Originally Posted by Knotlob

Some lenses are coated (plasma) to improve wettability/comfort but this tends to change the chemical/physical structure of the lens surface, so it is integrally bonded to the lens and provided you don't use an abrasive cleaner, it should stay put.

Some lenses may be soaked in some sort of 'comfort' agent (Air Optix), but that sometimes causes more problems than it solves and the lenses will last longer than the comfort agent, if used according to the manufacturer's guidelines.

Monthly lenses may be slightly thicker than Daily lenses if made of the same material (e.g. B&L SofLens Daily & 59) to better withstand mechanical handling and cleaning.

Some Daily Disposable lenses clearly last longer than other Daily Disposable lenses (i.e. for someone who doesn't need the specific benefits a Daily Disposable Lens offers).

As far as I can ascertain, the two factors, which would limit the life of any lens will be the Mechanical Integrity (does it stand up to proper cleaning/rubbing and general handling?) and the degree of protein deposit build up on the lens.

You have to consider users of Vial/Annual Lenses to put it into perspective. I used to wear Annual lenses and they would last 12-16 months say. By that time there was some deposits on them, but if I had perhaps used Ultrasonic Cleaning, they would probably have lasted much longer. So even without ultrasonic cleaning these lenses were lasting 365-487 days. Now I don't really think there is that much difference between a monthly and an Annual Lens as far as mechanical integrity goes. The Monthly lenses are available in higher Dk values but that shouldn't be a factor in the life of the lens. In fact, some manufacturers claim that silicone hydrogel is less prone to protein build up than the typical hydrogels used in vial lenses.

Lurker2010 has suggested that less efficient cleaning of disposable lenses with 'no rub' cleaning solutions may be allowing protein deposits to accumulate rapidly. Maybe this is a factor in the convenience age, in which we live.

If you want to be charitable to the lens manufacturers, they are applying a conservative lens life policy, which is safe for the majority of users, including a percentage who are a bit lax in their lens care.

knotlob