Effect of Refractive Correction Error on Retinal Nerve Fiber Layer Thickness: A Spectralis Optical Coherence Tomography Study

BACKGROUND Identifying and assessing retinal nerve fiber layer defects are important for diagnosing and managing glaucoma. We aimed to investigate the effect of refractive correction error on retinal nerve fiber layer (RNFL) thickness measured with Spectralis spectral-domain optical coherence tomography (SD-OCT). MATERIAL AND METHODS We included 68 participants: 32 healthy (normal) and 36 glaucoma patients. RNFL thickness was measured using Spectralis SD-OCT circular scan. Measurements were made with a refractive correction of the spherical equivalent (SE), the SE+2.00D and the SE-2.00D. RESULTS Average RNFL thickness was significantly higher in the normal group (105.88±10.47 μm) than in the glaucoma group (67.67±17.27 μm, P<0.001). In the normal group, +2.00D of refractive correction error significantly affected measurements of average (P<0.001) and inferior quadrant (P=0.037) RNFL thickness. In the glaucoma group, +2.00D of refractive correction error significantly increased average (P<0.001) and individual quadrant (superior: P=0.016; temporal: P=0.004; inferior: P=0.008; nasal: P=0.003) RNFL measurements compared with those made with the proper refractive correction. However, -2.00D of refractive correction error did not significantly affect RNFL thickness measurements in either group. CONCLUSIONS Positive defocus error significantly affects RNFL thickness measurements made by the Spectralis SD-OCT. Negative defocus error did not affect RNFL measurement examined. Careful correction of refractive error is necessary to obtain accurate baseline and follow-up RNFL thickness measurements in healthy and glaucomatous eyes.