Presbyopic correction follows multiple directions

"Surgical correction of presbyopia has been termed the new frontier, the final frontier, and the holy grail for cataract and refractive surgery, and based on demographics and emerging technology, we can expect a tremendous increase in demand for this type of procedure. However, it is clear many factors play a role in presbyopic correction, a good outcome will be determined by the patient according to his or her needs, and no one procedure will suit all," said Dr. Jackson, professor and chairman, department of ophthalmology, University of Ottawa, Ontario, Canada.

The development of treatments for presbyopia is hampered in some respects by a lack of complete understanding of the etiology of presbyopia, disagreement on the mechanism of accommodation, and controversy over how it should be measured. Nevertheless, the goal for presbyopia correction is clearly to provide good distance and near visual acuity under all conditions.

The sclera-based procedures include anterior ciliary sclerotomy, laser presbyopia reversal, and scleral expansion surgery using bands or segments. In anterior ciliary sclerotomy, eight radial incisions are made in the oblique quadrants to expand the sclera and increase equatorial zonular tension. Results achieved with this approach show that it results in increased accommodative amplitude of up to 2.2 D, but the effect is not durable.

"Unless there are barriers placed with titanium or silicone, regression occurs," Dr. Jackson said.

Another alternative is to make incisions in the sclera by ablation with the erbium:YAG laser. Clinical trials of that procedure are in progress, and increases in accommodation of 2.3 D have been reported to date.

With placement of scleral expansion bands or segments under a scleral belt loop, up to 3 D of increased accommodation has been reported. For various reasons, however, this is very controversial surgery, Dr. Jackson said.

"There are a number of complications associated with this procedure, including the variability of an unexplained effect on the fellow eye as well as poor cosmesis and even anterior segment ischemia," he noted.

In the realm of cornea procedures, various inlays are being investigated. A biocompatible, microporous, hydrogel intracorneal lens is under investigation in clinical trials sponsored by Intralens Vision (formerly Anamed). In addition, Acufocus has developed an ultrathin inlay based on small-aperture optics that has been associated with good preliminary results.

The cornea has also been the target for laser-based presbyopia correction procedures since 1991. In various protocols, the ablations have been placed in various patterns, including off center, in the center of the cornea with the periphery for distance, and the reverse-center distance, periphery near.

"There are many advantages to excimer laser surgery because it is less invasive relative to some other techniques and uses available technology. However, it also can be associated with a risk of visual symptoms and may result in loss of quality of vision," Dr. Jackson said.