Retina: Color Vision

Color Vision

Color vision defects may be congenital (especially in men as they are inherited and X-linked recessive) or acquired, for example in macular dis-orders such as Stargardt’s disease. Qualitative red-green vision defects are evaluated with pseudoisochromatic plates such as the Ishihara or Stilling-Velhagen plates. They contain numerals or letters composed of small color dots surrounded by confusion colors (Fig. 12.10) that patients with color vision defects cannot read. The Farnsworth-Munsell tests (Fig. 12.11) can detect blue-yellow color vision defects.

Pseudoisochromatic plates contain numerals that patients with color vision defects cannot read. In the Farnsworth-Munsell test, patients with a color vision defect cannot sort markers with different hues (according to the colors of the rainbow) in the right order.

The Nagel anomaloscope permits quantitative evaluation of color visiondefects. The test plate consists of a lower yellow half whose brightness can beadjusted, and an upper half that the patient tries to match to the lower yellow color by mixing red and green. The anomaly ratio is calculated from the final adjustment. Green-blind patients will use too much green, and red-blind patients too much red when mixing the colors.