PURPOSE: To evaluate error of corneal thickness measurement in different gazes in Orbscan topography. METHODS: Sixty eyes of 30 normal subjects were investigated using the Orbscan topography system. The central corneal thickness (Kc) and the thinnest corneal thickness (Kt) on topography map were obtained in 5 different gazes. Gaze directions were classified into center (C), nasal I (NI), nasal II (NII), temporal I (TI), and temporal II (TII), in which I means 13 degree deviation from visual axis and II means 22 degree deviation. RESULTS: Kc in right eye was 540.4+/-37.7 micro meter(mean+/-standard deviation) at central gaze (C) and 550+/-36.9 micro meter at NI ; there was no significant change, but there were in Kc at NII (563.0+/-40.5 micro meter), TI (566.5+/-32.8 micro meter), TII (595.2+/-54.5 micro meter). In addition, the same patterns were seen in left eye in Kc analysis. In contrast, Kt did not change even in 5 gaze changes. In comparison between Kc and Kt at the same gazes, there were significant differences except in central gaze (C). CONCLUSIONS: Though the gaze direction changed, the most reliable measurement for evaluation and follow up of corneal thickness is the thinnest corneal thickness (Kc) in Orbscan topography system. In case that the central corneal refractive power and thickness were needed, it is important that Orbscan topography is performed in exact central fixation.
Axis, Cervical Vertebra ; Corneal 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.
Corneal Pachymetry* ; Lakes ; Ultrasonics* ; Ultrasonography

PURPOSE: To compare the measurements of central corneal thickness (CCT) obtained using two kinds of spectral domain optical coherence tomography (OCT), Pentacam®, and ultrasound pachymetry (USP). METHODS: CCT was measured by Cirrus OCT®, Spectralis OCT®, Pentacam®, and USP in 32 eyes from 32 subjects without ocular disease of the anterior segment. RESULTS: The average CCT measurements using Cirrus OCT®, Spectralis OCT®, Pentacam®, and USP were 549.2 ± 28.7 µm, 545.2 ± 25.4 µm, 554.0 ± 27.8 µm, and 548.4 ± 27.9 µm respectively. The measurements were significantly highly correlated with each other (Pearson's correlation coefficient r > 0.9, all p-values < 0.001), but were significantly different (p < 0.001). The CCT 95% limits of agreement between Cirrus OCT® and Spectralis OCT®, Cirrus OCT® and Pentacam®, Cirrus OCT® and USP, Spectralis OCT® and Pentacam®, and Spectralis OCT® and USP were 27.70 µm, 26.1 µm, 26.97 µm, 22.91 µm, 35.59 µm, and 32.15 µm, respectively. CONCLUSIONS: The CCT values measured using the four devices were highly correlated with each other, but the measurement using Pentacam® was significantly thicker than that using USP. The measurements of the two kinds of spectral domain OCT were similar to those using USP. Therefore, these differences should be considered in clinical use, and measurements cannot be considered interchangeable.
Corneal Pachymetry* ; Tomography, Optical Coherence* ; Ultrasonography*

PURPOSE: To evaluate central corneal thickness and pachymetry maps in myopic eyes. METHODS: 104 eyes of 52 myopic patients were investigated using the Orbscan (Orbtek, Inc., USA). The pachymetry maps were designated as round, oval, decentred round, and decentred oval. Corneal thickness was evaluated at the central, eight-paracentral, and the thinnest sites on each of the corneas. We studied difference of corneal thickness under sex and myopic degree. And got the symmetry of the cornea under location of the thinnest sites. RESULTS: Superior cornea had the greatest average thickness (605.5+/-35.3 mu m). Average central corneal thickness (+/-SD) was 552.2 (+/-34.9) mu m. All corneas had the thinnest sites on 0.86 mm from the visual axis and most of all inferotemporal area (76.0%). There was no significant difference of corneal thickness in sex and myopic degree. Average thickness of the thinnest sites was 544.2 (+/-35.6) mu m and significantly thinner than center. 61.5% of the persons had symmetrically located thinnest corneal sites and most of all (57.7%) had temporal side symmetry. In the pachymetry maps, oval pattern was 47.1% of 104 eyes, andround, decentred oval, decentred round were observed in 43.3%, 5.8%, and 3.8% of eyes, respectively. CONCLUSIONS: Of all myopic eyes evaluated in this study, the thinnest sites were on average 0.86 mm from the visual axis. And oval type was the most common pachymetry map pattern.
Axis, Cervical Vertebra ; Cornea ; Corneal Pachymetry* ; Humans

