I found this in google: http://community.skype.com/t5/Mac/OS-X-10-8-5-Broke-Skype-Video/td-p/1891729/pag e/2
The Skype for Mac Engineer:
Hey all!
After some investigation, we have found that the OSX 10.8.5 update is missing a specific file that would allow some apps such as Skype or iMovie to access the built-in facetime camera on Mid-2013 MacBook Airs.
At this point, we are not sure how this can be fixed, and we'll get in touch with Apple to see how we can solve this.
From our tests, however, external webcams should work. It's not the best workaround, but until something gets fixed, that is the only known (and hopefuly temporary) solution.
For the more tech-savvy readers:
The 10.8.5 update updated a CoreMediaIO plugin that accesses the MBA camera, but didn't bundle the 32-bits version of it.
Other (older and newer) versions of the OS do include a universal version (32 and 64 bits), but not 10.8.5.
This means 32-bits apps such as Skype or iMovie cannot load the plugin, making the built-in facetime camera invisible to these them.
--
Thibault
Skype for Mac Engineer