Ophthalmologists have developed a formula that slashes by nearly two-thirds
the likelihood that patients will need repeat visits to an eye surgeon to adjust
their vision after their initial LASIK visit. That's because the formula makes
it more likely that surgeons will get it right the first time.
The new results, presented at the European Society of Cataract and Refractive
Surgery meeting in London, are the result of a complex computer formula compiled
by doctors and scientists at the University of Rochester Medical Center that takes into account
myriad imperfections within the eye that weren't even known to exist a decade
Even though most patients come out of refractive surgery with vision that is
20/20 or better, doctors have noticed that some patients exit the surgery
slightly farsighted - not enough to seriously degrade their quality of vision or
to require contact lenses or reading glasses, but enough to be a leading reason
why people complain about the results of the surgery. A few others end up
slightly nearsighted. While many of these patients still see at a level around
20/20, the slight farsightedness or nearsightednessis is one of the chief
barriers preventing them from seeing even better, at a level around 20/16.
Eye surgeon Scott MacRae, M.D., of the University of Rochester Eye Institute
presented the results showing a dramatic drop in farsightedness among LASIK
patients. In a recent study where MacRae and colleagues used the formula, known
as the University of Rochester Nomogram, during surgery, just six of 445 eyes or
1.3 percent were slightly farsighted after LASIK. He compared this to results
from a previous study five years ago without the formula. In that study of 340
eyes, even though 91 percent of patients had 20/20 vision or better - the
highest known percentage of any large study in the world at the time - 74 of the
340 eyes treated, or 21.8 percent, were slightly farsighted.
"Though those results were among the best anyone had gotten to date, we
thought we could do better," said MacRae, who worked for two years with
post-doctoral associate Manoj Venkiteshwar, Ph.D., to develop the formula.
While some doctors have noticed that patients are more likely to be slightly
farsighted than nearsighted after LASIK, doctors have had no way to predict
which patients would be affected, MacRae said. If a doctor adjusted all of his
or her surgeries to avoid the problem, then the other 80 percent of patients
would wind up slightly nearsighted.
The new formula takes the guesswork out of the picture and establishes a
scientific basis for the phenomenon.
The software developed by Venkiteshwar and MacRae controls how the laser beam
dances around the surface of the cornea during a LASIK procedure, allowing the
surgeon to sculpt the cornea into just the right shape so that it produces as
flawless an image as possible. During a procedure that typically might last
anywhere from 15 to 60 seconds, the laser beam hits the cornea about 50 times
per second, with generally 750 to 3,000 pulses. The timing and aim, controlled
by both the surgeon and the software, have to be precise.
By taking into account the unique anomalies in each person's eye, the formula
predicts which patients are most likely to be slightly farsighted after a LASIK
procedure, then adjusts the laser to avoid that outcome.
Ironically, Venkiteshwar and MacRae found that the cause of the shift was the
new capability doctors have to fix subtle visual imperfections that weren't even
known to exist until David Williams, Ph.D., at the University of Rochester
developed a system to see them.
Williams' system opened the door, for the first time in history, to the
possibility of fixing not only the three major flaws in the eye that reading
glasses and contact lenses have corrected for decades, but also approximately 60
additional imperfections that were never known before. Nearly everyone has these
flaws in their eyes to some extent; while most people don't notice them, they
hurt our quality of vision in subtle ways. Since Williams' discovery, several
companies have introduced technology that makes possible a technique known as
customized ablation, a form of LASIK that corrects these imperfections, bringing
about a super-crisp quality of eyesight. Beyond making vision on the order of
20/15 or 20/16 possible or even commonplace in some groups of patients, the
technology also increases the eye's ability to see in situations where there is
low light or little contrast.
MacRae and Venkiteshwar were surprised to find that fixing these subtle
imperfections affects vision in unexpected ways. They found that some of the
improvements make an eye undergoing LASIK more prone to becoming slightly
farsighted in some patients, and slightly nearsighted in a few patients. They've
found the relationship in at least three different laser systems used in LASIK
"This is not something anyone would have predicted," said MacRae, who is a
professor of Ophthalmology and of Visual Science. "When you fix these flaws, it
can affect vision in ways that were previously unpredictable."
For instance, the team found that treating coma - a subtle imperfection where
a point of light looks like it has the tale of a comet - affects a patient's
astigmatism as well as his or her degree of nearsightedness or farsightedness.
Other common flaws that can now be fixed, but which also affect a person's
vision more broadly, include spherical aberration, where a point of light
appears to have several rings of light around it; trefoil, where a point of
light seems to be surrounded by three other points; and others such as secondary
astigmatism, quadrafoil and pentafoil.
MacRae credits the new formula, part of a procedure he calls
second-generation customized ablation, with slashing the need for repeat
treatments in patients from about 8 percent to 3 percent.
The latest results are part of an ongoing program by MacRae, a pioneer in the
field of customized ablation, to bring Williams' findings to the clinic and
improve patients' vision to unprecedented levels. Each year, MacRae says,
scientists and physicians learn new things that help future patients.
"We've taken a very good procedure and made it even better. I am extremely
confident in this technology, which I've even had done on myself. A
conscientious, systematic approach to evaluating patients is key. Not everyone
is a good candidate for LASIK. Surgeons need to be extremely diligent about
their pre-operative evaluations to maximize safety and the outcomes for their
patients," said MacRae, the author of the best-selling book on customized
ablation, Customized Corneal Ablation: The Quest for Supervision.