On the structural origin of refractive instability and corneal haze after excimer laser keratectomy for myopia.
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Biomedical subjects
Torben Møller-Pedersen
Publications and source records attributed to Torben Møller-Pedersen.
[Supervision].
Within the past year, the idea of supervision has been introduced and promoted in the media by the manufacturers of wavefront-guided excimer lasers for refractive surgery. The concept is related to the ability of obtaining supernormal visual acuity and contrast sensitivity by correction of higher order aberrations in the biological optics of the human eye. However, the ocular aberrations fluctuate continuously and dynamically over time with the functional state of several of the individual optical components, including: thickness of the tear film, size of the pupil, and the degree of lens accommodation. These temporal variations represent major obstacles for achieving aberration-free images. In addition, the central perception of ideal aberration-free images may be hindered by neuronal limitations in the retina and brain. So far, only a few patients have experienced an increase in best corrected visual acuity following wavefront-guided refractive surgery. Also in the first prospective clinical trials with myopic individuals, only modest differences in visual performance have been detected between wavefront-guided and conventional treatment. Thus, immediate expectations from the new technology should be tuned down; supervision is not waiting around the corner.
Computer Simulation↗
Validation of confocal microscopy through focusing for corneal sublayer pachymetry.
PURPOSE: To evaluate the accuracy and precision of confocal microscopy through focusing (CMTF) for corneal sublayer pachymetry. METHODS: A tandem scanning confocal microscope equipped with a nonapplanating contact objective was used to perform CMTF. The accuracy of CMTF measurements was evaluated using nine custom-made calibration contact lenses (PMMA) with varying thickness (300-600 microm) and radius of curvature (7.0-9.0 mm). The influence of immersion fluid stabilization and the consequence of prolonged corneal examination were assessed by performing CMTF in rabbits. Additionally, factors related to the instrumental setup and to sedation of experimental animals were examined. RESULTS: For all calibration contact lenses, the thickness measured by CMTF was within +/-1.0 microm of the certified value. Varying the target thickness or radius of curvature had no consistent impact on the high accuracy of CMTF. When performing CMTF in vivo, z-axis motion was readily identified by sampling and comparing both in- and out-scans. Apart from involuntary eye movements, z-axis motion was due to initial thinning of the immersion fluid with stabilization obtained after approximately 1.5 minutes. Continued confocal examination led to slight but significant swelling of both the stroma (0.5 microm/min) and epithelium (0.1 microm/min). CONCLUSIONS: CMTF is an accurate and precise technique for corneal sublayer pachymetry with concurrent display of cellular morphology. The precision of CMTF can be improved by allowing time for methylcellulose stabilization and by performing repeated two-way (in and out) scans to account for z-axis motion.
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