Abstract
Purpose :
Myopia is a major cause of visual impairment worldwide, and myopic eyes are known to be larger with more irregular shape. Here, the relationship between axial length (AL) and retinal shape was investigated using optical coherence tomography (OCT).
Methods :
Participants were recruited from ophthalmology clinics in South Australia. Macula and extra-macula OCTs were taken of 54 eyes with AL 21.11-33.48 mm (median 24.71 mm). The images were classified into 17 regions, consisting of inner and outer regions in 8 directions around a central macular region. Retinal shape in each B scan was represented by the retinal pigment epithelial line, from which the best fit quadratic curve was subtracted and defined by its vertex curvature (Κ). From Fourier transformation of the difference between the best-fit curve and retinal shape, the sum of the 30 lowest frequency moduli was compared with an average normal scan (sumdiff) via 5-fold cross-validation.
Results :
For all scans, median sumdiff was 2.20 mm2 (range 0.61-48.34 mm2), and median Κ was 0.03 mm-1(range -1.56-2.10 mm-1). After Bonferroni-Holm correction, Spearman’s rank correlation found positive correlation between eye median sumdiff and AL (range 1.82-10.66 mm2, ρ= 0.67, p < 0.005), and no correlation between eye median Κ and AL (range 0.00-0.07 mm-1, ρ = 0.15, p = 0.25). Eye interquartile range (IQR) sumdiff (range 0.55-9.77 mm2) and IQR Κ (range 0.01-0.33 mm-1) both correlated with AL (ρ = 0.57, p < 0.005, and ρ = 0.68, p < 0.005 respectively). These remain significant after correcting Κ for axial length induced error. Increased IQR Κ without increased median Κ in myopia was from a wider distribution of B scan retinal curvatures in larger eyes, including convex inward retina (negative Κ) at the edge of staphylomata.
Within individual regions, the correlation between sumdiff and AL was significant at the macula, immediately above and below the macula, and supero-nasally. IQR Κ correlated with AL in 8 of 17 regions, including at and temporal to the macula, and most nasal regions.
Conclusions :
Both local retinal shape variation and range of curvature increased with axial length. The increased shape variation in myopic eyes at and near the posterior pole is a quantified representation of staphyloma shape. OCT shape analysis gives accurate, high resolution information about local retinal shape. This method enables the study of links between regional shape and retinal disease.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.