Morphologic changes and functional retinal impairment in patients with Parkinson disease without visual loss

To investigate the anatomic and electrophysiologic changes of the macula and the optic nerve in patients with Parkinson disease (PD) without visual impairment.

Thirty-two eyes of 16 patients with PD (group A) without visual impairment were tested. Visual acuity was 20/20 or better and visual fields as well as color vision testing results were normal. Also, no retinal lesions were assessed. Patients in group B (40 eyes of 20 patients) were age- and sex-matched control subjects. All study participants underwent a comprehensive ophthalmic examination, multifocal electroretinogram (mfERG) recording, and optical coherence tomography (OCT) scan. Thickness of retinal nerve fiber layer (RNFL) along a 3.4-mm-diameter circle centered on the optic nerve head was evaluated using third-generation OCT.

The mean P1-response density amplitude of ring 1 of mfERG was 136.69 nV/deg2 in patients with PD and 294 nV/deg2 in control subjects and the difference was highly significant. On the contrary, these values in ring 2 and 3 did not differ statistically between controls and patients with PD. The mean inferior and temporal RNFL thickness was significantly lower in patients with PD than in control subjects (p<0.0001 and p=0.0045, respectively).

In patients with PD with normal vision, we found a decrease in the electrical activity of the fovea as well as in the thickness of the RNFL. Multifocal electroretinogram and OCT scan objectively detect early subclinical PD-associated visual functional impairment.