CLEARVISION EYE CLINIC



43) What future advances are in store for Lasik surgery?
The Microkeratome The microkeratome is the cutting device used to create the cornea flap in Lasik surgery. Its invention dates back over 40 years to 1958 when Barraquer from Spain conducted the first experiment on creating a circular cornea flap using a prototype of the modern day microkeratome. The next milestone was in 1989 when Buratto did the first Lasik on the human eye with a free cornea cap. Two years later, Pallikaris improved upon the procedure with the introduction of the "hinge" technique where a small amount of cornea is left uncut nasally to form a cornea hinge. The surgeon could then lift the cornea flap, perform the laser sculpting and reposition the flap onto its original site without the need for stitches. In 1996, Buratto modified the technique further with a down-up vertical cut that places the resulting hinge superiorly beneath the upper eyelid. This was thought to be more physiologic as it follows the dynamic movements of the eyelid with reduced possibility of the flap becoming decentred or developing wrinkles in the immediate post operative period. Today's modern microkeratomes are automated and refined, offering better suction, more efficient cutting mechanisms and more ergonomic handling. As a result, the serious complications rate from this stage of the procedure is now down to less than 1% in the hands of the experienced surgeon. Future developments in the pipeline include using water-jets or laser keratomes to cut the cornea flap instead of the present steel blade in the hope of achieving an even smoother and complication free cut.		The microkeratome is the surgical cutting tool used to create the cornea flap.
The Excimer Laser Laser refractive surgery was developed with the hope of replacing the variability of the surgeon's microsurgical skills with the consistency of the laser. The dream became reality with the advent and application of the excimer laser to the human cornea in 1983. For the first time, there became available a precise and delicate way to directly and very accurately sculpt the refractive power of the eye onto the cornea, very much the same way a skilled lensman would grind a spectacles lens. The excimer laser is often described as a "cool" cutting laser that uses high energy ultra-violet light to vapourise the cornea tissue without generating too much tissue heat. The early generation lasers delivered the laser energy via a fixed broad beam aimed at the cornea through a progressively widening aperture. The sculpting effect of these broad beam lasers were not completely smooth with rings, ridges and irregular surface protrusions. These protrusions, also known as "central islands" are areas of uneven ablation resulting from blockage of the incident laser beams by tissue fumes. Presently, most of the modern lasers in use utilise small scanning beams of 1 to 2 mm spot size rather than a fixed broad beam.		Modern excimer lasers utilise advanced flying spot technology and eye tracking systems when sculpting the cornea.
The laser pulses are programmed by software to move ("fly") rapidly in a randomised pattern with slight overlap to accurately sculpt the cornea with an extremely smooth surface. All modern lasers also come with an eye tracking system with feedback mechanisms to ensure well-centred laser ablations. Future developments will revolve around improving the laser ablation software for even smoother and precise ablation and integration of "wavefront technology"(see below). Also, eye tracking systems are being further refined to be fast enough to measure and compensate for even the small rapid (saccadic) movements of the eye, thus further improving the accuracy of the cornea sculpting.		Future developments will centre around the laser ablation software, intergration of wavefront technology and refinements to eye-tracking hardware.


Light travels in a process of flat sheets, known as wavefronts. In a perfect optical system, these flat sheets would look like a piece of paper standing on end.


The eye is not a perfect system. Irregularities in the system will cause the flat sheets or wavefronts to be deformed into variations that look like anything from a potato chip to a sombrero hat. Every eye has its own unique wavefront map.

Customised Ablation Incorporating Wavefront Technology This is billed as the next step in the evolution of refractive surgery. Today's laser and the computers that run them all assume the cornea as regular sphero-cylindrical refracting surfaces. However, we know that there exists in every person's eye, unique optical aberrations that cannot be corrected by simple sphero-cylindrical optical systems such as spectacles and contact lenses. Previously, there was no way these so-called higher order aberrations could be measured, represented and treated. Now, using wavefront technology adapted from astronomical science, wavefront analysers have been developed that are able to map out point by point, aberrations that occur across the entire surface of the cornea. The information is translated into a three-dimensional (3-D) color coded cornea map. This information is then fed into the excimer laser's computer together with data from the pre-Lasik evaluation and a reciprocal point by point customised laser ablation computed and delivered. The effect hoped to achieve is an effective neutralisation of the eye's optical aberrations. Such careful customised reshaping of the cornea should in theory enable consistent and astounding improvement in visual clarity. Clinical trials are presently underway. Already, hopes for routinely correcting vision to better than 6/6 or "eagle vision" are being touted. With wavefront technology, it is now possible to capture and represent these irregular wavefronts as a three-dimensional colour map. By feeding this information and that obtained from the pre-Lasik evaluation into the excimer laser's computer, a customised ablation profile can be computed and delivered. This could in theory, make perfect vision correciton routinely attainable.