My Long Quest: The Optimal Approach for Customised Laser Ablation

by Olivia Serdarvic

Prior to 1980 I already had investigated in animals the effects of surface absorption of photon energy on the cornea and had focused on the benefit of the high absorption and very limited penetration length into the cornea of far-ultraviolet light below 230 nanometers.

While still in medical school, I presented in 1980 in the USA and Europe some of my results that led me to conclude that the carbon dioxide laser, an infrared laser that Beckman and others had been evaluating under computerised control for corneal cutting, would not be useful for corneal surgery and that far-ultraviolet lasers would be superior for corneal removal.

My research had made me aware of documented photochemical mechanisms, including the fact that absorption of photon energies above 6ev associated with radiation wavelengths below 200nm. resulted in breakage of bonds. My physical chemistry professors from college provided further evidence of the correct orientation of my conceptions.

At a meeting in 1980 where I was speaking, J. James Rowsey, M.D. presented a paper reviewing available and investigational corneal refractive surgical techniques, all of which modified optical properties of the eye by only indirectly altering corneal power and curvature. He also described his work on computer digitisation of the anterior corneal surface to reconstruct the corneal profile. I was excited by Rowsey's discussion of the usefulness of corneal topographic analysis to allow more thorough understanding of corneal refractive power and to refine the experimental technique of astigmatic keratotomy. I then proceeded to conceive of integrating digitised data regarding corneal shape and contour with far-ultraviolet laser surgery of the cornea to improve optical properties of the eye.

It was apparent to me, in contrast to the opinions and research directions of the few keratorefractive surgeons at the time, that non-direct procedures, including radial keratotomy, astigmatic keratotomy and keratomileusis, for altering corneal contour were not optimal. Many of these techniques, such as radial keratotomy, destabilised the cornea. Keratomileusis, which was conceived by Jose Barraquer, MD was performed at that time by removing a portion of the patient's cornea, freezing and lathing the posterior side of this lenticle and then suturing back the lenticle on to the patient's cornea, thereby indirectly altering the anterior corneal surface curvature. The cutting, freezing and suturing of the lenticle caused optical aberrations and loss of visual acuity.

Mechanical techniques for removing and grinding of the anterior cornea had never been successful without suturing back on corneal grafts. I knew that even the more controlled and less traumatic mechanical technique of grinding the cornea with a diamond, as performed in animals by Randall Olson, MD in that same year, caused blood vessel ingrowth, scarring and subsequent loss of corneal clarity. The far-ultraviolet laser, I speculated, could remove corneal tissue so completely that the cornea could be fooled into thinking that nothing had been done to it, thereby making the direct approach feasible.

After disclosing in 1980 my invention of corneal recontouring with a computer-controlled far-ultraviolet laser to some European ophthalmologists, I was given a European laser book in which I noted a reference to a near-ultraviolet laser study in which a physicist, Dr. Ebbers, measured corneal epithelial damage thresholds using a Helium-Cadmium laser at 325nm. I focused on several components of the laser delivery system described by Dr. Ebbers and then first conceived of modifying and incorporating some of them into far-ultraviolet light delivery systems for removal and recontouring of the exposed corneal surface. These features included optically varying the spot size and irradiation area, using a beam splitter, using a Helium-Neon beam for alignment and incorporating a scanning device.

It has taken more than two decades for excimer laser vision correction to achieve optical results that even a perfectionist like myself finally can start to be proud of. Technological advances to enable successful and practical application of many of my original concepts finally are now available. Nevertheless, much work remains to develop the optimal customised corneal ablation laser systems and techniques integrating more accurate refractive, optical and corneal data.