Objective: To investigate the reliability and validity of the Thai version of the "Disease-Specific Questionnaire for Health-Related Quality of Life" in patients with Blepharospasm (BS) and their response to botulinum toxin treatment.

Study design: Cross-sectional study.

Materials and methods: Twenty patients with BS were asked to complete a newly developed Thai version of the 25-item National Eye Institute Visual Functional Questionnaire (NEI-VFQ-25) as well as a six-point disability rating scale before and between four and six weeks after botulinum toxin injections. Peak improvement (0-100%) in the condition was also evaluated between four and six weeks after treatment. Before their treatment commenced all the patients were asked to answer the existing Thai SF-36 questionnaire to help test for the correlation with the Thai NEI-VFQ-25. A second group of ten patients who had no injections completed the Thai NEI-VFQ-25 and then a second identical copy after a two-week interval. Subsequently the reliability, validity and responsiveness were analysed.

Results: The Thai NEI-VFQ-25 showed a Cronbach's alpha coefficient of 0.80 and no significant difference in test-retest reliability. The total content validity was 0.8 (range 0.7-1.0). There was good correlation between the Physical Health part of the Thai NEI-VFQ-25 and Thai SF-36 (r = 0.58, p < 0.01). However, the correlation between the Mental Health part of the Thai NEI-VFQ-25 and the SF-36 was not so strong (r=0.39). The Thai NEI-VFQ-25 also demonstrated a response to treatment similar to the six-point disability rating scale and the peak improvement.

Conclusion: The Thai NEI-VFQ-25 is a reliable, valid and responsive instrument for disease-specific healthrelated quality of life assessment.