Corneal surgery or phakic lens? The future of refractive surgery is debated

An anterior chamber phakic lens using diffractive optics may hold the potential for correcting presbyopia.

Advances in both keratorefractive surgery technology and phakic lens designs will determine the dominant refractive procedure of the future, according to presentations given here.

During a debate session at VisionQuest 2002, Terrence P. O’Brien, MD, and Lee T. Nordan, MD, took opposing viewpoints and discussed what might be the dominant refractive surgical procedure in the year 2010. While keratorefractive surgery and lens implantation procedures each have significant advantages, both surgeons agreed clear lens extraction for correction of myopic refractive errors presents unreasonable risk.

Dr. O’Brien, director of refractive eye surgery at the Wilmer Eye Institute, Johns Hopkins University School of Medicine, was assigned the pro-keratorefractive surgery position. He said he believes keratorefractive surgery in some form will remain the dominant procedure in the year 2010 because of the low incidence of serious, vision-threatening complications and the control afforded by the precision of the excimer laser. Improvements in wavefront technology, microkeratome design and eye-tracking technology will further enhance the effectiveness of such procedures, he said.

Dr. Nordan said the reproducibility and high quality of vision that phakic lens technology can provide will overtake keratorefractive procedures. The potential for cataract surgeons to expand their surgical expertise into refractive lens surgery without the necessity of purchasing high-cost lasers will additionally drive the phakic lens market, he said.

Pro-keratorefractive

Dr. O’Brien said IOL surgery can adjust the power of the optical system, but the cornea still accounts for the majority of the dioptric power and remains an important factor in the pseudophakic patient. He noted that placing any lens inside the eye presents additional risk compared to extraocular procedures.

According to Dr. O’Brien, there are definite advantages to extraocular surgery, and certainly the excimer laser offers additional advantages, he said.

“The excimer laser itself, that technology, affords us the precision and accuracy, the ability to titrate treatments with the potential for accurate and subtle re-treatments,” he said.

Advances in wavefront technology will also expand the LASIK treatment capabilities to include higher-order aberrations as well as irregular astigmatism. Advances in excimer laser beam shaping and delivery will likely allow surgeons to create smooth ablations and possibly reduce aberrations, he said.

“In the future, we hopefully will be able to produce just about any optimal corneal shape desired with excimer laser technology to reduce aberrations and preserve contrast sensitivity performance across a range of illumination conditions, treating the corneal surface and sculpting the cornea,” he said.

“We have scanning spot ablation systems that can give us custom ablations. We have active tracking getting better, allowing us to center the procedures. And, as Ron Krueger, MD, and others have pointed out, we are at the point with current technology where we can remove a little bit here and back off a little there,” Dr. O’Brien said.

Keratorefractive complications

Future trends

Both keratorefractive surgery and phakic lens implantation have the potential to be the preferred refractive surgery approach for the future. Sources agree that clear lens removal holds “unacceptable” risk as a refractive surgery option. Surgeon preferences and advances in technology will help drive the refractive market and shape future trends.

Dr. O’Brien acknowledged that there are complications with LASIK as with any refractive procedure. However, complications are principally related to the devices used, including the microkeratome and excimer laser.

“Tremendous advances in microkeratome designs have reduced microkeratome-related complications and thus made the procedure safer. Currently, all [microkeratomes] work well, producing excellent flaps. The likely trend for the future is that this will continue to get better and safer for refractive surgeons,” he said.

Additional technologies in development, such as the femtosecond laser being manufactured by IntraLase, will potentially further reduce microkeratome-related complication rates and perhaps provide smoother beds, which may help in wavefront-guided treatments, he said.

“It will be interesting to see what the flap of the future will be, but I have a feeling that refractive surgery will still involve some corneal treatment to account for the majority of our procedures,” he said.

