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  • Applications: Keeping an Eye on Lasik

Photonics Spectra
Jan 2009
Patricia A. Vincent,

Research into lasik (laser-assisted in situ keratomileusis) refractive eye surgery indicates that, besides focusing on improving the procedure, the trend is moving toward developing different techniques or, in some cases, going back to one that predates lasik.

Lasik has been performed in the US since 1991. Methods and instrumentation have changed as the procedure has evolved, and, no doubt, we will see further refinements as practitioners seek to give more patients access and to provide even better outcomes.

Besides lasik, which involves creating a corneal stromal “flap,” there are several “no flap” procedures – referred to as photorefractive keratectomy (PRK), lasek, hydrolasek, advanced surface ablation and epilasek – that are differentiated by the various ways in which the epithelial cells are removed.

The original lasik technique employed an oscillating metal blade, called a microkeratome, to cut the corneal flap. The more recent “all laser” procedure uses two computer-guided lasers and no blade. A femtosecond laser creates the flap, and an excimer laser removes a small amount of corneal tissue and reshapes the cornea.

According to Dr. Neal E. Ginsberg, a corneal and refractive surgery specialist at Berkshire Eye Center in Pittsfield, Mass., “This is safer for the patient, more reproducible, more reliable and less destabilizing of the corneal structural integrity.”

The IntraLase from IntraLase Corp. of Irvine, Calif., was the first femtosecond laser to receive FDA approval for this use. There are now others, including the Femto LDV from Ziemer Group of Port, Switzerland, whose clinical advantages include a smooth surface for the stromal bed, smooth edges for optimal flap closure, thin flaps of even thickness, rapid healing and visual recovery, and excellent visual outcomes.

New methods being studied

Both Z-Lasik (from Ziemer) and iLasik (from IntraLase) techniques use millions of precise laser pulses to create an accurate flap. Studies comparing the two are ongoing, but some advantages of the former have been identified. Z-Lasik does not produce transient light sensitivity syndrome, or aversion to light, experienced by some iLasik patients for days after surgery, perhaps because of its more tightly focused laser energy pulse and reduced energy dispersion through the cornea.

The use of wavefront-guided or “custom” lasik techniques is increasing. A wavefront aberrometer takes a snapshot of each eye to identify minor imperfections. The patient’s “prescription” – individualized for each eye – is then programmed into the computer, which guides the laser to correct the deformities. Higher-order aberrations that degrade both vision and contrast sensitivity now can be identified and corrected.

“For the patient,” Ginsberg said, “this means better results and decreased glare and halo effects, which have been common problems after lasik surgery.”

Bausch & Lomb recently launched its Zyoptix Advanced Control Eyetracking technology, a dynamic rotational eye-tracking system that also compensates for static rotational movement, pupil shift, saccadic (small, rapid, jerky) movements of the eye in the X and Y planes, and movement along the Z plane. It adjusts the ablation pattern during the procedure, reducing the risk of misalignment and providing more predictable outcomes.

Dr. Peter S. Hersh, director of the Cornea & Laser Eye Institute in Teaneck, N.J., where hydrolasek was introduced, believes that improvements can be made in the way patients are evaluated for lasik. He also would like to see better ways to measure corneal biomechanics, improvement in the computational techniques used to program the lasers and improvement of the laser algorithms. “The further development of femtosecond laser technology to make custom flaps would potentially lead to better outcomes in a wide group of patients.”

Dr. Peter S. Hersh performs lasik surgery at the Cornea & Laser Eye Institute in Teaneck, N.J.

Ginsberg agrees that the key to positive results and satisfied patients lies in careful preoperative screening to select good candidates who have reasonable expectations. The technology and the lasers, he said, are constantly improving. “We are absolutely astounded by what [laser manufacturers] are coming up with.”

Despite the improvements in lasik, many surgeons, including Ginsberg, prefer surface ablation or “no flap” procedures, which eliminate problems associated with the flap (creating it, traumatic dislocation, epithelial ingrowth, wrinkles) and reduce occurrence of the rare but serious condition called ectasia, a deformation of the cornea that can require a corneal transplant to correct.

“Surface ablation requires a longer recovery period and involves slightly more patient discomfort,” he explained, adding, however, that it can be safer. “Patients who are not viable candidates for traditional lasik sometimes are for surface procedures.” These would include people who have thin or irregular corneas, which would be destabilized too much by a flap.

“Surface ablation preserves more corneal tissue and better maintains the structural integrity of the eye,” Ginsberg said.

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