This organization is instutionally officious. I suffered a retinal mini-sroke that eliminated vision from 10% of the periphery of my right eye. This wouldn't matter proving my left eye was perfect - well, at least able to pass driving vision test. Unfortunately I am waiting for a cataract operation - due in a week or so.
Anyway, I wrote to the DVLA to tell them this. Then they did nothing for two months. Finally I got a very long form to fill in myself and also to take to my optician. Fine. Two months later they wrote to me again saying I had been booked in for an eye field test - at the same place I had the identical test two months ago. But first I had to fill in three forms. The first contained only questions that I had answerted two months earlier. The second wanted detailed and extensive information on my use of illegal drugs. The third wanted equal detailed and very intrusive information on my abuse of alcohol. I emailed DVLA saying that surely there must be some mistake since I was reporting a defective cataract. Within 24 hours I received a reply telling me I was required by law to fill in these forms and failure to return them within 21 days would result in my licence being revoked. Indeed all their communication comes with this 21 deadline or you lose your licence.
I hope none of you are planning to go on holiday for four weeks otherwise when you get home you may find you don't have a licence any more - but it may take DVLA three months to inform you.