Background & objectives:�Amblyopia as one of the most important social and visual problems is common in the world including Iran. It plays a major role in visual dimness. The aim of this study was to determine prevalence and causes of amblyopia in middle school students in Ardabil city, Iran in 2004.

 Methods: In this descriptive cross-sectional study 4548 middle school students were included. The subjects primarily were screened by optometrists and an ophthalmologist by using of Snelen chart. The doubtful cases were referred to eye clinic for further checking and re-examined by ophthalmologist. The data were collected by questionnaire and the results were analyzed by descriptive and analytical statistics using SPSS software.

  Results: The results cleared that 11.4% of subjects (520) had refractive errors, 2.63% (120) showed the amblyopia and 0.9% (43) experienced strabismus. The most common cause of amblyopia was anisometropia (59% of all cases) and for strabismus was isotropia (69.5% of all cases). These findings showed that there is a significant correlation between type and rate of refractive defects with amblyopia. The highest rate for refractive amblyopia was over 3 Diopter hyperopia (29.5% of refractive amblyopia). Hyperopia revealed to occur in males more than females and vice versa for astigmatism

  Conclusion : It seems that the prevalence of amplyopia in Ardabil is similar to other cities in Iran and other countries. But the refractive amblyopia in Ardabil shows more prevalent than other areas. Its reason may be due to less knowledge to use glass and low socio-economic conditions as well as low quality of treatment.