PURPOSE: To evaluate the corneal thickness values before and after refractive keratoplasty with the Topcon SP-2000 noncontact specular microscope(Topcon American Corp.) and the common standard ultrasonic pachymeter. METHODS: Corneal thickness was measured in 40 eyes of 20 patients, 5 times each before and after keratoplasty, with the Topcon SP-2000P and an ultrasonic pachymeter (DGH 1000, DGH Technology Inc.). The main outcome measures were accuracy and reproducibility as assessed with coefficient of variation (CV) of corneal thickness measurements. RESULTS: The reproducibility of corneal thickness measurements was better with the ultrasonic pachymeter (CV 0.36%) than with the Topcon SP-2000 (CV 1.23%). Mean corneal thickness measured by the Topcon SP-2000P before and after keratoplasty was significantly less than the mean values obtained with the ultrasonic pachymeter (14.4 micro meter; P<.0001, 5.6 micro meter; P<.01; respectively). Compared with theoretical ablated corneal thickness, ablated corneal thickness measured with the Topcon SP-2000P was significantly less (P<.01) than values obtained with the ultrasonic pachymeter (P=0.07) CONCLUSIONS: The noncontact Topcon specular microscope provides measurements of corneal thickness that are significantly less than those of the ultrasonic pachymeter, both before and after keratoplasty. These results indicate that these 2 techniques are not clinically comparable, thereby precluding interchangeable use of their data in planning or assessing keratoplasty.
Corneal Pachymetry* ; Corneal Transplantation ; Humans ; Outcome Assessment (Health Care) ; Ultrasonics*

PURPOSE: To assess the the accuracy and variability in pachymetry measurements obtained by Orbscan and ultrasonic pachymeter in laser in situ keratomileusis (LASIK). METHODS: Thirty two eyes of 16 patients before LASIK were measured by ultrasonic pachymeter and Orbscan. Thirty eyes of 16 patients that had LASIK were measured by ultrasonic pachymeter and Orbscan postoperatively. The theoretical residual corneal thickness was compared to measurements by both instruments in eyes that had LASIK procedures. RESULTS: The ultrasound pachymeter measurements (543.8+/-24.2 micrometer) were thicker than the Orbscan pachymetry measurements, (541.2+/-24.9 micrometer) by mean of 2.7+/-7.4 micrometer (SD), preoperatively. But this is not statistically significant (p>0.05). Postoperatively, the ultrsound measurements were consistent with theoretical residual corneal thickness, 461.8+/-37.4 micrometer versus 467.9+/-30.71 micrometer (p=0.064), while Orbscan measurements were statistically less than the theoretical residual corneal thickness, 433.2+/-48.75 micrometer versus 464.32+/-33.4 micrometer (p<0.001). CONCLUSIONS: In LASIK eyes, the ultrasonic pachymetry was a more accurate measurement of corneal pachymetry than Orbscan topography system.
Corneal Pachymetry ; Humans ; Keratomileusis, Laser In Situ* ; Ultrasonics* ; Ultrasonography

PURPOSE: To report the difference of the values of the corneal thickness measurement measured by Orbscan topography system and ultrasonic pachymetry is different between pre-LASIK and post-LASIK. METHODS: The corneal thickness measured by these two methods was compared in 32 pre-LASIK eyes of 18 subjects and 31 post-LASIK eyes of 20 subjects passed 3 months after laser in situ keratomileusis (LASIK). RESULTS: In the pre-LASIK eyes, the cornea measured thicker by Orbscan topography system than by ultrasonic pachymeter (16.94+/-13.1 microgram, average +/- standard deviation, p=0.001). In the post-LASIK eyes, there was no statistically significant difference in the values of corneal thickness measurement between two methods (-9.58+/-27.88 microgram, p=0.0653). CONCLUSION: We must give attention to the interpretation of values of corneal thickness measurement measured by Orbscan topography system and ultrasonic pachymetry because the correlations between the two methods in pre and post-LASIK eyes are different. We assume that differences of the values of measurement between the two methods may result from either technical errors of the measurers , interference of corneal interface, or change of tear film.
Cornea ; Corneal Pachymetry* ; Keratomileusis, Laser In Situ* ; Tears ; Ultrasonics*

