Rasch calibrated Symptom Questionnaire for Childhood Intermittent Exotropia

Abstract

Purpose : To Rasch calibrate and evaluate performance of a previously developed questionnaire evaluating symptoms of childhood intermittent exotropia (IXT).

Methods : An initial 22-item questionnaire was developed based on interviews of children with IXT and their parents. The questionnaire had been previously reduced to 7 items by selecting items associated with reduced health-related quality of life (Hatt SR et al,2016). In the present study, the 7-item child IXT symptom questionnaire, with 3 response options, was completed by 386 children age 3 to 10 years old who were enrolled in an RCT comparing overminus to non-overminus glasses, with follow-up exams at 6 and 12 months on treatment and at 18 months (after overminus had been weaned). Factor analysis was performed to determine dimensionality, and Rasch analysis was performed to evaluate questionnaire performance and obtain logit values(converted to a 0 (no symptoms) to 100 scale). Overall differences between time points were assessed using the paired t-statistic. Differences between treatment groups and 95% confidence intervals (CIs) were estimated using ANCOVA, adjusted for baseline scores.

Results : The childhood IXT symptom questionnaire was unidimensional. Response ordering was appropriate. There was no notable local dependence, no significant differential item functioning for sex or age, but suboptimal targeting (mean -1.62 logits) and poor person separation (0.95). Overall, 6-, 12-, and 18-month scores were similar, and all showed significant improvement from baseline (Mean differences from baseline: -5.3 pts, 95% CI -7.2 to -3.4 at 6 months, -6.6 pts 95% CI -8.6 to -4.6 at 12 months, -5.7 pts 95% CI -8.1 to -3.4 at 18 months). There was no significant difference in the IXT symptom score between children treated with overminus and non-overminus glasses while on treatment (mean 28.8 vs 31.1 points; mean difference -3.0, 95% CI -6.2 to 0.1 at 6 months, and 28.4 s vs 28.1 points; mean difference 0.2, 95% CI -2.9 to 3.4 at 12 months).

Conclusions : The Rasch scored childhood IXT symptom questionnaire showed reasonable psychometric performance and was able to detect improvement in symptoms after 6, 12, and 18 months of either overminus or non-overminus glasses treatment. Overminus glasses treatment does not appear to reduce child-reported symptoms of IXT more than non-overminus.

This is a 2021 ARVO Annual Meeting abstract.