Biomarkers are generally biological molecules, such as protein or DNA, but the definition can be extended to imaging and even to specific observations that help diagnose or monitor a disease state. The latest of these is the suggestion that eye (ocular) tremor could be used as an early biomarker for Parkinson's disease diagnosis.
In a case control study (a study that compares people with and without the condition), researchers tracked the eyes of 112 people with Parkinson's disease (including 18 new and untreated patients) and 60 controls, asking them to fix their eyes on a target, and then to follow a moving target.
All the patients with Parkinson's disease had an eye tremor when they tried to fix their eyes on the stationery object, but this had no link with length or severity of disease, or treatment. Only two control patients had a similar tremor.
"The major finding of the present study was that using modern eye movement tracking, oscillatory fixation instability was universally seen in a large cohort of 112 patients with PD," the authors wrote.
Because this instability is seen whether patients are treated or not suggests that the disease and not its medication causes it--Parkinson's disease medications, including levodopa, can cause dyskinesia (involuntary movements). While this biomarker doesn't provide any prognostic information, a test for eye tremor could be useful in early diagnosis of Parkinson's disease, allowing patients and their families to get early support, and also helping doctors to treat the disease early, which may have long-term benefits.
- read the press release
- see the abstract