Additive Role of Optical Coherence Tomography Angiography Vessel Density Measurements in Glaucoma Diagnoses

Optical coherence tomography angiography in glaucoma

The use of optical coherence tomography angiography (OCTA) holds significant promise for optometrists in the diagnosis and management of glaucoma. It offers reliable differentiation of glaucomatous eyes from healthy ones and extends monitoring capabilities for advanced cases. OCTA represents a valuable addition to traditional assessment methods, particularly in complex cases. Glaucoma, a major cause of irreversible blindness, is traditionally diagnosed using structural and functional metrics. With growing interest, OCTA is being explored to diagnose, monitor, and manage glaucoma. This review focuses on the application of OCTA in glaucoma patients. A database search was carried out using Embase Elsevier (n = 664), PubMed (n = 574), and Cochrane Central Register of Controlled Trials (n = 19) on 15 August 2023. After deduplication and screening, 272 original papers were included in the narrative review. Inclusion criteria comprised English-language original studies on OCTA use in human glaucoma patients, with or without healthy controls. Exclusion criteria encompassed animal studies, in-vivo/in-vitro research, reviews, and congress abstracts. OCTA has good repeatability and reproducibility. OCTA metrics have good discriminatory power to differentiate glaucomatous eyes from healthy eyes and show strong associations with structural changes and visual field defects. OCTA can extend the monitoring of advanced glaucoma, addressing the 'floor effect' of traditional structural measurements. OCTA metrics can be affected by the choice of OCTA machine, post-image processing algorithms, systemic diseases, and ocular factors. Image artefacts can affect the accuracy of OCTA measurements, and proper scan quality evaluation is crucial to ensure reliable results. Additionally, artificial intelligence techniques offer promise for enhancing the diagnostic accuracy of OCTA by combining data from various retinal layers and regions. OCTA complements traditional methods in assessing glaucoma, especially in challenging cases, providing valuable insights for detection and management. Further research and clinical validation are needed to integrate OCTA into routine practice.

Comparison of the Effect on Vessel Density and RNFL between Carteolol and Latanoprost

The aim of the study was to compare the treatment of hypertensive glaucoma (HTG) in the early stages with carteolol and latanoprost by assessing the change in vessel density (VD) and retinal nerve fibre layer (RNFL). Methods: The first group with diagnosed HTG consisted of 46 eyes treated with carteolol; the second group consisted of 52 eyes treated with latanoprost. The following examinations were evaluated in all patients: intraocular pressure (IOP), retinal nerve fibre layer (RNFL), vessel density (VD) and visual field examination (glaucoma fast threshold test). The results were compared before treatment and 3 months after treatment. Results: There was no difference in the overall visual field defect (OD) between groups before treatment. After treatment, there was a decrease in IOP in both groups (carteolol-treated group had a mean decrease of 5.8 mmHg and latanoprost-treated eyes had a mean decrease of 7 mmHg). This difference was not statistically significant (p = 0.133). No similar difference was observed for RNFL (p = 0.161). In contrast, the change in the VD parameter was statistically significant between groups (p < 0.05), with a greater difference observed in the carteolol-treated group of eyes. Carteolol had a better effect on the VD.

Comparison of Retinal Nerve Fiber Layer and Ganglion Cell-Inner Plexiform Layer Thickness Values Using Spectral-Domain and Swept-Source OCT

Purpose

To compare peripapillary retinal nerve fiber layer (pRNFL) and macular ganglion cell-inner plexiform layer (mGCIPL) thickness measurements obtained with spectral domain optical coherence tomography (SD-OCT) and swept-source OCT (SS-OCT) using an OCT-angiography scanning protocol, and their ability to distinguish among patients with glaucoma, glaucoma suspects (GS), and healthy controls (HC).

Methods

Cross-sectional study of 196 eyes (81 glaucoma, 48 GS, and 67 HC) of 119 participants. Participants underwent peripapillary and macular OCT with SD-OCT and SS-OCT. Parameters of interest were average and sector-wise pRNFL and mGCIPL thickness. Inter-device agreement was investigated with Bland-Altman statistics. Conversion formulas were developed with linear regression. Diagnostic performances were evaluated with area under the receiver operating characteristic curves.

Results

Both SD-OCT and SS-OCT detected a significant pRNFL and mGCIPL thinning in glaucoma patients compared to HC and GS for almost all study sectors. A strong linear relationship between the two devices was present for all quadrants/sectors (R2 ≥ 0.81, P < 0.001), except for the nasal (R2 = 0.49, P < 0.001) and temporal (R2 = 0.62, P < 0.001) pRNFL quadrants. SD-OCT and SS-OCT measurements had a proportional bias, which could be removed with conversion formulas. Overall, the two devices showed similar diagnostic abilities.

