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The approved use of wavefront-guided technology for mixed astigmatism may help ophthalmologists to reach another potential groupof patients.
Reviewed by Robert K. Maloney, MD
Patients with mixed astigmatism can be challenging to treat with LASIK. The recent FDA approval of a new indication for wavefront-guided technology (iDesign Advanced WaveScan Studio System, Abbott) could make treatment for this patient segment a little easier.
Used in tandem with an excimer laser system (Star S4 IR, Abbott), the wavefront technology provides surgeons with detailed information for precise and individualized treatment. Previously approved for hyperopia, myopia, and astigmatism, the approval with mixed astigmatism helps reach another potential group of patients, said Robert K. Maloney, MD, Los Angeles. He was involved with FDA trials for the system and has used it for about 4 years.
About 5% of his patients have mixed astigmatism. Though this may seem a small percentage, it is a large enough chunk that surgeons would not want to turn them away, he noted.
“It’s not terribly common, but if you want to be a comprehensive refractive surgeon, you have to be able to handle those patients,” he said.
Rising to the challenge
Mixed astigmatism is probably the hardest refractive error to correct with LASIK, Dr. Maloney noted.
“You have to steepen one meridian and flatten the opposite,” he said. “The ablations are more complex in terms of shape.
“One challenge is you may not get a full correction,” Dr. Maloney said. “Another challenge is that you may correct the astigmatism well but cause a shift in spherical equivalent that can be myopic or hyperopic. You correct one problem but create another. The [system] offers the possibility of more accurate correction.”
Additionally, mixed astigmatism is fairly common after a patient’s original LASIK, he added.
A clinical study of the system for mixed astigmatism in 149 eyes found that 91.9% of all eyes had uncorrected visual acuity of 20/20 or better without glasses at 3 months after surgery. Additionally, about 90% of eyes were within a half-diopter of their target refraction, and roughly 90% had 0.50 D or less of astigmatism.
“Those are really good results,” especially when up to 5 D of preoperative astigmatism was treated, Dr. Maloney said.
The new indication is for mixed astigmatism with a magnitude of 1 D to 5 D of cylinder that is greater than the magnitude of sphere and in which the cylinder and sphere have opposite signs, according to an Abbott press release.
Additionally, there must be an agreement between manifest refraction and the system refraction with a magnitude of difference of less than 0.625 D in spherical equivalent and a magnitude of difference of less than or equal to 0.5 D for cylinder.
Robert K. Maloney, MD
Dr. Maloney is a consultant for Abbott, Calhoun Vision, and Presbia.