The Barraquer microkeratome

Long before the lasers, one surgeon set out to reshape the cornea the way a joiner shapes a plank.

Carving the cornea

In 1949, José Ignacio Barraquer published a note entitled Queratoplastia refractiva. In it he proposed correcting an ametropia not by placing a lens in front of the eye, but by altering the thickness and curvature of the corneal tissue itself. The method would come to be called keratomileusis — from the Greek, literally to carve the cornea. The idea is so structuring that it would earn its author the title of father of refractive surgery.

An instrument capable of executing that carving to the precision it demanded was still needed. The idea dates from 1949; the instrument took a decade to find its form. Barraquer described his frozen-cornea cutting method in 1958, and devoted a whole paper to the microkeratome in 1966.

The principle of the plane

The instrument rests on a simple mechanical intuition. A pneumatic ring fixes itself to the globe by suction and immobilises it. A flat plate comes down onto the cornea and applanates it. An oscillating blade, set to a fixed depth, then crosses that plane and raises a lamella with parallel faces.

This is exactly the principle of a joiner’s plane: the sole presses the material flat, and the iron, protruding by a constant amount, takes a shaving of even thickness whatever the curvature of the workpiece. On the very first hand-held models, the lamella did in fact simply curl up above the exposed blade, like a plane shaving.

The quality of the idea lies there: on a surface that is convex, soft and mobile, you cannot cut to a constant depth. You have to make it flat first. Applanate in order to cut straight — the principle would outlive the instrument.

The disc was the operation

What follows seems almost unreal today. The lamella that was raised was not an access route, it was the subject of the procedure. Frozen and then mounted on a cryolathe, it was turned over and its posterior face machined to a new curvature. It was thawed, replaced and sutured.

Removing more tissue at the centre of that face flattened the cornea and corrected a myopia; removing it peripherally steepened the cornea and corrected a hyperopia. The calculation was made from tables, and the precision depended as much on the lathe as on the surgeon.

Brilliant and brutal

The operation had the shortcomings of its era. Freezing killed the keratocytes and left a lasting stromal haze. The sutures needed to replace the disc induced an irregular astigmatism — precisely the kind of aberration that no optical correction puts right cleanly. And a cap was sometimes lost.

The instrument itself was sound. It was the procedure around it that had to give, and it did so in stages, each one removing one of the three central defects.

What became of the instrument

Krumeich and Swinger did away with freezing: the lamella is worked fresh, on the bench. Ruiz automated the pass and operated directly in the stromal bed rather than on the disc, which made the cryolathe unnecessary. Then came the decisive step, for all its apparent banality: stopping the blade’s travel before the end of its run. The lamella is no longer detached, it stays attached by a hinge. The cap becomes a flap you fold back.

In 1990, that flap met the excimer laser. Keratomileusis became LASIK, and stromal ablation moved from the machine lathe to photoablation. The femtosecond laser would later replace the steel blade for cutting the flap itself, and lenticule extraction (KLEx) would eventually dispense with the flap altogether.

What remains

The microkeratome has gone from the operating theatres, displaced by light. It would be easy to make a museum piece of it.

Look, though, at what happens today at the moment of a lamellar cut. A suction ring fixes itself to the globe and immobilises it. An interface applanates or conforms the cornea against a reference surface. The cut is then made at a programmed depth within that plane. The mechanism has changed — photons instead of a steel blade — but the sequence is that of 1949: immobilise, build a predictable surface, and only then cut.

Barraquer did not bequeath an instrument, nor even an operation. He bequeathed a physical constraint and the way to neutralise it: on a cornea that is convex, soft and mobile, depth cannot be controlled until a reference plane has been built. Cryolathe, oscillating blade, excimer and femtosecond are only successive ways of removing tissue once that plane has been obtained.

That may be the mark of the instruments that count: what they solve outlives the way they solved it.

Techniques pass. The discipline that grounds the indication endures.

References

1. Barraquer JI. Queratoplastia refractiva. Estudios e Informaciones Oftalmológicas. 1949;10:1-21.
2. Barraquer JI. Method for cutting lamellar grafts in frozen cornea. New orientation for refractive surgery. Arch Soc Amer Oftal Optom. 1958;1:271-286.
3. Barraquer JI. El microqueratomo en cirugía corneal. Arch Soc Amer Oftal Optom. 1966;6:69.
4. Barraquer JI. Keratomileusis. Int Surg. 1967;48(2):103-117.
5. Swinger CA, Barker BA. Prospective evaluation of myopic keratomileusis. Ophthalmology. 1984;91(7):785-792.
6. Swinger CA, Krumeich J, Cassiday D. Planar lamellar refractive keratoplasty. J Refract Surg. 1986;2(1):17-24.
7. Krumeich JH, Swinger CA. Nonfreeze epikeratophakia for the correction of myopia. Am J Ophthalmol. 1987;103(3 Pt 2):397-403.
8. Ruiz LA, Rowsey JJ. In situ keratomileusis. Invest Ophthalmol Vis Sci. 1988;29(suppl):392.
9. Pallikaris IG, Papatzanaki ME, Stathi EZ, Frenschock O, Georgiadis A. Laser in situ keratomileusis. Lasers Surg Med. 1990;10(5):463-468.