However, the chameleon’s brain and eyes do not work together thus, their binocular vision, stereopsis, depth perception are impaired and their distance vision is not like ours. As a result, chameleon’s use their instincts to find their prey. Once found, they fix themselves on the prey and adopte a binocular vision that lets them estimate distances.
Source: http://ophtasurf.free.fr/vue/animaux/oeil_cameleon.htm