This exploratory mixed method sub-study aimed to establish the impact of colour vision deficiency (CVD) on the usability of sputum colour charts in chronic obstructive pulmonary disease (COPD) patients. Participants with CVD and those with at risk of acquiring CVD were recruited for the study. Colour vision was tested using Chroma Test, which is a software program that analyses the tritan and protan colour contrast thresholds. Qualitative interviews (individual and focus groups) comprised of participants with COPD assessed for undiagnosed CVD, as well as a group with known CVD (with or without COPD). Interviews were analysed using the framework method. Refer to Protocol 1.
In addition, a cross sectional study was conducted to determine the prevalence of CVD in The Health Improvement Network (THIN) using colour blind diagnostic read codes. A limitation of this could be failure of general practitioners to record CVD causing underreporting. Refer to Protocol 2.