Close-up microkeratome blades reveal variation

By Stefanie Petrou Binder MD

Heidelberg - A close-up look at a number of different disposable microkeratome blades using electron microscopy revealed considerable variation in size and cutting edge between both different manufacturers and among blades made by the same manufacturer.

Researchers at Mainz University Eye Clinic examined ten different microkeratome blade types, comparing five blades of each type. They studied scanning electron microscopic images (Phillips PFEM 500) up to a magnification of 700x the original size and measured blade length, width, and cutting edge. The researchers also examined the blades for any irregularities.

Lars Frisch MD presented the study results at the annual meeting of the DGII (German-Speaking Organisation of Intraocular Lens Implantation and Refractive Surgery).
"Each of our surgeons examines the microkeratome blade he wishes to use. We usually use the operation microscope to check the surface and cutting edge of the blade for inconsistencies before implementing it. We have had to return blades to the manufacturer at times when they did not pass muster. This encouraged us to examine blade characteristics more thoroughly," he explained.

The researchers looked at blades manufactured by Bausch & Lomb, Nidek, Moria, Allergan, Oasis, Schwind, Beaver, Alcon, and Asclepion-Meditec.
They found variations between the ten different blade groups and among the five blades within each microkeratome blade group. The differences noted included length, width and cutting edge.

Dr Frisch expressed concern about the diversity of size and cutting edge seen in blades created by different manufacturers for the same microkeratome, which could potentially
compromise the procedure's precision.

Impurities and unsharpened blades
The blades studied also revealed different degrees of impurities and surface smoothness. These were readily visible at a magnification of 175x. Some blades were coated with impurities or showed deposits.

The scanning electron microscope brought to light much variation in the manner in which the blades were worked up. For example, the cutting edge of a particular blade was left relatively unsharpened by some manufacturers.
Other blades revealed an additional cutting edge, while the same blade made by another manufacturer lacked it.

He noted that some blades were fine, revealing no irregularities along the length of the cutting edge, no impurities or deposits on the blade surface and no variations in size. Such smoothness and consistentency were particularly evident with Amadeus (Allergan®) microkeratome blades.

A key feature of microkeratomes includes the reproducibility of cut thickness and flap size. Both of these parameters largely result from the consistency of microkeratome blade characteristics. Inconsistencies in the size or surface structure of different disposable blades will likely give a different cut than the last when a new blade is implemented.

Metal foreign bodies have been reported at the cut interface following LASIK procedures. Researchers believe these to be blade particles. It follows that a smooth, clean and consistent blade surface and cutting edge are desirable to avoid metal particles and inconsistencies.

"The effect of an irregular blade cutting surface on flap size, cut thickness and visual outcome remain to be determined. However it is likely to play a decisive role.
"What is known is that metal particles on the cut interface, along with other foreign bodies which researchers identified as impurities, cause DLK (Diffuse Lamellar Keratitis).

This widespread inflammation of the cut corneal layers can substantially reduce visual acuity, and is not uncommon following LASIK," Dr Frisch said.
He stressed that the findings underscore the importance of preoperative blade inspection under the operation microscope to ascertain surface smoothness and irregularities.

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