OCT retinal imaging as differential diagnostic tool between Parkinson disease and essential tremor

Purpose To evaluate neuroretinal measurements in Parkinson disease (PD) and essential tremor (ET) patients, and to compare results with healthy controls. Methods A total of 214 subjects (214 eyes) were included in our study (146 healthy controls, 42 PD patients and 26 ET patients). Retinal examination in the peripapillary zone and the macular zone (retinal nerve fiber layer [RNFL] and ganglion cell layer [GCL] thickness) was performed for each subject using Swept source ocular coherence tomography (OCT) Triton and Spectralis OCT. Additionally, macular vascularization was analysed with OCT angiography (OCT‐A). Results A significant reduction in the peripapillary RNFL and CGL was observed in PD patients compared to ET patients (p < 0.001). Also, the RNFL in the macular area was significantly thinner in PD patients compared to ET (p < 0.001).ET patients showed significant thinning in both GCL and RNFL compared with controls only in nasal sectors (p < 0.001) Although vascularisation showed higher density in healthy controls compared to PD and ET, this parameter did not reach significance levels. According to the correlation analysis, global OCT angiography was associated inversely with disease duration in PD (r = −0.600; p = 0.018). Logistic regression analysis was performed, obtaining two linear discriminant functions (LDF) for differencing PD from ET or controls. These LDF included density of OCT‐A and GCL macular thickness (for Triton OCT) and RNFL peripapillary thickness (for Spectralis). They yielded a receiver operating characteristic curve (ROC) of 0.796 (p = 0.020) for Triton OCT; and 0.627 (p = 0.033) for Spectralis OCT. Conclusions Both PD and ET present retinal thinning compared with healthy controls. However, compared to ET, PD has a higher decrease affecting more areas of the RNFL and GCL, which might help differentiate both diseases. Considering the fact that OCT test is non‐invasive, quick and mostly available in every ophthalmological clinic, it could be considered as a potential tool for differential diagnosis between these two entities.