This answer says:
The ISS live feed uses the cameras of the HDEV experiment. This is a group of four cameras in a pressurized housing attached to the outside of the ISS.
A hermetically sealed atmosphere is one possibility, but there are several problems with that strategy. Leaks can happen, and outgassing from structural materials and the electronics themselves can raise the pressure (only slightly I suppose) and possibly built up contaminants on the surface of the optics causing scattered light when hit by strong illumination (e.g. sunlight).
Another strategy might be a very slow, controlled leak to space, compensated by a very slow make-up air line from a supply line from the ISS, or from an attached bottle of nitrogen.
Yet another would be to exchange atmosphere with the rest of the ISS via small tubes.
How is this actually done? Was it necessary to address outgassing?