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In a retrospective study including 14 eyes with high astigmatism that was naturally occurring, post-penetrating keratoplasty, or associated with a corneal scar, astigmatic keratotomy using a femtosecond laser (IntraLase FS, IntraLase Corp.) was safe and effective for reducing astigmatism and improving visual acuity.
He reported the findings from a retrospective chart review of 14 eyes of 11 patients who underwent paired arcuate astigmatic keratotomy with the femtosecond laser at Bascom Palmer Eye Institute, Miller School of Medicine, University of Miami. In the procedure, laser pulses are stacked on each other to create an angled cleavage plane that is then opened manually in an instrument-assisted procedure.
The astigmatism was naturally occurring in six eyes, associated with penetrating keratoplasty in seven eyes, and scar-induced in one eye. A nomogram was used to tailor treatment for each eye. Two eyes required an enhancement with either the addition of another incision or incision deepening.
"Correcting astigmatism of 4 D or more with the excimer laser is problematic, and manual astigmatic keratotomy for such eyes is unreliable and unpredictable. The femtosecond laser-based procedure holds promise for patients with high levels of astigmatism that are naturally occurring, post-corneal transplantation, or scar-induced, and our experience shows it is possible to use a nomogram to select a treatment protocol accurately," Dr. Hammonds said.
Excellent results also were achieved when analyzing the outcomes with patients divided into diagnostic subgroups. Among the eyes with naturally occurring astigmatism, refractive cylinder decreased by an average of 4.48 D, and there was a mean 3.1-D change in astigmatism, according to topographic measurement. UCVA in those eyes improved from a mean of 20/250 to 20/25–, and BCVA remained the same at 20/25+.
In the eyes with astigmatism after penetrating keratoplasty, mean change in refractive astigmatism was 4.36 D, and topographic astigmatism was reduced by an average of 4.77 D. Mean UCVA improved from 20/225 to 20/70, and mean BCVA improved from 20/40 to 20/32.
"Once the sutures are removed after penetrating keratoplasty, many eyes are left with more than 4 D of astigmatism. With that high level of astigmatism, most patients cannot tolerate spectacles, nor can they be successfully fitted with rigid contact lenses over the long term. The [femtosecond laser-based] procedure appears to be a useful method to help these patients," Dr. Hammonds said.
When the procedures were performed, the existing parameters for the femtosecond laser only allowed creation of a 400-μm deep incision. New parameters that are now available through the keratopathy software (version 2.41) allow two incisions to be created simultaneously at different depths and deeper than 400 μm.
"With this new flexibility, it may be possible in the future to use the laser to fine-tune even lesser degrees of astigmatism," Dr. Hammonds said.