Dr. O’Brien noted that improved results are being reported with wavefront technology over previous generations of technology. Referring to data compiled as part of the Visx custom wavefront trials, he said, “We are already finding nearly 100% of patients seeing 20/20 at 6 weeks and 6 months, and a significant portion are closer to 20/16 or 20/10.”

He said advances in molecular biology and understanding of corneal wound healing will also influence outcomes and whether refractive surgery will remain on the surface.

Risk vs. reward

Dr. O’Brien acknowledged that IOL refractive procedures are tempting for certain patients, particularly patients with higher refractive errors that cannot be treated by corneal procedures.

“Are the risks worth the reward?” he asked. “Even with perfect surgery we could end up with significant complications leading to devastating loss of vision.”

Refractive lensectomy carries the potential for complications, which can include subtle changes such as opacification of the posterior capsule requiring a subsequent capsulotomy, or more serious ones, such as increased risk of retinal detachment. Additionally, removing a clear lens causes immediate loss of accommodation and, like cataract surgery, can result in vitreous loss.

Dr. O’Brien said there are advantages to phakic IOLs, such as excellent refractive results, fast visual recovery, preservation of accommodation and potential reversibility. They do not alter the cornea, and the outcome is not subject to wound-healing effects.

Phakic IOLs have the potential for serious complications as well, as noted in European clinical trials, Dr. O’Brien said, citing hemorrhage and corneal edema as potential untoward events.

There is also a risk of chronic inflammation, cataract development, pigment dispersion, glaucoma and endothelial cell loss.

“The devastating complications that can occur with these conditions make them, for the moment and the mid-future at least, potentially risky,” he said.

“We need to have ethical principles for greater safety for elective surgery, have a careful risk-vs.-benefit ratio and assess the long-term risk of problems, especially late occurrence of retinal detachment with phakic implants,” he said.

“In addition to design issues, difficulty in inserting some of the phakic implants, the requirement for multiple iridectomies and careful biometry, we have a long-term intraocular risk. The advantages of keratorefractive surgery — namely, that it is extraocular, precise, accurate, has titratable re-treatment and can treat higher-order aberrations — will help these keratorefractive surgeries remain dominant,” he said.

“The addition of wavefront, customizability and advances in understanding and modulating corneal wound healing at the molecular level will also allow the corneal procedures to dominate,” he added.

Lenses to dominate

Dr. Nordan took the view that IOL procedures, in some form, will dominate refractive surgery by the year 2010.

“I absolutely agree with Dr. O’Brien that to remove a clear lens and cause problems from a posterior chamber intraocular procedure is not where we are going. We’re here to talk about phakic lenses. What we are really talking about is aberration-free refractive surgery,” he said.

According to Dr. Nordan, corneal excimer laser surgery has limitations; namely, that the quality of visual function decreases as the refractive error increases. Additionally, he said, presbyopia cannot be corrected, and attempts to do so on the cornea will fail because distance vision is destroyed.

Dr. Nordan explained that keratorefractive surgery always induces aberrations; thus, the quality of the laser or the stromal bed are relatively unimportant since they are not the primary factor in good visual results.

“Keratorefractive surgery is good, it’s the best we’ve had, but it is inherently defective,” he said. “What gives us good vision is healing of the epithelium. The concept of changing the surface of the cornea an eighth of a micron vs. a quarter of a micron is irrelevant to the result because healing of the epithelium sets in and distorts the result.”

Transition zones between the center of the cornea and the periphery of the cornea result in some degree of glare, he said.

“All this discussion of custom corneas, quite frankly, is a bunch of engineering nonsense. We can’t change the central cornea because the correction of myopia [requires] a curve. At the periphery you can do it, at the expense of making the optical zone smaller. But if you wait 2 years, blinking is going to blend it all to the same curve because the cornea cannot withstand the blinking action of the lid without changing under pressure,” he said.

Blend zones and custom corneas will not prevent higher-order aberrations because some degree of aberration will always be created, Dr. Nordan said.

“We will always get aberrations when we change or bend the cornea,” he said.

