I am not an opthalmologist but if your acuity has been effected other than by age related deterioration, you have to inform Gatwick do you not? You cannot fly without taking expert advice about the acuity and that then has to be relayed to the CAA
The CAA may simply wave you on but the question is academic as the CAA will determine the outcome.
There is also the very small risk of injecting steroids via the lacrimal duct which might be relevant