Conclusions

Thickness values obtained with SD-OCT and SS-OCT are not directly interchangeable but potentially interconvertible. Both devices have a similar ability to discriminate glaucoma patients from GS and healthy subjects.

Translational Relevance

OCT-Angiography scans can be reliably used to obtain structural metrics in glaucoma patients.

Wedge Defects on Optical Coherence Tomography Angiography of the Peripapillary Retina in Glaucoma: Prevalence and Associated Clinical Factors

PRCIS

Among subjects with glaucoma, wedge-shaped defects on optical coherence tomography angiography (OCTA) were associated with disc hemorrhages (DH), paracentral visual field (VF) defects, increased cup-to-disc ratio (CDR), and thinner retinal nerve fiber layer (RNFL).

PURPOSE

To examine determinants of wedge defects on peripapillary OCTA in glaucoma.

MATERIALS AND METHODS

A total of 278 eyes of 186 subjects with mild to severe primary open-angle glaucoma underwent 6×6 spectral-domain OCTA imaging of the superficial peripapillary retina from 2016 to 2020 at an academic practice. Wedge defects were defined as focal microvasculature loss that extends outward from the optic nerve in an arcuate, wedge shape. Logistic regression models controlling for intereye correlation identified variables significantly associated with wedge defects. Eyes with profound microvasculature loss in both hemispheres were excluded. Candidate variables included: age, sex, race or ethnicity, diabetes, hypertension, follow-up duration, baseline untreated intraocular pressure, intraocular pressure at time of imaging, DH history, paracentral VF defects, CDR, central corneal thickness, spherical equivalent, VF mean deviation, RNFL thickness, and glaucoma stage.

RESULTS

Of 278 eyes, 126 (45.3%) had wedge defects in at least 1 hemisphere. In our multivariable logistic regression model, wedge defects were associated with DH history [odds ratio (OR): 3.19, 95% confidence interval (CI): 1.05-9.69, P=0.041], paracentral VF defects [OR: 4.38 (95% CI: 2.11-9.11), P<0.0001], larger CDR [OR: 1.27 (95% CI: 1.03-1.56), P=0.024, per 0.1 increase], and thinner RNFL [OR: 1.71 (95% CI: 1.25-2.34), P=0.0009, per 10 μm decrease].

CONCLUSION

DH history and paracentral VF defects were independently associated with wedge defects on OCTA, which was present in 45.3% of primary open-angle glaucoma patients. These findings may provide insight into glaucoma pathogenesis.

Combining Structural and Vascular Parameters to Discriminate Among Glaucoma Patients, Glaucoma Suspects, and Healthy Subjects

Purpose

Compare the ability of peripapillary and macular structural parameters, vascular parameters, and their integration to discriminate among glaucoma, suspected glaucoma (GS), and healthy controls (HCs).

Methods

In this study, 196 eyes of 119 patients with glaucoma (n = 81), patients with GS (n = 48), and HCs (n = 67) underwent optical coherence tomography (OCT) and OCT angiography to measure peripapillary retinal nerve fiber layer (pRNFL), macular ganglion cell-inner plexiform layer (mGCIPL) thicknesses, radial peripapillary capillary perfusion density (RPC-PD), and macular GCIPL perfusion density (GCIPL-PD). Parameters were integrated regionally with logistic regression and globally with machine learning algorithms. Diagnostic performances were evaluated with area under the receiver operating characteristic (AUROC) curves.

Results

Patients with glaucoma had mild to moderate damage (median, -3.3 dB; interquartile range, -6.5 to -1.4). In discriminating between patients with glaucoma and the HCs, pRNFL thickness had higher AUROC curve values than RPC-PD for average (0.87 vs. 0.62; P < 0.001), superior (0.86 vs. 0.54; P < 0.001), inferior (0.90 vs. 0.71; P < 0.001), and temporal (0.65 vs. 0.51; P = 0.02) quadrants. mGCIPL thickness had higher AUROC curve values than GCIPL-PD for average (0.84 vs. 0.68; P < 0.001), superotemporal (0.76 vs. 0.65; P = 0.016), superior (0.72 vs. 0.57; P = 0.004), superonasal (0.70 vs. 0.56; P = 0.01), inferotemporal (0.90 vs. 0.72; P < 0.001), inferior (0.87 vs. 0.69; P < 0.001), and inferonasal (0.78 vs. 0.65, P = 0.012) sectors. All structural multisector indices had higher diagnostic ability than vascular ones (P < 0.001). Combined structural-vascular indices did not outperform structural indices. Similar results were found to discriminate glaucoma from GS.

