Psychometric Assessment of the Persian Version of the Revised Convergence Insufficiency Symptom Survey in Young Adults with Convergence Insufficiency

PURPOSE: To translate the Convergence Insufficiency Symptom Survey (CISS) to Persian and to assess its validity and reliability in a group of young adult Iranian patients with convergence insufficiency (CI). METHODS: The questionnaire was translated in backward and forward phases. Face validity was measured using a 6-point scale (very weak, weak, moderate, good, very good, best), and a score of ≥4 for each item indicated an acceptable face validity. The content validity was assessed using three indices of relevancy, clarity, and comprehensiveness. Relevancy and clarity were checked for each item and for the whole scale using a 4-point scale (1-undesirable, 2-relatively desirable, 3-desirable, 4-completely desirable), and Item Content Validity Index (I-CVI) and Scale Content Validity Index (S-CVI) were calculated for the above indices. Comprehensiveness was measured at the scale level using a 4-point scale (1-incomprehensive, 2-relatively comprehensive, 3-comprehensive, 4-totally comprehensive), and S-CVI was calculated. The internal consistency and test-retest reliability were assessed using Cronbach's alpha coefficient and interclass correlation coefficient (ICC), respectively. To evaluate discriminant validity, CI was categorized into mild, moderate, and severe stages, and the mean overall CISS score was compared between these groups. RESULTS: Thirty CI patients aged 18–34 years participated in this study. On face validity assessment, all items finally had a score of ≥4. As for relevancy and clarity, I-CVI was above 80% for all items, and S-CVI was 98.8% and 96.6%, respectively. The S-CVI was 100% for comprehensiveness. The overall Cronbach's coefficient and ICC were 0.77 and 0.95, respectively. There was a significant difference in the overall score between the three severity groups. CONCLUSION: The Persian CISS is a valid and reliable tool for clinical and research applications.