Understanding Your Keratome Options
Although encouraged by the promise of the femtosecond laser, this surgeon still relies on the mechanical keratome. Here's why.

Throughout my career, I've used just about every microkeratome that's made its way to the market. I currently use AMO's Amadeus mechanical microkeratome and the IntraLase femtosecond (FS) laser microkeratome. Both have significant advantages and some disadvantages to consider.

Amadeus Pluses

Among mechanical microkeratomes, the Amadeus is in a class by itself. With it, I can customize a flap by:

• Shifting the orientation of the hinge by upwards of 40° in either direction
• Changing the hinge width over a wide range
• Changing the diameter of the flap using the 8.5-, 9.0-, 9.5- and 10-mm rings
• Changing the flap thickness by adjusting the aspiration setting up or down from 24.5 mm Hg.

The Amadeus is epithelium-friendly and user-friendly. It's preassembled, mounts on the eye in a single piece and creates a flap in 6 seconds with one click of the pedal.

IntraLase Pros and Cons

A theoretical advantage of the FS laser is that it can create up to a 9-mm diameter flap; however, its limitation is that it can't make a flap larger than 9 mm.

Another theoretical advantage is that the hinge can be placed temporally, nasally or superiorly. What we've noted, however, is that if the hinge is not placed superiorly, it's technically more demanding to lift the flap.

A real advantage of the FS laser is that because the flap margin is nearly vertical, it creates more of a 'manhole' cover fit for the flap. Because of this, it's possible to have a narrower hinge and still have a tectonically stable flap on the eye.

We've had the IntraLase FS laser for almost a year, and probably the single greatest advantage it offers is in marketing. Patients are intrigued by the concept of an 'all-laser' LASIK procedure. To the lay public that's appealing.

On the down side, marketing follow-up entails a fairly lengthy discussion with the patient to explain the pros and cons of either the FS laser or the mechanical microkeratome. Unfortunately, any time you talk about anything negative with respect to LASIK, you tend to confuse patients and lose them altogether.

Two major disadvantages of the FS laser are the length of time it takes to create a flap, and the fact that some blunt dissection is necessary to complete the flap. In my experience, the entire process of creating and lifting a flap with the FS laser requires nearly 30 times greater time commitment than with the Amadeus.

Centration and Suction Concerns

In any comparison of mechanical keratomes and the FS laser keratome, we need to address centration issues. Compared to a vertically passed microkeratome, such as the Bausch & Lomb Hansatome, the IntraLase achieves better centration. But in comparison to a horizontally passed microkeratome, such as the AMO Amadeus, the IntraLase does not provide as reliable a centration. The reason for this is the keratome configuration.

With the mechanical microkeratome, only the keratome is attached to the eye. With the IntraLase, the suction ring attaches to the cone of the laser, which then attaches to the entire laser so that the entire laser mechanism is attached to the eye. This platform limitation makes it somewhat more difficult to achieve precise centration compared to a horizontally passed keratome.

Another disadvantage associated with the IntraLase laser being attached to the patient's eye is that a subset of our patients who undergo IntraLase LASIK experience excruciating pain throughout the procedure, lingering for several hours afterward, comparable to a splitting headache.

This results from multiple attempts at achieving suction. These patients also experience a great deal of chemosis because of the difficulty in maintaining suction. This tends to happen primarily when you're trying to push the flap diameter to its most extreme limits and thus you engage and reengage the suction.

Preserving corneal sensation

A keratome's orientation and hinge placement both factor into preservation of corneal sensation. It's quite plausible that compared to the Hansatome, the IntraLase would preserve more sensation -- given that the Hansatome produces a superior hinge and the IntraLase hinge may be horizontal -- because most of the nerves that supply the cornea are horizontal. With a horizontal hinge, you'll cut the nerves from one side, whereas with a superior hinge you'll cut the nerve bundles from both sides.

I've found no difference between the IntraLase and the Amadeus with respect to preserved corneal sensation. The Amadeus makes a horizontal hinge, thereby sparing a portion of the horizontally oriented long ciliary nerves. This also equates to fewer dry eye issues with the Amadeus than most of the other mechanical microkeratomes that are vertical and make a superior hinge.

Wow Factor

All of these factors -- the time that flap creation takes with the IntraLase, the potential for loss of suction during that time, the potential for pain in cases where suction is reattempted several times -- markedly diminish the 'wow factor' that we rely on for word-of-mouth LASIK referrals.

Healing time is similar for cases performed with the FS and with our mechanical microkeratome, but 1 day postoperatively, the FS eyes have a significantly greater degree of conjunctival injection and redness, and some discomfort remains.

We've noted less interface debris with the IntraLase, but a higher degree of inflammation in the interface to the extent that some FS users observe diffuse lamellar keratitis. That may be associated with the degree of energy from the laser, or it might be due to a lack of care in lifting the flap.

For patients who are predisposed to dry eye, I'd steer clear of the Hansatome and consider either the IntraLase or the Amadeus.

Patient Choice

We give all our LASIK patients the choice between the Amadeus mechanical microkeratome and the IntraLase FS laser. To help put the decision into perspective for patients, we explain that the mechanical device is computer-driven and conducts its own calibrations. We explain that prior to making the pass, it performs a calibration and if it's not prepared to make a proper pass it won't initiate it. This information helps level the playing field, so to speak, with respect to deciding between LASIK with or without a blade.

Patients who have requested the IntraLase would receive it; the rest would get the Amadeus. About 95% of our LASIK patients receive the mechanical microkeratome.

Promising Future

Despite some of the negatives associated with the IntraLase FS laser, I think it's significant for several reasons. It's taught us more about how to produce an ideal flap, such as having a more prominent flap margin, and it's taught us more about the science behind what causes inflammation, as well as about healing rates.

This technology is still in a fairly early stage of development. In 3 to 5 years, the IntraLase could overcome a lot of its current drawbacks. It might be able to make larger flaps; it might be able to make flaps much more quickly; it might have a more user-friendly suction device that's more comfortable for the patient's eye; and it might even become less expensive. If all of those things happen, it will be interesting to revisit our comparison of mechanical microkeratomes with the FS laser and see if mechanical microkeratomes have advanced sufficiently to compete effectively with that type of a platform.

In my practice, we're continuing to work with the IntraLase and to create internal enthusiasm for using it because we believe it has great potential. However, right now, in my hands it doesn't provide my patients with quality of care equal to what I can provide with my mechanical microkeratome.

Dr. Assil is the medical director and CEO of The Assil Sinskey Eye Institute in Santa Monica, Calif.