Astigmatism is very common eye disorder, which coexist with other refractive errors. Two third of the population worldwide who have myopia has astigmatism as well. Many diagnostic methods to detect these visual disorders have been developed in the last 10 years. Most of them are computer based techniques for better accuracy and fast response. In this paper an image processing based method for diagnosing astigmatism and classifying its types has been presented. The proposed technique is implemented on sagittal maps from latest topographic instruments.