquely highlights significant quantitative alterations in perfusion density mapping in a qualitative display, with minimal obscuration of OCT-A image detail.

Novel Development of Parafoveal Capillary Density Deviation Mapping using an Age-Group and Eccentricity Matched Normative OCT Angiography Database

PURPOSE

We evaluate the impact of age and signal strength index (SSI) on foveal avascular zone (FAZ) metrics and parafoveal capillary density measured using optical coherence tomography angiography (OCT-A), and propose a deviation mapping approach that accounts for age-group, SSI, eccentricity, and variation in FAZ size.

METHODS

Parafoveal OCT-A with full vascular layer was obtained for 261 controls and four patients with retinal abnormalities. Parafoveal capillary densities were measured within eight consecutive 200-μm wide annuli from the FAZ border. In controls, the impacts of age and SSI on FAZ metrics and parafoveal capillary density were evaluated. Deviation maps highlighting regions with density at the lower and upper tails of the age-group and eccentricity matched distribution were generated.

RESULTS

Linear regressions showed significant correlations between age, SSI, and mean parafoveal capillary density. There was a significant difference in FAZ metrics and parafoveal capillary densities with different age groups after controlling for SSI using univariate analysis. However, the effect of age on parafoveal capillary density disappeared after controlling for SSI using multivariate linear regression analysis. Our deviation mapping approach was able to identify regions with abnormal density in four patients.

CONCLUSIONS

Our findings suggest that the relationship between parafoveal capillary density and age is confounded by SSI. Parafoveal capillary density is SSI- and eccentricity-dependent. An age-group and eccentricity matched normative database was used as the basis for a parafoveal capillary density deviation mapping technique, providing an intuitive way to assess the status of parafoveal capillary density in individual eyes.

TRANSLATIONAL RELEVANCE

Understanding the impact of age and SSI on parafoveal capillary density is critical for providing accurate interpretation of OCT-A. We demonstrate an age-group and eccentricity matched deviation mapping technique for an intuitive assessment of retinal regions with abnormal density.

Reproducibility of macular and optic nerve head vessel density measurements by swept-source optical coherence tomography angiography

PURPOSE

To assess the reproducibility of swept-source optical coherence tomography angiography (SS-OCTA) for macular and optic nerve head (ONH) vessel density (VD).

METHODS

Cross-sectional study using the Triton OCTA (Topcon, Tokyo, Japan), for VD (%) measurements in 40 eyes of 40 healthy subjects on two 6 × 6 mm scans of the macula and ONH across five subfields (central, superior, inferior, temporal, and nasal) at different segmentation levels: superficial capillary plexus (SCP), deep capillary plexus (DCP), outer retina, and choriocapillaris. Reproducibility values were summarized as intraclass correlation coefficients (ICCs) and coefficients of variations (CV).

RESULTS

ICCs for the macular VD measurements in the central zone were 0.874, 0.770, 0.575, 0.718 at the levels SCP, DCP, outer retina, and choriocapillaris, respectively, while worse ICCs were obtained for the parafoveal subfields (ICC ⩽ 0.589); CVs were 2.8%-6.7%. The reproducibility of the ONH superficial VD was ICC = 0.941 for the papillary region and was ICC = 0.499-0.853 for the peripapillary zone; CVs ranged from 4.8% to 17%. Peripapillary VD showed an ICC = 0.533-0.770 in the DCP layer, and 0.572-0.828 in the choriocapillaris. Lowest VD were obtained for the macular SCP and DCP (23% and 22%, respectively), in the foveal zone, while greatest VD were recorded in the nasal and temporal peripapillary subfields at the level of the choriocapillaris (both 68%).

CONCLUSIONS

The new SS-OCTA software served to quantify macular and ONH VD with a reproducibility that was good in the central zones (foveal and papillary, respectively) and moderate in the peripheral zones (parafoveal and peripapillary).

The Utility of Frame Averaging for Automated Algorithms in Analyzing Retinal Vascular Biomarkers in AngioVue OCTA

Purpose

This study proposes an optical coherence tomography angiography (OCTA) frame-averaging method and investigates the effects of the number of frames acquired and averaged on metrics quantifying the foveal avascular zone (FAZ), vessel morphology, and parafoveal intercapillary area (PICA).

Methods

Ten OCTA frames were acquired for each of the 19 subjects without known retinal disease using the AngioVue OCTA system. For each subject, acquired frames were ranked by an image quality metric. A subset of frames was then registered and averaged. The effects of the number of frames acquired and averaged on FAZ segmentation and metrics of FAZ geometry, vessel morphology, and PICA were analyzed.

Results

Frame averaging increased the accuracy of the automatically segmented FAZ region; for example, the absolute error in FAZ area decreased from 0.026 mm² (1 frame) to 0.005 mm² (5 frames). Averaging multiple frames exponentially decreased the estimated number of vessel endpoints and increased the average vessel length with a 32% decrease in number of endpoints and 14% increase in average vessel length when averaging five frames compared with one. Frame averaging also improved the precision of PICA estimates.

Conclusions

Averaging multiple OCTA frames using the Optovue AngioVue system reduced error in FAZ segmentation and improved the robustness of OCTA vessel morphology and perfusion metrics. The study demonstrated limited benefit in acquiring and averaging more than five frames.

Translational Relevance

Averaging multiple OCTA frames improved the robustness of OCTA foveal biomarkers with limited benefit when averaging more than five frames.