Parkinson’s Affects Both Low- and High-Contrast Vision

A new study confirms that people with Parkinson’s disease (PD), as compared to healthy individuals, experience trouble with certain aspects of vision, including contrast sensitivity (e.g., distinguishing between shades of gray) and using high-contrast vision at a distance. The results appear in the February 17 online edition of the Journal of Parkinson’s Disease.

People with PD typically have normal vision when reading black letters on an eye chart – a test for high-contrast visual acuity. Yet they may still have trouble seeing clearly because PD affects contrast sensitivity – the ability to tell apart subtle differences in gray, or the colors of objects, especially in low light. This makes it difficult to see when walking, or driving at night, even if a person’s vision tests as 20/20.

For the new study, researchers led by Charles H. Adler, M.D., Ph.D., at the Mayo Clinic College of Medicine in Scottsdale, AZ, evaluated a new tool for testing low- and high-contrast vision sensitivity. They recruited 32 people whose PD was diagnosed, on average, as Hoehn and Yahr stage 2 (mild PD) and 71 healthy individuals of similar age to participate in the study. Vision tests were carried out using an iPad® application for which eye charts were developed specifically to evaluate contrast vision. The researchers tested study participants’ ability to read black (100 percent contrast) and gray (2.5 percent contrast) letters on a white background, at two different distances, 30 cm (16 inches) and 2 m (6.5 feet).

Results

  • Near and far, people with PD scored lower than healthy individuals on the test for low-contrast, indicating impaired visual sensitivity.
  • On the test for high-contrast vision (black letters), study participants with PD scored the same as healthy individuals when reading close-up (30 cm or 16 inches), but worse when reading at a distance (2 m or 6.5 feet).
  • Among people with PD, close-up low-contrast vision worsened with disease severity (with PD progression measured by scores on the standard UPDRS, or Unified Parkinson's Disease Rating Scale, scale of symptoms).

What Does It Mean?

People affected by PD often complain of blurred vision. Yet complaints are often non-specific, and unfortunately specific treatments are not available. Furthermore, testing for low-contrast vision is often overlooked in standard eye exams for people with PD. The authors of this study advocate testing people with PD for contrast acuity, and suggest that the specially designed iPad® application used in this study could provide a quick screening tool to supplement traditional vision testing techniques. If difficulty with low-contrast vision is diagnosed, then doctors can recommend therapies and lifestyle adjustments to help compensate for this, and allow people with PD to safely continue to do the things they want to do.

Future studies should focus on understanding the mechanism of low-contrast vision in PD and hopefully on treatments to improve low-contrast vision.

Reference

Lin, T. P., Rigby, H., Adler, J. S., Hentz, J. G., Balcer, L. J., Galetta, S. L., Devick S., Cronin R., Adler C.H. (2015). Abnormal visual contrast acuity in Parkinson's disease. Journal of Parkinson's Disease, 5(1), 125–130. http://doi.org/10.3233/JPD-140470

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