CK may provide better vision than contact-lens monovision.
Artículo extraído del sitio www.eyeworld.org
A new study suggests conductive keratoplasty (CK) for presbyopia has visual advantages over contact-lens monovision.
Daniel S. Durrie, M.D., director, Durrie Vision, and clinical associate professor, University of Kansas Medical Center Overland Park, Kan., tested 10 presbyopic patients that were at least 50 years old and who only wore reading glasses, each of whom received three different-powered contact lenses in their non-dominant eye before receiving CK treatment with the ViewPoint CK System (Refractec, Irvine, Calif.).
Dr. Durrie was to present his results at last month's meeting of the American Academy of Ophthalmology, New Orleans, but said that both distance vision and near vision was better with CK.
He said he also has evidence to explain why CK's results were more impressive.
A closer - and farther - look
Dr. Durrie selected patients that were 50 or older, had 20/20 UCVA distance vision, were presbyopic, and hated their reading glasses.
“What we did was put them through a series of objective and subjective tests to look at their quality of vision, wavefront analysis, depth perception, and contrast sensitivity,” Dr. Durrie said. “We also did an extensive patient questionnaire to see what their functional visual acuity was at near and distance.”
Patients received a +0.75 D extended wear soft lens in their non-dominant eye, adapted to it over a week or two, then their vision was re-tested. The same process occurred with +1.50 and +2.50 lenses, and finally with CK.
Functional visual acuity and subjective response results of the lens wear and CK were compared at one day, one week, one month, and three months post-op.
“CK performed better than contact-lens monovision in both the objective performance and the patient's perception,” Dr. Durrie said. “When we asked patients which one of the contact lenses does CK compare to, their comments were: ‘CK is better than any of those contact lenses.'”
Dr. Durrie also said he performed a second study in 50 patients that also had the three lens contact lens fitting and then they were randomized.
Half received CK for presbyopia in their non-dominant eye and half received hyperopic LASIK with the Alcon system in their non-dominant eye to improve their vision. Those results, which were not available as of press time, are slated to be discussed during Dr. Durrie's lecture.
Conductive Keratoplasty: a thermokeratoplasty technique that uses RF energy to heat & reshape the cornea:
One reason Dr. Durrie performed his studies on CK was that he found that in clinical practice, presbyopes corrected by CK had surprisingly good distance vision.
“Even six years ago, during the first hyperopia clinical trials, we'd have 60-years-olds that come back and see 20/20 at distance uncorrected and 20/20 up close uncorrected in the same eye,” Dr. Durrie said. “That shouldn't be possible. If a 60-year old sees J1 up close, he should see 20/200 at distance, not 20/20.”
Now with scientific evidence that superior distance and near vision is possible with CK, Dr. Durrie said that the better vision has to do with spherical aberration.
He said that in a young eye, the cornea has positive spherical aberration and the lens has negative spherical aberration, and they cancel each other out to get good optics.
But with age, he said, the lens not only gets harder, it gets rounder.
“As the lens gets rounder, it loses its negative spherical aberration, and therefore the cornea and the lens do not match as well,” Dr. Durrie said. “What CK does is it reduces the cornea's positive spherical aberration to better match the middle-aged lens.”
Monovision with a contact lens or glasses would just change the spherical refractive error without changing the slope of refraction, Dr. Durrie said. But CK does change the slope of refraction, he said.
“This is one of the reasons I feel that CK gives a better vision than expected,” Dr. Durrie said.
During Dr. Durrie's CK study, he said he showed with wavefront that when contact lens power was increased from +0.75 to between +1.5 and +2.5, the positive spherical aberration worsened. But wavefront showed that the spherical aberration changed toward the correct direction with CK to better match the lens, he said.
“One thing that might come out of this study is people may make a better contact lens for monovision,” Dr. Durrie said.
ViewPoint CK System components
ViewPoint CK System components. Source: Daniel S. Durrie, M.D.