I would check with your vet to see if Optimmune has produced an improvement in tear gland function. If not, there is little point in continuing with its use.
From what I have read, Optimmune is usually only effective in the early stages of keratoconjunctivitis sicca. Charley has "dry eye" but unfortunately it was not diagnosed until he was about six months old, and Optimmune was totally ineffective. If Optimmune has not produced an increase in tear production then treatment with Maxitrol and Viscotears is a better alternative.
I have been treating Charley with Fradexam, which is similar to Maxitrol but not available in the UK, Viscotears, and Fucithalmic when he has the occasional eye infection. His vet is an eye specialist, and she has commented on how well his eyes are considering his eye condition.