An observational study of the correlation between axial length and retinal nerve fibre layer thickness in myopic eyes in a tertiary care centre in south india

Abstract

Objective: To assess the correlation between axial length and retinal nerve fibre layer (RNFL) thickness in myopic eyes in a tertiary care hospital in a two-year period (August 2017 to June 2019). Methods: Institutional ethics committee approval was obtained. Written and informed consent was obtained from all the participants. One hundred eyes of 58 patients were screened. Myopic patients with > -0.50 D myopia in the age group of 18 to 40 years with intraocular pressure (IOP) <20 mm Hg were included in the study. Patients with a history of ocular trauma, glaucoma, ocular surgeries, optic nerve or macular diseases, pathological myopia, and media opacities were excluded from the study. An ophthalmic evaluation was done by assessing the visual acuity, IOP, slit-lamp examination, and perimetry using Humphrey field analyser II (Swedish interactive threshold algorithm SITATM testing strategy). After dilating the pupils with Tropicamide plus, posterior segment evaluation was done using a 90 D lens with slit lamp bio-microscopy as well as indirect ophthalmoscopy and 20 D lens. The axial length was measured using Lenstar LS 900. Optical Coherence Tomography (OCT) images were obtained using a 3 D OCT 1 Maestro machine by a single observer. Results: There was a statistically significant association between axial length and RNFL thickness in myopic eyes (P = 0.0003). As the axial length of the eyeball increases, the RNFL thickness decreases in all four quadrants except the temporal quadrant, producing a statistically significant negative correlation (r = -0.3551). Conclusion: There is a statistically significant association between axial length and RNFL thicknesses in all quadrants except the temporal quadrant. The negative correlation between axial length and RNFL thickness would be useful in avoiding misdiagnosis of glaucoma since RNFL thickness is low in both glaucoma and myopia.