Purchase this article with an account.
L. Zickler, M. Arnoldussen, S. Somani, E. Gross, L. Cheng; Using Wavefront Aberrometry for Automated Calibration and Quality Control of Corneal Excimer Laser Ablation . Invest. Ophthalmol. Vis. Sci. 2006;47(13):546.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
The laser fluence level that governs the fundamental ablative process in refractive surgery on the VISX STAR excimer laser systems is calibrated by ablating a well defined target lens into test plastic, which is then manually analyzed by a technician using a conventional lensometer. The accuracy of this method is limited by the lensometer to anout 0.25 D. Wavefront aberrometry is widely used in assessing the performance of optical systems, including the human eye. The purpose of this study was to transfer the technology of integrated wavefront aberrometry to a compactly designed, objective, automated calibration and quality control method for excimer laser ablation.
A wavefront–based calibration instrument (wavefront lensometer) was developed, comprising an LED source (=640 nm), a lenslet array, beam–guiding optics, and a CCD camera. The accuracy of the wavefront lensometer was determined by using it offline to measure a set of well characterized spherical and cylindrical glass lenses . To accomplish automatic laser calibration, a test plastic card held by the wavefront lensometer is ablated with target lenses. Once the target lenses are ablated, the wavefront lensometer performs a full wavefront analysis, which includes sphere, cylinder, and higher order aberrations. The ablation measurement plane is conjugate to the lenslet array plane. Pupil size is 5 mm. Results were compared to measurements made on high precision surface profile scanners and interferometers. The correct laser fluence set–point was iteratively derived from the measurements made by the wavefront lensometer.
In the power range of –6 to +4 D, accuracy of the wavefront lensometer was greater than 0.04 D; repeatability was greater than 0.01 D. Higher order information also matched well. The measurement of excimer–ablated plastic lenses agreed very well with high precision measurements performed on surface profile scanners and interferometers. Additionally, the wavefront lensometer detected ablation artifacts caused by degrading pulse delivery optics. The ablation response on calibration plastic_as characterized with the wavefront lensometer _correlated with the ablation response in human tissue.
Wavefront technology–based, high precision measurements of calibration lenses can enhance the accuracy and reduce variability in refractive laser vision correction. Additionally, the instrument, which is compact in design, removes operator subjectivity and automates the daily calibration and quality control process.
This PDF is available to Subscribers Only