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By Cheryl Guttman

Refractive surgeons agree that obtaining a quality lamellar flap is a critical factor in achieving good results after LASIK.
The market now contains a myriad of microkeratome choices offering safe and predictable performance. So how do surgeons decide which one to use?

A group of American LASIK surgeons spoke to EuroTimes about features, usage tips, and outcomes achieved with five different microkeratomes.

Their comments focus on the established Summit Krumeich-Barraquer Microkeratome (SKBM, Alcon) and the Hansatome (B&L Surgical), as well as three newer market entries - the M2 (Moria), the Amadeus (Allergan) and the disposable One Use (Moria).
For R Bruce Grene MD, time-tested reliability is one of the greatest assets of the automated SKBM.

"The SKBM is now mature technology, not the new kid on the block. We were one of the first practices to use it and our experience in approximately 5,000 cases confirms that the SKBM is a microkeratome we can count on to produce consistently sized and quality flaps with a very low incidence of any complications," said Dr Grene, Clinical Assistant Professor, University of Kansas School of Medicine, and CEO, Grene Vision Group, Wichita, KS.

He reported he has never encountered any button-holes using the SKBM, and when used in the setting of careful case selection, the rate of development of epithelial damage or any other flap-related events has been very low.

The automated SKBM is easy to use and safe. Its handpiece features dual motors which regulate blade oscillation and translation speed independently, and a drive band controls the blade's traverse across the cornea.

This platform avoids the risks associated with gear-driven blades, and recently-introduced new drive bands offer the benefit of even more consistent locking to the keratome ring.
Another key feature of the SKBM is its "preview window" - a calibrated, transparent applanation plate that provides surgeons complete visualisation of the cornea and the diameter available for the flap.

"With this window, I can optimise ring selection and make last minute console adjustments that will ensure I obtain the best possible flap," said Dr Grene.

The SKBM has five vacuum rings defined by their diameter and the height of the vertical sidewall along with a standard head and an alternative H-head that features a lower window and exerts more pressure on the cornea.

As a result, the SKBM is adaptable to eyes varying in orbit configuration or corneal steepness.
However, Dr Grene indicated he completes the vast majority of cases, up to 90%, using the 20/4 ring and the standard head.

Other elements of Dr Grene's technique include blade settings of 16,000 oscillations/min with a 2.5 mm/sec traverse, along with a hydration protocol he has developed for maintaining a thin continuous moisture layer over the ocular surface which will assure a quality keratectomy.

Safety and versatility of Moria M2
The M2 (Moria) is a relatively new automated version of the manual Carriazo-Barraquer microkeratome.

Like the SKBM, the M2 also features the safety of a dual motor system and versatility. Users have the option to place the hinge either superiorly or nasally by simply rotating the ring position.

In addition, they can choose from between 110 and 130 micron plates and can alter flap dimensions with the availability of four ring sizes ranging in 0.5 mm increments between 8.0 mm and 9.5 mm and various choices of stops for the hinge size.

"Being able to tailor the flap characteristics with these features is gaining increasing importance as we move toward use of larger ablation diameters for patients with larger pupils and for customised treatments with larger blend zones.

"In addition, the M2 offers a small diameter ring allowing for placement on deep-set eyes and those with tight lids," commented Dr Salz, Clinical Professor of Ophthalmology, University of Southern California, Los Angeles.

He added that the manufacturer recommends the M2 not be used in eyes where there is a >3 D difference between Ks in the two meridians or with a pachymetry value <500 microns. In appropriate candidates, ring selection is based on the steepest K.

Then, the stop value, which is equivalent to the amount of stroma available when the ablation is centred over the pupil, is chosen according to the desired ablation zone.
The reproducibility of flaps created with the M2 has been demonstrated in a study performed by Raymond Stein MD, Toronto, Canada. Using the M2 fitted with the 130-micron plate in 300 eyes, the average flap thickness obtained was 157 microns with a standard deviation of only 22 microns.

Flap thickness varied by preoperative pachymetry and K values. Thicker flaps were achieved in corneas which were flatter and thicker, while flaps were relatively thinner than average in thinner and flatter corneas.

For example, average flap thickness was 161 microns in eyes measuring 535 to 575 microns, but was 175 microns in eyes >575 microns thick and 141 microns in those with a pachymetry measurement of <535 microns.

Regardless of corneal thickness, however, there was minimal variability in flap thickness, with the standard deviation being 22 microns or less in all groups.

To achieve optimal performance of the M2, Dr Salz advises several steps for assuring accurate applanation and proper suction.
• initial drying of the central cornea before the suction ring is applied;
• pressing down on the suction ring using both the handle and a finger on the post before suction is engaged
• verifying the suction with tonometry, pupil dilation when possible and visual blackout

Hansatome changes with the times
Recent upgrades to the Hansatome (B&L Surgical) have brought added dimensions of versatility and safety to this reliably performing microkeratome, said Randy J Epstein MD, Associate Professor, Department of Ophthalmology, Rush University, Chicago.

