According to a study published in Parkinsonism & Related Disorders, thinning of the peripapillary retinal nerve fiber layer was revealed in the ipsilateral eye (to the body side most affected by bradykinesia) in patients with Parkinson disease, indicating the potential involvement of retinal processes in the disease mechanism.
This study sought to evaluate retinal neurodegeneration in Parkinson disease and glaucoma by comparing the thickness of the macular ganglion cell complex and the peripapillary retinal nerve fiber layer. The study sample included 146 eyes from 130 patients similar in age; participants were grouped according to a glaucoma diagnosis (60 eyes of 60 patients), Parkinson disease (46 eyes of 30 patients), and healthy control (40 eyes of 40 patients). Patients underwent standard ophthalmic examinations, and optical coherence tomography was used to image and segment the inner retinal layers, measuring the thickness of the macular ganglion cell complex and the peripapillary retinal nerve fiber layer.
Correlation analyses were then performed on the ganglion and peripapillary measurements. Further relationships were evaluated between disease duration, dopamine dose, olfactory testing, and retinal thickness. Glaucoma patients additionally had their intraocular pressure tested.
Both eyes of patients with Parkinson disease compared with the healthy controls showed no significant differences in the overall macular ganglion cell complex; however, in patients with Parkinson disease, the retinal thickness of the ipsilateral eye to the most-affected body side with bradykinesia was significantly thinner than in the healthy controls. In all groups, the thickness of the macular ganglion cell complex and peripapillary retinal nerve fiber layer were highly correlated. Disease severity did not significantly affect the macular ganglion cell complex or the peripapillary retinal nerve fiber layer, nor was there a correlation between disease duration, dopamine dose, olfactory testing, and optical coherence tomography.
Limitations of the study included a small sample size, meaning the differences in retinal thickness between patients with Parkinson disease and control groups did not reach statistical significance. Disease duration of patients with Parkinson disease ranged from 1 to 27 years, which may have also contributed to differences in retinal thickness.
The study authors indicated that macular and peripapillary inner retinal layers were not proven as diagnostic biomarkers for predicting neurodegeneration in Parkinson disease. However, the thinning of the peripapillary retinal nerve fiber layer reported in the superior sector of the ipsilateral eye to the body side most affected by Parkinson disease was notable. A larger, more homogenous cohort is needed to detect the effects of retinal thinning over time and the retina’s relationship to Parkinson disease.
Matlach J, Wagner M, Malzahn U, et al. Retinal changes in Parkinson’s disease and glaucoma [published online June 21, 2018]. Parkinsonism & Relat Disord. doi: 10.1016/j.parkreldis.2018.06.016