Just to add to this, I declared my keratoconus to the DVLA. They sent back a letter telling me it's made no difference and I can simply state, 'medical condition - DVLA aware - no restrictions'
You must tell DVLA if you’ve got any problem with your eyesight that affects both of your eyes, or the remaining eye if you only have one eye. If you can’t, you’ll fail your driving test and the test won’t continue. DVLA will be told and your licence will be revoked. https://www.gov.uk/driving-eyesight-rules
Tell the DVLA of any condition. Let them decide. Whether the rules state you should or shouldn't it is best to be upfront. When I was diagnosed I informed them immediately and got a letter back saying that having reviewed my case they were happy for me to continue driving so long as my eyesight met the minimum requirements as laid down in law and I wore the necessary corrective equipment.
Nowadays it is more complex I guess because the requirements have shifted from just a number plate test to a minimum visual acuity in one eye and a field of vision. But KC should not necessarily affect this anymore than the abilit to read a number plate at 20M.