When I was in optometry
school, a well-meaning clinician told me not to bother doing a
sphero-cylinder over-refraction (SCOR) when fitting soft toric
lenses. They just don't work, she told me. You get very strange,
meaningless numbers that don't tell you anything about how the lens
is fitting. She was very wrong, but it took me a while to realize
this and to learn to make sense of the data from an SCOR.
important and useful for just about any type of contact lens
correction. The data provides you with two pieces of information:
the quality of vision attainable with that lens brand or design, and
how to change the power for optimal vision. This is especially true
for soft torics.
For example, if you can't
get better acuity than 20/30 with the SCOR, but the patient has
20/20 best-corrected acuity, then something is really wrong about
the lens. It could be that it doesn't fit well and the axis doesn't
maintain a stable position. Some lenses just don't work well with
some eyes and you may never know why; the bottom line is that if you
can get a good, stable acuity with the SCOR, then no matter what the
numbers are, it's possible to refine the power so the patient can
see well. If you can't get stable acuity with an SCOR, try another
base curve or another lens brand.
What about the numbers you
get from an SCOR? They're strange because they can result from
cross-cylinders. If the term cross-cylinders gives you night sweats
and you don't want to know what the numbers actually mean, you can
simply use one of the many calculators available to find the best
lens power. You simply input the refraction, toric lens power, the
SCOR and, sometimes, the observed amount of rotation.
My favorite calculator is
called OphthalmiCalc, available online from the University of
or just Google OphthalmiCalc.) I like it because it tells
you how much rotation you should see when
you look at the lens, given the SCOR you obtained. This is a nice
feature, because if the lens doesn't appear to be rotated this
amount, then something is probably wrong with the lens power or it's
not maintaining a stable axis position. Other useful calculators
include Coopervision's ToriTrack and one available through
What's most important,
though, is knowing when to use a calculator in the first place. For
lenses that come in 10-degree axis steps and cylinder powers below -
2.00D, I usually just use LARS to adjust for any observed rotation.
In such cases, I use the SCOR only to make sure I can get good
acuity with the lens.
But for higher cylinder
powers and smaller axis steps, LARS isn't as useful because it's
harder to measure the rotation precisely enough. For these lenses, I
usually use a calculator to determine the final lens power.
In my next column, I'll
discuss why you get such strange numbers
with soft toric SCORs and how to interpret them.