I’m going by what several opticians and hospital opthamologists have told me and the case studies.
When you get AK in your eye - what happens is they will cling to your contact lens, often go inside the lens as at microscopic level soft lenses are like sponges, especially the high water content ones.
If you have lenses that you wear more than once, that you take out, you clean & disinfect and then re-insert into your eye, the AK amoebas are not killed by the disinfectant. It only kills bacteria not amoebas. So your lens becomes a portal from which they can multiply and attack your cornea. (Only exception is the 8hr hydrogen peroxide disinfecting systems as hydrogen peroxide does kill amoebas)
That is why you can wear rigid or gas permeable lenses and shower or swim- AK amoebas can’t get inside them.
You can also wear disposible contact lenses that you then remove and throw away after swimming because if there is any AK amoebas, you toss them in the rubbish with the lenses. You can then flush your eyes with eye drops for extra safety and wait a few minutes before putting in new lenses.
Then your chances of developing AK are the same as anyone without contact lenses- usually our tears are enough to was the amoebas out, so those who get AK have compromised immune systems or have a scratch or eye injury for it to get a toe hold on.
You can only get AK from fresh water or tap water- so this doesn’t apply salt water.
Wearing swim goggles is an extra safety measure as well as keeping the water out of your eye works for everyone whether disposable contact lens wearer or no.