PURPOSE: To investigate the accuracy and reproducibility of Optical Low Coherence Reflectometry (OLCR) corneal thickness measurements compared with the Orbscan system and ultrasound pachymeter (IOPac, Mentor). METHODS: Two examiners measured corneal thicknesses of 78 normal eyes and in 36 eyes that had undergone LASIK, and five sequential measurements of corneal thickness with OLCR, Orbscan system, Mentor, and IOPac were performed. Remeasurements of corneal thickness in 24 normal eyes were performed after two days to investigate intra-examiner reproducibility. RESULTS: The average corneal thickness measured in normal subjects was 536.3+/-23.8 micrometer in OLCR, 542.4+/-25.3 micrometer in the Orbscan system, 535.4+/-23.7 micrometer in Mentor, and 534.2+/-24.1 micrometer in IOPac. The average corneal thickness measured in patients who had undergone LASIK was 487.3+/-30.8 micrometer in OLCR, 492.5+/-36.5 micrometer in the Orbscan system, 487.5+/-30.8 micrometer in Mentor, and 485.3+/-30.8 micrometer in IOPac. There was no statistically significant difference between the four pachymeters. The inter-examiner and intra-examiner reproducibilities were shown to be highly reliable. CONCLUSIONS: The OLCR showed similar measurments of corneal thickness with the Orbscan system and ultrasound pachymeter, and showed no difference in reproducibility with different examiners.
Corneal Pachymetry* ; Humans ; Keratomileusis, Laser In Situ ; Mentors ; Ultrasonography*

PURPOSE: To investigate the relationship among optical coherence tomography (OCT), ultrasound pachymetry, and Orbscan in central corneal thickness measurement and to evaluate the reproducibility of flap thickness using an IntraLase femtosecond laser. METHODS: Central corneal thickness was measured by OCT, ultrasound pachymetry, and Orbscan in 59 eyes of 30 patients before LASIK. After IntraLASIK, the corneal flap thickness measured using OCT was compared with the intended corneal flap thickness. RESULTS: Central corneal thickness measured by OCT was thinner than that measured by other instruments preoperatively, but there was no significant difference among these methods (p>0.01), and corneal thickness values obtained by ultrasound pachymetry and Orbscan correlated well with those obtained by OCT (r ranged from 0.804 to 0.889, p<0.01). After IntraLASIK, there was no significant difference between the mean measured flap thickness and the intended flap thickness (p>0.01). CONCLUSIONS: OCT is a relatively accurate instrument for measuring corneal thickness and can easily measure the corneal flap thickness after LASIK. Compared with the results of a previous study, the mean measured flap thickness in this study was more reproducible with the IntraLase femtosecond laser.
Corneal Pachymetry ; Humans ; Keratomileusis, Laser In Situ ; Tomography, Optical Coherence* ; Ultrasonography

PURPOSE: To compare corneal pachymetry assessment using four measurement methods in normal and post-femtosecond laserassisted LASIK eyes. METHODS: Central corneal thickness was measured sequentially using Orbscan II, Pentacam, Galilei and ultrasonic pachymetry in 30 normal, non-surgical eyes (Group I), 30 eyes one to six months after femtosecond laser-assisted LASIK (Group II), and 30 eyes six months or longer after femtosecond laser-assisted LASIK (Group III). RESULTS: In Group I, corneal thickness measurements were similar for all four methods (P=0.202, one way ANOVA). In Groups II and III, corneal thickness measurements were significantly different (P=0.000, respectively, one way ANOVA). Compared to the Pentacam, Galilei and ultrasonic pachymetry, Orbscan significantly underestimated the corneal thicknesses in Groups II and III (P<0.005, respectively, one way ANOVA). CONCLUSIONS: Central corneal thicknesses of normal eyes were similar for all four measurements, therefore corneal thickness measurements before refractive surgery using all four measurements is suitable. However measurements obtained with the Orbscan II were thinner than those obtained with the Pentacam, Galilei or ultrasonic pachymetry in post femtosecond laserassisted LASIK eyes. Further studies are needed to determine which instrument is more accurate in measuring central corneal thickness before and after refractive surgery.
Corneal Pachymetry ; Eye ; Keratomileusis, Laser In Situ ; Refractive Surgical Procedures ; Ultrasonics