Incisional techniques still have a place in the era of toric intraocular lenses

The introduction of astigmatism-correcting IOLs to the U.S. market gives ophthalmologists another option to choose from for addressing refractive error.

Toric IOLs fit a niche in a market that desires refractive results after cataract surgery. To some, toric lenses offer an entry point to the premium IOL market in that they address a refractive component in addition to the cataract removal; also, their price affords them a midpoint status between less expensive monofocal lenses and the more expensive presbyopia-correcting IOLs.

The introduction of these lenses has caused many to question where they fit into the already crowded IOL marketplace. Some also question whether older means of addressing astigmatism, namely limbal relaxing incisions (LRIs), are still relevant and worthy of use.

LRIs can equip the surgeon with a means to improve visual outcomes after cataract surgery, but they cannot offer the level of accuracy and predictability that a toric implant potentially provides.

Louis D. Nichamin, MD, says that ophthalmologists will continue to increase the use of toric IOLs, but relaxing incisions will still play a role in improving visual outcomes. Image: Courtney Katherine Photography

“There are good reasons that LRIs and [astigmatic keratotomies] should be in the armamentarium of the contemporary refractive cataract surgeon,” Robert H. Osher, MD, OSN Cataract Surgery Board Member, said. “I am comfortable with both incisional and IOL options for correcting astigmatism, but I believe that the toric lenses are a better procedure with greater accuracy than incisional techniques.”

Refining the science

Dr. Osher introduced combined cataract surgery and astigmatic keratotomy to correct pre-existing astigmatism in the early 1980s. He said he admits that his protocol has changed since the Alcon toric lens became available.

“While astigmatic keratotomy is far more powerful than limbal relaxing incisions, both of these incisional techniques have a variable result based on surgical technique, the surgeon’s experience and the patient’s individual wound healing,” Dr. Osher said. “[Astigmatic keratotomies] and LRI are an art, while toric lenses are a more exact science. And the accuracy will continue to improve as more precise methods of marking the intended axis of IOL orientation are developed.”

According to Dr. Osher, the predictability of response after a toric implantation increases the chance for achieving emmetropia. At one time, astigmatic keratotomy combined with 2.2-mm microcoaxial phacoemulsification was his preferred method for dealing with pre-existing astigmatism in the cataract patient. However, toric lenses yield more predictable results.

“No ophthalmologist would perform a refraction and prescribe a spectacle without correcting astigmatism,” he said. “So why should we perform surgery and miss the opportunity to correct astigmatism as precisely as possible?”

Richard J. Mackool

Richard J. Mackool, MD, agrees that toric lenses provide a level of accuracy that incisional techniques cannot.

“Toric IOLs are demonstrably more accurate than incisional astigmatic surgery. There really is no question about that,” he said. “The problem with any incisional surgery is that the results vary from patient to patient.”

Even with a well-performed incisional surgery that goes according to plan and matches the intent of the preferred nomogram, the postoperative healing process may alter the outcome.

“Some patients, after their healing occurs — no effect. Some patients will get twice as much effect as the nomogram predicts. In the majority of patients, you can get pretty close to what the nomograms call for, and that’s nice,” Dr. Mackool said. “But you can’t compare that to a toric IOL. Nobody gets zero effect from a toric IOL; nobody gets twice the effect from a toric IOL.”

Still a role for LRIs?

Toric IOLs are growing in market share and popularity, but there still may be a role for incisional techniques in the foreseeable future.

According to Dr. Osher, patients may not want to pay the additional charge for a toric implant or their astigmatism may be outside the current range of correction. The AcrySof T5 (Alcon) was designed to correct 2 D of astigmatism at the corneal plane, and according to information on its Web site, the STAAR toric IOL can correct up to 2.3 D of astigmatism.

“For the cataract patient with 3 or more diopters of cylinder, pairing a toric IOL with an [astigmatism keratotomy] or LRI is our best option in the U.S., where the range is still limited,” Dr. Osher said.

Another reason for an incisional technique may be to reduce lower amounts of cylinder.

“With a 2.2-mm microcoaxial temporal incision, I induce 0.25 D of cylinder,” Dr. Osher said. “If the patient has 0.5 D of with-the-rule astigmatism, I anticipate 0.75 D following surgery, so I have no problem placing a very conservative incision at 90°. This is the beauty of 2.2-mm surgery: We can anticipate the amount of postoperative cylinder and have the capacity to improve the result.”

Robert H. Osher

LRIs may often be used in patients who opt for a presbyopia-correcting IOL and have both cataract and astigmatism. These patients expect unaided clear vision after surgery, so reducing astigmatism is crucial to success, according to Drs. Osher and Mackool.

