Correlation between retinal morphological and functional findings and clinical severity in Parkinson's disease

Background To measure the parapapillary retinal nerve fiber layer and macular thickness and macular volume in vivo and to evaluate whether retinal structural changes and visual cortical responses may be related to the clinical severity of the PD. Methods We included 17 patients with Parkinson's disease and 11 healthy subjects of a similar age. Unified Parkinson's disease rating scale scores in Parkinson's disease and control subjects were assessed for clinical evaluation. The retinal nerve fiber layer thickness, macular thickness and volume were measured by commercially available optical coherence tomography Model 3000 unit. Peak latencies of P100 component were measured by pattern visual evoked potential examination. Results The mean retinal nerve fiber layer average thickness was significantly reduced in Parkinson's disease patients (98.76 +/- 10.90 mu m) when compared with those of control subjects (114.54 +/- 5.72) (P < 0.05). The retinal thickness reduction was statistically significant in superior inner macula; temporal, nasal and inferior quadrants of outer macula (P < 0.05)(Table 2). The mean total macular volume of Parkinson's disease patients (6.82 +/- 0.32 mm(3)) was significantly reduced when compared with those of control subjects (7.09 +/- 0.23 mm(3)). Highly significant inverse correlation between foveal retinal thickness and total and motor subscores of Unified Parkinson's disease rating scale was observed in Parkinson's disease patients, respectively (r = -0.660; P = 0.004), (r = -0.625, P = 0.007). There was a moderate nearly significant inverse correlation between total macular volume and P100 latency in PD (r = -0.328; P = 0.058). Conclusions In Parkinson's disease patients there is a reduction of retinal nerve fiber layer thickness, macular thickness and volume evaluated in vivo by optical coherence tomography. Reduced foveal thickness which is not found to be statistically different from normal is correlated to the severity of disease.