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Biomedical subjects

S Pieger

Publications and source records attributed to S Pieger.

5 recordsLinked to original sources
PubMed1998

Laser in situ keratomileusis for hyperopia.

PURPOSE: To examine the initial results of laser in situ keratomileusis (LASIK) for hyperopia. SETTING: Arzt für Augenheilkunde, Mannheim, and Photoingenieur, Wendelstein, Germany. METHODS: This retrospective study evaluated 43 eyes having hyperopic LASIK using the Automatic Corneal Shaper (Chiron Vision) and the MEL 60 excimer laser (model 94, Aesculap-Meditec). Patients were divided into two groups. Group 1 consisted of 20 eyes with a refraction from +1.00 to +4.00 diopters (D) and Group 2, 23 eyes from +4.25 to +8.00 D. Objective refraction and visual acuity were measured over 12 months. RESULTS: One year after LASIK, Group 1 had a mean spherical equivalent of +0.33 D (range -0.79 to +1.45 D) and Group 2, +1.91 D (range -0.08 to +3.71 D). Best corrected visual acuity remained unchanged in 35.0% in Group 1 and 56.5% in Group 2. Five percent in Group 1 and 7.3% in Group 2 lost more than 2 lines of best corrected visual acuity. CONCLUSIONS: Laser in situ keratomileusis for hyperopia resulted in less regression, minimal haze, and better predictability and stability than surface photorefractive keratectomy. Preoperative corneal radius appeared to be an important factor in eyes with high hyperopia.

Adolescent↗
PubMedDate not supplied

Effect of an elliptical optical zone on outcome of photoastigmatic refractive keratectomy.

BACKGROUND: This study presents the effect of an elliptical optical zone on the accuracy of correction of astigmatism in patients undergoing photorefractive astigmatic keratectomy (PARK) for myopic astigmatism. METHODS: We reviewed a consecutive case series of 102 eyes that underwent PARK with a Nidek EC-5000 excimer laser by a single surgeon. Group A consisted of 50 eyes treated using a circular optical zone of 6.5 mm x 6.5 mm with a 7.5-mm x 7.5-mm transition zone. Group B consisted of 52 eyes treated using an elliptical optical zone of 5.5 mm x 6.5 mm with a 6.5-mm x 7.5-mm transition zone. Refraction was measured preoperatively and postoperatively, and vector analysis was used to study the change in astigmatism induced by surgery. RESULTS: Mean correction index improved from 75% in Group A to 100% in Group B. Mean angle of error was reduced from 15.8 degrees in Group A to 7.5 degrees in Group B. Hyperopic shift was reduced from +0.70 D in Group A to +0.20 D in Group B. CONCLUSIONS: Excimer laser photorefractive astigmatic keratectomy using an elliptical optical zone improved the correction index for astigmatic change and reduced the mean angle of error. An elliptical optical zone is more effective than the circular optical zone for the treatment of astigmatism in patients with compound myopic astigmatism.

Astigmatism↗
PubMedDate not supplied

Laser in situ keratomileusis nomogram development.

BACKGROUND: There is no standard laser in situ keratomileusis (LASIK) nomogram for the Nidek EC-5000 excimer laser when used with current software versions 2.23 or 2.25. Nomogram tables developed by various EC-5000 users differ significantly from one another. METHODS: We analyzed the results of our first 138 eyes treated for myopia and myopic astigmatism with the Nidek EC-5000 excimer laser, model 2b, long working distance. In addition to analyzing standard clinical outcomes, the correction values entered into the laser were compared to the achieved change in refraction for these eyes. A global nomogram parameter was created, incorporating the effect of optical zone size and patient age. After observing initial overcorrections, we elected to treat most of the eyes using a 20% reduction of the attempted spherical correction. RESULTS: The mean value for the attempted change in spherical equivalent refraction was -6.85 D. This correction was achieved with a standard deviation of -0.04 D at 1 month, -0.08 D at 3 months, and -0.09 D at 6 months after LASIK. The postoperative values for the uncorrected and spectacle-corrected visual acuity were similar to other published studies. However, scatterplots comparing the laser settings to achieved postoperative refractions showed a clear 20% trend toward overcorrection. This trend increased with patient age and optical zone diameter. CONCLUSIONS: The basic calibration values (factory standard) for software versions 2.23 and 2.25 are too aggressive for LASIK treatments. When using optical zone diameters of 6 mm and above, the spherical refraction values entered into the laser must be reduced by at least 20%. LASIK nomograms for the Nidek EC-5000 excimer laser should be specific for optical zone diameter and patient age.

Adolescent↗
PubMedDate not supplied

Correlation of laser profilometry scans with clinical results.

BACKGROUND: The homogeneity of the ablation profile of excimer lasers can be disturbed by various reasons. Laser profilometry scans may serve as a preoperative laser quality control if they can be correlated with clinical results. METHODS: Four lasers from different manufacturers were calibrated for normal photorefractive keratectomy. Preoperatively, -3.00 D ablations were performed on a standardized PMMA Exci-Check plate. Two- and three-dimensional surface scans were taken from the PMMA samples. The optical zone and the ablation depth were measured. Surface roughness and regularity of the ablation profile were compared. The PMMA ablation depth was plotted with the postoperative refraction. Surface regularity was correlated to loss of spectacle-corrected visual acuity. RESULTS: The ablation depth on PMMA changed with time in all four tested lasers. For one laser we measured an ablation depth between 6 and 9 microns which we could correlate to a postoperative refraction of -0.50 to +2.00 D at 2 months after PRK. Surface roughness of these different lasers different significantly from each other. Asymmetric ablation profiles produced a loss of spectacle-corrected visual acuity. CONCLUSION: This study indicates there may be a correlation between results of laser surface profilometry scans and clinical outcomes. A more sophisticated quality control than currently available seems possible and is necessary. Laser profilometry (Exci-Check) provided detailed information about the laser and the ablation conditions, and may help to avoid undesirable clinical outcomes from ablation profile irregularities.

Calibration↗