Abstract
Background: Measuring contrast sensitivity for each of the three cone types
separately allows for a more precise and clinically valuable assessment of color vision. This
study examined how pupil size affects cone contrast sensitivity (CCS). Methods: This study
included 50 participants of equal gender. The mean age was 20.88 (±1.8) years. Using
the ColorDx, a Landolt C stimulus of various sizes in an adaptive screening mode, we
sequentially determined contrast sensitivity for long-, medium-, and short-wavelength
stimuli. Two consecutive measurements were performed on participants, one with their
natural pupil size (range 4–5 mm diameter) and, subsequently, with six artificial eye pupils
(1 mm to 6 mm). Results: Generally, the 1 mm pupil size caused the greatest reduction
in contrast sensitivity for two of the three cones. There was no significant main effect of
sex (F = 0.96, df = 1, p = 0.32) on the log cone contrast sensitivity of the L-cone. However,
pupil size had a significant main effect (F = 116.1, df = 6, p < 0.001). Within each sex, the
log CCS was significantly reduced as the pupil size decreased compared with the normal
pupil size. Conclusions: New technologies that assess individual cone pathway functions
could potentially assist in identifying early or progressive conditions that may impact color
vision pathways from the retina to the brain. Standardized protocols—such as controlled
retinal illumination—are critical to avoid misinterpretation.