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Intracorneal lenses pursued for myopia and hyperopia
Early human studies indicate tolerance and good vision.
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NEW ORLEANS — Imagine performing a microkeratome cut and then inserting a lens that is biologically similar to human corneal tissue but made of permeable plastic. Theoretically, vision could be changed without removing tissue, and the procedure might be reversible. Building on this scenario, a new intra-corneal lens is being investigated.
“The possibility of an intracorneal lens that can be easily inserted under a microkeratome flap may permit refractive surgery in the office, without use of an expensive laser and with a high degree of reversibility,” said Herbert E. Kaufman, MD, director of the department of ophthalmology at the Louisiana State University Health Science Center here.
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FIGURE COURTESY ANAMED INC. |
The disc does not require any tissue removal.
“Flaps could be lifted and the lenses removed,” Dr. Kaufman said. Although uncertainty remains, “it is likely that these flaps in most cases never achieve the tensile strength of normal cornea and thus can be removed a very long time after the initial procedure.” As a result, lens exchange may be possible.
Biocompatible lens
The artificial lens under investigation is comparable to human corneal tissue in refractive index.
“The plastic is optically clear, biocompatible and convertible. The lenses themselves are 4.5 mm to 5.5mm. With the cornea over the top, this is a fairly good size optical zone,” Dr. Kaufman said.
The central thickness of the lens is very thin and edges are no more than 10 µm in thickness.
“The proper fabrication of thin lenses is very important because the cornea doesn't like spaces. Deposits tend to form at thick edges,” he said.
The discovery of new alloplastic materials with permeability exceeding that of normal corneal tissue and a refractive index and clarity equal to the cornea is a recent development that increases the likelihood of success for a intracorneal lens.
“In terms of glucose penetration and water penetration, this biopolymer lens compares favorably with normal corneal tissue. In fact, it may very well be better than nature,” he said.
Animal studies
Animal testing of the artificial lens in rabbits and pigs indicated there were no dislocations of the flap or lens. Mitchell Shultz, MD, described the histology from a pig.
“The flap anterior to the lens is perfectly normal. The epithelium is multilayered and perfectly normal. There are no epithelial defects, no corneal ulcers and no problems 6 months after the procedure.”
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FIGURES COURTESY ANAMED INC. |
Human studies are at an early stage, involving eight eyes, all outside the United States. The investigators are treating hyperopia in patients aged 21 to 53 years old. These patients have achieved good best corrected visual acuity and have no glare. In a few patients, contrast sensitivity was measured and seemed to be normal.
“There is virtually no reaction to these lenses inside the eye. So far it looks like a promising procedure. The device is being studied in many countries; U.S. studies should begin in a few months,” Dr. Kaufman said.
Presbyopic possibilities
In the case of presbyopia, a monovision approach might be tried. Even more likely is the use of multifocal lenses. For patients who do not tolerate monovision, the lens could be simply removed and exchanged.
“Most people like monovision, but some people don't. Most people enjoy multifocal lenses, but clearly some tolerate the multiple images poorly. In those people who are unsatisfied, the multifocal lens could be removed and perhaps exchanged with another lens,” Dr. Kaufman said.
He said that laser treatment for hyperopia “at the moment is not ideal.” A number of doctors have demonstrated that intracorneal lenses appear effective in refractive corrections without serious complications. Also fueling speculation that these lenses could eventually become a part of the refractive landscape is the now-common technique of creating a flap of cornea with a microkeratome that can be replaced without sutures, as in LASIK.
“This makes the operation easy and recovery rapid,” Dr. Kaufman said.
“Nobody knows for sure that this particular lens will be the future, but in my heart of hearts, I believe that 5 years from now the excimer laser will be used far less than currently. Whether it is this biopolymer lens or some other kind of surgical procedure, I think something reversible, or nearly reversible, will be used much more frequently,” he said.
For Your Information:
- Herbert E. Kaufman, MD, can be reached at LSU Eye Center, 2020 Gravier St., Suite B, New Orleans, LA 70112; (504) 412-1301; fax: (504) 412-1321; e-mail: hkaufm@lsuhsc.edu. Dr. Kaufman has a direct financial interest in the product mentioned in this article.
- Anamed Inc. can be reached at 25651 Atlantic Ocean Drive, Suite A1, Lake Forest, CA 92630; (949) 707-2740; fax: (949) 707-2744.