Prospective Cross-Sectional Study of Repeatability of Peripapillary Capillary Density Measurement Using Optical Coherence Tomography Angiography in Eyes With Optic Nerve and Retinal Vascular Pathology

Peripapillary and macular microvasculature features of non-arteritic anterior ischemic optic neuropathy

Purpose

The hallmark of non-arteritic anterior ischemic optic neuropathy (NAION) is vascular compromise to the anterior optic nerve and thinning of the retinal nerve fiber layer (RNFL) and secondary degeneration of the retinal ganglion cell body or thinning of the ganglion cell complex (GCC). This study investigates optical coherence tomography (OCT) and OCT Angiography (OCTA) changes in chronic NAION and identifies imaging biomarkers that best predict disease.

Methods

We performed a retrospective case-control study of 24 chronic NAION eyes (18 patients) and 70 control eyes (45 patients) to compare both whole-eye and regional OCT, OCTA, static perimetry measurements. OCT measurements were quantified automatically using commercial software, and OCTA was analyzed using custom MATLAB script with large vessel removal to measure 154 total parameters per eye.

Results

We confirmed that static perimetry mean deviation (MD) was significantly worse in chronic NAION (-13.53 ± 2.36) than control (-0.47 ± 0.72; P < 0.001) eyes, and NAION eyes had 31 μm thinner RNFL (control: 95.9 ± 25.8 μm; NAION: 64.5 ± 18.0, P < 0.001), and 21.8 μm thinner GCC compared with controls (control: 81.5 ± 4.4 μm; NAION: 59.7 ± 10.5, P < 0.001). Spearman correlation analysis of OCTA parameters reveal that vessel area density (VAD) and flux are highly correlated with visual field MD and OCT measurements. Hierarchical clustering two distinct groups (NAION and control), where standardized measurements of NAION eyes were generally lower than controls. Two-way mixed ANOVAs showed significant interaction between patient status (control and chronic NAION) and structure (optic disk and macula) for annulus VAD and flux values and mean RNFL and GCC thickness. Post-hoc tests showed this effect stems from lower peripapillary values in NAION compared to controls. Separate logistic regression models with LASSO regularization identified VAD and flux are one of the best OCTA parameters for predicting NAION.

Conclusion

Ischemic insult to the optic disk is more severe likely from primary degeneration of the affected peripapillary region while macula is affected by secondary retrograde degeneration and loss of retinal ganglion cells. In addition to OCT measurements, peripapillary and macular vascular parameters such as VAD and flux are good predictors of optic nerve and retinal changes in NAION.

Effect of Optic Disc Tilt on the Measurement of Peripapillary Vessel Density Using Optical Coherence Tomography Angiography

PRECIS

Eyes with tilted disc had significantly lower peripapillary vessel density (pVD) and lower long-term measurement reproducibility in OCTA. After adjusting for confounding factors, disc tilt still contributed to the reduction of pVD in most sectors.

PURPOSE

To investigate the effect of optic disc tilt on the measurement of sectoral peripapillary vessel density (pVD) by optical coherence tomography angiography (OCTA) and on the long-term measurement reproducibility.

METHODS

This retrospective observational case control study included 70 healthy eyes. Average and eight-sector pVDs and peripapillary retinal nerve fiber layer (pRNFL) thicknesses were obtained from OCTA at two visits at 1-year intervals. The disc tilt was quantified by ovality ratio (the longest/shortest disc diameter) on fundus photography, with a tilted disc (TD) defined as an ovality ratio ≥1.3. pVD and pRNFL thickness of each sector were compared in the TD and non-tilted disc (NTD) groups. Long-term reproducibility was assessed by the intraclass correlation coefficients (ICC) for both groups. Factors associated with pVD were evaluated by uni- and multivariable linear regression analyses.

RESULTS

Thirty-five eyes each had TD and NTD. Average pVD was lower in the TD than in the NTD group (47.0±3.5% vs. 51.7±2.8%, P<0.001), as were pVDs in all eight sectors. The long-term reproducibilities of average and sectoral pVD measurements were lower in the TD (ICC 0.46-0.83) than in the NTD (ICC 0.67-0.96) group. Disc tilt was significantly associated with pVD in average and all sectors except for nasal inferior sector after adjusting for axial length, pRNFL thickness, and signal strength index of OCTA image.

CONCLUSION

OCTA measured pVD and the long-term reproducibility were lower in eyes with TD than NTD. These findings should be considered when interpreting OCTA measured pVD.

Performance Assessment of Two Different Approaches of Measuring Skeletonized Radial Peripapillary Capillary Vessel Density in Glaucoma Patients

Objective

To compare performance assessment of two methods of measuring radial peripapillary capillary (RPC) vessel density (VD) after skeletonization using MATLAB and Image J in glaucoma clinical setting.

Methods

Seventy-three eyes of 73 glaucoma patients from Beijing Tongren Hospital were included in this prospective study. Original images of RPC were obtained using optical coherence tomography angiography. Two approaches were executed before measuring. Method 1 (M1) required image sharpening, removal of big vessels, and skeletonization. Method 2 (M2) required skeletonization and removal of major vessels. Each method was executed twice. Repeatability and correlations with glaucomatous parameters were assessed. Factors associated with retinal nerve fiber layer thickness (RNFLT) and visual field mean deviation (MD) were analyzed.

Results

Average VD was 13.86 ± 2.73 and 7.50 ± 2.50% measured by M1 and M2. Percentage of total elimination of the major vessels was 36.99 and 100% by M1 and M2, respectively. The intrasession and intersession reproducibility was higher by M2 (ICC = 0.979, ICC = 0.990) than by M1 (ICC = 0.930, ICC = 0.934). VD measured by M2 showed stronger correlations with glaucomatous parameters than by M1. By stepwise multiple linear regression, thinner RNFLT was associated with smaller VD measured by M2 (B = 4.643, P < 0.001). Worse MD was associated with smaller VD measured by M1 (B = 1.079, P = 0.015).

Conclusion

The VD measured by M2 showed better reproducibility and higher correlation with glaucomatous structural parameters. Image sharpning helps display of hazy vasculature in glaucoma, which may reflect visual function better. Researchers should carefully choose image processing methods according to their research object.