Stereopsis and ocular alignment in Parkinson's disease patients with and without freezing of gait symptoms

Abstract

Background

Parkinson's disease patients are classically described by having motor disorder symptoms. Freezing of gait is one of these motor symptoms that presents in some of these patients. Even though freezing of gait is classically considered as motor dysfunction, it is now widely accepted that deficits in other sensory systems, for example visual system, may lead or contribute to freezing of gait. The purpose of this study is to characterise some of the binocular vision functions in freezing of gait patients, non‐freezing of gait Parkinson's disease patients and age‐matched healthy controls.

Methods

Binocular vision measurements included local and global stereopsis using different clinical stereo tests, along with fixation disparity and fixation disparity curves. The fixation disparity measures were primarily an assessment of the vergence motor system, and the clinical stereo tests assess the combined effects of motor and sensory aspects of binocular vision. Twenty‐two freezing of gait patients, 25 non‐freezing of gait patients, and 25 aged‐matched healthy controls completed all of the measurements in this study.

Results

The freezing of gait group had worse stereopsis than the non‐freezing of gait group, and the non‐freezing of gait group had worse stereopsis than the healthy controls. The impairment of global stereopsis was more common than local stereopsis in Parkinson's disease patient groups. The reduction in stereopsis among Parkinson's disease patients was not associated with fixation disparity.

Conclusions

Results from this study clearly indicate that the freezing of gait patients group has a greater loss in stereopsis than the other two groups, especially for the global tests. Whether these impairments are contributing to the freezing of gait or just associated with freezing of gait is uncertain.

Key words:

• binocular vision
• fixation disparity
• freezing of gait
• Parkinson's disease
• stereopsis

ACKNOWLEDGEMENTS

Special thanks to the Movement Disorder Research Center, Wilfrid Laurier University, Waterloo, ON, Canada. This project was funded by the Cultural Bureau of Saudi Arabia in Ottawa, the College of Optometrists in Vision Development (COVD), and the Canadian Optometric Educational Trust Fund (COEFT).

Additional information

Funding

the Canadian Optometric Educational Trust Fund (COEFT)

The College of Optometrists in Vision Development (COVD)

the Cultural Bureau of Saudi Arabia in Ottawa