Retinal nerve fiber layer measurements in myopia using optical coherence tomography

ABSTRACT

@#<p style="text-align justify;"><strong>OBJECTIVE:</strong> To evaluate the relationship between retinal nerve fiber layer (RNFL) thickness measured by optical coherence tomography (OCT) and the degree of myopia.<br /><strong>METHODS:</strong> A total of 28 eyes of 14 healthy subjects with myopia, 9 eyes with low myopia (spherical equivalent [SE] between -0.75 D and -3.00 D) and 19 eyes with moderate to high myopia (SE >-3.0 D), were included. Total average<br />and mean quadrant RNFL thicknesses were measured by Stratus OCT. Associations between RNFL measurements and spherical equivalent refraction were evaluated by linear regression analysis.<br /><strong>RESULTS:</strong> Twenty two out of 28 eyes were classified as below normal limits with reference to the normative database of the RNFL thickness. There was a significant correlation between refraction and average RNFL thickness (p=0.04), indicating that for every decrease of 1.00 D in refraction (more myopic), there was a 2.86 µm decrease in the average RNFL thickness. The most frequently abnormal sector was at the nasal quadrant, where 78% of myopic eyes were below normal limits. A significant correlation was seen between refraction and nasal RNFL thickness (p=0.02), showing a decrease of 3.37 µm in the nasal RNFL thickness for every 1.00 D decrease. There was also a significant correlation between refraction and inferior RNFL thickness (p=0.007). For every decrease of 1.00 D in refraction, there was a decrease of 6.27 µm in the inferior RNFL thickness. There were no significant correlations between the refraction and the superior and temporal RNFL thickness (p = 0.12 and 0.64, respectively).<br /><strong>CONCLUSION:</strong> There was a decrease in the average RNFL thickness as the refractive error became more myopic, suggesting the need for the Stratus OCT RNFL normative database to have corrective factors for refractive error among myopic patients. Although both the nasal and inferior quadrants positively correlated with myopia, majority of the nasal quadrant showed below normal thickness based on the Stratus OCT normative database. A careful interpretation of RNFL measurements, especially the nasal quadrant, should be done among myopic subjects to avoid mislabeling them as glaucoma suspects.</p>