Ob That -- and for those with the patience (patients?) to read it:

http://snipurl.com/kkuy

[snipped]

Discussion

For patients using soft contact lenses, rinsing off the lens with
contact lens care solutions before applying the lens onto the eye is
common. However, the contact lens keeps attached a few microliters of
the contact lens care solution. We found by gravidity measurements
that up to 50 µl of solution remained on the contact lens surface
(data not shown).

It was our aim to examine the influence of different soft contact lens
care solutions on human conjunctival cells. The four solutions tested
are well tolerated in cell culture at concentrations of 5 µl/ml medium
as shown with the MTT test. At 10 µl/ml medium, OptiFree and Titmus
showed an inhibited cell viability. At the highest concentrations of
50 µl/ml medium for all four solutions investigated, a significant
damage to the mitochondria with the MTT assay was observed. The MTT
test measures the activity of mitochondrial dehydrogenases and is
therefore a sensitive test for cell viability, because damages of the
cells can be recognized early [35]. Depending on the concentration,
all contact lens care solutions have the potential to be harmful.

With the cell analysis system (CASY 1) the cell count, the cell volume
and the cell diameter can be determined by a passage through a
measuring pore and the results appear in a display and can be printed
out. With this test, no significant changes in the number of viable
human conjunctival fibroblasts after incubation of contact lens
solutions could be observed. Although these solutions induce a
reduction in mitochondrial activity in a concentration-dependent
manner, this damage is probably reversible since no cell death could
be observed with the CASY 1 system. Even at longer duration of
incubation (up to 72 h) and higher concentrations, no negative effect
was observed in the CASY system, indicating an outweighing tolerance
of the tested products.

It is noteworthy that these commercially available soft contact lens
solutions contain a mixture of different components (table 1) which
are not comparable to each other. We attached importance to the
cumulative effect of all the ingredients of the tested products.
Surprisingly, the effect on the conjunctival cells tested with the MTT
assay and the CASY 1 system was quite similar for each solution.

The constant physiologic lacrimal secretion causes a rapid dilution
and losses due to nasolacrimal drainage away from the ocular surface.
Normal drainage of an instilled dose of topical ophthalmic medication
begins immediately and the drug is essentially completely removed from
the ocular surface within 5 min [36]. In addition to tear film
production and drainage, the effect of topical application of
solutions is influenced by blink rate, concentration, penetration and
total dosage. Although rinsing off contact lenses is happening once a
day and only small volumes of contact lens care solutions are getting
in contact with the ocular surface, in long-term contact lens wearers,
reflex secretion may be decreased [37], therefore toxic substances
remain longer in contact with the ocular surface.

An in vitro study that examines a limited number of parameters cannot
alone predict the outcome of an in vivo use. But the MTT test and the
cell analysis system (CASY 1) enable objective statements on the
cytotoxicity of chemical substances and drugs on cell cultures such as
conjunctival cells [38, 39] and can decrease the number of animal
experiments. The tests described above provide initial information
concerning the kind of possible negative effects caused by contact
lens care regimens.

In summary, we found that all four soft contact lens care solutions
demonstrate slight toxic effects at higher concentrations on
conjunctival fibroblasts in vitro. It must, however, be pointed out
that these effects observed in vitro do not necessarily predict the
situation in vivo. Nevertheless, contact lens care solutions should
not be used carelessly. Every solution, even unpreserved, contains
certain active agents which should kill germs. It seems reasonable
that not only germs are attacked but also cells of the ocular surface.
Therefore, patients have to be informed about possible irritations and
if these occur then replacement of the contact lens care regimen
should be considered.

I'd like to add a couple, also.  I've posted these before, but perhaps
it's time again.

1.  The air makes a difference.  I've had problems at work, both with
eye dryness and respiratory problems.  It took a few years, but I
eventually learned (I guess I'm a slow learner) that when I had a bad
cold, going to work meant an eventual ear infection, which meant even
more time off work.  A bad cold isn't fun, but an ear infection can be
downright painful.  Once I learned, I stayed home, because it was less
time off of work in the end.  Once I started wearing contacts, I
discovered that I needed more eye drops at work.  The plain saline drops
worked at home.  Especially in the winter, when the air was dryer, they
didn't hack it at work.  I bought special drops, but only for work.

2.  We went hiking one day, when I was wearing contacts.  We only had a
pint of water for the five of us.  Not a problem, it was a short hike.  
It was a loop trail.  We got lost.  Not a problem, it was a lake.  We
were half way around the lake before we realized we had missed the
turnoff for the loop.  OK, we're doing a loop.  We'll just continue
around the lake.  Bad idea.  We get most of the way around and the trail
is gone.  Well, we aren't going back now.  Up the mountain and through
the brush.  It was pretty hard.  I get home, blink, and a contact falls
out.  I was dehydrated.