Are you in the UK perhaps? You may want to connect with some of our other UK members who have found some of the better doctors there for dry eye. There are far fewer doctors who understand dry eye than those who do.
Regarding opatanol (called patanol here): This is a good allergy drop, and a number of people here use it. I've used it in the past occasionally and also Pataday more recently. It is effective but it is drying, and the preservative can be harmful if used long term and irritating to some in the short term. I'm sure our Sjogrens members can comment more on what it's like to use it when you've got Sjogrens but in the meantime I'd just say that you'll have to take even better care of keeping your eyes well lubricated when you're using this drop.
What else did the optician say about your eyes? Did they comment on your meibomian glands or suggest any other treatments?
The Dry Eye Zone