June 2010

 

COVER FEATURE

 

Presbyopia

Measurement and technique key to toric IOL results


by Rich Daly EyeWorld Contributing Editor

 

View Toric IOLs chart

 

Surgeons report good astigmatic correction with toric lenses depends on careful measurement and marking pre-op, along with implantation techniques to minimize rotation post-op

Surgeons are increasingly comfortable with the use of toric lenses instead of older techniques to treat astigmatism. However, they caution that careful measurements and marking of the axis pre-op and surgical techniques to prevent rotation are critical to obtain reliable results from the two available toric lenses.

Surgical correction of astigmatism with toric IOLs also can correct spherical refractive error, while preserving the corneal contour. The use of toric lenses also allows surgeons to reverse the correction, unlike the older techniques of astigmatic keratotomy and limbal relaxing incisions (LRIs). These advantages have led to the growing popularity of the lenses among cataract surgeons and refractive surgeons.

Between the two types of toric lenses used domestically, the STAAR Surgical Toric IOL (Monrovia, Calif.) was the first widely available in the United States when the Food and Drug Administration (FDA) approved it in 1998. The two versions of the STAAR lens correct up to 2.00 D and 3.50 D of astigmatism. The second FDA-approved toric lens is the AcrySof IQ (Alcon, Fort Worth, Texas)—available since 2005—which can correct between 1.5 and 3 D of astigmatism.

More U.S. surgeons have turned to these toric lenses for astigmatism correct, according to surgeon surveys in recent years. For instance, the 2008 Leaming survey of ASCRS members found toric use jumped from 22% of cataract surgeons in 2007 to 45% of those surgeons in 2008. Samuel Masket, M.D., clinical professor of ophthalmology, Jules Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, is among surgeons who have found a prominent role for toric lenses. He prefers the AcrySof lenses because of concerns over the rotational stability of plate haptic silicone lenses, among other reasons. Like many surgeons, Dr. Masket has found that one of the challenges in obtaining reliable results from toric lenses is the lack of an efficient and reliable method for determining the visual axis.

“This is a really weak link in our science,” Dr. Masket said, about the need for technology that uses limbal or iris markings to guide the placement of the toric lenses.

Although some advanced systems are under development, Dr. Masket and other surgeons rely on surgical pens to manually mark the nasal and temporal limbus of patients while they are sitting upright before surgery. The accuracy of such markings is critical because for every one degree of misalignment toric lenses lose 3% of their corrective effect, he noted.

Steven G. Safran, M.D., Lawrenceville, N.J., uses a slight variation on manual markings that integrates natural landmarks on the cornea “Most older patient’s have a natural indicator of the 180-degree axis, such as a little limbus girdle or cornea shape change at the limbus to indicate the 180 axis,” Dr. Safran said.

He compares these natural marks to his marks for the 180-degree axis. Additionally, when marking the astigmatic axis Dr. Safran uses both a surgical marker and a tiny cornea/limbal “nick” with a blade that will be visible to him later. While pen marks can fade away, the small incision and minute bleeding remains visible through the end of the procedure. Thomas A. Oetting, M.D., professor of clinical ophthalmology, University of Iowa, Iowa City, Iowa; and chief, Eye Service, and deputy director, Surgery Service, VA Medical Center, Iowa City, Iowa, also manually marks the eye pro-op but follows up with final axis marks after removing the cataract and leaving ophthalmic viscosurgical device (OVD) in the capsular bag. He also compares the results of a toric IOL calculator (Alcon) to his view at the surgical microscope to ensure accuracy.

Jay S. Pepose, M.D., Ph.D., director, professor of clinical ophthalmology, Washington University School of Medicine, St. Louis, opts for one of the slightly more advanced marking systems. For toric lens placement he relies on a bubble marker along with components of the Mastel Toric Marker System (Mastel Precision Instruments, Rapid City, S.D.).

Rotation Problem

Another challenge to obtaining the best results from toric lenses is to ensure that the IOL does not rotate beyond the desired axis of alignment, such as during the removal of viscoelastic.

Dr. Oetting uses the common technique of leaving the IOL about 15-degrees short of the markings with OVD in the eye. Only then does he go under the IOL to remove OVD below before nudging the IOL into position.

“You must go under to remove the OVD to help seal the IOL in the bag,” Dr. Oetting noted.

This situation is complicated when a malyugin ring (MicroSurgical Technology, Redmond, Wash.) is used to keep the iris open, such as in intraoperative floppy iris syndrome cases. Use of the standard technique of removing the ring after placement of the IOL may result in the pupil dropping to a point where the toric markings are obstructed. A couple of ways to avoid this problem are either to leave the ring in place while the OVD is removed from under the IOL and move the IOL into final position before adding OVD above the IOL to remove the ring without disturbing the IOL placement, or use hooks instead of the ring in these cases.

Additionally, Mark Packer, M.D., clinical associate professor of ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, Ore., and Dr. Oetting use the irrigation/aspiration port to hold the IOL in the periphery before moving it into the final postion.

“This works most of the time and can be especially useful if the pupil has come down a bit,” Dr. Oetting said.

If these techniques fail, then surgeons need to remain vigilant for early signs of off-axis lens rotation.

Like many surgeons, Shannon M. Wong, M.D., Austin, Texas, aims to review the toric placement within days of surgery and immediately correct any movement.

“It’s best to correct misaligned lenses as soon as the condition is diagnosed,” agreed Dr. Packer.

Dr. Safran takes a more cautious approach to toric lens rotation in highly myopic patients, preferring to wait a few weeks because clockwise rotation in the first week can occur when the capsular bag is too big for the lens.  

“Better to wait a few weeks to fix this because if you go in right away it will likely happen again,” Dr. Safran said. “Some people have advocated waiting two to four weeks to go in the second time in this situation.”

Editors’ note: Dr. Masket has financial interests with Alcon (Fort Worth, Texas,). Dr. Pepose has financial interests with with Abbott Medical Optics (Santa Ana, Calif.) and Bausch & Lomb (Rochester, N.Y.), neither of which makes toric IOLs at this time. Dr. Packer has financial interests with WaveTec (Aliso Viejo, Calif.). Drs. Safran, Oetting, and Wong have no financial interests related to their comments.

Contact information

Masket: sammasket@aol.com
Oetting: thomas-oetting@uiowa.edu
Packer: mpacker@finemd.com
Pepose: jpepose@peposevision.com
Safran: safran12@comcast.net
Wong: shannon@austineye.com

Measurement and technique key to Toric Intraocular Lens results Measurement and technique key to Toric Intraocular Lens results
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