Spanish Cross-Cultural Adaptation and Rasch Analysis of the Convergence Insufficiency Symptom Survey (CISS).

Purpose: To culturally and linguistically adapt the Convergence Insufficiency Symptom Survey (CISS) to Spanish and assess the psychometric performance of the new version through Rasch analysis and classical test theory methods.

Methods: The Spanish version of the CISS (CISS) was completed by 449 subjects (9-30 years old) from the general population. The validity and reliability of CISS were assessed through Rasch statistics (precision, targeting, item fit, unidimensionality, and differential item functioning). To test construct validity, we calculated the coefficients of correlation between the CISS and the Computer-Vision Symptom Scale (CVSS17) or Warwick-Edinburgh Mental Well-Being Scale (WEMWBS). We determined test-retest reliability in a subset of 229 subjects. We used differential item functioning (DIF) to compare the CISSS and the CISS after administering the CISS to 216 English children.

Results: After applying exclusion criteria, the responses of 420 participants (mean age, 18.62 years; female, 54.95%) revealed good Rasch model fit, good precision (person separation = 2.33), and suboptimal targeting (-1.37). There was some evidence of multidimensionality, but disattenuated correlations between the Rasch dimension and a possible secondary dimension were high, suggesting they were measuring similar constructs. No item bias according to gender or age was detected. Spearman's correlation was 0.34 ( < 0.001) for CISS-CVSS17 and non-significant for CISS-WEMWBS. The limits of agreement for test-retest reliability were 9.67 and -8.71. Rasch analysis results indicated no difference between CISS and CISS.

Conclusions: According to our results, CISS is a valid and reliable tool for measuring the symptoms assessed by CISS in Spanish people 9 to 30 years of age.

Translational Relevance: CISS can measure convergence insufficiency symptoms in Spanish-speaking subjects.