Now it's been a while since I did my initial Cat 1 medical exam (1985), but I initially did not pass the vision requirements, as the limit was (at that time, if I recall correctly) -3.00 diopters. (-5.00 for the Cat 2 medical for PPL.)
My eyes were -2.25 and -4.75. The Regional Medical Examiner at the time required I get contact lenses and wear them for 6 months. They were apparently worried about my peripheral vision with thicker glass lenses.
I received the Cat 1 medical shortly afterwards. I have had it ever since, and my latest prescription is -3.25 and -5.25.