Retinal nerve fiber layer thickness in Parkinson disease

Dopaminergic neuronal cells have been identified in the inner nuclear and inner plexiform layers of the human retina. The dopaminergic content of the retina is reduced in patients with idiopathic Parkinson disease (PD). These observations led us to study the retinal nerve fiber layer (RNFL) thickness in patients with PD without visual impairment compared to healthy controls using spectral-domain optical coherence tomography (SD-OCT). Eighty-two subjects, including 42 patients with PD, newly diagnosed and untreated (24 men, 18 women, age range: 47-66 years), and 40 healthy controls, were enrolled. Both eyes of patients with PD and controls were imaged with SD-OCT. The mean RNFL thickness was 77 ± 11.5 μm in PD patients and 89 ± 8.7 μm in healthy controls (P = 0.001). Selective thinning of the RNFL was found in the temporal region with mean temporal RNFL thickness of 66 ± 6.7 μm in PD patients and 75 ± 4.8 μm in controls (P = 0.001). The thickness of the RNFL is decreased in PD patients. Demonstrating progressive thinning of RNFL over time will be critical for validating optical coherence tomography as a viable biomarker of patients with PD.