Development and Preliminary Validation of an Instrument to Measure Symptoms and Impacts in Patients with Proliferative Diabetic Retinopathy

Introduction: Following a review of patient-reported outcome (PRO) instruments in the literature, existing PRO instruments may not adequately capture the experience of receiving treatment for proliferative diabetic retinopathy (PDR). Therefore, this study aimed to develop a de novo instrument to comprehensively assess the patient experience of PDR. Methods: This qualitative, mixed-methods study comprised item generation for the Diabetic Retinopathy-Patient Experience Questionnaire (DR-PEQ), content validation in patients with PDR, and preliminary Rasch measurement theory (RMT) analyses. Adult patients with diabetes mellitus and PDR who received aflibercept and/or panretinal photocoagulation within 6 months of study initiation were eligible for participation. The preliminary DR-PEQ comprised four scales: Daily Activities, Emotional Impact, Social Impact, and Vision Problems. DR-PEQ items were generated using existing knowledge of patient experiences in PDR and conceptual gaps identified from existing PRO instruments. Patients indicated the level of difficulty conducting daily activities and frequency experiencing emotional impacts, social impacts, and vision problems attributed to diabetic retinopathy and its treatment in the past 7 days. Content validity was evaluated in two rounds of in-depth, semi-structured patient interviews. Measurement properties were investigated via RMT analyses. Results: The preliminary DR-PEQ comprised 72 items. Overall, mean (SD) patient age was 53.7 (14.7) years. Forty patients completed the first interview; of these, 30 completed the second interview. Patients reported that the DR-PEQ was easily understood and relevant to their experience. Minor revisions, including removal of the Social Impact scale and addition of a Treatment Experience scale, were implemented to generate 85 items spanning four scales: Daily Activities, Emotional Impact, Vision Problems, and Treatment Experience. RMT analyses provided preliminary evidence that the DR-PEQ performed as intended. Conclusion: The DR-PEQ evaluated a broad spectrum of symptoms, functional impacts, and treatment experiences relevant to patients with PDR. Additional analyses are warranted to evaluate psychometric properties in a larger patient population.