Do question phrasing and long wavelength cone sensitivity influence red cap test responses in healthy patients?

Abstract

This study investigates the influence of question phrasing and long wavelength cone sensitivity on red cap test responses in healthy patients. A chart review of 230 adult patients assessed responses to two different phrasings of the red cap test. Phrasing 1 asked the patient to describe the left eye relative to the right while Phrasing 2 asked the patient to name the brighter eye and provided an option for the patient to report no difference. Long wavelength cone thresholds were measured using the Konan CCT. Across both phrasings, 33 % of patients reported red saturation asymmetry, with a significant difference in positive responses between the two phrasings (43.6 % for Phrasing 1 vs. 11.3 % for Phrasing 2, (χ² = 121.694, p < .001). No significant interocular differences in long wavelength cone sensitivity were found in those patients with a positive red cap response. Phrasing contributes to the high false positive rate of the red cap test reported in healthy patients.