Comparison of Ultrasound and Scheimpflug Methods for Central Corneal Thickness.

Aim: The central corneal thickness (CCT) of healthy individuals was measured with an ultrasonic pachymeter (UP) and the Scheimpflug imaging system (SIS) and the results were compared to evaluate the agreement between the two methods in this study. Materials and Methods: The 61 subjects who had no ocular pathology or systemic disease except blepharitis were included in the study. CCT measurements of all subjects were performed with the UP (Sonomed 300P Pacscan) and SIS (Nidek Optical biometer AL-Scan) devices and the results were compared. The t test and the Bland-Altman plot were used as the statistical methods. Results: The study sample consisted of 61 cases including 20 males and 41 females. The mean age was 41.8±12.4 (20-58) years for the males and 46.2±9 (24-60) years for the females with no statistically significant difference (P=0.116). The mean CCT measurement of all the 61 subjects was 544.5±31 μm in the right eyes and 547.3±33 μm in the left eyes with UP, 530.7±27.6 μm in the right eyes and 531.6±25.5 μm in the left eyes with SIS. The CCT in the SIS results was an average of 13.8 μm thinner than the UP results in the right eye, 15.7 μm in the left eye and this difference was statistically significant (p=0.001 in right and left eyes). A high degree of agreement was found between the two methods with the Bland-Altman plot. Conclusion: A high degree of agreement was found between SIS and UP regarding CCT measurements and the mean SIS results were 13.8 μm and 15.7 μm thinner than the UP results in the right eyes and left eyes respectively.

Orbscan System for Measurement of Corneal Thickness

PURPOSE: To investigate the accuracy of Orbscan system in measuring corneal thickness before refractive surgery, the authors conducted a comparative study of Orbscan system and ultrasonic pachymeter in their agreement and repeatability. METHODS: 84 patients (168 eyes) who were examined between December, 2000 and March, 2001 were divided into two groups: those who exceeded -6.00 D, and those who did not. Orbscan and ultrasonic pachymeter were employed. Correlation and regression were analyzed to assess their agreement. The repeatability was measured by analyzing mean, standard deviation, and 95% confidence interval of each method. RESULTS: The average central corneal thickness was 542.3+/-34.2micro meter by Orbscan system, and 528.6+/-29.7micro meter by ultrasonic pachymeter. Correlation coefficient was nearly 1 between them, and therefore we obtained statistically significant linear regression equation. In the analysis of repeatability, 95% confidence interval of Orbscan system was -17.2micro meter~+11.8micro meter which was superior to the interval of ultrasonic pachymeter (-23.2micro meter~+14.4micro meter). CONCLUSION: Orbscan system measurements of corneal thickness was greater than ultrasonic pachymeter measurements by 9 to 19 m. Because Orbscan system also showed superiority in repeatability, it may be a useful method in the clinical field.

Central Corneal Thickness Measured by Ultrasonic Pachymeter in Normal Koreans

Corneal thickness is not only a major indicator of corneal diseases but an important parameter for the safety and the prevention of complications in various refractive surgeries widely performed nowadays.Therefore, we tried to acquire the basic data of corneal thickness in normal Koreans through this study. Central corneal thickness was measured using ultrasonic pachymeter in 460 eyes of 238 normal Koreans and analyzed according to the difference in age, sex, left &right, refractive error, and mean keratometry.Mean CCT was 529.67+/-32.18 micrometer.There is no statistically significant difference in CCT according to the difference in age, sex, left and right, refractive error, and mean keratometry in normal Koreans.

Comparison of Corneal Thickness Measurements with the Orbscan and Ultrasonic Pachymetry

To verify the accuracy and reproducibility of corneal thickness measurements obtained with Orbscan (Orbtek, Inc., Salt Lake City, USA), the measurements were compared with those taken with an ultrasound pachymeter (Omega Compuscan, Storz). Central corneal thickness was measured by each method in 100 eyes of 50healthy subjects. The averages by the two methods were compared. One examiner took the measurements twice by each method in 20 eyes of 10 subjects, and intraexaminer reproducibility was evaluated. Two examiners measured the thickness in 20 eyes of 10 subjects and interexaminer reproducibility was assessed. The average corneal thickness was 550.27+/-3.56 micrometer in the Orbscan measurements and 526.62+/-3.70 micrometer in the ultrasound pachymetry: There was a statistically significant difference between the two methods. Significant difference was noticed but this showed a constant corresponding correlation with the Orbscan showing a 4.4%lower average. The intraexaminer and interexaminer reproducibility showed high reliability(Guttman split-half point<0.99). The Orbscan pachymetry is a highly reliable method and may be widely used in clinical practice.