Photoreceptor layer thinning in idiopathic Parkinson's disease

This study was undertaken to quantify retinal and intra-retinal layer thicknesses in Parkinson's disease (PD), and to evaluate whether retinal structural changes may be related to altered discrimination of color vision and to severity and duration of PD disease. We examined 97 PD patients and 32 healthy controls (HC) with spectral-domain optical coherence tomography (OCT), including intra-retinal layer segmentation. In total, we compared 111 retinal nerve fiber layer (RNFL)-scans and 114 macula scans from 68 PD patients with 62 RNFL and 63 macula scans from 32 HC. For clinical evaluation of disease severity, we used the Unified Parkinson's Disease Rating Scale (UPDRS) motor examination. To determine color discrimination, we performed the Farnsworth Munsell 100 Hue Test (FMT) in a subgroup of PD patients. We found significant combined outer nuclear and photoreceptor layer thinning in PD versus HC (118.6 vs. 123.5 µm, P = 0.001). Differences in RNFL, total macular volume, or the other retinal layer thicknesses were not detected. The OCT measures were not associated with disease severity, duration, or color vision. By showing photoreceptor cell layer thinning, our findings support previous in vivo and autopsy studies demonstrating retinal alterations in PD. Optical coherence tomography may help to assess morphological retinal changes in PD patients; however, the utility of OCT in routine clinical practice may be limited because many PD patients have difficulties complying with OCT investigation because of disease-related symptoms such as tremor, axial rigidity, or cognitive impairment.