Objectives: Psychometric development of the Retinopathy-Dependent Quality of Life (RetDQoL) questionnaire in a cross-sectional study of 207 German patients with diabetic retinopathy. Forty patients (19%) also had clinically significant macular edema.
Methods: Principal component analyses identified factor structure, and Cronbach's alpha assessed internal consistencies. Construct validity was examined by testing the additional impact of macular edema and expected relationships of RetDQoL scores with visual impairment, stage of diabetic retinopathy, subscales of the SF-12, and scores of the Retinopathy Treatment Satisfaction Questionnaire (RetTSQ). Analyses were conducted using the RetDQoL's AWI score (average weighted impact of diabetic retinopathy on 26 life domains) and its two overview items (present QoL in general and retinopathy-specific QoL). Content validity was investigated using an open-ended question to identify any additional items needed.
Results: A forced one-factor solution of the 26 specific weighted impact ratings showed all items except working life (applicable to 27%) to load>0.55, and Cronbach's alpha was 0.96, showing very high reliability. Greater impairment, worse diabetic retinopathy, and macular edema were associated with greater negative impact on scores. AWI correlated as expected more highly with retinopathy-specific QoL (r=0.71, P<0.01) than with present QoL (r=0.28, P<0.01). RetDQoL scores correlated moderately with SF-12 subscales (r=0.22-0.51, P<0.01) and RetTSQ scores (r=0.27-0.51, P<0.01). For six domains, >60% of patients reported no impact. No additional domains were needed.
Conclusions: The RetDQoL is valid and reliable for patients with diabetic retinopathy with or without macular edema. It may be shortened if findings are confirmed cross-culturally.