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

Abstract

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_VE) was completed by 449 subjects (9-30 years old) from the general population. The validity and reliability of CISS_VE 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_VE 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_VE 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 (P < 0.001) for CISS_VE-CVSS17 and non-significant for CISS_VE-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_VE.

Conclusions: According to our results, CISS_VE 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_VE can measure convergence insufficiency symptoms in Spanish-speaking subjects.

Keywords: CISS; Rasch analysis; convergence insufficiency; cross-cultural validation; patient-reported outcomes.

Figure 1.

Category probability curves of the CISS_VE. The figure shows the performance of the five response categories of the CISS_VE, which asked about the frequency for each of the assessed symptoms. The curve at the extreme left represents “never,” and the curve at the extreme right represents “always.”

Figure 2.

Plot of estimated measure (x-axis) for any CISS_VE raw score (y-axis). Different symbols represent distinct levels of performance as indicated in the figure inset.

Figure 3.

Item-person map for the CISS_VE. The Rasch item-person map orders the self-reported level of symptoms of the patients in our study (left side) and the item difficulty (right side).

Figure 4.

Scatterplots of correlations between the CISS_VE and the CVSS and between the CISS_VE and the shortened version of WEMWBS. The regression line is shown as a dotted line.

Figure 5.

Bland–Altman plot for the CISS_VE. The dotted line indicates the mean difference (MD) between scores obtained when completing the questionnaire on two occasions. The solid lines indicate the lower and the upper 95% limits of agreement (MD ± 1.96).