Third generation microkeratome technology swings pendulum in new direction

Stefanie Petrou-Binder, MD

Heidelberg - If the early promise of the new third-generation Carriazo -Pendular microkeratome (Schwind) holds up during clinical studies, ophthalmic surgeons will have a tool that offers numerous features unavailable with any other microkeratome, says ophthalmologist Ralf Gerl MD.

At a session of the DGII (German-Speaking Organisation of Intraocular Lens Implantation and Refractive Surgery), Dr Gerl said the new microkeratome produced safe and predictable flaps in the preclinical setting.

The preclinical studies involved 34 pig eyes. The results showed no bad cuts and there was a constant flap diameter of 9.0 mm. The hinge width was 4.5 mm to 5.0 mm and flap thickness was very predictable with a standard deviation of 27 microns measured with a mechanical dial gage.

Dr Gerl was particularly enthusiastic about the flap thickness results. He noted that reproducible flap thickness has become the requirement surgeons look for most in a microkeratome.

High degree of safety
He also said the device offers a high degree of safety which is the other essential element surgeons are interested in. The Carriazo-Pendular microkeratome did not cause free caps or buttonholes in any of the pig eyes tested.

There is no shear-effect on the cornea when cutting and so there is less likelihood of aggravating striae. Striae are common complications in LASIK and are often the cause of diminished visual acuity postoperatively, he explained.

He said the Carriazo-Pendular microkeratome has a number of features that set it apart from other microkeratomes. The keratome head and blade are constructed to mould the cornea more in the centre than in the periphery to protect the sensible cornea's centre during the cut.

A convex blade runs parallel to the corneal surface throughout the cut and the keratome swings over the corneal surface to achieve a consistent flap thickness.
The microkeratome can be operated manually or automatically and has separate motors for the pendular motion and blade oscillation. There is no blade oscillation during reverse movement and the device uses disposable blade.

He noted that the new microkeratome creates a superior hinge that may be better adapted to the anatomy of the eye. The choice of hinge placement is 360°, however, allowing a modicum of flexibility.

The device also has a larger vacuum chamber in the suction rings than earlier microkeratomes which provides more grip and safety during the operation, even in higher astigmatic cases.

By modifying the height of the vacuum chamber, the oscillation frequency of the blades and the speed of the procedure, flap thickness can be moderately influenced.
A small ring diameter of only 19 mm allows the small suction ring to occupy less space on the eye. It can therefore be properly placed in smaller eyes or eyes with narrower lid space.

Reduced margin for error
He reported that four different ring sizes are available to fit onto steep and flat corneas. A snug fitting ring again reduces the margin of error.
The rounded-out keratome head pushes the central cornea inward, flattening it out during cutting, while the surrounding side-corneal areas remain unflattened.
Safety, precise fit, reproducible corneal cut and flap size and the ability to modify flap thickness are all attractive features of the Carriazo, according to the research team in Ahaus.

It is also easy to put together in a few simple steps and requires no exterior gearing. The research team proposed some further work on the development of the Pendular to enable thinner flaps to be achieved. Clinical trials are currently being held.
Cesar Carriazo MD, the noted pioneer in microkeratome design, is reported to have treated a handful of patients with the new device in Baranquilla, Columbia. A European multi-centre clinical study - co-ordinated at the University of Mainz - is expected to get underway soon.

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