Age-related Temporal Loss Of Retinal Nerve Fibers In Parkinson Disease: A Mitochondrial Pattern?

Abstract

Purpose: : To investigate the involvement of optic nerve in the neurodegenerative process characterizing Parkinson Disease (PD). There is mounting evidence of mitochondrial dysfunction, particularly affecting complex I, in the molecular pathogenesis of PD. Mitochondrial optic neuropathies, such as Leber's hereditary optic neuropathy (LHON) and dominant optic atrophy (DOA), are associated with complex I defect and preferential involvement of papillo-macular bundle.

Methods: : We evaluated the retinal nerve fiber layer (RNFL) thickness by means of optical coherence tomography (StratusOCT) in 63 eyes of 34 PD patients (mean age 64 ± 9) and in 168 eyes of 84 sex and age-matched controls (mean age 64,3 ± 12). Disease duration in PD patients was 7.6 ± 5.2 years and Hoehn and Yahr stage of disease was 1.9 ± 0.7. Differences between groups were assessed by Student’s t-test and significance was assumed for p<0.05

Results: : Average RNFL thickness was not different between PD and controls. However, a significant reduction of RNFL thickness was observed in the temporal quadrant (OD; p=0.01 and OS; p=0.004) in PD patients. Further, we stratified both PD and control groups by age choosing 65 years as the cut-off for aging process, based on previous studies. Thus, PD patients younger than 65 years of age (n=18) failed to show differences from controls (n=39) in all sectors. However, PD patients older than 65 years of age (n=17) had a significant reduction of RNFL thickness (OD; p=0.01 and OS; p=0.004) in the temporal sector compared to controls (n=45). Furthermore, OCT measurements did not correlate nor with disease duration or with stage of disease.

Conclusions: : Our study reveals a selective loss of RNFL in the temporal quadrant in PD patients, which is age-dependent. The temporal fibers belonging to the papillo-macular bundle are characteristically vulnerable in mitochondrial optic neuropathies. Thus, the current study supports a mitochondrial dysfunction in PD, which is contributed by the aging process.

Keywords: neuro-ophthalmology: optic nerve • nerve fiber layer • mitochondria