WASKA Analyzer (COAS or Complete Ophthalmic Analysis System )

Wavefront Technology

Wavefront technology is an additional refining tool used to enhance an already safe and effective procedure. As the most common form of vision correction surgery, LASIK has already benefited millions of patients. The increased safety and the improved quality of vision benefits of customized procedures are an important technological advancement for patients and physicians alike.

Until recently, optical corrections have been limited to measuring the best spherical and cylindrical visual errors. The same conventional method of testing is used for prescribing eye glasses, contact lenses and conventional PRK and LASIK procedures.

The light entering the eye has to go through the tear film, the cornea, the fluid behind the cornea (called aqueous humor), the lens and finally the fluid behind the lens (called the vitreous) before it is finally focused on the retina. Because of the “obstacle course” the light comes across the pathway the light waves reach the retina in different “phases” giving rise to “aberrations” resulting in distortion of the image. If the pupil is small and the correction is small this distortion may not be noticeable. If the pupil is large or the correction is large the distortion of image may be noticeable in the form of night vision problems or decreased appreciation of the contrast or sharpness of vision. Now these “aberrations” can be measured and can be rectified.

The Wavefront Aberrometer

The instrument used to analyze the aberrations is called the “abberometer” The most common technique of measuring is by the Hartmann-Shack wavefront sensing method. The light waves as they come out of the eye are analyzed by an array of microscopic lenses called”lenslets”. The array of lenslets dissects the emerging light to a large number of sub apertures and measures the wavefront slope across each aperture. Because each eye has different pattern of the emerging light it provides a unique “blue print” for “custom” correction of the aberrations of that particular eye. The information from such a measurement is captured on a computer disk to be used by the computer delivering the Excimer laser when that particular eye is treated.

There are several aberrometers using the Hartmann-Shack (or Shack-Hartmann) method. The similarity ends there. At Eyetech Lasik Clinic we use WASCA analyzer (made by Wavefront Sciences) measures 1400 spots on your cornea-each sample on the eye covers a region of 0.2mm by0.2mm! Compare this to 200 spots in the same (some as few as only 78 spots) area by other systems using the same Shack-Hartmann principle. WASCA analyser gives finer and more precise details for customizing your treatment. The difference is like listening to digital audio from a CD player compared to the AM radio on an old car speaker.

Not all wavefront analyzers are the same.

Commercially Available Sensor Resolution Comparison (Nideck is not included as it is not Shack-Hartmann system which is the gold standard for true wavefront analysis)

Unit	Lenslet Pitch(Microns) from Published Sources	Approximate Number of Spots analyzed(6mm pupil)
WASCA at Eyetech	210	650
Wavescan (VISX)	400	180
Ladarwave (ALCON)	450	140
Allegreto (WaveLight)	600	80
ZyWave (B&L)	700	60

Shack-Hartmann Lenslet Resolution Comparison of WASCA at Eyetech and Wavescan (VISX)

Resolution from WASCA analyzer at Eyetech		Resolution from Wavescan (VISX}

The laser at Eyetech Lasik Clinic is Zeiss-Meditec MEL 80 laser which delivers a truly Gaussian beam. The spot size is the finest, being only 0.7mm. The combination of high resolution of the wavefront with the 0.7mm laser beam to correct the unique blueprint of your correction, gives you the best possible correction.

Wavefront technology is relatively new to the United States. The U.S. Food and Drug Administration (FDA) issued its first approval of a wavefront system in August 2002 although the treatment is limited to a total of -6.0 including astigmatism of -3.0 at this present time In USA.

In Canada we do higher corrections and Hypermetropia as well. The 5th generation laser used at Eyetech Lasik Clinic, Zeiss-Meditec MEL 80, is not yet available in USA for wavefront corrections.