The effect of axial length to basement-membrane opening to fovea distance on optical coherence tomography.

Background: Optical Coherence Tomography (OCT) lateral scaling is influenced by axial length (AL). There is a need to incorporate a method to correct this measurement bias for accurate lateral OCT measurement.

Purpose: To identify the correlation of optic-nerve-to-fovea distance measurement to AL by OCT) as an internal factor for lateral scaling.

Methods: Using Heidelberg Spectralis OCT, distance from the basement membrane opening at the optic disc margin to the centre of the fovea (BMO-fovea distance) was measured in 135 eyes (77 subjects, ages 25-85). These measurements were correlated with AL measurements from Zeiss IOLMaster 700 using linear regression before and after correction for ocular magnification. Statistical analysis including Shapiro-Wilk test for normality, Pearson correlation, and multivariate analysis of the association between disc-fovea distance and AL was performed using Wizard statistical software for mac.

Results: After lateral scaling, the mean distance between the fovea and BMO was 3.60 ± 0.25 mm (median: 3.59; range 3.07-4.23 mm). There was a significant positive correlation between AL and Bennett's formula-corrected BMO-fovea distance (p <0.001, r = 0.354).

Conclusions: While there is significant variability in BMO-fovea distances, it is positively correlated with AL. A standard method is needed to improve the lateral scaling measurements in order to unify the results for enface OCT imaging.