June 2011

 

COVER FEATURE

 

Corneal approaches to presbyopia: Creating multifocal corneas


by Enette Ngoei EyeWorld Contributing Editor

   

EyeWorld takes a look at corneal approaches to presbyopia treatment that have been successful in Europe

Multifocal corneas article summaryAt present, monovision LASIK is the only FDA- and Health Canada-approved corneal procedure for presbyopia treatment, according to W. Bruce Jackson, M.D., professor of ophthalmology, director of refractive surgery, University of Ottawa Eye Institute, Ottawa.

Routinely performed in presbyopia patients who have not developed cataracts, monovision LASIK creates a distance focus in the dominant eye and a near focus in the non-dominant eye. Newer procedures presbyLASIK and INTRACOR (Technolas Perfect Vision, St. Louis), however, create multifocality in the cornea. PresbyLASIK is performed with an excimer laser while INTRACOR utilizes the femtosecond laser.

Multifocal LASIK

In presbyLASIK, surgeons reshape the cornea into different zones for near, distance, and intermediate vision, allowing patients to regain good vision at all distances. The procedure is indicated for any potential refractive surgery patient with presbyopia who hasn't developed cataracts and especially if the patient also has astigmatism because excimer laser ablation presents the most accurate approach to astigmatism correction. PresbyLASIK can be preformed in eyes previously implanted with a monofocal IOL.

"We did research on [presbyLASIK] and found that in the hyperopes that we treated, we got very good results," Dr. Jackson said.

But without approval in North America, Dr. Jackson said what is happening primarily is surgeons are trying different presbyLASIK techniques with an off-label approach. Meanwhile, surgeons in Europe are performing much more presbyLASIK, and there they have more flexibility with their lasers, Dr. Jackson noted. There are a number of programs that have been developed to do presbyLASIK in Europe, he said. Some surgeons create a central zone for near vision, surrounded by a peripheral zone for distance vision (central presbyLASIK); others create a central zone for distance vision and the periphery is ablated for near vision (peripheral presbyLASIK). Still others are treating the dominant eye for distance and the non-dominant eye with a sort of blended visionit's different from monovision in that they have more range for distance and near created by altering the spherical aberration, Dr. Jackson explained.

"There are a number of approaches that surgeons are using, but [presbyLASIK] certainly does enhance near vision," he said.

In fact, studies in Europe have shown presbyLASIK to provide good distance and near vision. Some surgeons have reported patients achieving bilaterally 20/20 or better for distance and J3 or better for near with a majority of satisfied patients. Experts note that careful patient selection is key for good outcomes.

If patients are unsatisfied, presbyLASIK is reversible with a wavefront laser treatment.

PresbyLASIK vs. monovision LASIK

Even with the positive results the procedure has produced, however, some surgeons have fairly strong feelings against it.

"I think there are better ways to treat presbyopia than presbyLASIK," said D. Rex Hamilton, M.D., associate clinical professor of ophthalmology, and director, Laser Refractive Center, Jules Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles. By creating a multifocal cornea, function is traded for quality of vision, and by performing LASIK or PRK, tissue is permanently removed from the cornea, he explained.

Dr. Hamilton said he thinks monovision LASIK is a better option, and ultimately a lens-based option is the best as it gets at the root of the problemthe natural lens's loss of accommodation and overall stiffening. On the other hand, if a multifocal cornea is created, once a cataract develops later in life requiring lens surgery, the surgeon then has to deal with a cornea that's somewhat compromised optically.

There are also some downsides to presbyLASIK, the biggest of which, as with monovision LASIK, is the temporal nature of the treatment approach. As presbyopia progresses over time, the surgical effect becomes less optimal.

Still, according to Dr. Jackson, as North America tends to be a bit more conservative than Europe, presbyLASIK, if FDA-approved, would be embraced as part of a two-stage approach. "I think a lot of surgeons would do [presbyLASIK] first and then, when the patient really does have a cataract, move to cataract surgery," he said.

If presbyLASIK receives FDA approval, Dr. Jackson said it will be very popular because some surgeons are convinced of its value and are already performing it off-label.

Shaping without dissecting

A different treatment approach from presbyLASIK, INTRACOR makes use of the femtosecond laser to create multifocality in the cornea. Surgeons focus the laser beam at a specific depth without dissecting the corneal surface, said Mike P. Holzer, M.D., associate professor and director, refractive surgery, University of Heidelberg, Germany.

The procedure changes the shape of the cornea, making the central part of the cornea a bit steeper, essentially creating a magnifying glass in front of the eye, he said.

Without cutting open the corneal surface, as would be done for a flap procedure, the surface remains untouched and there is no risk for infection because there's no way bacteria can get into the cornea, Dr. Holzer explained. This results in an extremely quick recovery time and no risk of severe side effects. In fact, patients achieve results within the first day post-op, he said.

In near reading tests, patients typically gain between four and five lines of near visual acuity. With a follow-up period of more than 2.75 years, Dr. Holzer said patients showed no change in the shape of the cornea or in the refraction. This shows the procedure is stable.

"We had some discussions that maybe this biomechanical change that we induce with the femtosecond laser will change later on and then the outcome will not be as it should, but that's not the case. We can say that after 1 week, the outcome is achieved and stable over time," he said.

In fact, patients who don't achieve the expected results after 1 week typically do not improve.

"You have your final results very early," Dr. Holzer said.

What has been observed are differences in near reading ability gained between patients, Dr. Holzer noted. Some patients can read the finest print easily, while others can read or recognize things in the near distance but find it stressful to read a book for an hour and require a bit more near vision. Therefore, this is one area of uncertainty.

Selecting the right patients

The typical INTRACOR patient has not developed cataracts, although it is possible for a post-cataract surgery patient to have the procedure. IOL calculation after INTRACOR is not a problem, Dr. Holzer said.

The best candidate for INTRACOR is a patient with no further ocular disease, with a near add of 2.0 D or more, and with a distance refraction that should be between +0.5 D and +1.25 D spherical equivalent. The subjective cylinder should not be higher than half a diopter, he said.

Surgeons should first test the patient's level of expectation with a simulation of the effect of INTRACOR by adding a contact lens to the patient's eye with myopia to mimic the myopic shift that the patient might have later on, Dr. Holzer said.

"We ask [the patient], 'Will you be satisfied with this vision for distance?' and if he or she tells us it's fine, this would be a good candidate," he said.

One reason why patient selection for INTRACOR is important is because the procedure is not easy to reverse. "To reverse it would mean doing a kind of topography and a wavefront-guided surface excimer laser. It's not as easy to reverse it as taking a multifocal IOL out of the eye," Dr. Holzer said.

Managing patient expectations

As with all currently available presbyopia treatment approaches, none can offer the same vision as patients had in their 20s, Dr. Holzer said. To prepare them for this, he spends time talking with them. "What I tell my patients is no matter what kind of procedure I perform, they will be able to see near and distance, but they have to compromise. The compromise could be, for example, a change in contrast sensitivity," he said.

Patients need to know that with current presbyopia treatment procedures, good light conditions are important. Patients always have a near point at a specific distance from the eye, and they need to adapt to this new situation, Dr. Holzer said.

Editors' note: Dr. Hamilton has no financial interests related to his comments. Dr. Holzer has a financial interest with Technolas Perfect Vision. Dr. Jackson has financial interests with Abbott Medical Optics (Santa Ana, Calif.) and Allergan (Irvine, Calif.).

Contact information

Hamilton: hamilton@jsei.ucla.edu
Holzer: +49 6221-566995, mike.holzer@med.uni-heidelberg.de
Jackson: 613-737-8759, bjackson@ohri.ca

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