Effects of Dopaminergic Treatment on Contrast Sensitivity, Visual Evoked Potentials and Visual Field in the Parkinson’s Disease

Abstract

OBJECTIVE: Since recent three decades, generalized dopaminergic system dysfunction is being proposed in the etiology of the Parkinson’s disease (PD) rather than the dysfunction of nigrostriatal dopaminergic pathway in the basal ganglia. Some studies suggested that multi-synaptic visual pathways are also effected beside this generalized dopaminergic malfunction. In this study, we aimed to evaluate visual pathways in the patients with Parkinson’s disease by the means of contrast sensitivity, visual evoked potentials (VEP) and visual field measurement.

OBJECTIVE: To evaluate the effect of dopaminergic treatment on visual parameters in Parkison’s disease.

METHODS: MATERIALS-METHODS: Between the years of 2003 and 2006, a total of 20 patients who were recently diagnosed as Parkinson’s disease and who had not taken any anti-Parkinsonism drug was included in the study. In these patients, the parameters of contrast sensitivity, visual evoked potentials (P100) and visual field were evaluated before any treatment was initiated and six months after treatment. In addition, another total of 20 patients with Parkinson’s disease on treatment for a minimal period 5 years (mean 7,7 years) were included to observe any affect related to the duration of the disease. Patients with any systemic disease or other neurological disease other than Parkinson’s disease and the patients with any ocular disease other than refractive disorders were not included.

RESULTS: When pre-treatment P100 values were compared with the control groups, they were found to be significantly long in the right eyes with 32 square stimulus and in the left eyes with 64 square stimulus. When the post-treatment values were compared with the control groups, there was no significant difference. There was no difference between the pre and post treatment values of P100. When the patients who were previously diagnosed as Parkinson’s disease were compared with the control group, there was a significant lengthening in the latency with both stimuli. The visual field evaluation revealed significant increase MD value in the study group compared to the control group. After treatment, MD values improved significantly. The evaluation of contrast sensitivity of the recently diagnosed patients revealed a significant decrease in the mean value of contrast sensitivity scale and its logarithmic equivalent, compared to the control group. After treatment, these values increased significantly and were similar to the values of control group. Previously diagnosed patients had significantly low total score and logarithmic equivalent compared to the healthy control group.

CONCLUSION: Even though there might be no complaint related to the vision in the early period of the Parkinson’s disease, we observed visual impairment which can be detected by visual tests and be corrected with dopaminergic treatment in the early period of the disease. In the advancing period of the disease, the treatment is ineffective for the visual impairment similar to the motor findings. This may be a result of the progressive nature of the Parkinson’s disease. Contrast sensitivity is the most sensitive test in the evaluation of the involvement of the visual pathways. With the studies performed in the field of basic science field, dopamine has been found in the retina and it has been suggested to have major roles in the visual acuity and contrast perception. In the evaluation of the patients with Parkinson’s disease, complaining blurry vision or inability to perceive details, retinal dopaminergic hipoactivity should be kept in mind in case of no explanatory finding with the examination of the eye.