I guess we should talk a bit about these strange beasts known
as TORIC contact lenses. They come in many hard and soft flavors
but I will limit this month's discussion to the SOFT DISPOSABLE
variety. As of this writing, there are only three available. The
first one on the market was made by Ciba Vision Corporation. Their
lens is called Focus Toric and it is designed for one-month replacement.
The other two are made for three-month replacement and the manufacturers
are Bausch & Lomb and CooperVision. We can call these lenses
"planned replacement" instead of disposables, if you
wish, since we think of the "true" disposables as one-day,
one-week, or two-week lenses.
Soft toric contact lenses are not new. If memory serves, the first
soft toric lens was a Hydrocurve lens and it hit the market in
1977-78, so that's nearly 20 years of soft torics! So what's the
big deal with planned replacement soft torics? The ability to
manufacture large quantities of a very sophisticated design, and
to do it with consistent quality and reproducibility, and at a
reasonable price, is quite an accomplishment. And it's great for
all you folks with astigmatism who have been asking for disposable
contacts. TORIC refers to astigmatism, so when you hear (and you'll
be hearing quite a lot shortly) a reference to toric contact lenses,
you'll remember they're talking about contact lenses for people
with astigmatism. (See my August, 1996 column)
So what makes these torics so sophisticated? If you recall my
story about the egg and the ping-pong ball as they relate to the
shape of the astigmatic and spherical corneas, respectfully, then
you remember that astigmatic eyes are "stronger" across
one direction of the eye than another. This condition demands
that you correct that eye in the same manner, i.e., the contact
lens must be stronger in one direction across the lens than another.
Now that's all fine but how do we affirm that the contact lens
lines up properly and in the right direction? That's right, we
weight them! Not with tiny barbells or anything, but by creating
a slightly thicker edge that will rest near the bottom of the
lens as it sits on that eye. (You're chuckling at my barbell statement….but
there was actually an attempt to ballast one of the early torics
with a certain metal alloy, although the details have escaped
me)
POSITIONING is everything! The success of soft toric contact lenses
is 90% dependent on POSITIONING. Well, almost….you still
have all the other factors that contribute to any soft lens fitting
success, but the rotation, or lack of it, is certainly primary
if we are to achieve good vision. And this rotation can vary,
causing transient blurring of vision; therein is the real challenge….predicting
the final positioning of that contact lens on the eye during normal,
everyday activities.
Hence, we arrive at the real significance of PLANNED REPLACEMENT
toric lenses, and that is the ability to "try before you
buy". This was never as big an issue with regular soft disposables,
because of their easier predictability. Predicting the performance
of a toric lens is much more of a crap shoot. Now we can order
a "test" pair for our patients that they can even take
home and wear for a week or so before a final determination of
contact lens parameters is made. I have, on occasion, even ordered
up to three pair for a patient, although this is rarely necessary.
Planned replacement (nearly disposable) toric soft lenses are
now a reality for many people who have been asking for them for
years. This is one group of folks that really deserve a "trial
run" with their contacts.