Conclusions

Combining structural and vascular parameters in a structural-vascular index does not improve diagnostic ability over structural parameters alone.

Translational Relevance

OCT angiography does not add additional benefit to structural OCT in early to moderate glaucoma diagnosis.

Analysis of the perfusion of the optic nerve using angio-OCT in glaucoma

The introduction of optical coherence tomography angiography (OCT-A) has generated interest in evaluating vascular dysfunctions in the optic nerve head for the diagnosis and monitoring of glaucoma. The purpose of this study is to compare perfusion of the optic disc between normal subjects and subjects with glaucoma using OCT-A in order to detect changes in perfusion of the optic disc. Using the OCT-A AngioVue® system, an examination was performed on 40 eyes of 40 patients (20 with glaucoma and 20 healthy controls). Total radial peripapillary flow density (4.5×4.5mm) was measured at different levels of segmentation. The study demonstrated that the peripapillary vascular flow of OCT-A and exploration of the optic nerve head was better in the normal eyes compared to glaucoma patients. This review provides a comprehensive summary of the most important current and potential applications of OCT-A in glaucoma.

Clinical Utility of Triplicate En Face Image Averaging for Optical Coherence Tomography Angiography in Glaucoma and Glaucoma Suspects

PRéCIS:: Averaging triplicate en face angiograms of the radial peripapillary capillary (RPC) plexus with optical coherence tomography angiography (OCTA) improves vessel visualization, reduces vessel density parameters, and increases the diagnostic accuracy for glaucoma of one such parameter.

PURPOSE

The purpose of this study was to test the hypothesis that triplicate averaging of the RPC layer improves visualization and diagnostic accuracy of OCTA for glaucoma.

MATERIALS AND METHODS

This is a cross-sectional study involving 63 primary open-angle glaucoma patients and 70 age-matched glaucoma suspects. Triplicate 6×6 mm OCTA scans of the optic nerve head were acquired, and the RPC layer was extracted. RPC en face images were registered and averaged. Parameters of global entropy, global standard deviation, local texture correlation, local homogeneity, signal-to-noise ratio, and intercapillary distance were used to measure the change in visualization with averaging. Vessel area density (VAD), vessel skeleton density (VSD), and flux parameters were calculated in a 2.8 mm annulus excluding the optic disc. The diagnostic accuracy of these parameters for glaucoma was assessed by calculating the area under the receiver operating curve (AUC) values.

RESULTS

Three-frame averaging resulted in decreased global entropy and global standard deviation (Ps<0.001), and increased local texture correlation, local homogeneity, signal-to-noise ratio, and intercapillary distance (Ps<0.001). Averaged images also had reduced VAD, VSD, and flux (Ps<0.001). AUC was significantly increased for VSD after image averaging (P=0.018), while no significant change in AUC was observed for VAD (P=0.229) or flux (P=0.193).

CONCLUSIONS

Triplicate averaging improves visualization of the RPC layer and the diagnostic accuracy of VSD for glaucoma. The impact of image averaging on OCTA diagnostic performance and other potential applications warrants further exploration.

Signal Strength as an Important Factor in the Analysis of Peripapillary Microvascular Density Using Optical Coherence Tomography Angiography

The quality of the scan image is important in peripapillary circulation analysis using optical coherence tomography angiography (OCTA). We aimed to investigate the effects of signal strength (SS) on the peripapillary microvascular density acquired from OCTA. A total of 259 eyes from 259 young healthy subjects were included. Peripapillary OCTA images using 3 × 3 mm angiography scan were acquired from all participants. Subjects were divided into four groups according to the SS: SS 7, SS 8, SS 9, and SS 10. Vessel density (VD) and perfusion density (PD) of the superficial capillary plexus were calculated. VD and PD were compared among the four groups, and linear regression analyses were performed to identify and evaluate the clinical factors associated with average VD. As the SS increased from 7 to 10, the average VD and PD increased; these increases were statistically significant (all, p < 0.001). Regression analyses showed that four factors were significantly correlated with average VD: age (partial r = 0.133), average retinal nerve fiber layer thickness (partial r = 0.169), cup/disc ratio (partial r =-0.481), and SS (partial r = 0.413). SS is a significant factor affecting peripapillary microvascular density, and its influence is similar to well-known structural parameters associated with glaucoma.