DVLA contacted me and sent me the forms to fill in.
If you have been driving a vehicle between 3,5 - 7.5 tonnes and want to continue to do so, as I did, you will have to have a medical examination and make an application for (if I remember rightly) C2 entitlement. But it will all be explained in the documentation.
As I suffer from glaucoma I have to have field tests done by an optician not of my choosing before they will renew my licence . The loss of vision I have is really small but that does not matter in fact you can be blind in one eye and still drive. You have to admit if you have cataracts thank goodness I no longer have that to worry about . My renewal comes in soon and I am fretting about it already .