Activecontour "leakage" due to noise in image

I'm using activecontour to track an open eye (dark pixels). However, in some frames, the eye edge is virtually non-existent in a small section of the eye due to the filming angle, meaning that active contour thinks the eye and background are one, and starts leaking through that narrow section of the eye. This creates a contour shaped like an hourglass. Is there any way I can limit activecontour's ? As of now, I'm limiting size only. I would like to, ideally, get rid of that narrow part of the hourglass, so that activecontour remains focused on the eye.