Impaired contrast sensitivity does not reflect nigrostriatal defect in Parkinson disease

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

Methods PD subjects (n=27; mean age 63.6 +/- 6.9, Hoehn and Yahr stages I-III) underwent vesicular monoaminergic type 2 (VMAT2) (+)-alpha-[11C]dihydrotetrabenazine (DTBZ) PET imaging and visual contrast sensitivity testing using the Pelli-Robson Contrast Sensitivity Test.

Results 7 out of 27 PD subjects demonstrated abnormal binocular contrast sensitivity (less than or equal to 1.65 OU at 1 meter). There were no significant differences in striatal VMAT binding in subjects with and without impaired contrast sensitivity (1.87 +/- 0.30 vs. 1.96 +/- 0.31, t=0.67, P=0.51).

Conclusions The presence of impaired contrast sensitivity in PD does not reflect the nigrostriatal deficit in PD. Findings indicate that retinal dopaminergic denervation may not parallel nigrostriatal dopaminergic denervation in PD providing support for the heterogeneity of the Parkinson syndrome.

Research Support NIH P01 NS01565