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Femtosecond intrastromal keratotomy reduces astigmatism after LASIK, PRK
The rate of reduction was associated with age and amount of astigmatism.
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CHICAGO — Intrastromal femtosecond laser astigmatic keratotomy appears to be safe and a viable method of correcting low to moderate astigmatism after previous refractive surgery, according to a study presented here.
“There are many advantages of doing intrastromal astigmatic keratotomy,” Steven C. Schallhorn, MD, said during Refractive Surgery Subspecialty Day preceding the joint meeting of the American Academy of Ophthalmology and Asia-Pacific Academy of Ophthalmology. “There’s no epithelial injury. It’s a very quick procedure with fast visual recovery.”
Study results also showed refractive stability and no complications. However, the study had a small patient population with a relatively short follow-up interval. Additionally, refinements to the nomogram are needed to provide more predictable outcomes, Schallhorn said.
Steven C. Schallhorn
“We’re relatively new at this,” he said. “Nomogram adjustments, technique refinement and more experience will undoubtedly improve the results.”
The study included 55 eyes of 49 patients with an average age of 50 years. Patients previously had LASIK or PRK and underwent astigmatic keratotomy 3 months to 5 years after excimer laser ablation.
Investigators used a simple nomogram based on amount of astigmatism with a 7-mm optical zone. Astigmatic correction was titrated by varying the arc angle by 30° to 75°.
Reduction correlates with severity
Study results showed that low to moderate levels of astigmatism decreased after 1 month and 3 months. Spherical equivalent refraction remained around 0 D from before surgery to after surgery.
“There was no change in spherical equivalent, meaning that just like regular manual incisions, there was a coupling effect,” Schallhorn said.
Vector analysis showed scatter in the reduction of astigmatism vs. intended values, Schallhorn said.
Correction was generally higher in eyes with a greater amount of astigmatism. However, there was some degree of undercorrection on average, Schallhorn said.
“This also shows up in the correction ratio, stratified by the intended cylinder, where the correction ratio does show an undercorrection. But it is titratable,” he said. “Again, the higher levels of correction achieved similar correction ratios, meaning that the nomogram was effective.”
Age, previous refractive surgery
Greater reduction of astigmatism correlated with patient age.
“That is very similar to the results that have been observed and published,” Schallhorn said. “Age seems to play a factor in the amount of cylinder correction.”
The reduction of astigmatism was slightly greater among patients who had previously undergone LASIK than among those who had PRK. However, the significance of the between-group difference is dubious because only 13 patients had undergone PRK, Schallhorn said.
Most patients had little to no astigmatic axis shift, he said.
A subanalysis of stability data for 16 patients showed that the refraction was stable between 1 week and 3 months postop.
“Refractive results appear stable in this small group, at least through 3 months of follow-up,” Schallhorn said.
Data showed a significant improvement in uncorrected visual acuity but no change in best corrected visual acuity, Schallhorn said.
Additionally, data showed no intraoperative or postoperative complications, he said. – by Matt Hasson