The correlation between optical coherence tomography retinal shape irregularity and axial length

Purpose: To describe the retinal contour in optical coherence tomography (OCT) images, and report the relationship between retinal contour and axial length. Methods: Retinal contour was defined by the path of the retinal pigment epithelial (RPE) line in macular and extra-macular OCTs of 70 eyes of 70 participants recruited from ophthalmology clinics in South Australia. The shape of this contour was described by the best-fit curvature (K), and Fourier analysis of the difference between K and the RPE. The Fourier transformation was summarised by total difference (sumdiff), maximum single frequency difference (MaxE), and root mean square difference (rmse) between each B scan residual and the average normal. All-of-eye and regional median and interquartile range (IQR) shape features were correlated to axial length. Results: Retinal shape irregularity measured by Fourier transformation correlated with axial length: all-of-eye median and IQR sumdiff (ρ = 0.66 and ρ = 0.60 respectively), median and IQR rmse (ρ = 0.67 and ρ = 0.48), median MaxE (ρ = 0.61), and IQR K (ρ = 0.61) all correlated with axial length. Correlation with axial length was also seen in these parameters for 11 of 17 regions. Retinal irregularity was greatest at the macula and in inferior regions. Conclusion: Retinal OCT shape becomes increasingly irregular as axial length increases. The range of curvature correlates with axial length, while median curvature does not.