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Science News

Eye Tremors are Pervasive in Parkinsonís

A test that measures eye movements may become a powerful biomarker for Parkinson’s disease (PD). According to new research published in the April 9 online issue of the Archives of Neurology, people with Parkinson’s demonstrate tremors of the eye, while people without Parkinson's do not.

Small, anecdotal studies in the past have found a connection between Parkinson’s and tremors of the eye. However, no study to date had systematically investigated the pervasiveness and nature of eye tremors in people with PD. 

In this study, a group of researchers at Virginia Commonwealth University led by Mark S. Baron, M.D., used advanced eye tracking equipment to monitor the eye movements of 112 people with PD and 60 age-matched controls without Parkinson’s.  Those people with PD included nearly 20 newly diagnosed individuals who were not yet taking medications.  The researchers looked at the eye movements both during fixation, when subjects are told to hold their eyes still and to simply look at a central point on a screen, and during saccades, when subjects are told to quickly direct their vision away from a central point toward a target on the left or right.

Results

  • During the test, all 112 people with PD had unstable gazes or eye tremors, meaning their eyes moved even while they were attempting to hold them still.  Only two of 60 people without a PD diagnosis demonstrated this instability.
  • In 71 of the people with Parkinson’s, the eye movements were severe enough that they may have obscured the person’s vision, making reading difficult.
  • The eye tremors were always characterized by oscillatory behavior: the eyes moved rhythmically, not randomly, much like classic parkinsonian tremors of the hand.
  • There was no difference between the two groups during saccades.
  • There was no relationship between eye tremors and other measures of PD, like tremor of the hand or medication status, and any of the eye movement parameters measured. 
  • Of the two control participants with eye tremors, one demonstrated symptoms of PD during a follow-up visit a year later.

What Does It Mean?

This study is the first, in depth look at eye movements in a large number of people with PD and found that eye tremors are an under-appreciated and likely universal feature of people with PD.  The authors found that eye tremors were not correlated with age, medication status, or presence of other tremors.  In one case, eye tremors were seen in a person before they were diagnosed with PD.  Together, these findings suggest that eye tremors may be an early symptom of PD and that PD medications do not stop them. 

The study did not address some issues, which could affect the results.  For instance, the researchers did not analyze the effects of individual medications on eye tremor.  It is possible that some medications may make the tremors worse or may be effective in reducing their severity.  In addition, the researchers did not perform any tests of vision per se—low vision may contribute to the tremors observed.  Lastly, the team only used one type of saccade task, so it is possible that alternate approaches could identify additional problems during purposeful eye movements.  As a result, future studies will need to address these issues and seek to replicate the findings

Nevertheless, the study is promising because it identified a potentially universal feature of PD that, for one individual, was found to precede the symptoms that lead to a PD diagnosis.  If this finding is confirmed in future studies, it is possible that monitoring eye movements could become a part of a routine exam that would allow for earlier diagnosis of PD.

Reference: Gitchel, G.T., Wetzel, P.A., Baron, M.S. (2012). Pervasive Ocular Tremor in Patients with Parkinson Disease. Archives of Neurology. Published online April 9, 2012: doi: 10.1001/archneurol.2012.70.

Source Date: Dec 31 1969