Toric Iol Implantation
By Joseph Colin, MD
The reduction or elimination of preexisting corneal astigmatism during or after cataract surgery can be achieved with several surgical strategies; however, the refractive changes induced by several of these procedures, such as corneal or limbal incisions, are relatively unpredictable and may be unstable in the long term. Toric IOL implantation, however, is a safe and predictable method for managing corneal astigmatism in cataract patients. There is a wide range of toric IOL models available, recently including multifocal toric IOLs to correct both presbyopia and astigmatism.
CHARACTERISTICS OF TORIC IOLs
Toric IOLs have the ability to reduce refractive astigmatism immediately and to maintain a stable position within the capsular bag in the long term. Several characteristics contribute to the stability of the IOL, including the size and configuration of the haptics, the overall diameter of the lens, and the ease of handling during surgery. Of course, perfect centration of the lens is critical as well.
Most manufacturers today report accurate, stable results regarding rotation of the IOL. In the US Food and Drug Administration trial of the AcrySof Toric IOL (Alcon Laboratories, Inc.), the average lens rotation at 6-month follow-up was less than 4°.1 This is important because the astigmatic correction effect of an IOL decreases by 10% for every 3° rotation from the correct axis. Rotation may also increase higher-order aberrations
Depending on the manufacturer and model, toric IOLs can correct a wide range of astigmatism, including higher levels. The current indication for toric IOL implantation is corneal astigmatism of more than 1.00 D.
TORIC IOLs VERSUS LRIs
Toric IOLs have several advantages over corneal limbal relaxing incisions (LRIs). First, toric IOLs provide stable and predictable results, whereas incisions produce less stable and predictable results. IOLs can be adjusted if correction is unsatisfactory—the axis of astigmatism can be realigned. Incisions are not adjustable in this way in most cases. IOLs are reversible, whereas incisions are not.
There are benefits to incisions, however. Toric IOLs are a source of revenue for industry, while LRIs can be a source of revenue for the surgeon. Once you own a femtosecond laser, there is no need for additional, expensive equipment to create LRIs; however, the initial purchase of the laser is a substantial investment.
A patient presented with myopia and a very deep capsular bag. I implanted a toric IOL in the vertical axis, and on postoperative day 5 the IOL was in the horizontal axis. This case is a prime example of two aspects of toric IOLs: (1) they can rotate, but (2) they are adjustable. I was able to easily put the IOL back in the proper axis of alignment. I saw the patient several days later, and the IOL remained stable in the bag.
Each method for correcting astigmatism at the time of cataract surgery has advantages and disadvantages. The safety, predictability, and adjustability of toric IOL implantation make this procedure a highly attractive option for the management of astigmatism.
Joseph Colin, MD, is a Professor of Ophthalmology and Chairman of the University Department at CHU Université de Bordeaux, France. Dr. Colin states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +33 55 679 56 08; e-mail: joseph.colin@chubordeaux. fr. See In Memoriam: Joseph Colin, MD on page 9.
- Horn JD. Status of toric intraocular lenses. Curr Opin Ophthalmol. 2007;18(1):58-61.
Femtosecond Laser Incisions
By Stephen G. Slade, MD
We all know that residual astigmatism degrades vision after cataract surgery. We also know that it degrades vision dramatically in multifocal IOL patients, more so than in monofocal IOL patients. In the United States, surgeons do not have access to the toric multifocal IOLs that are currently available in Europe. Therefore, the question for us is, do we want to correct the patient’s presbyopia and astigmatism, or just the astigmatism? Of course, we would rather correct both, so what is the best way for us to do that?
Femtosecond laser arcuate incisions are a very effective method for correcting astigmatism. Poll et al1 conducted a retrospective study (n=192) comparing the efficacy of astigmatic correction achieved using toric monofocal IOLs versus peripheral corneal relaxing incisions. The investigators found that the average residual astigmatism was 0.42 D with toric IOLs and 0.46 D with corneal incisions. In other words, toric IOLs achieved slightly better results than laser incisions. Higher degrees of astigmatism favor the use of toric IOLs, and US surgeons now have a full range of astigmatism-correcting monofocal IOLs with the availability of the AcrySof Toric IOL (Alcon Laboratories, Inc.).
Although 0.42 D residual astigmatism is good, we have been able to achieve 0.41 D residual astigmatism using femtosecond laser-created arcuate incisions. The key term in femtosecond laser cataract surgery is image guidance. With this technology, I can place a precise arcuate incision with controlled depth, set directly at the point where I want to put that particular incision. In our early experience with laser incisions, we have achieved outcomes that are more favorable than published toric IOL results. That is very important because US surgeons can now accomplish with the laser what our colleagues in Europe are accomplishing with toric multifocal IOLs.
ADVANTAGES OF LASER INCISIONS
Femtosecond laser incisions are adjustable. With toric IOLs, it is possible to go back into the eye and rotate the lens, but that is an intraocular surgery; laser incisions can be adjusted externally. It is not common that we need to adjust these incisions, as the results we achieve are generally accurate. However, we can reopen the incisions if necessary.
Additionally, we can treat lower astigmatic powers with femtosecond laser incisions. With IOLs, the lowest amount of astigmatism that can be corrected is generally 1.00 D. Seventy-two percent of people have at least 0.75 D of astigmatism. We would correct 0.75 D of astigmatism during excimer laser refractive surgery, so why not at cataract surgery? With the femtosecond laser, it is possible to treat 0.50 D or 0.25 D, just as we would with the excimer laser.
Another advantage of the LRI approach is the general consensus that if a patient’s astigmatism is on the cornea, there are optical advantages to correcting it on the cornea. With a toric IOL, as the capsular bag contracts, the IOL can move forward or backward and can rotate out of the proper axis. Incisions do not rotate out of the axis where they are created. IOLs can be reversed, but it is also possible to reverse the effect of an incision with a suture.
As for cost, as Dr. Colin noted, once you own the femtosecond laser, you do not have to pay extra to perform arcuate incisions. If you perform refractive cataract surgery and you want to meet patients’ expectations, you must also have the ability to perform LASIK for enhancement if needed. If you perform LASIK and own your excimer laser, you paid twice as much in capital outlay for the equipment compared with a femtosecond laser, and you have twice the per-procedure and service fees.
Comparing toric IOLs and LRIs is not so much a debate as a discussion. If toric multifocal IOLs and toric accommodating IOLs were available in the United States, as they are in Europe, I would employ that strategy as well. The femtosecond laser is a technology in transition. With image guidance, we should, in the foreseeable future, be able to match asymmetric incisions with patients’ asymmetric astigmatism. We should also be able to make these incisions absolutely reproducible and develop better nomograms.
Stephen G. Slade, MD, practices at Slade and Baker Vision in Houston, Texas. Dr. Slade states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +1 713 626 5544; e-mail: email@example.com.
- Poll JT, Wang L, Koch DD, Weikert MP. Correction of astigmatism during cataract surgery: toric intraocular lens compared to peripheral corneal relaxing incisions. J Refract Surg. 2011;27(3):165-171.