Comparison between optic nerve head minimal waist of the nerve fibre layer and retinal nerve fibre layer thickness with regard to angular distribution

Abstract

Aims/Purpose: To compare angular distribution of the minimal waist of the nerve fibre layer in the ONH, Pigment epithelium central limit‐Inner limit of the retina‐Minimal distance (PIMD) and Retinal nerve fibre layer thickness (Rnfl) in not pathological eyes.Methods: Altogether, one eye from each of 17 subjects were included. SS‐OCT of the optic nerve head with vicinity was captured 3 times in each subject with Triton (Topcon, Japan). PIMD was resolved in 500 angles in the frontal plane. Rnfl‐angle estimates were provided by the Topcon software integrated over 30 degrees steps in the frontal plane. The corresponding PIMD steps were estimated by averaging the corresponding steps in the frontal plane. For each step, the 3 iterated captures were averaged. The mean difference between PIMD and Rnfl, respectively averaged over 2π radians was estimated. The angular distribution of PIMD‐angle and Rnfl‐angle were compared using cross correlation over ±130 degrees (+: upper half. ‐: lower half).Results: The mean difference between PIMD and Rnfl estimates averaged over angle within subject and then over subjects was CIμ(0.95) = 228 ± 8 um (d.f. = 16). In 16/17 subjects the angular distribution in the upper half was correlated in 16/17 and in 16/17 the lower half was correlated. The lack of correlation for the upper and lower half, respectively, was present in different eyes.Conclusions: The collection of nerve fibres in the ONH increases the thickness at the waist in the ONH on an average 2.8 times. The angular distribution of PIMD and Rnfl is usually completely correlated in not pathological eyes but deviations occur. Thicker PIMD than Rnfl provides a wider dynamic range for PIMD to detect change due to glaucoma.