Q: In light of the recent advances in laser correction of astigmatism, should I now recommend femtosecond laser-assisted treatment when my cataract patients with corneal astigmatism undergo cataract extraction with intraocular lens (IOL) implantation? Or should I continue to recommend a toric IOL for patients with significant astigmatism?
A: It depends on the amount of corneal astigmatism (and, of course, patient preference).
“My prediction is that femtosecond laser incisions will be most effective and predictable for a diopter and a quarter or less of astigmatism,” says Eric Donnenfeld, MD, who performs refractive and cataract surgery on Long Island. “Over this level of cylinder, IOLs will rule.”
Limbal relaxing incisions (LRIs) are one of the more prevalent surgical options for astigmatism management in patients who do not want to wear glasses after cataract surgery. Yet despite moderate procedural success, the perceived risk and required surgical expertise for manual LRIs has prevented many cataract surgeons from even attempting this operation, Dr. Donnenfeld says. As a result, toric IOLs evolved as a safe and effective alternative for astigmatism.
However, these lenses, while revolutionary, are also not without problems. Toric IOLs can rotate off axis, significantly affecting a patient’s uncorrected visual acuity—more so than with a spherical IOL. This effect is even more extreme at higher cylinder powers.1
The growing use of femtosecond-assisted cataract surgery, in which the laser replaces or augments manual techniques in several steps of the procedure, has led many surgeons to find advantages in femto-created LRIs. Capable of making safe, reproducible incisions at the desired optical zone, depth and length, femto laser technology allows surgeons to operate with greater precision compared to incisional procedures performed manually. Additionally, the laser-made incisions can be opened and adjusted following surgery to improve the refractive result as needed.
Femto procedures to treat corneal astigmatism still harbor some of the same restrictions of bladed incisions, cautions Douglas D. Koch, MD, a Texas-based ophthalmologist who specializes in cataract surgery and laser vision correction. These include “limited range of correction, some unpredictability of the corneal biomechanical response and potential complications including dry eye (from incising corneal nerves) and foreign body sensation (from the incision edges, albeit very rare).”
Overall, however, femtosecond laser technology is much improved over bladed incisions for surgical astigmatism treatment.
“So the issue is, which is better for low amounts of astigmatism: femtosecond laser relaxing incisions or toric IOLs?” says Dr. Koch. “Early data suggests that results are comparable. For less than 1D, the choice is likely relaxing incisions,” he says. “In the 1D to 1.25D range, both work well. Ultimately, much depends on surgeon comfort, outcomes and expertise.”
In his practice, Dr. Koch typically uses femto LRIs to correct up to 1.0D or 1.25D of astigmatism. Femto-laser intrastromal relaxing incisions in particular help eliminate the risks of dry eye and foreign body sensation. But above 1.25D, “toric lenses are more accurate and better tolerated,” he says.
Dr. Donnenfeld recommends femto LRIs—using either intrastromal or penetrating arcuate incisions—in cases of low levels of cylinder (0.75D or less). From 1D to 1.5D, either femto LRIs or toric IOLs would be viable options, he says.
Femto lasers and toric IOLs may someday play complementary roles for surgical treatment of astigmatism at the time of cataract surgery.
“My ultimate prediction is that both toric IOLs and femtosecond laser incisions will emerge victorious,” says Dr. Donnenfeld, when used in tandem. He envisions a surgical protocol that combines “the safety and precision of femtosecond cataract surgery with a toric IOL, and a femtosecond laser astigmatic incision created but not opened” during the procedure; the presence of the latter will allow “for postoperative adjustment of any residual refractive error,” if needed.
1. Patel AS. Toric IOLs. EyeWiki website. Updated Sept 30, 2014. Available at: http://eyewiki.aao.org/Toric_IOLs. Accessed Oct 15, 2014.