Prediction of Parkinson’s disease severity based on RNFL thickness evaluated by OCT

Purpose To determine the relationship between peripapillary retinal nerve fiber layer (RNFL) thickness in Parkinson disease (PD) with the severity of this neurological disorder and to define a simple biomarker to predict clinical severity. Methods Peripapillary RNFL thickness was measured in 102 eyes from 52 PD patients by using optical coherence tomography (OCT) and compared with 97 eyes from 50 age-matched healthy controls. The Unified Parkinson's Disease Rating Scale (UPDRS) total score was used and responses in the ON medication state were measured. Results PD patients showed a statistically significant decrease in average peripapillary RNFL thickness compared with control eyes (p<0.001). This reduction was observed in every quadrant: inferior (p<0.001), superior (p<0.001), nasal (p<0.001) and temporal (p=0.017) in PD patients. Furthermore, a strong inverse correlation was found between PD severity measured according to the UPDRS score with either the average peripapillary RNFL thickness (r= –0.615; p<0.001) or PD duration (r= –0.303; p=0.002). From these results, we defined the following regression equation, which is able to predict the UPDRS score from the mentioned variables: UPDRS = 81.6 + 29.6 * log PD duration (yr) – 0.6 * RFNL thickness (µm). Conclusion As the evolution and severity of PD progress, the peripapillary RNFL thickness gradually diminishes. These results suggest that the average peripapillary RNFL thickness measured by OCT might be useful as a biomarker to detect the early onset and progression of PD.