I cannot speak with any authority, just from my own experience. I have a hearing loss which was attributed to rifle shooting in the Air Cadets without ear defenders. I passed my Initial Class 1 but my hearing deteriorated over the years and AMEs often mentioned that whilst it was OK for renewals it wouldn't get through an initial. I believe that something similar applies to eyesight. I.e you must achieve a certain standard in the first place but thereafter a certain amounht of deterioration can be acceptable.
Rather than wait for opinions on here why not telephone the medics at Gatwick. They are very helpful people and could probably provide an answer quite quickly.
Good luck.