Hello and welcome. My name is ***** ***** I'm a biologist with over 40 years of experience raising guinea pigs and rabbits. Incidentally, my neighbor has a dog named Dog, so you're not alone. I'm sorry to hear of Guinea's problem.
There are several conditions that can cause an eye to protrude like this. One of the most common is a dental problem. If a tooth is abscessed or growing abnormally into the area behind the eye, the eye can protrude. Abscesses or tumors in the nasal cavity or behind the eye can also cause this to happen. All of these conditions must be treated by a vet. You can read more about guinea pig eye problems at this site:
The cloudiness may be related to whatever caused the eye to protrude because of increased pressure in the eye (similar to glaucoma as you suspect). Or, Guinea may have a cataract in that eye.
Regardless of exactly what has happened, I'm afraid there is no home treatment. I recommend seeing a vet. This link will take you to a directory of guinea pig vets:
In the meantime, keep the lights low in Guinea's room because bright light can be painful to an eye in this condition. If you have more questions, just let me know. I hope Guinea will be fine.
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