This article is from June 2011 and may contain outdated material.
Cataract surgeons have been slow to embrace toric IOLs for their patients with astigmatism. But that hesitation is changing. Today’s toric IOLs offer greater predictability and precision in both the surgery and the patient’s ultimate visual outcome, experienced cataract surgeons say.
Ralph Chu, MD, a cataract and refractive surgeon in Bloomington, Minn., has experience with both the Staar toric lens and Alcon’s AcrySof toric lens—the only toric lenses currently approved in the United States.
“Staar was the original toric lens that was approved many years ago,” said Dr. Chu, an adjunct associate professor of ophthalmology at the University of Minnesota. “It’s on a different platform from the AcrySof device and is made of silicone. Staar is a clear single-piece lens and has a plate-haptic design.”
The AcrySof toric IOL is a single-piece acrylic lens with loop haptics and a blue-blocking yellow tint. Dr. Chu noted that both devices can treat a patient’s astigmatism after cataract surgery, but in his experience, the acrylic AcrySof toric lens is more stable and more resistant to rotation inside the eye.
A number of new toric IOLs are waiting in the wings for FDA approval. “The higher-power toric IOLs from Alcon, which are already in use in other countries, will likely be available in the United States soon,” said Robert J. Cionni, MD, medical director of The Eye Institute of Utah in Salt Lake City. “These IOLs should be able to reduce up to about 4 D of astigmatism.” He added that other companies also are working on toric IOLs.
For now, Alcon offers three models of the AcrySof lens—T3, T4 and T5 (corresponding to cylinder powers of +1.50 D, +2.25 D and +3.00 D, respectively), and Staar has two models—AA4203-TF and AA4203-TL (corresponding to cylinder powers of +2.00 D and +3.50 D, respectively).
Patient selection and preoperative assessment are critical to surgical success with toric IOLs:
Preferred candidates. The ideal candidate should have a vision-compromising cataract, astigmatism and an interest in reducing the need to wear glasses for distance, Dr. Chu said. “As long as the eye is healthy enough to achieve the good outcome that the patient is expecting and has the necessary degree of astigmatism, there is little downside. The quality of vision for patients receiving a toric lens is excellent.”
Dr. Cionni noted that any patient with enough astigmatism to require glasses with cylinder correction after cataract surgery could benefit from a toric IOL. “The only word of caution is that these IOLs are meant to treat regular astigmatism, not irregular astigmatism as is found in patients with a history of radial keratotomy, penetrating keratoplasty or keratoconus.
Preop workup. Toric IOL patients “need more of a workup, and you have to gather more information preoperatively,” Dr Chu said. “At the least, you need to get corneal topography to determine whether the astigmatism is regular or irregular.” Like Dr. Cionni, he noted that toric lens implants are more effective in patients with regular astigmatism, and he said that patients need to be counseled about this fact before they undergo the surgery. Corneal topography also helps the surgeon assess lens placement. Dr. Chu obtains corneal thickness measurements on his toric IOL patients as well.
Four Surprises to Avoid
Cataract surgeons who have been working with toric IOLs have several tips to share with those who are considering adding these lenses to their practices:
Beware the wrong cylinder. “Commit to treating only keratometric cylinder,” Dr. Cionni said. “Do not even talk to a patient about toric IOLs until you have documented keratometric astigmatism by at least one reliable method. We use auto keratometry or Lenstar keratometry, and if the patient wants to proceed with a toric solution, Atlas keratometry.”
Beware induced astigmatism. Surgeons should assess their level of induced astigmatism by measuring keratometric cylinders before and after surgery in at least 20 patients, Dr. Cionni said. He recommended using the Surgically Induced Astigmatism Calculator1 created by Warren E. Hill, MD, medical director of East Valley Ophthalmology in Mesa, Ariz.
