Is the cloudiness on the surface? In this case, it is an eye ulcer as the result of a scratch or poke and needs to be seen and treated by a vet.
If the cloudiness is inside the eye, then you are looking at a cataract, which is untreatable in guinea pigs. Cataracts usually develop over a time, so piggies can get used to the gradual loss of their sight and learn to compensate with their other senses. Very often, the second eye is going coming down with another cataract within weeks/months of the first one.
Sadly, I have just lost the last members of my dedicated cataract group due to old age, but blind/sight impeded piggies can still live a normal life.