It’s a bit like Health insurance. You pay a monthly premium which entitles you to the services of the optician of your choice. Most insurers have a network of providers and a fixed price for each type of service. Some policies allow you to ‘shop’ off-network, though this is often more expensive.

Your policy will act like a ‘club card’ and entitle you to discounts on eyewear, including designer frames and multiple lens enhancements.
Some policies include discounts on elective treatments and corrective surgery such as laser treatment.