Comparison between measurements of the circumpapillary nerve fiber layer thickness and the thickness of the waist of the nerve fiber layer in the optic nerve head

Abstract

Aims/Purpose: To compare measurements of circumpapillary Retinal Nerve Fiber Layer Thickness (cpRNFLT) and Pigment epithelium central limit Inner limit of the retina Minimal Distance (PIMD), respectively, between healthy and glaucoma eyes with regard to angular distribution of the measurements in the frontal plane and the variation coefficients for measurements of cpRNFLT-2π and PIMD-2π.

Methods: 17 eyes without ocular pathology and 7 with glaucoma, each from a different subject, were included. In each eye, the ONH was captured in 3 iterated volumes at one occasion with the OCT-Triton (Topcon, Japan). In each volume, the nerve fiber layer thickness was resolved in 12 frontal plane clock hrs as cpRNFLT with the Topcon software, and as PIMD with an automatic custom-made software. Finally, the 12 clock hrs were averaged and the inter-volume errors were determined with ANOVA for comparison of variation coefficients (CV:s) between cpRNFLT-2π and PIMD-2π.

Results: PIMD-2π was approximately 3 times higher than cpRNFLT-2π in the healthy eyes and 2.5 times higher in the glaucoma eyes. In both groups, PIMD peaked superiorly and inferiorly, slightly shifted nasally, and cpRNFLT peaked superiorly and inferiorly, slightly shifted temporally. The CV for iterated measurements at the same occasion was slightly higher for PIMD-2π than for cpRNFLT-2π in the healthy eyes, and of the same order for PIMD-2π and cpRNFLT-2π in the glaucoma eyes.

Conclusions: PIMD-2π and cpRNFLT-2π were lower in glaucoma- than in healthy eyes, probably due to less ganglion cell axons. PIMD-2π was generally 2.5-3 times higher than cpRNFLT-2π. The CV:s were on the order of 1.5-2.5 x10^-2 for both healthy- and glaucoma eyes and both quantities measured. Thus, averages of 3 volumes at each occasion is sufficient for comparison of measurements among occasions within subjects.