Toric Lenses Offer Clear Vision for Astigmatism Correction

BY JOHNNY L. GAYTON, M.D.

Limbal relaxing incisions (LRIs) and laser refractive surgery have been the traditional methods of correcting astigmatism at the time of, or soon after, cataract surgery. Each brings its own advantages in terms of ease, accuracy, cost, duration of effect and potential for complications. Toric IOLs are a relatively new addition to the cataract surgeon's armamentarium that compare favorably to both of these other options, rivaling the LRI for ease and laser vision correction for accuracy.

Astigmatism management was the primary reason that I proposed a routine temporal approach to cataract surgery in 1985, and what prompted my use of LRIs in the recent past. However, there are now commercial lenses available that preclude my need for performing LRIs.

While I personally find the AcrySof Toric IOL (Alcon, Fort Worth, Texas) to be the most simple, precise and forgiving, Advanced Medical Optics (Santa Ana, Calif.) offers the Tecnis Z9000 SofPort, Bausch & Lomb (Rochester, N.Y.) the Advanced Optics IOL and STAAR Surgical Company (Monrovia, Calif.) the STAAR Toric IOL.

LRI Procedures After Lens Surgery: Safe, Simple and Less Costly

LRI is a safe, simple and effective treatment for the correction of astigmatism and an excellent supplement to premium lens surgery. It can be performed preoperatively, intraoperatively or postoperatively with patients noticing improvement immediately and generally stabilizing within 4 to 6 weeks. The procedure is less costly than laser surgery, but the outcomes are somewhat more variable and there can be regression, particularly with higher levels of astigmatic correction.

LRIs are not without their challenges. Patient responses do vary and additional procedures may be required to resolve complications. The most common complication is an over- or under-correction but other complications such as dry eye, wound leaks, ulcers and even endophthalmitis are possible. Patients should be advised of the potential for such complications, even though the latter issues are extremely rare.

As noted in my LRI nomogram shown in Table 1, correction of more than 2 D of astigmatism may require the creation of an incision that is susceptible to wound gape. It is generally advisable to make another incision anterior to the limbal incision instead of making excessively long incisions.

Temporal cataract incisions spare the superior conjunctiva for future glaucoma procedures and have an advantage for patients with deepset eyes, those who cannot be positioned flat, or who are undergoing clear-corneal surgery. They stabilize quickly and tend to induce very little astigmatism. This makes them perfect to combine with LRIs or toric IOLs.

Excimer Laser After Lens Surgery: Accurate, More Costly

Laser vision correction after cataract surgery is another way to reduce residual astigmatism and this can be important when patients have chosen a multifocal IOL for presbyopic correction. Clear uncorrected distance vision is a key component of patient satisfaction with these lenses and the patients are typically more critical in their visual demands. While largely successful, the slightly higher variability and potential for regression with LRIs may be unacceptable in this patient group. Laser vision correction, unlike LRI's, can also be used to effectively correct larger amounts of astigmatism.

Issues with excimer laser enhancement of cataract surgery results are similar to those for any LASIK or PRK procedure. There is the potential for increased dry eye, always a concern in this age group. Complication rates are low, but complications can occur. And it is a second and unrelated procedure, so the cost of the additional surgery can be a barrier for some patients.

Results with laser refractive surgery after multifocal implants have been very good, improving both the spherical and cylindrical refractive error. Ten percent to 20% of premium IOL patients may require this type of enhancement.

Getting the "Wow" Factor and Predictable, Accurate and Affordable Results

My patients' experience with the AcrySof Toric IOL can only be termed as a "wow." In my practice, results have been superior to the other methods of astigmatic correction I use. In an evaluation of our first 100 cases, the average preop astigmatism was 1.78 D, while the postoperative cylinder was 0.26 D. Patients are often amazed at, and appreciative of, the clarity of their distance vision. Table 2 contains my selection criteria for use of the lens.

