image analysis in matlab

hello everyone. I'm tryng to analyze images in matlab, to detect the refractive index of some substances. For that, i'm using a laser beam passing through said substance. Problem is, i don't know exactly how to process the images. I figure the important thing to look for is the displacement of the center of the beam, due to the refraction of the beam, but, how can i find out how much, and in what direction, has the beam been displaced?. Another probable thing to look for is the intensity of the beam, and perhaps the amount of diformation suffered by it. Any help would be gratly appreciated. Also, any suggestions as to how to determine the index are very welcome.

Thanks to everyone.