Anterior chamber IOLs

According to Dr. Nordan, posterior chamber phakic IOLs can cause cataract, therefore anterior chamber phakic IOLs hold the most potential. He presented a new anterior chamber phakic lens called the Vision Membrane (Vision Membrane Technologies).

The lens is not in commercial development and to date only two patients have been implanted. Dr. Nordan told Ocular Surgery News the lens is only just preparing to start Food and Drug Administration trials.

The Vision Membrane is a diffractive lens. Most lenses in ophthalmology use refractive optics, which use lens shape to bend light. Diffractive optics do not use shape to bend light, and so the thickness remains unchanged, regardless of the dioptric power needed, Dr. Nordan said.

Baïkoff-style refractive lenses, which use a 4.5-mm optic, have a higher incidence of glare than LASIK, he said. The lenses generally use small optics and center on the geometric center of the cornea.

“If you want to get a bigger optic into the eye, either the lens moves closer to the iris or you go to a thinner IOL, which is what diffractive optics allows us to do,” he said.

The Vision Membrane lens is a 200-µm-thick silicone lens designed to be angle-fixated. The lens shape is vaulted and fits into the anterior chamber away from the endothelium and iris. According to Dr. Nordan, this should help prevent the need for peripheral iridectomies and should reduce the chances of pupillary block.

Dr. Nordan said the Vision Membrane’s thinness allows it to incorporate a larger optic than refractive-optic anterior chamber lenses.

“Other lenses have to remain small to avoid hitting the endothelium. The ones we implanted had a 7-mm optic, which should prevent glare,” he said.

The current lens is monofocal in design. However, the company plans on producing a bifocal, Dr. Nordan said.

“It would be a bifocal anterior chamber refractive lens, which means we could fix patients’ myopia or hyperopia and presbyopia all at the same time,” he said.

Potential market expansion

Dr. Nordan said anterior chamber IOLs will dominate refractive procedures by 2010 because the quality of vision is the same for all refractive errors. The only real advantage of keratorefractive surgery is that it is extraocular, he said.

“I agree with Dr. O’Brien that we are not going to be destroying a clear lens and implanting IOLs. But we are going to have phakic IOLs. It doesn’t matter if you are doing a +7, a –2 or a –20. All patients see equally well, as well as they did with their previous correction,” he said.

According to Dr. Nordan, the long-term results of anterior chamber IOLs is not an issue because simpler aphakic lenses have been around for about 25 years. Pupil mobilization remains an issue, but should be resolved with newer designs and materials.

The potential for cataract surgeons to expand into the refractive market without the need for expensive, specialized equipment could also speed the adoption of lens procedures as an alternative to keratorefractive procedures, Dr. Nordan said.

He said only a relatively small portion of ophthalmologists currently perform refractive surgery. A large proportion of cataract surgeons are sitting off to the side because they are not interested in keratorefractive surgery, he said.

“Remember, 80% of all anterior segment surgeons don’t do refractive surgery. That means only 20% of cataract surgeons perform LASIK. [The remaining surgeons] might use a cataract-type procedure to fix presbyopia,” he said.

VisionQuest 2002 was jointly sponsored by Stanford University and the LASIK Institute. The LASIK Institute is a division of the American Society of Cataract and Refractive Surgery.

For Your Information:

• Terrence P. O’Brien, MD, can be reached at Wilmer Eye Institute, 10753 Falls Road, Pavilion 2, Suite 305, Lutherville, MD 21093; (410) 847-3510; fax: (410) 847-3519; e-mail: tobrien@jhmi.edu. Dr. O’Brien has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.
• Lee T. Nordan, MD, can be reached at 6183 Paseo Del Norte, Suite 200, Carlsbad, CA 92009; (760) 930-9696; fax: (760) 930-0737. Dr. Nordan is president of Vision Membrane Technologies Inc. He has a direct financial interest in the products mentioned in this article.