EFFECT OF AXIAL LENGTH ON PERIPAPILLARY RETINAL NERVE FIBRE LAYER THICKNESS MEASURED BY SPECTRAL DOMAIN OPTICAL COHERENCE TOMOGRAPHY

Retinal Nerve Fibres & Spectral Domain Optical Coherence Tomography

Abstract

Objective: To determine the relationship between mean axial length and mean peripapillary retinal nerve fibre layer (RNFL) thickness using spectral domain optical coherence tomography (SD OCT) in healthy subjects.
Study Design: Cross sectional study.
Place and Duration of Study: Armed Forces Institute of Ophthalmology (AFIO) Rawalpindi, from Dec 2014 to Aug 2015.
Material and Methods: Data of 300 eyes of 300 healthy volunteers were collected at AFIO from December 2014 to August 2015 and analysed. Axial length and RNFL thickness of each volunteer was calculated using laser interferometer (IOL master) and SD OCT respectively. Eyes were divided in three groups based on axial length. Statistical analysis of the data were done using SPSS version 17.0.
Results: Mean age of study population was 23.16 ± 3.73 years. Mean axial length was 24.40 ± 1.50 millimetres (mm). Mean of average peripapillary RNFL thickness was 128.87 ± 9.94 micrometres (μm). Mean peripapillary RNFL thickness of superior, inferior, nasal and temporal quadrant was 158.27 ± 11.04 μm, 152.92 ± 14.54 μm, 103.85 ± 5.01 μm and 100.45 ± 11.59 μm respectively. Mean RNFL thickness, as well as RNFL thicknesses of each quadrant was also significantly different between hypermetropic, emmetropic and myopic eyes (p-value<0.001). There was also a strong negative correlation between axial length and peripapillary retinal nerve fibre layer thickness (r= -0.964, p-value<0.001).
Conclusion: Variation in axial length significantly affects the measurement of RNFL thickness and must be counted for, while diagnosing glaucoma on basis of thinning of RNFL.