Personally, I think it should be the number of times you wear the lens, i.e. 30 times. However, I think this may be a moot point amongst eye care professionals and I will try to remember to ask my optician next week for her opinion. She is sensible and practical.

Logically deposit build up, wear and tear on the lens, etc. will be a function of how many times you wear the lens, not how many days there are in a calendar month. However, if you do change the lens at the same date in each month, then you run less risk of wearing the lenses too many times (i.e. more than 31 days).

Proper cleaning and disinfection will take care of the infection risk.

I wear Biofinity monthly lenses and disinfect/clean them every night when I take them out. I use a 2 step peroxide system and neutralise just before I put the lenses back into my eyes (20 mins before or so).

I seldom take my lenses out and then put them back in during the same day. However, I would think it is sensible to clean them before putting them back in the same day. Peroxide systems are going to be difficult, but if you use a Multi Purpose Disinfecting solution, then it's easier.

knotlob