Filter the noise of a measurement at the edges of a surface

I use an optical device to measure a rectangular surface, then I have a 3d point cloud. However, there are noises at the 4 edges of this rectangular (the points that is above the surface - see image https://dl.dropbox.com/u/8702546/1.png) These points have an important sensility when I simulate a planar contact between this surface and an other surface (same dimension as the first one). They become the points in contact while in reality, they dont existe! So I'd like to filter these points automatically by a Matlab code. Your suggestions are welcome! Regards,