Laser microkeratome may reduce flap complications and improve visual outcome

Cheryl Guttman In San Francisco

MYOPIC "IntraLASIK" performed using the femtosecond laser microkeratome (IntraLase) and the Nidek EC-5000 excimer laser appears to produce better refractive and visual outcomes and lower rates of complications and enhancements compared to traditional LASIK, a recent study suggests.
G. Peyton Neatrour, MD compared three-month outcome data from 68 eyes he operated on using a mechanical microkeratome, the Moria M2, and 46 eyes using the femtosecond laser. He presented the data at the annual ASCRS Symposium on Cataract, IOL and Refractive Surgery.

The eyes in the mechanical microkeratome group represented a consecutive series of the last eyes he operated on during August 2002. The femtosecond laser group included eyes operated on in December 2002, during the fourth month after he switched to that device for flap creation. The spherical equivalent in both groups ranged up to -7 D.
He used the femtosecond laser to create flaps with a temporal or superior hinges with thickness set to 130 microns except in eyes with thinner corneas or needing higher amounts of correction, in which case he created a 100 micron flap. The Moria M2 flaps had superior or nasal hinges created with the 130 head. All data were entered into the Refractive Surgery Consultant (RSC) Elite for analysis, but the ablations in both groups were performed with a pre-RSC nomogram developed by Howard Gimbel MD.

At three months after surgery, the results showed a significant difference favouring the IntraLASIK group for better treatment accuracy, with a smaller standard deviation in the refractive error analyses and a higher rate of eyes corrected to within 1 D of intended. Those benefits translated clinically into better UCVA outcomes, and the all-laser group also experienced fewer flap-related complications and less problematic dry eye.

"With all other surgical factors the same except for the microkeratome used, the overall results were clearly better with IntraLASIK, and we expect the outcomes to be improved even further as we now use RSC software to personalise the nomogram," said Dr. Neatrour.
At three months after surgery, UCVA was 20/20 or better in 63% of IntraLASIK eyes and 58% of those having the mechanical microkeratome-created flap. Some 80% of the IntraLASIK eyes versus only 61% of the mechanical microkeratome group had UCVA of 20/25 or better. The corresponding rates for UCVA of 20/40 or better in the two groups were 96% vs. 69%, respectively.

In the IntraLASIK group 67% of eyes achieved SE within 0.5 D of target compared to only 56% that had flaps constructed with the mechanical microkeratome. The difference was more striking in the analysis of eyes within 1 D of intended correction, with 94% of IntraLASIK eyes and only 68% of eyes in the mechanical microkeratome group reaching that goal.

Analyses of cylinder results showed similar scatter and predictability with IntraLASIK and the mechanical microkeratome procedure. Their mean postoperative values of 0.34±0.35 D and 0.28±0.35 D, respectively, in the two groups and nearly all eyes had less than 1 D of residual cylinder. However, in the scattergram plot of intended versus achieved spherical equivalent for examining the effect on the nomogram, undercorrections were much more common in the mechanical microkeratome group, particularly when higher amounts of treatment were attempted.

"With the laser flap creation procedure, we consistently achieve a very dry bed, whereas even after wiping the stroma with a Weckcel sponge following the mechanical microkeratome pass, there is still some residual moisture that can vary in amount and confound the accuracy of the ablation," Dr. Neatrour said.
Safety was excellent overall. In both groups, approximately 15% of eyes gained one or more lines of BSCVA. While there were no cases of loss of two or more lines, a significantly higher proportion of IntraLASIK eyes than the standard treatment group temporarily lost one line of BSCVA, 22% vs. 16%, respectively.

However, all other safety analyses favoured IntraLASIK. For example, about twice as many eyes in the mechanical microkeratome group needed punctal occlusion postoperatively compared with the femtosecond laser group, 15% vs. 6.8%, respectively.
"We perform punctal occlusion preoperatively in any eye with less than 6 mm of wetting in Schirmer testing, if the patient is symptomatic, or there is clinically significant superficial punctate keratitis. In this series, about 20% of eyes in both groups had punctal occlusion before surgery. We believe the reduced need for punctal plug placement postoperatively after IntraLASIK reflects the fact that the femtosecond laser procedure causes less nerve damage because it is much gentler and reliably produces a flap with a large hinge," Dr. Neatrour said.

The IntraLASIK group also had lower rates of other complications compared with the mechanical microkeratome group, including epithelial defects (1.7% vs. 6%), diffuse lamellar keratitis (7% vs. 3.5%), and peripheral striae (<2% vs. 9%).
"The side architecture of the femtosecond laser flap is like a manhole cover, and that allows for better repositioning with a reduced rate of peripheral striae. Having recently adjusted our procedure by lowering the Intralase energy levels for the raster and side cut, we also expect to see further reduction in the rate of diffuse lamellar keratitis using IntraLASIK," Dr. Neatrour said.

In presenting enhancement rates, Dr. Neatrour noted that the duration of follow-up is only up to seven months in the eyes with mechanical microkeratome-created flaps and only three months for the femtosecond laser group. Against that background, he noted the overall enhancement rates have been 3% of eyes in the traditional LASIK group and 1.2% of the IntraLASIK group.
Dr. Neatrour acknowledged his associates Mark A. Lipton, OD, and Guy M. Kezirian, MD, for their help with data analysis.

G. Peyton Neatrour MD
Virginia Beach, Virginia, US
info@beacheyecare.com

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