“A few surgeons believe that they don’t induce astigmatism with their clear corneal incisions,” Dr. Hill said. “My guess is that they probably have never actually calculated it or looked closely at a series of patients.” He added, “Over a period of several years, I collected surgically induced astigmatism spreadsheets for standard coaxial phacoemulsification from physicians all over the world, and I have never seen a data set where some amount of astigmatism was not induced. It just doesn’t happen. So surgeons need to use a real-world, surgically induced astigmatism value to come up with a valid postop astigmatism value.”
Following the creation of a clear corneal incision, Dr. Hill said, “What typically happens is that the steep axis rotates away from the location of the incision, and the corneal power meridian where the incision is made is decreased and the axis orthogonal to it is steepened. In other words, if the surgeon is operating temporally, this meridian is flattened and the vertical meridian is steepened.”
He continued, “The calculator adds the vector of the surgically induced astigmatism to the preexisting corneal astigmatism, calculating a new value—and it’s this new value that is corrected by the toric IOL. Failing to take into account the amount of surgically induced astigmatism will typically result in an undercorrection at an unanticipated axis.”
Dr. Hill suggested that surgeons enter about 60 of their cases into the Surgically Induced Astigmatism Calculator. “They may be surprised at what they find.”
Beware the wrong axis. To avoid placing the IOL in the wrong axis, Dr. Cionni recommends hanging the printout of the AcrySof Toric IOL Calculator2 where it can be seen from the OR microscope, oriented to the surgeon’s view. “If you sit superiorly, hang it upside down,” Dr. Cionni noted. “If you sit temporally, hang it sideways. Failing to do so can fool you into placing the IOL 90 degrees off axis.”
Dr. Chu agreed and underscored the need for surgeons who are new to the procedure to double-check their orientation in the operating room. “Surgeons who have not treated astigmatism in the OR may feel ‘upside down’ when sitting at the head of the bed,” he said. “It’s important to mentally flip that orientation when taking the topography.” He added that the AcrySof Toric IOL Calculator gives a good depiction of the orientation of the lens, which enables the surgeon to place it on the correct axis.
Take care with premarking. Dr. Cionni recommends premarking the horizontal or vertical axis, or both, as a reference and determining the alignment axis with a degree marker, using the reference marks as guides. He added that when the IOL is placed, it should be left about 15 degrees short of the intended axis until all viscoelastic is replaced with BSS. After the viscoelastic is removed, the IOL is rotated the final few degrees to achieve perfect alignment.
Another pearl from Dr. Chu is to make sure that the patient is upright during the marking. This is important because some eye rotation can occur when the patient moves from a seated to a supine position. He noted that various devices and techniques are available to assist with the marking, but the key to all of them is to have the patient in an upright position. He added that the surgeon should make sure that all viscoelastic is removed from behind the lens to keep the lens secure in the capsular bag and to minimize rotation.
Postop care after implantation of a toric IOL is the same as that provided for patients undergoing a standard cataract extraction and IOL implant.
The potential complications associated with toric IOLs are similar to those associated with cataract surgery in general and thus are very few, Dr. Chu said. “Complications specific to toric lenses would be rotation of the lens or mispositioning of the lens in relation to the axis of astigmatism. But that happens very rarely, is usually recognized early on after surgery and can be easily corrected by rotating the lens back into place in the OR.” Occasionally, residual astigmatism persists even though a toric lens has been well-positioned, he added. In these rare instances, patients will need an enhancement procedure, such as laser vision correction.
Looking not too far down the road, Dr. Cionni sees advances such as real-time photographic documentation of patients and registration being achieved with microscope overlays that will make premarking unnecessary and the results more accurate.
For now, toric lenses continue to grow in popularity as cataract surgeons adopt the procedures and patients become increasingly aware of their options in cataract surgery.
Dr. Chu is a consultant to AMO and Bausch + Lomb; Drs. Cionni and Hill are consultants to Alcon.
1 Available free from Dr. Hill at www.doctor-hill.com/physicians/download.htm
2 Available free from Alcon at www.acrysoftoriccalculator.com.