Journal of Clinical and Experimental Ophthalmology
Open Access

Abstract

Cluster Analysis of Glaucoma Patients Using the Retinal Nerve Fiber Layer Thickness of the Optic Nerve and DTI Parameters of the Optic Radiation

Georg Michelson, Simone Wärntges, Tobias Engelhorn, Ahmed El Rafei, Joachim Hornegger and Arnd Doerfler

Background: In glaucoma the optic radiation may be affected by ascending degeneration and/or ageing. This study classified groups of patients who are distinguishable related to their age, retinal nerve fiber layer thickness (RNFL), axonal integrity (measured by fractional anisotropy and mean diffusivity) and demyelination (measured by radial diffusivity) of the optic radiations. The goal was to separate glaucoma-induced damage of the optic radiations from impairment caused by the ageing effect.
Design: Prospective comparative observational study. Participants: Fourty-five patients diagnosed with glaucoma of different entities and 17 patients with vital papilla (mean age 57.5 ± 13.8 years).
Methods: Multimodal MRI including diffusion tensor imaging (DTI) of the optic radiations and measurement of the RNFL thickness by Spectralis Optical Coherence Tomography. Hierarchical cluster analysis selected the optimal number of patient groups. Data were corrected for age. The t-test and a multiple linear regression model were applied.
Main Outcome Measures: Fractional anisotropy, and mean, axial, and radial diffusivity.
Results: Four clusters, two middle-aged and two older groups with different RNFL thickness each but same age, were classified. Multiple linear regression analysis showed a significant effect of the RNFL thickness on fractional anisotropy, mean diffusivity, and radial diffusivity of the optic radiations in the older patients having the stronger RNFL reduction (p = 0.019, 0.021, and 0.010, respectively). The slope of the radial diffusivity versus RNFL was different between the two older groups (p = 0.025).
Conclusions: In middle-aged glaucoma patients with reduced RNFL we found no change in the optic radiation. An ascending degeneration to the optic radiation was not verifiable. In contrast, in older glaucoma patients with reduced RNFL the axonal integrity/ demyelination of the optic radiation was impaired. The impairment was significantly associated with loss of RNFL and ageing.