Visual electrophysiology in parkinson's disease : relation to clinical and functional impairments

Abstract EN

Background : degenerative changes in Parkinson's disease (PD) may cause visual problems that may interfere with the quality of life.

Special tests measuring electrical activity in the eye and the brain such as visual evoked potentials (VEP) and electroretinogram (ERG) have shown abnormalities in PD patients.

It is not clear whether these visual abnormalities are the result of degeneration in the brain or whether some may be due to lowered dopamine levels in the retina.

The interest in visual deficits in PD is enhanced by the possible relation between vision and control of balance.

Objective : the aim of this work was to assess visual electrophysiological abnormalities in PD patients and their relation to clinical and functional (postural) impairments.

Methodology : the study included ten parkinsonian patients and ten apparently healthy control subjects.

Assessment of disease severity was conducted using the Hahn Yarer scale.

Visual electrophysiological studies included pattern reversal VEP and ERG.

The ability to effectively use visual information to control balance was assessed using sensory organization test (SOT).

Results : compared to the control group, PD patients had significantly prolonged VEP latencies mainly for bilateral full field and temporal halves of the retina.

VEP amplitude was significantly increased for binocular stimulation.

Flash ERG showed significantly low b-wave amplitude.

Performance on SOT revealed the presence of significantly low visual ratio and visual preference ratio.

Electrophysiological abnormalities were not correlated with clinical manifestations.

VEP amplitudes were found to correlate with some ERG parameters.

SOT findings were not found to correlate with electrophysiological abnormalities.

Conclusions : disturbed visual function as evidenced by visual electrophysiological abnormalities seems to be an inherent property in PD.

Contribution of visual dysfunction to balance problem in these patients is evident.

The mechanism by which visual disturbance contributes to balance disorders seems to differ from that responsible for VEP and ERG abnormalities signifying the important role played by dopamine in mediating different visual functions through different pathways.