Date Published: June , 2018
Publisher: Makerere Medical School
Author(s): Nishanee Rampersad, Rekha Hansraj.
Accurate and repeatable measurements of the retinal nerve fibre layer (RNFL) thickness are important in the diagnosis and management of glaucoma and other disorders.
To assess the repeatability and reproducibility of the iVue-100 optical coherence tomographer (OCT).
The thickness of the RNFL was measured for 50 healthy participants using the iVue-100 OCT. Although both eyes per participant were measured, only right eyes were analysed here. Repeatability and reproducibility of the iVue-100 OCT were assessed using the intraclass correlation coefficient (ICC), coefficient of variation (CoV), paired t-tests and Bland-Altman analysis.
Good intra-observer repeatability was obtained as indicated by the ICC of observer 1 (range: 0.941 – 0.976) and observer 2 (range: 0.829 – 0.953) as well by the CoV of observer 1 (range: 0.098 – 0.137) and observer 2 (0.091 – 0.132). In terms of inter-observer reproducibility, significant differences (p< 0.05) in mean measurements between the observers were noted for the average RNFL readings and in the superior and inferior quadrants as assessed with paired t-tests. Even though significant inter-session differences were found for the average RNFL thickness and the superior quadrant (p = 0.003 and p = 0.013, respectively), excellent ICCs were obtained for inter-session reproducibility (range: 0.914 – 0.979). The iVue-100 OCT demonstrated good repeatability and reproducibility for RNFL thickness measurements.
The retinal nerve fibre layer (RNFL) lies between the ganglion cell layer and inner limiting membrane of the retina.1 As it comprises of the axons of the ganglion cells, it is sometimes referred to as the axon layer. These axons transmit the chemical message from the retina to synapse at the lateral geniculate nucleus before reaching the occipital cortex. There is a varied but definite retinotopic arrangement of the nerve fibres as they (neural impulses) make their way through the visual pathway in preparation for impulses to be received optimally at the occipital cortex. The thickness of the RNFL on the optic nerve head is found to vary in the four quadrants (superior, inferior, nasal and temporal) being thickest in the inferior quadrant.1,2
Convenience sampling was used to recruit 50 participants, of all races, gender and ages in this observational cross-sectional study. The study followed the tenets of the Declaration of Helsinki and all participants were required to give written informed consent. Ethical approval was obtained from the Biomedical Research and Ethics committee (BE024/13) of the UKZN. All participants had normal corneal topography, visual acuity of at least 20/20 (aided or unaided) and no history of ocular injury and/or surgery.
The estimation of an instrument’s repeatability and reproducibility is of paramount importance19 particularly one that is being used for clinical and research applications. Accurate and reliable measurements of the RNFL thickness is necessary in both the diagnosis and management of retinal disorders particularly glaucoma and retinitis pigmentosa.4–6 Optical coherence tomography provides an accurate, non-invasive and rapid quantitative assessment of RNFL thickness.24 The iVue-100, a spectral domain OCT, has gained popularity in its usage in the clinical field, however it’s repeatability and reproducibility for measurement of RNFL thickness has not been extensively studied previously.