Evaluation of a retinal image is widely employed to help doctors diagnose many diseases, such as diabetes or hypertension. From acquisition process, retinal images often have low grey level contrast and dynamic range. This paper proposes indices of fuzziness for solving the problems of retinal image enhancement. Histogram of the retinal image is stretched by estimating the optimal parameters of the indices of fuzziness in S-function, which is designed for contrasting a field of view in the images. Our algorithm can achieve a number of significant properties for contrast stretching, such as compressed the noise in background and produced a high contrast in a field of view or foreground that provides feasibility in diagnosis from a retinal image.