Impaired color perception is associated with more severe nigrostriatal denervation in Parkinson disease

Objectives Dopaminergic degeneration affects both the nigrostriatal projections and retinal inner plexiform cells. Retinal function changes, such as impaired color discrimination, occur in Parkinson disease (PD). We explored whether the nigrostriatal deficit correlated with impaired color perception using the Ishihara color test.

Methods PD subjects (n=39; 10F/29M; mean age 68.2±7.9, mean Hoehn and Yahr stage 2.6±0.6, mean duration 7.2±4.6 yr, mean MMSE score 28.4±2.1) underwent vesicular monoaminergic type 2 (VMAT2) [C-11]dihydrotetrabenazine (DTBZ) PET imaging and color perception testing using the Ishihara color test.

Results 17 out of 39 PD subjects (43.6%) had abnormal color perception. Patients with impaired color perception had lower striatal VMAT2 activity compared to patients with preserved color perception: striatal DV 1.84±0.24 versus 2.04±0.30 (-9.8%, t= 2.3, P=0.026).

Conclusions The presence of impaired color perception in PD does reflect the severity of the nigrostriatal deficit in PD. Findings indicate that retinal dopaminergic denervation may in part parallel nigrostriatal dopaminergic denervation in PD.

Research Support Supported by NIH R01 NS070856, P01 NS015655 and the Department of Veterans Affairs.