The fields of research in which the Halle Eye Laser Centre is involved are related to aspects of the fundamental science of laser applications for the eye, experimental studies on the application of new laser technologies as well as clinical testing of new therapy approaches in refractive surgery. The following are four examples of projects in which the Eye Laser Centre staff are currently involved:
Femtosecond laser application
For laser in situ keratomileusis ( 
LASIK) a cornea flap ( Flap) of, as a rule, 150 µm thickness must be folded back. Up to now, the flap was prepared using an oscillating mechanical incision instrument. Today, various femtosecond laser systems allow a virtually contact-free microkeratome cut with the laser.
The institute carried out comparative studies with different Femtosecond lasers in order to analyse the quality of the cut for preparation of the flap as well as their application to reduce astigmatism. Currently, the most comprehensive results in Halle are obtained with the Femtec laser. One prospective study is expected to provide information on the possibility of using arcuate incision to reduce astigmatism even in patients who have had a cornea transplant. Comparative studies are planned with the Zeiss system and the Intralas femtosecond laser.
LASIK with wave front analysis
In the case of higher-order aberrations (severe refraction defects) , even a spherical correction to +/- 0 dpt does not achieve an optimal resolution. The aim of studies on Wave front LASIK is, therefore, to determine these image errors through wave front analysis prior to surgery and to correct them as much as possible through improved ablation algorithms.
To that end, a regular pattern of dots is projected onto the retina and the reflected pattern is detected. Wave front analysis then defines the distortions of the plane wave front, which are primarily created by the cornea and the lens and differ in each eye. The differences measured in the incident and emerging wave front then allow the so-called Zernike polynomials to be defined. They are equations that describe the aberrations mathematically. An optimal laser correction is then calculated based on those coefficients.
The Halle Eye Laser Centre continuously records the Zeiss data (CRS master) of all the patients that are examined and compares them with zyoptix measurements (Bausch & Lomb). This is to determine how exactly the wave front analysis can be applied to the corneal ablation parameters, the effect of, in particular, the cyclorotation of the eyes being systematically evaluated.
Tear secretion and moisturising after refractive corneal surgery
LASIK surgery in particular damages and cuts the corneal surface nerves (trigeminus). The consequence is impaired corneal sensitivity, reduced blinking frequency and reduced moisturising of the eye for about six months. The Halle Eye Laser Centre is studying whether and how different moisturising agents can prevent impaired moisturising caused by refractive corneal surgery and promote regeneration of the nerves.
UV-A-crosslinking ablation of the entire
Recently, in the case of corneal thinning ( Keratoconus) we were successful in cross-linking the corneal molecules by using riboflavin in conjunction with UV-A radiation, thereby stabilising the cornea’s radius of curvature. We also clinically and experimentally study whether a moisturising effect can also be achieved through ablation of the entire cornea with the excimer laser.
