T is blind (started with partial blindness) in her right eye. It has not affected her, after the adjustment period, on the trail. I do let her know at all times where I am, and try not to surprise her. She knows her fields by heart and every inch of her paddock and barn, so no problems there.
As far as extra vet care, much will depend on the actual cause of the blindness. For T it was caused by trauma induced uveitis, no bacterias were present , so other than an exam during spring shots, we're good to go. I do protect her eye on all trail rides with a special fly mask, and during daylight hours she wears it to protect any uv damage to her good eye (ounce of prevention).
She is just as steady and calm as ever, and I plan on enjoying our time on the trails for many years yet.