Determining the Correlation between Axial Length and Macular Thickness in Myopia

Purpose: To correlate macular thickness in the different degrees of myopia caused by increased axial length using Optical Coherence Tomography (OCT). Patients and Methods: In this cross-sectional study. 40 myopic eyes of 20 cases, all above age eighteen, were selected from the outpatient clinic of Kasr El-Aini, Cairo University Hospital between September and December 2011. They were subdivided according to axial length into low (24-26.5mm) and high myopes (above 26.5mm). Axial lengths were determined by A-scan ultrasound (Sonomed® A-2500 A-Scan). Macular mapping was obtained by spectral domain OCT (RTVue-100) to determine thickness overall and in nine quadrants subdividing the macula. Exclusion criteria included prior ocular surgery, best corrected vision less than 6/36 (Snellen), any other ocular pathology or macular abnormality detected by OCT.Results: On assessment of the cases as one group there was a negative correlation between increasing axial length and overall average macular thickness (highly significant, p 0.01) and in all quadrants (significant), except in the fovea (no correlation found, p=0.4). The macular thickness was significantly less in high than low myopes except in the fovea (no correlation found, p=0.284). In the low myope group the thicknesses could not be correlated except in the parafoveal superior (p=0.026) and inferior quadrants (p=0.04). In the high myope groups, there were no correlations of statistical significance found in any quadrants.Conclusion: The average overall thickness of the macula showed significant negative correlation with the degree of myopia; even though it is less in high myopes than in low myopes except in the fovea.