Visual dysfunction in patients with Parkinson's disease and essential tremor.

The aim of this study was to determine the specificity and sensitivity of the Pelli-Robson and Ishihara diagnostic methods in differing Parkinson's disease from essential tremor compared to DaTSCAN (dopamine transporter scan) findings. The intention was to investigate whether visual dysfunction appears in the early state of Parkinson's disease. Therefore, we included patients with the symptomatology of parkinsonism lasting between 6 and 12 months. The study included 164 patients of which 59 (36.0%) suffered from Parkinson's disease, 51 (31.1%) from essential tremor, and 54 (32.9%) healthy patients which presented the control group. The specificity of Pelli-Robson test in confirming Parkinson's disease was 53% and the sensitivity 81.4%. The specificity of Ishihara test in confirming Parkinson's disease was 88.2%, and sensitivity 55.9%. We found that the colour and contrast dysfunction are present as the earliest symptoms of Parkinson's disease. In this study the Pelli-Robson test is highly sensitive and the Ishihara tables are highly specific in the differential diagnosis between Parkinson's disease and essential tremor, but neither of these methods fulfils the criteria for the validity of a test. We suggest performing both of these methods to evaluate which patients are indicated for DaTSCAN.