SkyandTelescope.com September 2014 35What Is a Cataract?
diff raction spike is, they might not notice the new ones
in their fi eld of view. But amateur astronomers pay close
attention to what we see, and we most defi nitely notice the
eff ects of cataract surgery. We even hear horror stories of
people who have given up astronomy because of what the
surgery did to their vision.
That’s the bad news. The good news is that if you
go into the procedure with both eyes open, so to speak,
you stand a much better chance of coming out of it with
vision that still works for astronomy.The Surgery
We had heard other amateurs complain of diff raction
eff ects from lens edges in the light path, so Kathy asked
her surgeon for a large lens, one larger than her dilated
pupil. But the largest replacement lens he would use was
6 mm, a dicey proposition for a relatively young person
whose pupils might still open to 7 mm.
What’s worse, the diameter of the replacement lens is
only one consideration. When the surgeon removes the
natural lens and implants the artifi cial one, the fi rst step
is to remove the front of the lens capsule, a clear, paper-
thin sack of tissue that surrounds the lens, in a process
called capsulorhexis. That opening typically has a smaller
diameter than the lens, and for good reason: the lens cap-
sule helps hold the lens in place, and a smaller opening
helps prevent the migration of loose lens cells that might
later cause cloudiness in the rear part of the lens capsule.
But the smaller diameter of the capsulorhexis meant that
Kathy didn’t get a 6-mm clear aperture when she chose a
6-mm lens; the aperture was closer to 5 mm.
That was still better than having cataracts, so Kathy
went ahead with the surgery. Cataract surgery is done one
eye at a time. After the fi rst operation, Kathy immediately
noticed two improvements. Not only could she see clearly
again in that eye, but because the cataract had been acting
as a yellow fi lter, everything looked bluer, too. For the fi rst
few hours, she was very pleased with the outcome.
However, the moment she looked at a bright light that
evening, she knew something was wrong. The eye withCATARACT SURGERY These days, cataract surgery is
a routine procedure. First the surgeon performs a cap-
sulorhexis, carefully removing a front section of the lens
capsule.Next, the surgeon breaks up the natural lens using ultrasound
waves in a process called phacoemulsifi cation, then removes
the lens fragments from the lens capsule using suction.Finally, the surgeon inserts the replacement lens, folding the lens to
fi t it into the incision. Support wires called haptics extend from the
replacement lens to hold it in place in the lens capsule.If secondary cataracts develop after the surgery, they are removed
with a capsulotomy, where the back of the lens capsule is lasered
away. The patient sits upright for this follow-up procedure.The eye’s natural lens consists mostly of long, thin, trans-
parent cells called lens fi bers. Over time, ultraviolet light
from the Sun, and a host of other factors such as trauma
or diabetes, can damage proteins in these cells, hardening
and clouding the fi bers. The cells change their index of
refraction as a result, and they don’t do so uniformly. Dif-
ferent parts of the lens harden faster than others, creating
multiple focal zones. These changes muddy vision and
may even create multiple images of the same object.JERRY OLTION (4)IrisCorneaLens Lens capsuleCataract layout.indd 35 6/23/14 12:17 PM