In May, I had a test with Specsavers and passed with no probs. Now, 6 months on, DVLA say I have to have another with Specsavers. I don't mind, but interested if a 6 monthly check is standard.
DVLA Test: In May, I had a test with Specsavers... - Glaucoma UK
DVLA Test


Were you given a 1 year licence? If tested last May they would then likely notify you that your renewal is due around 90 days before your licence expiry date. Does that sound possible?
I thought it was every three years. Could your doctor have been in touch with them following a change in your vision
For glaucoma it can be every five years or every year if you are borderline. And anything in between if DVLA so choose.
Have you been under hospital for Glaucoma or anything changed ? I only have a year driving licence as I had an eye op. I have to have DVLA checks with Specsavers got info in Jan, licence renews in March.

You will be issued a license for 1, 2, 3 or 5 years. I guess it is possible that you was issued a 1 year license and they are sending you for your test way in advance. Any queries then please call them or contact their email on glaucomaqueries@dvla.gov.uk