What results can you expect from the typical patient? In my practice, a 78-year-old male presented with a cataract and astigmatism in his right eye. He complained of problems with glare during the day and at night, and also had decreased distance and near vision. The preop UCDVA was 20/50, UCNVA was 20/40, and the manifest refraction (MR) was –1.50 +1.50 × 010 = 20/40. Phacoemulsification and Acrysof T3 Toric IOL implantation was performed. The postop UCDVA improved to 20/20 with a plano refraction.

In another case study, a 77-year-old female presented with a cataract and astigmatism in her right eye. She experienced glare during the day and at night, and had poor vision that affected her ability to drive at night. Her preop uncorrected distance visual acuity (UCDVA) was 20/200, MR was +2.00 +3.75 × 010 =20/25, and keratometry was 43.37/46.37 × 010. Her goal was good intermediate vision without correction. She received a T5 Toric IOL. This was supplemented by two limbal-relaxing incisions of 40° length.

Postoperatively, she improved to 20/20 vision with a with -1.00 D lens, and keratometry of 44.20/45.75 × 178. She has 20/60 distance vision without correction.

Toric lenses provide great astigmatic correction and are also forgiving. Patients with 2 D of corneal cylinder will have better uncorrected vision if they get a toric, even if it is off axis by 20°, than they will with an aspheric non-toric lens. This is because the lens has to be off by 30° to negate its corrective effect. A lens that is placed 3° off axis will only have a 10% reduction in effect. With the highest power toricity (the T5 lens), this translates to 0.2 D, which is below the noticeable difference for a patient and below the typical cylinder refraction step size of 0.25 D. Rotation does not tend to be an issue, due to the tackiness of the AcrySof material. The lens stays where you place it — there is little to no rotation postoperatively.

Incorporating Toric Lenses in Your Practice

How do I incorporate the toric lens in my practice? The ideal patients are those who are able to have lens surgery and also have significant regular corneal astigmatism, whether or not it is asymmetric. It is the best alternative for patients with corneal astigmatism, who reject, or are not candidates for, presbyopia correction. Relative contraindications to presbyopic multifocal correction such as dry eye, diabetic retinopathy, macular disease or glaucoma, are not a concern with the toric IOL. We offer the toric lens to patients with significant astigmatism who desire the absolute best image quality and are interested in spectacle freedom for distance vision.

Tip for Success — Counsel Patients, Set Realistic Goals

As with all procedures, there are tips for success. Take a proactive approach to astigmatism. Be prepared to discuss the treatment plan and follow-up, as well as potential complications or adverse effects.

Patients should be informed that the lenses are limited to a maximum of 2 D, are non-aspheric and require an intact capsular bag.

During counseling, set realistic expectations. Discuss astigmatism and the probability of additional procedures (less likely with the toric IOL than with LRIs). Make sure the patient understands that the cornea and the lens are different anatomical entities and both may require treatment to maximize vision. Mentally prepare the patient to undergo bilateral surgery to maximize vision.

In our practice we double-check calculations, measure twice and cut once. We use the AcrySof Toric calculator (www.acrysoftoriccalculator.com) to help determine the power and position of the lens, using our unique "Surgically Induced Astigmatism" value for whatever incision we are making.

An important rule of thumb with any astigmatism correction is that patients should be advised that the surgery is meant to reduce astigmatism and may not eliminate it. For instance, LRIs vary with each patient in the ability to correct large amounts of cylinder. Patients should be advised that they will have to pay out-of-pocket expenses if the astigmatism was not caused by a prior surgery.

Toric IOLs are an ideal method of treating astigmatism and may be combined with multiple other methods for an optimal outcome. I believe that cataract surgeons should be bringing toric lenses to the forefront of their management options for patients with astigmatism. OM

Dr. Gayton is in private group practice at Eyesight Associates in Warner Robins, Ga. He is a speaker for Alcon and also receives research support from them.