Femtosecond laser-enabled approach allows treatment of high astigmatism

By Cheryl Guttman Krader

Las Vegas-Femtosecond laser intrastromal arcuate keratotomy (AK) under a corneal flap is feasible and appears to be safe and effective for reducing high astigmatism, according to the early experience of António Limão, MD.

Speaking at the 2015 meeting of the American Academy of Ophthalmology, Dr. Limão presented outcomes for a series of 10 eyes of 10 patients treated with the novel technique that he said combines the safety of purely intrastromal AK with the effectiveness of classical surface AK.

“Whereas intrastromal femtosecond laser AK can only be used to treat up to 2 D of astigmatism, intrastromal femtosecond laser AK under a corneal flap could treat higher levels of astigmatism just as traditional arcuate keratotomy can,” said Dr. Limão, IMO, Lisbon, Portugal.

“Unlike the latter procedure, however, intrastromal femtosecond laser AK under a corneal flap avoids the risks of corneal surface penetration and incision gaping on the corneal surface,” he said.

In addition, it maintains integrity of Bowman’s membrane and allows the possibility of later enhancements with the excimer laser after relifting of the flap, he noted.

“To our knowledge, this is the first study where intrastromal AK was performed under a corneal flap, and the results are promising,” Dr. Limão said. “However, this series includes a small number of eyes and further study is needed.”

Dr. Limão credited Thomas Neuhann, MD, Munich, Germany, for having the idea of performing femtosecond laser intrastromal AK under a flap to correct high astigmatism.

His series of ten eyes included six that were postpenetrating keratoplasty, one that had high astigmatism secondary to trauma, and three with postsurgical astigmatism.

The procedure was performed with a 150-kHz femtosecond laser (Intralase iFS, Abbott Medical Optics) to create paired arcuate incisions centered on the steep meridian and a 110 to 120 µm corneal flap, which was lifted for manual opening of the incisions and then replaced. Flap diameter was between 7.5 and 9.0 mm.

The arcuate incisions were made at 80% depth of the minimal local corneal thickness to 100 µm from the surface at an optical zone of 5.8 or 6.0 mm. Arc length was based on a modified Lindstrom nomogram and was 60º or 75º in all but one case.

Dr. Limão reported that mean topographic astigmatism was significantly reduced by more than 50% from 8.28 D to 3.49 D. Similarly, there was a >50% reduction in mean refractive astigmatism from 6.58 D to 2.96 D. Mean spherical equivalent was unchanged, which was expected because of the coupling effect. Mean BSCVA (decimal) improved significantly by more than 2 lines from 0.392 to 0.666.

The only complication was a single case of incision gap opening that was treated with suturing of both arcuate incisions after relifting of the flap. Astigmatism in the involved eye was +12.80 x 7º preoperatively and +5.15 x 105º at last follow-up.

Dr. Limão has no relevant financial interest to disclose.