Psychometric properties of the NEI-RQL-42 questionnaire in keratoconus.

PURPOSE To assess the psychometric properties of the National Eye Institute Refractive Error Quality of Life (NEI-RQL-42) questionnaire in keratoconus and compare these findings to patients with refractive error correction alone. METHODS The Portuguese version of the NEI-RQL-42 Quality of Life questionnaire was completed by 44 patients who had keratoconus before and after implantation of intracorneal ring segments. Rasch analysis was used to assess the use of response categories, success in measuring a single trait per subscale (unidimensionality), ability to discriminate person ability (precision), and targeting of questions to person quality of life (QoL). RESULTS Rasch analysis was performed for the questionnaire subscales using stacked preoperative and postoperative data. Three subscales (Symptoms, Dependence on correction, and Suboptimal correction) contained response categories that were not used as intended. Six subscales contained misfitting items indicating multidimensionality. Eleven subscales exhibited inadequate measurement precision. Only the Near vision subscale demonstrated adequate precision with a person separation greater than 2.0. Targeting of items to person QoL was adequate in 11 of the 12 subscales with a mean item location of less than 1 logit. CONCLUSIONS Only one NEI-RQL-42 subscale (Near vision) performed adequately in keratoconus. Targeting was better in patients with keratoconus than in patients with refractive error correction alone, but 11 of the 12 subscales remain manifestly inadequate. Better instruments exist for measuring patient-reported outcomes in keratoconus.