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

Precis: Eyes with tilted disc (TD) had significantly lower peripapillary vessel density (pVD) and lower long-term measurement reproducibility in optical coherence tomography angiography (OCTA). After adjusting for confounding factors, disc tilt still contributed to the reduction of pVD in most sectors. Purpose: The purpose of this study was to investigate the effect of optic disc tilt on the measurement of sectoral pVD by OCTA and on the long-term measurement reproducibility. Materials and Methods: This retrospective observational case-control study included 70 healthy eyes. Average and 8-sector pVDs and peripapillary retinal nerve fiber layer (pRNFL) thicknesses were obtained from OCTA at 2 visits at 1-year intervals. The disc tilt was quantified by ovality ratio (the longest/shortest disc diameter) on fundus photography, with a TD defined as an ovality ratio >= 1.3. pVD and pRNFL thickness of each sector were compared in the TD and nontilted disc (NTD) groups. Long-term reproducibility was assessed by the intraclass correlation coefficients (ICCs) for both groups. Factors associated with pVD were evaluated by univariable 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 8 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.