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.