If it's just slight cloudiness, recommend treat with Melafix. It's available at pet store's aquarium section and use according to the bottle label directions. That is important because they sell Melafix in different concentrations. Can use Melafix solution in the frogs water dish, in bath, in damp paper towels used for substrate, even dribbled over frogs back and eye. Since only that frog has it, it could have been a small scratch that got infected.

Do treatment daily and let us know how it goes. Melafix is slow acting; but should contain infection and show some improvement in next few days. Can continue treatment as long as there are symptoms. Once mixed with dechlorinated tap can store solution for couple days in a dark area. If eye does not improve; a stronger treatment with antibiotic might be warranted and for that recommend Maracyn Plus.

Since you had frog with others; it's your choice to observe them for any issues, or do a preemptive strike with Melafix. If adding to water area of an established system do make sure you know exact volume so there is no chance of an accidental overdose. Good luck !