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Role of neuroadaptation with use of multifocal IOLs merits more discussion
Talking to patients about this concept from the outset could help with their overall adjustment to the lenses.
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As more surgeons and patients turn to multifocal IOLs as a treatment option for presbyopia, patient complaints of overlapping images, reduced contrast sensitivity and halos have been on the rise. The process of neuroadaptation can help patients adapt more quickly and successfully to these lenses, according to several clinicians who spoke with Ocular Surgery News on the topic.
 David R. Hardten |
Because the visual cortex contains no prewired circuitry that allows it to digest information from multifocal lenses, the brain requires a period of adjustment known as neuroadaptation that involves suppressing near vision when gazing at distant objects and restricting distance vision when focusing up close.
The greater the disparity between images transmitted to the brain, the more difficult it can be for patients to adapt, OSN Cornea/External Disease Section Member David R. Hardten, MD, FACS, explained.
“With presbyopic IOLs, we are trying to get both distance and near [vision] out of the same implant,” he said. “In some sense, there is a simultaneous projection of different images on the retina — one that is focused on distance and one focused on near or intermediate. Neuroadaptation involves the brain learning to use these different images.”
“Neuroadaptation is a fancy way of our brains learning how to adapt. … It’s like if you move to a new city. At first it’s all strange and foreign, and you really can’t adapt to it. Then, after a while, it seems commonplace,” he said.
Image enhancement
Patients neuroadapt when they get new spectacles or a contact lens prescription or undergo an intraocular procedure. Because multifocal lenses require greater adaptation, the amount of adjustment the brain needs to make between images can be pushed to the limit of its capability, according to J.E. “Jay” McDonald, MD.
“In monovision, if you have one eye set at distance and the other eye at [near] and the separation is only up to 1.50 D, the spatial frequencies are close enough together that the visual cortex can put this information together and we get fusion at almost every distance,” he said.
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OSN Optics Section Editor Jack T. Holladay, MD, MSEE, FACS, explained how image enhancement works in unison with the optical and sensory systems. He has patients first look at a lower-contrast version of a picture and then instructs them to stare at a higher-contrast version. When he shows the original picture again, it does not look the same.
“After about 30 to 40 seconds, [the images] come back together because the brain readjusts and gets things right,” he said. “That’s the short-term neuroadaptation that is going on all the time. Studies have shown there is a long-term neuroadaptation, and the long term is the kind of thing that makes people get a better quality image than you would expect from their optics.”
At one time, the biggest challenge ophthalmologists faced was removing cataracts and having patients use thick pairs of aphakic spectacles. Patients were forced to adapt or they faced blindness. As new technologies have developed, greater demands have been placed on patients to adapt, said Robert M. Kershner, MD, MS, FACS.
“Neuroadaptation is a big part of what we do,” he said. “No ophthalmologist who operates on patients is immune from dealing with this phenomenon. Most ophthalmologists are not well versed in the neural mechanisms that are involved in neuroadaptation. For many it’s a crapshoot to see what the patient does. He either accepts it or he doesn’t. I think the ophthalmologist who understands the mechanisms of neuroadaptation is going to be a better surgeon overall.”
Adaptability changes with age
As a general rule, younger patients tend to adapt more quickly to alterations in their visual systems. “The older you are, the longer it’s going to take, if it happens at all,” Dr. Kershner said. “Cataract patients who are elderly, have their cataracts removed and have multifocal lenses implanted are oftentimes going to be miserable if they cannot adapt to the change. Some never will. Finding ways to determine who will be a good candidate and who will not will certainly become a challenge as more and more patients opt for advanced optical technology IOLs.”
Neuroadaptation can take several weeks to 12 months to occur. Dr. McDonald uses monofocal monovision for presbyopic IOL corrections in his practice, explaining to patients that adapting to IOLs is not that different from adapting to spectacle use.
“When you get your glasses changed, you go through a neuroadaptation to your new pair of glasses. It’s kind of using some of the same processes. Adapting to some of the multifocal technologies sometimes takes a little longer because it’s a little more complicated, especially when you are presenting two different images on the same retina. The brain is pretty plastic and can adjust,” he said.
Neuroadaptation tool
Several recent studies have shown that a neuroadaptation software program may have the ability to help patients improve vision.
At the American Academy of Ophthalmology meeting in November, Richard L. Lindstrom, MD, and Daniel S. Durrie, MD, presented the preliminary results of a study on NeuroVision, an Internet-based computer program that trains patients to improve vision, Dr. Holladay said. The program is designed to help patients improve near vision by training the brain to automatically sharpen images and accelerate the amount of time needed to adapt to new lenses.
The software works in much the same way that Adobe Photoshop does when enhancing low-resolution digital photographs.
In another study, reported at the European Society of Cataract and Refractive Surgeons meeting in Stockholm, Sweden, Ulrich Mester, MD, said that patients who received this training in one eye had improvements of one to two lines in their visual acuity compared with the fellow untrained eye.
“What we’re seeing is people are beginning to recognize that we can do something to improve the computer part of our vision system by doing training, and that’s what NeuroVision actually does,” Dr. Holladay said. “It’s exciting because some of these patients may not need an enhancement or a retrievement. … The other aspect is people who have had multifocal lenses or have had refractive surgery might be able to go through this training period and accelerate their recovery so they see better faster but also may end up with better vision down the road.”
Patient education
Educating patients on the relationship between neuroadaptation and multifocal lenses may be an important step.
Dr. Kershner said he introduces the concept early and tells his patients about possible changes in their visual systems. He said that most patients believe receiving an implant is a simple procedure and that they will have perfect vision.
“They don’t realize what goes into it,” he said. “It’s more than altering and hopefully correcting the visual focus of the ocular system. It’s a process of trying to get their brain to accept the alteration that we’ve induced. … I tell patients that some can adapt to this very quickly and some cannot.”
Dr. McDonald hopes to develop new technology that quantifies ocular dominance in order to help physicians identify who will adapt more easily to multifocal and monofocal lenses.
“There is a personality profile that I think is more readily adaptable to new things for something that’s not perfect, but there’s a neural basis in some people to adapt to, say, multifocality or monovision over others, just like some people are ambidextrous, and they can learn how to eat easily with their left hand. In other people, it’s a real struggle.”
For more information:
- David R. Hardten, MD, FACS, can be reached at Minnesota Eye Consultants, 710 E. 24th St., Suite 100, Minneapolis, MN 55404; 612-813-3600; fax: 612-813-3658; e-mail: drhardten@mneye.com.
- Jack T. Holladay, MD, MSEE, FACS, can be reached at Holladay LASIK Institute, Bellaire Triangle Building, 6802 Mapleridge, Suite 200, Bellaire, TX 77401; fax: 713-668-7336; e-mail: holladay@docholladay.com.
- Robert M. Kershner, MD, MS, FACS, can be reached at Eye Laser Consulting, Palm Beach, Florida; e-mail: kershner@eyelaserconsulting.com.
- J.E. “Jay” McDonald, MD, can be reached at McDonald Eye Associates, 3318 North Hills Blvd., Fayetteville, AR 72703; 479-521-2555; fax: 479-521-6761; e-mail: jaymcd@swbell.net.
- John Misiano is an OSN Staff Writer who covers all areas of ophthalmology.