Shingles in the eye called "optical shingles" is when the virus has invaded an ophthalmic nerve. It can cause painful eye inflammations that causes temporarily blindness or if more extensive, it can cause impairment of the vision.
The course and severity of the infection and nerve inflammation plays a great role in determining the extent of the effects on the ophthalmic nerve. Consultation with an ophthalmologist is important to have early symptomatic treatments and management to prevent problems. Antiviral medications to shorten the duration and intensity of the infection can be very helpful to avoid extensive damage.
With all the necessary treatments, hopefully,there is a very high possibility that the temporary loss of vision will be resolved once the infection has settled. If left untreated or treatment is delayed, then chance of more extensive nerve is possible. Usual treatment usually include antiviral eye drops, oral antiviral drugs, and other medications to help with the pain and inflammation.
Since his one eye is already blind, you must be very careful in protecting the other eye. Follow meticulously the advice of ophthalmologist and follow up with him/her very closely. If the duration of infection can be shortened, and corneal ulcerations can be avoided, and nerve inflammation controlled, he is supposed to be out from danger of having a permanent optical nerve damage.
Take care!