Three steps facilitate the implantation of toric IOLs

Uday Devgan

A couple of decades ago, in the early days of phacoemulsification, the “Three Steps to Phaco” method was devised in order to facilitate learning this important new surgical technique. With modern-day refractive cataract surgery, addressing corneal astigmatism becomes as important as choosing the right lens implant power in order to deliver the best vision to the patient. Adapting a “three-steps” approach to toric IOLs facilitates learning how to properly use these lenses and deliver sharp vision to our cataract patients.

Step 1: Measure

At the preoperative exam, the amount and meridian of corneal astigmatism must be accurately measured. Note that we want just the corneal astigmatism and not the refractive astigmatism of the whole eye because the latter includes lenticular astigmatism induced by the cataract.

To determine the amount and the axis of corneal astigmatism, using a manual keratometer is often best, with the corneal topographer or autokeratometer used as confirmation. A toric IOL that is misaligned will reduce the effectiveness of the cylinder treatment and may even induce distortion and a new axis of astigmatism that the patient may not tolerate. Toric IOLs are best for the correction of regular, symmetric corneal astigmatism and may not perform well when implanted in an eye with an irregular or asymmetric cornea.

The clear corneal incision used during phacoemulsification has an effect on corneal astigmatism, typically a flattening at the meridian of the incision of about 0.3 D to 0.5 D, depending on the size of the incision. This must be accounted for when implanting the toric IOL — placing the incision on the same axis of the astigmatism will enhance the effect of the toric IOL, whereas placing it 90° apart will reduce the effect. Use of a Web-based program such as the Alcon AcrySof Toric Calculator at www.acrysoftoriccalculator.com will facilitate these calculations by doing the vector mathematics for you. Note that these programs recommend choosing a toric power that may slightly undercorrect the astigmatism because that is better tolerated by the patient than an overcorrection.

The steep corneal axis is marked at the slit-lamp microscope before surgery using the Devgan Axis Marker from Accutome. The epithelial marks are enhanced by using a cystotome to perform anterior stromal puncture marks that are visible at the time of surgery via the red reflex of the operating microscope. Images: Devgan U

The corneal stromal puncture marks are seen in the yellow boxes and are aligned with the steep axis of corneal astigmatism indicated by the dotted yellow line. The capsulorrhexis is made with a 5-mm diameter so that it will overlap the edge of the optic and securely hold the IOL in position.

Alcon AcrySof SN6AT5 aspheric toric IOL is placed in the capsular bag and oriented in the correct axis. Note the alignment dots of the toric IOL are at the same axis as the corneal stromal puncture marks, all within the highlighted yellow box. The capsulorrhexis edge, seen inferiorly, securely overlaps the optic edge to help ensure stability of the toric IOL.

Step 2: Mark

The steep corneal axis must be accurately marked so that the toric IOL can be properly aligned. This is best accomplished with the patient sitting up so that the cyclotorsion of the eye that happens in the supine position on the operating room bed can be avoided. One option is using a surgical marking pen at the superior and inferior 90° meridians (12 and 6 o’clock positions) before surgery and then marking the steep corneal axis intraoperatively with a Mendez gauge.

I prefer a technique in which the actual steep axis is marked before surgery while the patient is seated at the slit-lamp microscope. The Devgan Axis Marker (Accutome) is placed in the applanation tonometer holder and rotated to the exact axis to be marked. Looking through the hollow core of the marker helps to center the marks on the pupillary axis. Gentle but firm pressure is used to score the epithelium. For more lasting marks that can be seen many days later, Byron Stratas, MD’s, technique of using a cystotome to perform corneal stromal puncture further enhances the alignment marks.

Step 3: Align

A capsulorrhexis that is smaller than the optic is important to securely hold the toric IOL in position during the postoperative period. Viscoelastic should be removed from behind the toric IOL, and while keeping the eye inflated with the irrigation and aspiration probe, the IOL can be nudged to the correct alignment. With the tacky nature of the hydrophobic acrylic toric IOL, a light tapping motion will help to secure the IOL in position against the posterior capsule.

To ensure correct alignment, simply line up the toric IOL orientation dots with the corneal stromal puncture marks. In the first postoperative exam, the IOL position can be confirmed by noting this same alignment. If the toric IOL is rotated or misaligned, it should be repositioned in a timely manner.

Correcting astigmatism at the time of cataract surgery is important to give our patients the best vision possible. This can be achieved with both incisional methods and toric IOLs. For smaller degrees of corneal astigmatism, I find limbal relaxing incisions to be very effective. For more significant degrees of corneal astigmatism, toric IOLs are my treatment of choice.

In the U.S., the only toric IOLs currently approved by the U.S. Food and Drug Administration are monofocal. However, in Europe and Asia, there are even more varieties, including multifocal toric IOLs, piggyback toric IOLs and others that will soon be available. It is time to take your cataract surgery technique to the next level by addressing corneal astigmatism and incorporating toric IOLs into your practice.

• Uday Devgan, MD, FACS, is in private practice at Devgan Eye in Los Angeles, chief of ophthalmology at Olive View UCLA Medical Center and an associate clinical professor at the UCLA School of Medicine. He can be reached at 11600 Wilshire Blvd., Suite 200, Los Angeles, CA 90025; 800-337-1969; fax: 310-388-3028; e-mail: devgan@gmail.com; www.udaydevgan.com. Dr. Devgan is a speaker for Accutome, a stockholder in Alcon Laboratories and has a financial interest in the Devgan Axis Marker.