The newest features include the availability of both a microsuction ring, which is designed for use in deep-set eyes or those with very small fissures, and a series of Zero Compression Heads (160, 180 and 200 microns), which essentially eliminate flap compression and thus the risk of epithelial defects.

The microsuction ring has a 19 mm footprint and can create 8.5mm or 9.5 mm flaps. Dr Epstein observed his experience with it has been very positive.

"The rate of suction 'build' is quite rapid with the micro-ring, and the level of suction achieved is excellent, so there is no tendency for the ring to move on the eye. Furthermore, with this relatively smaller ring, patients who are 'squeezers' and those with small fissures no longer pose a challenge to the successful completion of the case," he said.

For routine cases, Dr Epstein chooses to use the 160 micron standard head and 8.5mm suction ring. The 180 micron plate is preferred for eyes with a K value >45.0 D, corneal thickness permitting, and the 9.5 mm ring is used in eyes with a K value <41.0 D.

Amadeus is safe and user-friendly
The Amadeus microkeratome (Allergan) was designed with safety and user-friendliness in mind.
It is proving itself a dependable performer in the operating room, consistently yielding reproducibly sized flaps and smooth beds, according to Kerry D Solomon MD, Associate Professor of Ophthalmology, Storm Eye Institute, and Medical Director, Magill Laser Center, Medical University of South Carolina, Charleston.

Constructed to maintain the surgical field as a protected space clear of lids and lashes, the Amadeus design also affords the surgeon added safety with full visualisation of the flap during the cutting procedure and software that performs ongoing checks of numerous operation parameters.
Furthermore, the Amadeus offers versatility. With its high walls, it can be used without a speculum in eyes with tight orbits.

Users can vary the hinge width as well as the translation speed and oscillation rate of the motors and a number of choices are available for ring and plate sizes.
Currently there are two rings - 8.5 mm and 9.5 mm - and two more will be introduced. Plates are available in 140, 160 and 180 micron depths, and 220 and 300 micron plates will be added to the line-up.

Pre-assembled and featuring only three pieces, the Amadeus microkeratome is also easy to use and to clean. "Suction time is minimised using the Amadeus because it is easy to put on and take off the eye," noted Dr Solomon.

His personal technique for using the Amadeus microkeratome is based on the creation of a flap with a nasal hinge measuring 5 mm in width but adjusted based on keratometry, and ring size selection that also takes corneal steepness into account.

He sets the translation speed at 3 mm/sec, the oscillation rate at 8000 RPM and vacuum at 24.5 mm Hg. For added efficiency, he has customised the foot pedal operation so that forward motion, termination of blade oscillation at the end of the pass, direction reversal and suction release occur in sequence with a single depression.

One Use Moria gains support
The disposable One Use (Moria) is a valuable alternative for flap creation and based on an assessment of its pros and cons, perhaps considered the microkeratome of choice for laser vision correction centers, says Sadeer B Hannush MD.

"This well-constructed, disposable microkeratome has a number of advantages that translate into safety, reliability and efficiency," commented Dr Hannush, who is Attending Surgeon, Cornea Service, Wills Eye Hospital and Assistant Professor of Ophthalmology, Jefferson Medical College, Thomas Jefferson University, Philadelphia, PA.

The plastic One Use microkeratome comes with a pre-sterilised suction ring, vacuum tubing and keratome head, together with a completely disposable package including speculum, marker, retractor and cannula. This eliminates all cleaning and sterilisation procedures, he noted.

Thus, compared with reusable microkeratomes, the risk of contamination-related complications, including DLK, is minimised, and there are cost-effectiveness implications from savings in time, equipment and personnel devoted to instrument care.

The One Use also has advantages setting it apart from other disposable devices, including its consistent operation and opportunity to be used interchangeably with the manufacturer's reusable units using the same console.

He emphasised that the One Use is also easy to master. The head comes completely assembled with the 130 micron depth blade pre-inserted. Featuring a flange instead of a groove, the head is easier to place and pass as well.

"Consequently, the flap produced with the One Use adheres quickly, the interface is very clean, and in principle, the risks of dislocation, striae, ingrowth and epithelial defects are minimised. In fact, a number of users have reported experiencing decidedly fewer epithelial defects comparing series of eyes undergoing flap creation with the disposable One Use versus its reusable LSK 1 counterpart," he observed.

The microkeratome's suction ring can be used safely in eyes with K values ranging from 39 D to 49 D and can accommodate patients with deep set eyes, small fissures, and prominent brows. Featuring an adjustable stop gauge with continuous settings in the range of 7.5 mm to 9.5 mm, it also allows the user a wide range of choices for flap customisation.

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