Comparison of Modern Excimer Lasers

Different people have different opinions about most of the technological things. For example dispute whether Audi is better car than Mercedes or the other way round depends what the disputer thinks to be important for a car. Like with cars, excimer lasers also have extra stock, which is necessary when comparing them. There have been several studies about eximer laser efficiency and safety, including FDA's, but comparing still does not show the absolute truth as studies have been made using different versions and extra stock of the equipment. Especially important factors when comparing modern eximer lasers are:

• Laser's capability of removing corneal tissue so cornea's normal prolate shape is maintained. Older lasers changed the cornea's shape flatter, which made pupil widening in the dark cause visual disturbances. Carl Zeiss MEL80 and Wavelight Allegretto lasers, which are used in Estonia, allow us to grind eye surface so, that the natural prolate shape of cornea is maintained, wherefore visual disturbances with these lasers are very rare.
• Size of the laser spot. The large spots of older lasers caused uneven surface at laser ablation transition areas. MEL80 and Allegretto laser spots are 0,7 mm FWHM. Both laser's spots also fit with Gauss profile, which guarantees evenness of the surface. The evener the cornea's surface is after laser's effect, the better is vision quality.
• Laser's operating frequency/speed. The slower the laser is the more may the corneal tissue dry during laser's work, which can cause overcorrection. Also it is necessary, that laser's too fast operating does not cause thermal damage. MEL80 operating frequency is 250 Hz. Although Wavelight allegretto Eye-Q laser's maximal operating frequency is higher (400 Hz), this works slower in the end of the procedure to prevent thermal damage. Wavelight laser requires 2 seconds to correct 1 diopter, Zeiss laser 3 seconds. Even with a very high refractive error, these extra seconds are not enough for the cornea to dry to an inordinate level.
• Eye-tracker's mean total latency of both of these lasers is 6 milliseconds.
• Cyclotorsion compensation. Eye axes are a bit converted when a person is in a recumbent position. This converting of the eye is called cyclotorsion. Studies have shown that average axis turned is 4 degrees. But every fourth person has this turning over 7 degree, which with astigmatism causes at least 25% undercorrection. 8% of people have this cyclotorsion of over 10 degree. On Wavelight laser the cyclotorsion correction is based on patient's ability to watch diamond-shaped dots of light. With Oculign additional software Zeiss laser registers and traces eye's axis digitally using iris and blood vessels video image.
• Planning the treatment is at least as important as performing it. Zeiss aberrometer or wavefront analyzer is with 8 times better resolution than same Wavelight's product. Exactly wavefront analyzer's substantially higher resolution and digital control over cyclotorsion are the reasons why we decided to invest in Zeiss technology. We believe that Carl Zeiss MEL80 laser with Oculign additional software and CRS-Master TwinLine module is a laser system, which helps us to get the best possible result.