Retinal Nerve Fiber Layer Measurements in Myopes as Determined by Optical Coherence Tomography

Abstract

BACKGROUND Myopia is a common cause of visual disability throughout the world. One of the potentially blinding ocular diseases associated with myopia is glaucoma. Due to similar features of the optic disc in glaucoma and myopia, there may be a misdiagnosis of glaucoma in these individuals. Decrease in retinal nerve fiber layer (RNFL) thickness as measured by optical coherence tomography (OCT) is a sensitive indicator of early glaucomatous damage. However, it remains unclear if RNFL thickness varies with refractive status of the eye. We wanted to compare retinal nerve fiber layer thickness in low, moderate and high myopia patients and study the association between retinal nerve fiber layer thickness, axial length and myopic spherical equivalent. METHODS A total of 150 eyes of 150 subjects with varying degree of myopia presenting to the Department of Ophthalmology, Christian Medical College and Hospital, Ludhiana were included in the study group. Comprehensive ophthalmic examination was performed which included visual acuity, refraction by autorefractometer, axial length by NIDEK AL-SCAN and retinal nerve fiber layer thickness by optical coherence tomography (NIDEK RS 3000 LITE). RESULTS The average (360°) RNFL thickness was significantly lower in the high myopia group as compared to the low and moderate myopia groups (p < 0.0001). On quadrant wise analysis, the RNFL was thicker in the low myopia group than in the moderate and high myopia groups in the superior, nasal and inferior quadrants (p < 0.0001, p<0.0001 and p-0.0002 respectively). However, the RNFL thickness in the temporal quadrant was comparable in the three groups (p = 0.768). CONCLUSIONS Retinal nerve fiber layer thickness decreases as the spherical equivalent and axial length increases. Therefore, this profile should be taken into consideration while analysing RNFL thickness for glaucoma evaluation in subjects with highly myopia.