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Roles and designs of microkeratomes continue to evolve as laser ablation and corneal lamellar procedures improve.
The very limited role of microkeratomes for almost two decades was followed by widespread use over the last half decade as their predictability and safety increased - now their roles are changing again.
All refractive procedures that were performed two decades ago modified optical properties by only indirectly altering corneal power and curvature. Microkeratomes were introduced at that time to improve two of those procedures, keratomileusis and keratophakia.

First Barraquer Microkeratomes
Although those procedures were ingenious and their development by the Jose Barraquer in the 1950s, 1960s and 1970s underscored his creativity and insight as far as the potential of corneal refractive surgery, they did not gain large clinical acceptance because of the complexities of the techniques and problems related to safety and efficacy. The use of the microkeratome rather than free hand dissection with a knife improved removal of the corneal disc, but significant technical problems persisted.

Although those procedures could reduce spherical errors, the cutting, freezing and suturing of the disc caused loss of visual acuity, wound healing abnormalities and irregular corneas. Barraquer's work taught us, nonetheless, a great deal about optical, physiological and anatomical responses of the cornea to refractive surgery.
Contrary to the prevailing opinions and research directions of the few keratorefractive surgeons in 1980, I did not believe that those non direct procedures using cryolathes and microkeratomes for altering corneal contour were the right approach and therefore conceived my direct far ultraviolet laser approach. While I pursued my experimental and analytical work on laser wide area surface ablation, that for several years in the early 1980s no one else believed to be feasible, keratorefractive surgeons were still trying to make mechanical keratomileusis successful.

By the mid 1980s, the cryolathe had been abandoned in favour of two microkeratome cuts to avoid damaging effects of freezing stromal tissue.
Unfortunately, just as with the cryolathe technique, that I also had found intellectually interesting, because of their technical complexity but that I believed would not gain widespread acceptance, the BKS dual cut microkeratome system was also abandoned.
The proponents of mechanical keratomileusis nonetheless continued to focus their attention on improving the reliability and accuracy of the microkeratome. By that time, commercial exploitation of far-ultraviolet laser surface ablation had already occurred.

Combining Excimer And Microkeratome
At the time of the first blind eye excimer studies in 1987 and 1988, I was asked by one of the investigators for solutions to the problem of fine fibrillar haze and remodelling of corneal tissue relating to the activity of the keratocytes that might cause the procedure to be less effective than its ultimate capabilities. I suggested details of more refined delivery systems to create smoother ablations, which I believed to be the better approach for reducing aggressive wound healing response. I also disclosed to him another approach - the combination of combining ablation of the exposed corneal surface with the Barraquer variant of keratomileusis is which the lenticule is not completely severed. Although attachment and alignment problems could be partially alleviated by the incomplete severing, I felt that the irregular cuts produced by available microkeratomes made that approach less desirable at that time. In fact, it wasn't until a decade later that the safety of combining a microkeratome with excimer laser ablation achieved levels comparable to that of PRK.

Microkeratomes continued to evolve during the late 1980s and early 1990s while keratomileusis in situ and ALK were tried in further attempts to improve mechanical keratomileusis. Automated geared microkeratomes with improved suction rings were developed.

It was only after Ioannis Pallikaris, MD and Lucio Buratto MD ablated the stromal bed and posterior aspect of caps and flaps with the excimer laser after performing microkeratome cuts that mechanical keratomileusis was finally abandoned.

Increased Predictability And Safety
Fortunately, improvements in the late 1990s in mechanical microkeratome design increased the predictability of flap diameter and thickness, hinge size and edge characteristics and decreased flap complications such as incomplete or button holed flaps, free caps and epithelial defects. Those improvements provided safety and results that I could accept for my patients and finally enabled microkeratomes and LASIK to gain widespread acceptance.

Manual microkeratome designs first offered surgeons the ability to vary microkeratome parameters based on corneal diameter and curvature to decrease complications but required a certain degree of ambidexterity to achieve consistent flaps. The LASIK learning curve has shortened as a result of newer automated machines.
Blade quality is still an issue and not consistent from manufacturer to manufacturer. Metallic and other foreign body particles from blades are known causes of diffuse lamellar keratitis.

It still remains to be demonstrated whether laser and water-jet microkeratomes will be more convenient, safe and predictable than the latest generation mechanical microkeratomes. Will they offer advantages for wavefront guided ablations? Wavefront technology has been providing additional information regarding the optical effects of microkeratome cuts and creating another PRK versus LASIK controversy. It will be interesting to see the future of microkeratomes.

If you would like to read previous "Reflections on Refractive Surgery", check out the archive.

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