For Best Results, Control Astigmatism

Learn how to perform intraoperative peripheral corneal relaxing incisions.

BY JONATHAN B. RUBENSTEIN, MD

The goal of cataract surgery in 2009 isn't only to restore vision; it's also to allow patients to see as well as possible without correction. To accomplish this goal, we must learn to correct astigmatism along with the spherical refractive error. Managing astigmatism is especially important when implanting accommodating or pseudo-accommodating IOLs. For these lenses to provide excellent uncorrected visual acuity, the patients need to have a maximum of 0.50 diopters of postoperative astigmatism.

We can manage the spherical component of vision by choosing the correct IOL power. We can manage the astigmatic component intraoperatively by controlling the size and location of the wound, adding relaxing incisions or implanting a toric IOL. We can manage astigmatism postoperatively using astigmatic keratotomy, wound revision or excimer laser treatment. In this article, I describe my technique for performing intraoperative peripheral corneal relaxing incisions (PCRIs).

Peripheral Corneal Relaxing Incisions

While mid-corneal relaxing incisions are one of the options for intraoperative astigmatism management, physicians usually prefer PCRIs. They're made near the limbus and the limbal blood vessels, so they tend to heal faster. The refractive effect stabilizes more quickly, and they create less irregular astigmatism, glare and foreign-body sensation compared to more centrally located incisions.

Although the terms PCRI and LRI are used interchangeably, these incisions aren't really at the limbus. They're at the very far peripheral cornea, which is why I prefer to use the term peripheral corneal relaxing incision or PCRI.

Setting the Surgical Plan

In general, depending on patient age, doctors can use PCRIs to correct up to 4D of preexisting corneal astigmatism (Figure 1). Several nomograms are available to determine the extent and location of the incisions. Once you're comfortable with the technique, visit LRIcalculator.com or use an established nomogram, such as the Koch or Nichamin nomogram.

Figure 1. Depending on patient age, doctors can use peripheral corneal relaxing incisions to correct up to 4D of preexisting corneal astigmatism at the time of cataract surgery.

Most nomograms are based on the age of the patient, amount of preoperative astigmatism and the desired refractive effect. Astigmatic neutrality is usually the goal. Some nomograms utilize pachymetry; others don't. Most nomograms are separated into with-the-rule and against-the-rule calculations. Because astigmatism tends to drift toward against-the-rule with age, with-the-rule astigmatism requires more cutting. For example, for a 75-year-old patient with 2.50D of astigmatism at 180°, the Koch nomogram calls for two 45° (4.5 mm) incisions at 3 o'clock. The Nichamin nomogram calls for two 50° (5 mm) incisions at 180°.

Intraoperative PCRI Technique

PCRIs are created at 90% depth, in front of the limbus, in the steep meridian of the cornea. The most important aspect of the technique is operating on axis. To ensure this, mark the cornea. While the patient is sitting upright in the pre-op area, instill a drop of anesthetic in the eye. Have the patient look directly at your nose with both eyes wide open. Pull the lid down and bring the marking pen up from below so the patient doesn't see it. Then, make a simple mark right at the 6 o'clock limbus.

Once in the operating room:

• use a marked fixation ring, astigmatic ruler or arcuate marker to identify and mark the steep corneal axis
• create the paracentesis as usual
• instill nonpreserved lidocaine with or without epinephrine, depending on pupil size
• fill the eye with viscoelastic through the paracentesis until firm, or approximately 25 mmHg
• Use a preset diamond knife (Figure 2) set to 600 microns (alternatively, you could measure the thinnest limbal corneal thickness and set the diamond knife) and make the incision(s).

Figure 2. For performing peripheral corneal relaxing incisions, I prefer to use a 600-micron preset diamond knife with a single footplate.

I prefer to use a single-footplate knife rather than a double-footplate knife. This allows visualization of the knife for the entire extent of the incision. Also, I prefer a double-cutting blade that can cut in either direction.

After I make the PCRIs, I make my cataract incision in the usual temporal location. If I've made an against-the-rule PCRI, I make my cataract incision within the PCRI. I recommend limiting the size of the PCRI to 3 mm, enlarging only if it becomes necessary after the IOL is in place. Otherwise, with manipulation of the phaco instrument, the peripheral corneal relaxing incision may extend or tear.

IOL power can be calculated in the usual way. PCRIs don't change the spherical equivalent, because for every 1 diopter of flattening where the incisions are made, the cornea steepens one diopter, 90° away.

Staying Alert for Complications

As with any procedure, complications may occur with PCRIs.

• Undercorrection and overcorrection are possible. Undercorrection is less of a concern and can be fixed by extending the incisions. Overcorrection can flip the axis. Fixing this situation might require closing the incisions with sutures to reduce their effect.

• Perforation can occur in corneas with areas of thinning and previous scarring, but these conditions should be ruled out at the slit lamp preoperatively.

• To avoid interference between the paracentesis and PCRIs, make the paracentesis peripheral and the with-the-rule relaxing incisions slightly more central.

• Wound leak can occur when the cataract incision is created coincident with a PCRI and the size of the relaxing incision wasn't limited to 3 mm or less. Wound leaks should be sutured.

• Epithelial plugging can cause the wounds to gape, thereby producing a great flattening effect. When this happens, you can clean it out at the slit lamp with a 25-gauge needle.

As long as the surgeon plans and performs PCRIs with precision, the technique is highly predictable and a very useful adjunct to cutting-edge cataract surgery. ■

Dr. Rubenstein is vice chairman, Deutsch Family Professor of Ophthalmology and director of Refractive Surgery at Rush University Medical Center.