Difficult to say what is causing the eye's to sink in. Chameleons sink in their eye's when something is bothering them. I would make certain your Chamaeleo calypatratus is well hydrated, has good UV lighting and is eating well. If the sunken eyes continues for a while you may want to have a checkup with your local vet. A lot of the time sunk in eye's go away on their own with healthy husbandry.
Your Chamaeleo calpatratus eye's are not sunk in that much.
Best Regards
Jeremy A. Rich