Built-in Isight for External Monitor with Macbook closed

Hello Apple Community,

I'm having trouble using my built-in iSight through my external monitor. My set-up is that the Macbook is closed and I run everything through an external monitor. I'm unable, however, to use that external monitor's iSight with any applications. They either say that there's no camera available or something along those lines. The iSight shows up in the system profile under USB, and I've tried resetting various things, but all of that seems geared more to the macbook than to the monitor. I've also woken up the macbook (where the iSight works fine) and tried mirror/non-mirror modes. When I use a camera-based application via the macbook, it doesn't give me an option of which camera to use, relying only on the macbook's. Is there a way to use the external monitor's camera instead?

Thanks,

Abe