Effects of Refractive Status and Axial Length of the Eye on Retinal Nerve Fibre Layer Thickness Measured by OCT

Abstract

<i>Background:</i> Retinal nerve fibre layer (RNFL) thickness is an important indicator in diagnosis and monitoring of optic disc diseases. RNFL thickness is affected by many factors such as race and age. Refractive errors are the most common ocular problem affecting all age groups, and affect ocular structures such as retina and optic nerve. Optical coherence tomography (OCT) is a non-invasive instrument that provides accurate measurements of RNFL thickness and detects early structural changes. This technique is safe, repeatable and quick. <i>Objective: </i> To evaluate the influence of refractive status and axial length of the eye on retinal nerve fibre layer (RNFL) thickness in emmetropics, myopics and hyperopics. <i>Materials and Methods:</i> It was a cross-sectional study, included 192 subjects (384 eyes) aged 18 to 30 years, who were divided into 3 main groups based on postcycloplegic spherical equivalent (SE), the subjects were also divided into groups based on their axial length (AXL). Retinal nerve fibre layer thickness was measured by OCT, axial length was measured by ultrasound A scan. <i>Results:</i> Thicknesses of Average RNFL, (Superior Temporal, Superior Nasal, Inferior Nasal, Nasal) sectors decreased with myopia and increased with hyperopia and this was statistically significant (p=0.0001), thicknesses also decreased with increasing of axial length and this was statistically significant (ST, SN, IN P-value =0.0001, N P-value =0.02, Avg. P-value =0.001). Thicknesses of (Temporal, Inferior Temporal) sectors decreased with hyperopia and increased with myopia and this was statistically significant (T P-value =0.0001, IT P-value=0.004), thicknesses also decreased with decreasing of axial length and this was statistically significant (T P-value=0.03, IT P-value= 0.001). <i>Conclusion:</i> Refractive status and axial length affect RNFL thickness, so they should be considered in mind before making any ocular diagnosis in which the RNFL is a diagnostic criteria.