Retinal morphological differences in atypical Parkinsonism: A cross-sectional analysis of the AlzEye cohort

Objective

Atypical Parkinsonian syndrome (APS) describes a heterogeneous group of disorders mimicking the clinical presentation of Parkinson disease (PD) but with disparate natural history and pathophysiology. While retinal markers of PD are increasingly described, APS has been afforded less attention possibly owing to its lower prevalence. Here, we investigate retinal morphological differences in individuals with APS in a large real world cohort.

Methods

We conducted a cross-sectional analysis of the AlzEye study, a retrospective cohort where ophthalmic data of individuals attending Moorfields Eye Hospital between January 2008 and March 31st 2018 (inclusive) has been linked with systemic disease data through national hospital admissions. Retinal features were extracted from macula-centered color fundus photography (CFP) and optical coherence tomography (OCT) and compared between individuals with APS and those unaffected. Individuals with idiopathic PD were excluded. Retinal neural and vascular features were measured using automated segmentation and analyzed with multivariable-adjusted regression models.

Results

Among a cohort of 91,170 patients, there were 51 patients with APS and 91,119 controls. Individuals with APS were older and more likely to have hypertension and diabetes mellitus. After adjusting for age, sex, hypertension and diabetes melitus, individuals with APS had a thinner ganglion cell-inner plexiform layer (-3.95 microns, 95% CI: −7.53, −0.37, p = 0.031) but no difference in other retinoneural or retinovascular indices. Optic nerve cup-to-disc ratio was similar between groups.

Conclusion

Our cross-sectional analysis of the AlzEye cohort reveals distinct retinal morphological characteristics in APS compared to healthy controls. The study notably identifies a thinner ganglion cell-inner plexiform layer in APS patients, without accompanying changes in the inner nuclear layer or significant alterations in retinovascular indices and optic nerve cup-disc ratio. These changes are distinct from those observed in PD, where thinning of the inner nuclear layer (INL) is a characteristic feature.

Significance

These findings demonstrate a retinal phenotype in APS, markedly different from both healthy controls and idiopathic Parkinson's disease, highlighting the potential of retinal imaging in differentiating neurodegenerative disorders. By establishing a distinct retinal phenotype for APS, our findings underscore the potential of retinal imaging as a valuable, non-invasive diagnostic tool. This advancement is particularly significant for enhancing diagnostic accuracy, facilitating early detection, and offering a window into the underlying disease mechanisms in APS, thereby aiding in the development of targeted therapeutic interventions and personalized patient care strategies.