Patients with AMD may be at increased risk for Parkinson's disease. Click image to enlarge.

Age-related macular degeneration (AMD) shares some risk factors with Parkinson’s disease (PD), and studies have reported a higher tendency for AMD patients to have PD. A recent study aimed to further evaluate this relationship and investigate the risk of PD among patients with AMD, as well as its association with confounding comorbidities.

A population-based retrospective cohort study was conducted, and AMD and non-AMD cohorts were established to determine the diagnosis of PD. A total of 20,848 patients were enrolled, half of which were AMD patients and the other half were controls. The follow-up period was from the index date of AMD diagnosis to the diagnosis of PD, death or withdrawal from the program.

During the analysis of AMD subtypes (unspecified, non-neovascular, neovascular AMD), there was no significant difference in risk of PD.

“The non-significant difference of PD risk between non-neovascular and neovascular may need further research stratified by the disease’s stage since it does not define the stage of AMD by the ICD-9-CM codes as non-neovascular or neovascular AMD,” the authors explained. “The follow-up time in our study started from when AMD was diagnosed rather than the true duration of the disease, which might be even longer than the time we recorded. Perhaps the duration or the stage of the AMD might be associated with different degrees of the risk of PD.”

There was an adjustment of sufficient clinical comorbidities and medications related to aging, with a large amount of data that could offer a statistically meaningful outcome, the authors noted. “Although we did not adjust the lifestyle, which was proven to be a confounder in the model, comorbidities such as hypertension and hyperlipidemia might also reflect the lifestyle.”

The study concludes that AMD is associated with a higher risk of PD with adjustment for sufficient clinical comorbidities and long follow-up time. However, the authors suggest further studies are needed to compare the association between PD and neovascular or non-neovascular AMD during long-term follow-up with more information, such as the stage of the disease.