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By Cheryl Guttman

ORLANDO, FL - The femtosecond laser microkeratome (IntraLase® FS, US) is a safe and effective alternative for LASIK flap creation and appears to offer advantages over mechanical microkeratomes, according to a US ophthalmologist.
Jonathan D. Christenbury MD presented results at the annual meeting of the American Academy of Ophthalmology from a series of 300 myopic eyes of 156 patients followed for one month after undergoing IntraLASIK with the femtosecond laser microkeratome for the lamellar keratectomy and the EC5000 excimer laser (Nidek) for ablation.
There were no intraoperative complications associated with use of the femtosecond laser microkeratome.

Although the keratectomy procedure was interrupted due to suction loss in six eyes, it was immediately re-initiated and completed successfully in all of those cases.
Vision and refractive outcomes at one month were very favourable in all eyes, with only a few minor complications encountered, he reported.
“Our experience with the femtosecond laser microkeratome now includes over 4,000 cases. In that large series we have not had a single intraoperative flap complication or any aborted flaps.

“This laser offers an accurate, reproducible way to make even very thin flaps which are precisely centered and have extremely smooth beds,” Dr Christenbury said.
Parameters used for flap creation in all eyes included a hinge angle of 60o, a side cut angle of 50o, diameter 8.5 mm to 9.3 mm, and thickness of 110 microns to 130 microns.
The majority of flaps had a superior hinge, while a nasal hinge was created in a very limited number of eyes. The ablations were performed using the same nomogram as standard LASIK, performed with a mechanical microkeratome.

“When we first started IntraLASIK, we continued with our standard LASIK postoperative regimen of a one-week course of a topical antibiotic and steroid administered four times a day. We found, however, that about 5% of patients returned during the second week with mild to moderate photosensitivity.

“We found nothing on slit-lamp examination and their sight was excellent, but the photosensitivity responded well to prolonged steroid treatment,” Dr Christenbury added.
For the study, postoperative treatment included a topical antibiotic for one week and topical steroid drops tapered from QID to QD dosing over four weeks and then discontinued. Currently, steroids are tapered over two to three weeks.

He noted that there was a little more flap oedema on the first postoperative day after the all-laser procedure, compared to eyes operated on with mechanical microkeratomes.
However, this had resolved quickly and at one month, vision was actually better than after standard LASIK. The safety has also been excellent, with a particularly noteworthy lower rate of dry eye complaints after IntraLASIK.
Uncorrected acuity was 20/20 or better in about 70% of eyes at the one-month follow-up visit. Some 98% achieved 20/40 or better UCVA.

About 70% of eyes were within 0.5 D of their target MRSE and 95% were ±1.0 D. Two eyes experienced a two line loss from baseline BSCVA and about 15% had a single line decrease. BSCVA was improved one line from baseline in 12% of eyes and unchanged in about 70%.
The results achieved in the six eyes in which flap creation was interrupted due to suction loss were comparable to the overall group. At one month, UCVA was 20/20 in five of the eyes and 20/30 in the sixth. Vision in all patients could be corrected to 20/20 or better.

The safety analysis was based on review of intraoperative and postoperative complications as well as patient subjective complaints and BSCVA results.
Notably, there were no thin/button-hole flaps or incomplete cuts. During follow-up over the next month, no eyes developed diffuse lamellar keratitis, corneal melts or epithelial ingrowth.
“While no cases of epithelial ingrowth were seen in this study, we have seen a few cases in our overall series. Still, the incidence of that complication has been very low and that may be accounted for by the very precise edge architecture of the flaps created with the femtosecond laser,” Dr Christenbury said.

The most common complications in the series of 300 eyes were epithelial defect/ abrasion (3.3%), striae/flap wrinkles (2.3%) and debris in the interface (1%).
In addition, subconjunctival haemorrhage, mild inflammation and flap oedema lasting more than seven days all occurred at rates less than or equal to 0.7% (i.e. one or two eyes).
Dry eye was the most common patient complaint but its incidence was only 15%, much less than with standard LASIK.

“When performing standard LASIK, we would routinely insert inferior collagen punctal plugs on the day of surgery in every patient.
“Even though we discontinued that practice once we started using the femtosecond laser microkeratome, the frequency of dry eye complaints has markedly decreased compared to what we observed performing standard LASIK with the punctal plugs,” Dr Christenbury said.

He mentioned that while use of a horizontal hinge has been shown to be beneficial for decreasing dry eye symptoms after standard LASIK, hinge location in the IntraLASIK procedure did not seem to affect the development of this problem.
“We performed IntraLASIK in a consecutive series of 100 eyes using a temporal horizontal hinge and found no difference in rates of dry eye symptoms compared to eyes with superior hinge, laser-created flaps.

“Our preference has always been for the superior hinge location, which we think is more stable against flap slippage, and this data provides no reason to stop doing what we are accustomed to,” Dr Christenbury explained.
Other patient subjective complaints included photophobia, ocular irritation and tearing, which were each reported at rates of about 2%, along with burning and discomfort or pain, which occurred at rates less than 1%.

The first major advantage of the IntraLase is safety and avoidance of keratome-related complications, which count for 95% of the vision threatening complications in LASIK.
Complications of microstriae and epithelial ingrowth are less with IntraLase. IntraLase allows total flexibility in customising the flap dimensions for LASIK, Dr Christenbury said.
He added that it is safe to create a thin flap, down to 100 to 110 microns, which allows more room for higher dioptre correction of eyes with thinner corneas.

“I now perform IntraLASIK for those patients rather than PRK or LASEK. I am finding outcomes are improved and I have not had to modify my excimer nomogram. The scattergram is tighter at six months compared to standard LASIK. I will be reporting a series of six month data at the 2003 ASCRS meeting,” Dr Christenbury remarked.

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