The CSTT aims to allow rapid estimation of the color saturation threshold in the bluish-purple region of the color circle, which is commonly preferentially affected in acquired dyschromatopsia. The test is intended to estimate monocular saturation thresholds and any differences between the eyes, and to monitor changes over time. The test parameters use the HSL format: hue is fixed at 0.753 (271° in the color circle) and lightness is fixed at 50%. Saturation is variable between 0 and 100%. Step size is 1% unit below 6% and 2% above 6%.
The test displays four squares. On opening the test, one square has 50% saturation; the others have a saturation of 0% and appear pure gray. Explain the test task, namely, to find "the least amount of color" needed to identify which one of the four squares is the test square. Click the Plus or Minus test button once to set the test square saturation to 0%. Then, increment saturation step by step by clicking the Plus button until the test subject correctly identifies the colored test square. Alternate a few clicks on the Minus button (which decrements saturation) and the Plus button to fine-tune the threshold estimate. Click the Query button to learn the current position of the test square and its saturation. These are shown unobtrusively below the display. Tap keyboard key F5 to reset to start conditions.
There are no fixed rules for screen type or viewing distance. Ambient illumination should be subdued. Select whichever conditions are most practical, and stick to these conditions. Normal limits have to be determined separately for each set-up. This is quickly done.
Saturation 50% © Lars Frisén 2018