Catquest-9SF functioning over a decade - a study from the Swedish National Cataract Register.

Background: The Swedish National Cataract Register (NCR) collects data on cataract surgery outcomes during March, including patient-reported outcomes using the Catquest-9SF questionnaire for over 11 years. Previous studies from NCR have shown that the preoperative visual acuity has improved over time. The main purpose of this study was to evaluate the Catquest-9SF Rasch scoring performance in this changing environment. A second purpose was to describe clinical data over the same period for those who completed the questionnaire.

Methods: The performance of the Catquest-9SF was analysed by a separate Rasch analysis for each year, resulting in a preoperative and postoperative score for each participating patient in the annual cohorts. The clinical data and questionnaire scoring were analysed for each year in the period 2008-2018 inclusive.

Results: Data were available for 42,023 eyes for 11 annual cohorts (2008-2018). The psychometric properties of the questionnaire were stable during the study period. Person separation (precision) for the whole period was 2.58 and varied between 2.45 and 2.72. The person reliability was 0.87 and varied between 0.86 and 0.88. The targeting of question difficulty to person ability became less accurate over time meaning that the item activities became easier to carry out without difficulty. The average targeting for the whole period was -2.06 and changed from -1.92 in 2008 to -2.31 in 2018. The person score improved both before surgery and after surgery, indicating that patients are undergoing surgery at a more able level and getting better outcomes. The average improvement by surgery decreased from 3.41 logits in 2008 to 3.21 logits in 2018 (p = 0.003). Over time, patient age decreased from 75 to 74 years (p < 0.001) and the proportion of women decreased from 63.9 to 57.9% (p < 0.001). The mean preoperative visual acuity in both the operated eye and the better eye improved over time (0.47 to 0.40 logMAR, p < 0.001 and 0.22 to 0.19 logMAR, p < 0.001, respectively), as did the mean postoperative visual acuity in the operated eye (0.14 to 0.09 logMAR, p < 0.001).

Conclusions: The Catquest-9SF retained stable psychometric properties over this 11-year period although more recent cohorts included slightly younger patients with somewhat better vision.