When paired with a premium channel lens, Dr. Mackool prefers a slight variation on the classic LRI. He performs a full-thickness penetrating incision on the cornea at the steep axis, much like a clear corneal phaco incision. The penetrating LRI is performed at the end of surgery after the IOL is implanted; before removing the viscoelastic and with the irrigation and aspiration tip in the eye, incisions of 2.75 mm to 3.2 mm are made at the predetermined axis.

Dr. Mackool does not discount the utility of classic LRIs; however, he said he believes that the penetrating incision produces less foreign body sensation, and because it is similar to a phaco tunnel, there is little to no learning curve involved.

He said he uses LRIs during the postoperative period outside the operating room setting to refine the refractive result.

LRI myths

Toric IOLs are a strong option for astigmatic correction with or without the presence of a cataract, and many surgeons are already adopting them into practice. They are widely viewed as an entry point into the premium channel market, offering a midpoint between traditional monofocal lenses and implants that mitigate presbyopia.

Lens manufacturers have responded to the demand for toric implants, and new models are in various stages of clinical development, including lenses that combine presbyopia and toric correction. Both the Acri.Lisa (Carl Zeiss Meditec) and Rayner toric and presbyopia IOLs are being used in clinical trials in Europe.

It is unknown when or if these IOLs will be introduced to the U.S. market. In the meantime, surgeons are sensing a need to augment the refractive correction component of premium lenses with a technique that further refines the results, such as an LRI.

“There is a lot of excitement with torics, and it’s going to continue. The number of toric offerings will expand, and we will continue to increase our use of them, but there will also continue to be a distinct role for relaxing incisions,” Louis D. “Skip” Nichamin, MD, OSN Cataract Surgery Board Member, said.

According to Dr. Nichamin, the LRI “is one of the most underutilized techniques available to anterior segment surgeons.” That may be due to some misperceptions about incisional techniques, namely that they are unpredictable; the effect regresses over time; they are only effective against low levels of astigmatism; and they are dangerous and difficult to perform.

None of those claims has been borne out in the literature, according to Dr. Nichamin. In fact, he said he has looked at data from his own clinic and compared it with the toric IOL literature and has seen remarkably similar results.

“It’s all technique dependent. If the surgeon is willing to make a concerted effort, in my experience, the result with a limbal relaxing incision is quite comparable to the best results with a toric [IOL],” he said.

How the incisional technique is performed will dictate outcomes, Dr. Nichamin said, and historically, variable results have occurred due to less than ideal techniques and instrumentation, which would explain why some surgeons remain hesitant to embrace this procedure. As with any astigmatic correction, centration on the proper axis is crucial, but placement of the incisions on the cornea may be an underappreciated aspect: too far central risks irregular astigmatism, but too close to the limbus yields inconsistent results that sometimes regress.

Another potential pitfall with LRIs, he said, is an incision not cut perpendicular to the corneal surface, which may result in an LRI with inadequate and inconsistent depth to flatten the astigmatism. Use of an inappropriate or improperly tuned cutting knife can result in inadequate depth or undercorrection.

“If — and this is a big if — the surgeon learns the proper technique, his or her results will closely match a toric,” Dr. Nichamin said. “This affords the surgeon the ability to reduce astigmatism and use whatever implant that they choose, whether it is monofocal, multifocal or accommodative. … It really provides the surgeon with a wider spectrum of surgical options. In addition, toric implants and LRIs may be combined to treat patients with larger degrees of pre-existing astigmatism.”

Tiered approach

Some surgeons, such as David R. Hardten, MD, OSN Cornea/External Disease Section Editor, prefer a tiered approach for LRIs, torics and wavefront-guided laser vision correction, with the latter perceived as the gold standard of astigmatic correction.

David R. Hardten

At lower levels of astigmatism — up to about 1.5 D — Dr. Hardten said he will use LRIs because there is negligible if any difference in the power of correction compared with toric IOLs.

Although no studies have documented it, he said he thinks that the correction is more powerful and predictable when toric IOLs are used in treating cylinder larger than 2 D either alone, up to about 2.5 D, or paired with an incision, up to about 3.5 D.

“When you get over that, at least with the currently available toric IOLs, you really aren’t able to get the full amount of astigmatism correction. But I still go ahead and do whatever I can for the astigmatism during the surgery and then go back and fine-tune with a laser,” Dr. Hardten said.

