Visual contrast response functions in Parkinsonʹs disease: evidence from electroretinograms, visually evoked potentials and psychophysics

Objectives: Visual contrast detection thresholds and suprathreshold contrast discrimination thresholds were compared to luminance and flash/pattern electroretinograms (ERG) and visually evoked potentials (VEP) in patients with Parkinsonʹs disease (n=31), patients with multiple system atrophy (n=6), patients with progressive supranuclear palsy (n=6) and control patients without central nervous disease (n=33). Methods: The stimuli were luminance modulated full-field (flash) or horizontally oriented sinewave gratings (pattern), the latter having either a low (0.5 cycles/deg) or medium (4.0 cycles/deg) spatial frequency. Stimulus contrast ranged from 10 to 80% so that contrast response functions could be derived. Results: Contrast thresholds were higher in the patients with Parkinsonʹs disease than in the control patients. Contrast discrimination thresholds were also somewhat elevated in patients with Parkinsonʹs disease. Pattern ERG amplitudes were significantly reduced in patients with Parkinsonʹs disease for the medium spatial frequency stimulus, but less for the low spatial frequency and flash stimuli. Conclusions: Our results suggest that Parkinson’s disease impairs contrast processing in the retina. VEP amplitudes did not significantly differ between the groups for the conditions tested. Patients with progressive supranuclear palsy also showed impaired contrast perception and reduced ERG amplitudes, whereas patients with multiple system atrophy were less impaired.