Effects of apomorphine on visual functions in Parkinson's disease

The effect of apomorphine on visual functions in Parkinson's disease (PD) was evaluated by use of a static contrast sensitivity test (VCTS charts), a colour discrimination test (Farnsworth-Munsell 100 Hue test) and the examination of achromatic and chromatic contour perception. 31 patients (14 male, 17 female; mean age 60.9 +/- 9.2 years) with idiopathic PD were tested before and after an individual dosage of subcutaneously applied apomorphine showing a significant effect on motor function during the whole experiment. The achromatic spatial contrast sensitivity improved significantly after apomorphine injection with respect to all spatial frequencies. The improvement of colour discrimination after apomorphine application was minimal and not statistically significant. The small advantage of apomorphine with respect to colour discrimination may be explained by negative cognitive side-effects of apomorphine interfering with the test performance. The achromatic contour perception before and after apomorphine injection was unaltered. The contour fusion latency for the green stimulus was shortened, the latency for the rest of the examined coloured stimuli was delayed (= normalized) after apomorphine application. We conclude that apomorphine may be used as a test-drug for the examination of the dopaminergic response of the visual system in patients with PD. The improvement of basal visual functions by dopaminergic stimulation with apomorphine underlines the role of dopamine deficiency for visual dysfunction in PD.