LRIs correct astigmatism at the corneal plane, whereas toric lenses do so at the lenticular level. From an optical standpoint, there may be little appreciable difference in where the astigmatism correction occurs. However, from a practical standpoint, surface correction may be more advantageous to follow-up procedures.

“[Toric IOLs] make you a little more dependent on wavefront to verify that the refraction makes sense because you cannot use the keratometry anymore to gauge your refraction,” he said.

The refraction component of vision measurement is a subjective test. Often, the topography will show objectively what the patient provides during the refractive examination; however, topography will not relay any information about the axial orientation of a toric IOL. In the case of residual astigmatism, Dr. Hardten said, keratometry becomes ineffectual in verifying the refractive results, and so it becomes difficult to know whether to rotate the lens or proceed surgically to further address the astigmatism.

“If I can correct [astigmatism] on the cornea, I prefer to do that because if you wind up with residual astigmatism later on, it’s easier to figure out what to do about that residual astigmatism because you have corneal topography. In general, that shows you the exact nature of the astigmatism because it’s on the cornea,” he said.

Predictability

Although no clinical trials have yet compared toric IOLs with LRIs, there is a general notion that the predictability of the astigmatic correction is better with implants than with incisions. Both may pale in comparison with laser vision correction, but the availability of all three modalities should not necessarily mean that any one should be left to the wayside.

“Laser correction is the best for correcting astigmatism. Toric lenses are the second best. And, certainly, the third best is an LRI,” William J. Lahners, MD, FACS, said. However, “there are people that won’t have LASIK or will not or cannot have a toric lens, and LRIs will still be there for those people.”

The advent of iris-tracking wavefront-guided excimer lasers and other laser surgery adjuncts have improved laser vision correction to such an extent that toric lenses have a lot of ground to make up in terms of accuracy, power and predictability.

“There are so many things we do now that enhance the accuracy of lasers that I do not think, at this point, that toric lenses can compete with the accuracy of LASIK,” Dr. Lahners said. “I think that LASIK and surface ablation with the excimer laser is going to be the ultimate technique for refining and correcting astigmatism because of the submicron accuracy of the excimer laser.”

Although LASIK offers benefits that neither toric IOLs nor LRIs can match, he said he thinks that incisions still fill a need. From a patient perspective, laser correction or an IOL may not be desirable. Some patients may opt for a non-toric lens and some may require an incisional technique to address underlying astigmatism. From the surgeon’s perspective, offering the full gamut of corrective choices may not be feasible, and toric IOLs require little capital outlay to the cataract or refractive surgeon compared with acquiring laser technology and training; LRIs offer an even lower line item expense that could pay off significantly.

“The toric lens is something you don’t have to have an excimer laser to do. It’s something you don’t have to have an IntraLase laser (Abbott Medical Optics) to do. You don’t have to be specially trained to do it. It’s really within the grasp of every intraocular lens surgeon to perform,” Dr. Lahners said.

“LRIs still have a place because they are easy to perform, they require a minimal capital investment on the part of the surgeon, and, while not the most predictable thing in the world, they are fairly forgiving, and it’s fairly difficult to make someone’s vision worse with an LRI, while it’s very likely you’ll improve their vision,” he said. – by Bryan Bechtel

When performing a limbal relaxing incision, is it preferable to use a single-depth nomogram or an adjustable-depth nomogram?

• David R. Hardten, MD, 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. Dr. Hardten is a consultant to AMO.
• William J. Lahners, MD, FACS, can be reached at Center For Sight, 2601 S. Tamiami Trail, Sarasota, FL 34239; 941-925-2020; fax: 941-330-2200; e-mail: wjlahners@centerforsight.net. Dr. Lahners is a consultant to Alcon, AMO, Bausch & Lomb, Allergan and Vistakon.
• Richard J. Mackool, MD, can be reached at Mackool Eye Institute, 31-27 41st St., Astoria, NY 11103; 718-728-3400; fax: 718-728-4882; e-mail: mackooleye@aol.com. Dr. Mackool is a consultant to Alcon.
• Louis D. “Skip” Nichamin, MD, can be reached at Laurel Eye Clinic, 50 Waterford Pike, Brookville, PA 15825; 814-849-8344; fax: 814-849-7130; e-mail: nichamin@laureleye.com. Dr. Nichamin has no direct financial interest in any of the products mentioned in this article, nor is he a consultant for any companies mentioned.
• Robert H. Osher, MD, can be reached at Cincinnati Eye Institute, 10494 Montgomery Road, Cincinnati, OH 45242; 513-984-5133; fax: 513-936-4881; e-mail: rhosher@cincinnatieye.com. Dr. Osher is a consultant to Alcon.