I've had annual retinal screening since I went on medication for type 2. A letter comes through, but since we've moved areas I've realised different health authorities do this differently. Where I used to live I was called to a clinic at my health centre. A specialist travelled round the area with all their equipment and called patients in when they were at their health centre.
Where I live now we get sent a list of approved opticians who we can make appointments with. Unfortunately my regular optician is not on the list and since they also do very thorough eye checks on me, I get a second annual check on my retinas with them (only they have some seriously posh, high-tech equipment). I certainly feel well checked these days!