Study design

This retrospective study included 308,340 patients 50 years or older from the Korean National Health Insurance Service Cohort. Patients with AMD diagnosed between the years 2003 and 2005 were flagged. All participants’ health records were queried for Alzheimer disease and/or Parkinson disease between January 1, 2006 through December 31, 2013.

Outcomes

Compared to patients without AMD, patients with AMD had an approximately 48% increased risk for developing Alzheimer disease and 46% increased risk of developing Parkinson disease. The risk remained elevated even among those who never smoked, did not consume alcohol and exercised regularly. The association between macular degeneration with Alzheimer disease and Parkinson disease was higher for patients younger than 70 years when compared with those aged 70 or older.

Limitations

This was a fairly homogenous group of patients from Korea whose macular degeneration may differ from patients in other study populations. As this was a large cohort database, there may not have been uniform standards in diagnosing macular degeneration, Parkinson disease or Alzheimer disease.

Clinical significance

This study adds to previous work suggesting that there may be some shared underlying pathophysiology between Alzheimer disease, Parkinson disease and macular degeneration. Earlier work found that compounds such as beta amyloid are present at higher levels in patients with neurodegenerative diseases and macular degeneration. However, a previous study that examined the role of inhibiting beta amyloid was not found to be helpful for AMD. Additional work needs to be done to further understand this association.