Studies? Yes indeed, but comparing specifically silicone hydrogel
overnight wear at 30 days, and lesser intervals. There was no clinically
significant difference between 30 days and 14 days but an increase in
infection rate with decreasing overnight intervals and a statistically
significant but still very small increase over daily wear use. However I
wouldn't put too much value into the studies as there was an issue with
control groups and monitoring patient lens care in the shorter term
extended wear protocols.

But that is exactly my point. The more you handle the lenses, the
greater the risk for some people----that group that doesn't wash their
hands prior to handling the lenses, stores the lenses in inappropriate
solutions or in dirty containers.  You'd be amazed at what some people
do!  Someone who is non-compliant with daily lens care is going to be at
LESS risk of infection if they stick the lens in and leave it there,
untouched.

On the other hand, someone who DOES follow appropriate lens care
protocol would be at less risk of infection using the lenses for daily
wear and NOT extended/continuous wear.  Wearing contact lenses in any
modality carries a certain risk.  So does wearing eyeglasses. So does
crossing the street, even at a crosswalk with the green light.

So which has the lower risk: extended wear or daily wear?  Compliance
being equal, daily wear by a small margin. Not doing the right
thing---all bets are off.

Not exactly. Bacteria do not accumulate on or adhere to silicone
hydrogel lenses. At least nothing like the older hydrogel lenses. The
thinking is  that the infection starts because the cornea epithelium has
been compromised--opened, cut, (rubbing a dry lens across the cornea, a
piece of sand or particulate in the air caught under the lens, the ashes
from the smoker in line next to you) and introduced bacteria (the dirty
finger syndrome, or someone coughing in your face, a contaminated
insect, a flake of dandruff) colonize in the wound. The presence of the
contact lens inhibits epithelial cell replacement at the cornea surface
repair mechanism isn't fast enough to knock out the germs and re-seal.
Once in a while, it's just because some exceptionally nasty pathogen
(bacteria or virus) get in there and wrecks havoc. (BTW, removing the
lens at the first sign of trouble will almost always reduce the risk
back to near zero. Leaving the lens in when it hurts is pretty damn
stupid. But too often the case.)

In any event, in real life, I've seen far more cornea infection in daily
wear lens users than in (current) extended wear lens users, and the
numbers in total are still very, very small, at least in my practice
patient group. And that mostly because patients of mine who are not
compliant with lens care (cleaning, disinfection, follow-up visits,
replacing lenses appropriately) are asked to leave and find another
doctor. The contact lens related infections I see each year occur
exclusively in non-compliant patients. It's never a mystery.

(The rate in extended wear users of the old, non-silicone lenses was
unacceptably high, even in compliant users, and I never recommended that
modality except for the few people who were carefully informed of the
risks and I knew would be compulsive about lens care and limited
overnight use to three days.)

All that being said, I remain cautious with overnight use of lenses.
I've dozens of patients doing 100% fine in 30 days continuous wear and
many of them self-limit to something less than that more often than not.
But most contact lens wearers are better off limiting overnight use to 6
or 7 days and more than a few do best at 3 or 4 days. Everyone is
different. Some people build up lipid deposits in a few days and others
have lenses that look pristine after a month. Someone who works long
hours in a hospital or around potential sources of infection is not a
good risk for extended wear lenses. The very nearsighted parent with a
young child who is in excellent health with no lens-related risk factors
is someone who might benefit from continuous wear lenses. And so being
lazy and too tired to take care of daily wear lenses might be considered
a GOOD reason to sleep in them!  Or perhaps no lenses at all!

This turned out far longer that I had planned. Sorry to go on so long. I
just hope to present a clear picture of the issue and to underscore the
need for contact lens wearers to seek quality professional care and
advice.  It's not a do-it-yourself thing.

--LB, O.D.

This is correct.  There is extensive scientific evidence demonstrating
adherence of bacteria to the undersurface of contact lenses, most likely via
the glycocalyx on the bacterial cell wall.  This adherence seems to be less
in silicone hydrogel lenses.  Hence another reason, in addition to increased
oxygen permeability, for using them for patients who insist on extended
wear.

As you say, the beginning of infection in extended wear patients is the
large bacterial load created by wearing a lens for a long time without
cleaning, as well as the disruption of the eyes normal mechanism for
clearing itself (blinking, tearing).

I wouldn't argue against the idea that disrupting the corneal epithelium by
removing the lens in a clumsy and unclean fashion could defeat the purpose
of cleaning the lenses.  That is common sense.  But given that patients
remove their lenses properly, I believe the "quick rinse in the morning"
suggestions is quite valid.  I recommend it without reservation.