Optimizing Flap Outcomes With the IntraLase FS Laser
With unmatched precision, we can make flaps that enhance treatment and minimize complications.

Now that we can customize our LASIK ablations, precise flap architecture and thickness are more crucial than ever. Flap creation using the IntraLase femtosecond (FS) laser is a significant advance in refractive surgery and, in my opinion, quickly will become the standard of care due to improved safety and visual outcomes.

Flaps created with the IntraLase FS laser induce fewer higher- and lower-order optical aberrations than those made with conventional microkeratomes, and evidence now shows less corneal nerve damage and clinical dry eye after LASIK surgery using IntraLase technology. With better flap creation, the FS laser simply produces better outcomes.

Compared with two mechanical micro-keratomes, the Intralase FS laser is much less likely to produce extremely thin or extremely thick flaps.

What's the difference?

IntraLase is fundamentally different from microkeratome technologies because it doesn't cut from the side. It compresses the cornea to create a planar surface against a glass applanation cone. Following this cavitation, bubbles are delivered in a raster pattern across the cornea to create an interface cut and then a side cut. The flap is lifted with blunt dissection using a spatula or similar instrument.

Another significant advantage is that you don't have to raise the intraocular pressure as high for IntraLase as you do for the microkeratome. What's more, the degree of monitoring and control you have with this device is far superior to what you have with a mechanical blade. At any point, you can turn back or modify the situation to yield a quality flap.

Create the flap you want

IntraLase makes the flap diameter and the hinge angle highly tunable. Also, because of the flap's architecture, you can achieve the ablation area you want with a smaller flap.

With a microkeratome, the flap diameter is a function of suction ring thickness and corneal diameter and curvature. IntraLase simply sees the corneal surface compressed flat against the glass, so it doesn't matter whether the cornea starts out at 47 diopters or 41 diopters.

The microkeratome creates a D-shaped stromal bed, leaving less room for the flap diameter you need. With IntraLase, you decide how big the hinge is. You can create a pocket dissection that dives back to vent the gas bubbles, along with a smaller hinge. If you're well centered on the pupil, you'll have the full flap diameter you want. I routinely create 8.8-mm flaps with IntraLase where a 9.5- or 10-mm flap would be necessary with a microkeratome.

	The IntraLase has also been shown to induce significantly less astigmatism than two mechanical microkeratomes.

Precise flap thickness

IntraLase makes flap thickness significantly more precise and predictable than microkeratomes do. Many variables can affect microkeratome flap thickness and variability. It works with a loosened, oscillating blade, and tissue compressibility varies at very high pressures. Corneal curvature and keratome translation speed also can affect flap thickness.

I compared my results for about 350 consecutive eyes evenly divided among three keratomes: The Moria MII, the hand-guided Moria LSKI and the IntraLase. The IntraLase flaps were closest to the intended thickness, and the standard deviation and range for the mechanical microkeratomes were about double that of the IntraLase. I also found that the mechanical microkeratomes were 10 times more likely to produce a seriously thin flap and 1,000 times more likely to create extremely thick flaps (see "Flap Thickness Distribution").

My study is now but one of five showing vastly improved standard deviation and range with IntraLase. IntraLase is clearly much more precise and can help us approach deeper ablations, such as those needed for custom ablation, with much more confidence than we could in the past. And this will bring more patients into the pool of LASIK candidates.

See the difference

Fewer aberrations. If you create aberrations at the same time you're treating them, your results won't be predictable. Emerging data show that IntraLase decreases induction of both lower- and higher-order aberrations. Several studies strongly suggest this is because of the IntraLase flap's planar architecture, compared to a microkeratome flap that's deeper in the periphery than in the center (meniscus-shaped). The very act of making a meniscus flap seems to induce aberrations.

Better induced cylinder predictability. Research has shown improved predictability of induced cylinder with the IntraLase versus two popular mechanical microkeratomes (see "Induced Cylinder"). Visual acuity data supports this finding.

Steeper edge configuration. With a microkeratome, the edge configuration is about 25° to 35°. You need to enter at that angle to make a flap without risking extremely deep penetration or anterior perforation. With the IntraLase, the side-cut angle can be varied over a wide range, and angles ranging from 40° to 70° seem to offer the most advantages. An increased side-cut angle can allow the flap to seat more easily and, more importantly, create an entry that's a powerful barrier to epithelial cells. In experience with more than 1,000 IntraLase cases at my practice, we have not seen a case of epithelial ingrowth. We attribute this to IntraLase's steeper edge configuration.

The results of this study show the excellent safety profile of the IntraLase.

Less dry eye and corneal denervation. LASIK-induced neurotrophic epitheliopathy can occur in up to 20% of patients with microkeratome flaps. Severe dry eye can last 6 months to 2 years after surgery. This is believed to be caused by the interruption of corneal sensory nerves and the lacrimal gland's biofeedback loop, which causes tear film secretion.

With IntraLase, you don't need to cut as deeply or create as large a flap as you do with a microkeratome. You don't transect as much nerve tissue, which may be one reason why there's more corneal sensation and less dry eye after IntraLase procedures. And anything we can do to prevent or minimize neurotrophic epitheliopathy will help us with our LASIK results.

Lower complication rates. In 410 consecutive eyes I treated with IntraLase, the incidence of serious flap complications intra- and postoperatively was zero (see "Femtosecond Pros: Safety"). Three studies presented at the 2003 meeting of the American Society of Cataract and Refractive Surgery showed no serious flap complications in 208, 300 and 5,000 cases (Lee T. Nordan, M.D. and Stephen G. Slade M.D.; Jonathan D. Christenbury, M.D.; and Brian Will, M.D., respectively). And with more than 100,000 procedures performed worldwide, there's a large enough body of experience with this device to confidently say the rare complications we experienced with blade keratomes are greatly reduced with the IntraLase.

New paradigm

IntraLase FS lasers are safer and more precise than blade keratomes for LASIK flap creation. It would be virtually impossible to duplicate the IntraLase results with a blade keratome, in part because the device lets us safely restart interrupted procedures to ensure a quality flap. The difference shows in its enhanced outcomes, which will help us improve custom ablation and other procedures in the future.

Dr. Talamo practices at Laser Eye Consultants of Boston in Boston and Waltham, Mass. He is an assistant clinical professor of ophthalmology at Harvard Medical School. He serves as a consultant to IntraLase.

SPONSORED BY

This is one of a series of articles recapping presentations given at the IntraLase booth during the 2003 meeting of the American Academy of Ophthalmology.