Femtosecond laser allows one-step LASIK in post-PK eyes

March 1, 2006

Chicago—IntraLASIK as a one-step procedure using the femtosecond laser microkeratome (IntraLase) for flap creation shows promise as a safe and effective approach for correcting ametropia after penetrating keratoplasty (PK), although the best refractive results may be achieved in eyes with only mild to moderate astigmatism, said Irina S. Barequet, MD, at the refractive surgery subspecialty day meeting sponsored by the International Society of Refractive Surgery of the American Academy of Ophthalmology.

Dr. Barequet, from the "Enaim" Vision Correction Centers, and lecturer, Goldschleger Eye Institute, Sheba Medical Center, Tel Aviv University, Tel Hashomer, Israel, presented a retrospective study of 10 eyes of 10 patients that showed favorable results at 2 months after IntraLASIK was performed for spherical errors and/or astigmatism. Flap creation and ablation were performed at a single session.

No complications were encountered intra- or postoperatively and no eyes lost more than 1 line of best spectacle-corrected visual acuity (BSCVA), while uncorrected visual acuity (UCVA) was improved in eight (80%) eyes.

She noted that despite achieving a clear cornea graft, patients who undergo PK often have impaired vision due to high astigmatism with high myopia or hypermetropia and anisometropia. Excimer laser surgery has provided a new method for treating post-PK refractive errors, but initial experience with PRK showed it was associated with stromal haze that was related to the magnitude of ablation and coupled with refractive regression. While LASIK provided several advantages, the lamellar cut at the graft-host junction has limitations and the release of contractile forces can lead to a change in the magnitude and axis of astigmatism to necessitate a sequential two-step procedure, Dr. Barequet said.

Controlled flap creation

"The femtosecond laser microkeratome allows controlled flap creation within the graft margins and avoids involvement of the graft-host junction as well as creation of a lamellar cut in a thin host area. Those benefits probably provide immunological and mechanical advantages and reduce the effect of the flap creation on astigmatism to allow for a one-step versus staged flap creation-ablation procedure," said Dr. Barequet.

Among the 10 eyes in the study she reported, eight had undergone corneal grafting for keratoconus and the indication for PK in the other two eyes was ectasia. The mean interval between PK and IntraLASIK was 47.2 months (range, 13 to 156).

The IntraLase-assisted flap was created with a diameter of 7.6 to 7.7 mm, so that it remained within the corneal graft margins. Flap thickness ranged from 90 to 100 µm.

"Intraoperatively, some minor difficulty was encountered lifting the flap in areas where there was some scarring from prior long-standing sutures, but in no case was there any significant problem with flap elevation," Dr. Barequet said.

Once the flaps were lifted, the ablation was performed with a Bausch & Lomb laser at an optical zone ranging from 4.5 to 6.0 mm at an average depth of 102 µm.