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Revised accommodation theory leads to new treatment option for presbyopia
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TALLMADGE, Ohio – Refractive surgery has enabled patients to overcome hyperopia and myopia and lessen their dependence on glasses and contact lenses. Ultimately, however, almost everyone feels the effects of presbyopia in middle age, and the need for spectacles returns. new thinking on the physiological changes that affect accommodation during presbyopia has led to a novel technique being investigated by ophthalmologists in the United States and abroad that may allow surgeons to conquer the next frontier in vision correction.
Accommodation theory
The current view of accommodation stems from the research of Hermann van Helmholtz, who theorized that when the eye accommodates, the ciliary muscle contracts, reducing tension on the zonules. The reduction in tension allows the elastic capsule of the lens to contract. According to this theory, during presbyopia, the lens hardens as a function of age and no longer changes shape when the zonules are relaxed.
Todd Beyer, DO, medical director of System Optics here, agrees with the basic Helmholtz theory of accommodation, but says this theory does not consider the ciliary muscles’ attachment to the sclera. Dr. Beyer believes that when the eye focuses, the ciliary muscle contracts, creating a force in the posterior direction that moves the vitreous anteriorly toward the lens. With age, the sclera becomes more rigid, which inhibits the movement of the ciliary muscle and reduces these forces.
“It is a more complicated mechanism than what Helmholtz originally envisioned,” Dr. Beyer said.
New treatment approach
Relying on this theory, Dr. Beyer has explored a new procedure, laser presbyopic correction (LPC), which ablates scleral tissue, thus allowing the ciliary muscle greater flexibility to move, relaxing tension in the zonules and allowing the lens to accommodate.
The procedure, performed under periorbital or retrobulbar block, consists of ablations in each of the eye’s four quadrants. “We are trying to decrease scleral rigidity in each quadrant so that when the muscle contracts it can pull in and indent, allowing the lens to change shape again and accommodate,” Dr. Beyer said.
Fornix-based conjunctival flaps are created in each quadrant. The blood vessels are coagulated, and two radials are measured in each quadrant. The radials are 1.5 mm apart, begin 0.25 mm behind the limbus and extend 3.75 mm posteriorly. Each ablation is 0.65 mm wide, at a depth of 90% of scleral thickness, and is performed with an erbium:YAG laser manufactured by Orlando, Fla.-based Surgilight Corp. According to Dr. Beyer, the erbium:YAG laser has a slight thermal effect, which facilitates coagulation during the procedure.
Developed in Venezuela
Dr. Beyer began investigating LPC after researching results in Venezuela, where he first observed the procedure in 1999. Because the procedure is still considered experimental by the U.S. Food and Drug Administration, it cannot be performed in the United States. Dr. Beyer is developing LPC with John Rodgers, MD, who currently performs the procedure in Nassau, the Bahamas.
Drs. Beyer and Rodgers have been performing LPC since December 2000. In Nassau, the surgery has been performed on eight patients, including Dr. Beyer, totaling 16 eyes. Of those patients, six have had very positive results, achieving 1 D to 2 D of improvement in uncorrected near vision without regression, Dr. Beyer said.
One of the remaining two patients experienced little effect, likely because of a problem with the laser tip, Dr. Beyer said. The other patient was Dr. Beyer himself, the second patient to undergo the procedure at the Nassau facility in December 2000.
“There was a good effect for the first month, and I saw four lines better than I had preoperatively,” Dr. Beyer said. “However, it was only the second procedure, and the ablations were too short and too shallow, so I experienced regression. Still, I am still seeing two lines better.”
Despite the regression, Dr. Beyer said the treatment was not uncomfortable, and he is still able to use his computer and do chart work without glasses.
“There was not much pain or discomfort, just redness, which lasted about 6 weeks,” he said. “During the postoperative period, I did not see a significant change for the first 2 to 3 weeks. Beginning with the fourth week, I noticed improvement, which continued through the third month, when my vision was J2. I had been J5 preoperatively. Now at 6 months, I’m at J3, but I don’t expect to regress completely.”
Procedure being improved
---Five days postop: This is the inferotemporal ablation quadrant of Dr. Beyer’s eye 5 days after LPC. The two blackish linear radial marks indicate the ablated areas.
Because LPC is relatively new, it is under constant revision and improvement, Dr. Beyer said. In addition to recognizing the need for longer, deeper ablations, the surgeons also have realized the importance of ablation placement.
“We have rotated the incisions so the eyelid covers them better,” Dr. Beyer said. “The incision and ablation create a small dark mark, where you can see the choroid coming through. We now want those incisions covered so they are not aesthetically displeasing.”
Because the central goal of the procedure is to reduce the rigidity of the sclera, Dr. Beyer also is evaluating the possibility of using chemicals or enzymes, either as an adjunct to or as a replacement for the laser procedure.
Dr. Beyer does not expect to follow the lead of other surgeons who take a more mechanical approach to the procedure. “Some surgeons are performing a sclerotomy, then using spacers inside the eye to prevent it from healing together,” he said.
Surgilight is conducting phase 1 studies for use of the laser for LPC in Spain, Dr. Beyer said. Centers in Korea and Japan also offer the procedure, and, in the next few months, it will be available in Canada.
Limitations
Dr. Beyer does not expect LPC to eliminate presbyopia altogether and said the effect of the procedure likely will be limited to providing 1 D to 2 D of near vision improvement.
“This procedure addresses only one component of presbyopia,” he said. “It does not address the weakening of the ciliary muscle, the hardening and flattening of the lens or the flattening of the cornea over time. All these factors are not being addressed, but we can address one factor and achieve some effect.”
Another limitation is that, similar to radial keratotomy, LPC can weaken the eye, making it more likely to rupture due to trauma. There also is limited long-term knowledge of how the surgery will affect the eye, although Dr. Beyer notes that he has followed patients for 2 years after surgery in Venezuela, and they are doing well.
Patient selection
Patients should need at least a 1 D add for reading and should be within a spherical equivalent of +0.75 D to –0.75 D and have 1 D or less of astigmatism. Patients are excluded if they have a history of ocular trauma that resulted in hyphema, angle recession or dislocated lenses; if they have had radial keratotomy; or if they have had collagen vascular disease, including rheumatoid arthritis and lupus.
Because LPC is still undergoing development, Dr. Beyer has been reluctant to push the procedure, although it is offered as an alternative for presbyopic patients.
“Usually, the patients asking for this procedure are those who are just becoming presbyopic and have just had LASIK,” he said. “Patients who have had LASIK really don’t want to wear glasses.”
Patients are required to wait at least 6 months after LASIK to ensure the eye has stabilized and enhancements will not be necessary.
“The best patients are between 44 and 50 years of age, have lost accommodation and would like to be less dependent on their glasses, but are not so demanding that J2 or J3 will not be acceptable,” he said. “Patients who want to have crisp J1 vision are not good candidates.”
For Your Information:
- Todd Beyer, DO, is in group practice in Tallmadge, Ohio, where he specializes in refractive and oculoplastic surgery. He can be reached at 518 West Ave., Talmadge, OH 44278; (330) 630-9699; fax: (330) 630-2173; e-mail: ToddBeyer@aol.com.