Ultrasound Pachymeter Research Articles

Combining corneal hysteresis with central corneal thickness and intraocular pressure for glaucoma risk assessment

To determine whether adjusting corneal hysteresis (CH) values for central corneal thickness (CCT) and intraocular pressure (IOP) improves its capability to differentiate primary open-angle glaucoma (POAG) from ocular hypertension (OH). This prospective, observational, cross-sectional study included 169 eyes of 169 subjects with a diagnosis of POAG (n=81) or OH (n=88). We utilized the Ocular Response Analyzer (ORA), Pascal Dynamic Contour Tonometer (DCT), Goldmann applanation tonometer (GAT), and ORA ultrasound pachymeter to obtain CH, IOP, and CCT values. Correlational, regression, and t-test analyses were conducted before and after the sample was divided into low, intermediate, and thick CCT subgroups. In the full sample, CH and CCT were moderately correlated (r=0.44, P<0.001). Although both were related to diagnosis in univariate regression analysis, only CH was independently related to glaucoma diagnosis in multivariate analysis. After the sample was divided into CCT tertiles, CH was significantly lower in POAG vs OH eyes within all three CCT subgroups, and CH was the only multivariate variable that differentiated POAG from OH in each CCT subgroup. Moreover, the relationship between CH and diagnosis was more robust within the CCT subgroups compared with the full sample, suggesting that integrating CCT into CH interpretation is beneficial. Adjusting CH for IOP did not aid diagnostic precision in this study. Our findings suggest that combining CH and CCT for glaucoma risk assessment improves diagnostic capability compared to using either factor alone. Conversely, adjusting CH for IOP provided no clear clinical benefit in this study.

Distribution of the central corneal thickness in adult residents of Lithuania

AbstractPurpose To determine the distribution of the central corneal thickness by age and gender in Lithuanian population.Methods Lithuanian residents in the age of 18 and senior, who were registered with the primary health care institutions (PHCI) of different Lithuanian cities and regions participated in the survey. Data including age, gender and measurement of central corneal thickness (CCT) of all tested persons was registered. CCT of each eye was measured by using the ultrasound contact pachymeter. The results were statistically analysed by SPSS 17,0 program.Results In total 1650 residents of Lithuania were tested, including 688 (41, 7%) men and 962 (58.3%) women. The average age among men was 57.31 ± 0.61, and among women ‐ 53, 63 ±0.74. The average CCT of individuals by age groups equalled to: 18‐29 (550,8 ±2,8 µm), 30‐39 (557,5±1,9 µm), 40‐49 (551,3±1,8 µm), 50‐59 (544,0±1,9 µm), 60‐69 (544,2±2,1 µm), 70‐79 (535,1±1,9 µm), and 80+ (530,1±1,1 µm)( p=0,000, p&lt;0,05). The central corneal thickness of the tested men and women by different age groups (under 40, from 40 to 60 years of age, and over 60) was calculated in percentiles. Corneas of persons under 40 are thicker than of persons in the age between 40 and 60, and corneas of the tested senior persons over 60 are thinner in comparison with other age groups.Conclusion The average CCT among Lithuanian residents in general is 544,6± 0,7 m, 545,0±0,8 m of men, and 544,4±1,1 m of women. The thickest cornea among Lithuanian residents was measured in individuals under 40. In senior persons it becomes thinner by each decade from 2 to 8µm. The central corneal thickness has no relevance to gender.

Agreement of Corneal Thickness Measurement Using Slitlamp and Ultrasound Pachymetry

To estimate central corneal thickness (CCT) using a slitlamp biomicroscope and analyze its agreement with ultrasonic pachymetry. Based on the clinical estimation of CCT on slitlamp examination, 133 eyes of 123 patients were assigned to 3 groups: CCT less than 500 μm, 500 to 600 μm, and greater than 600 μm. An average of three readings was obtained for each patient using an ultrasound pachymeter. The primary diagnoses at the time of presentation were glaucoma (42, 31.5%), corneal opacity (20, 15%), keratoconus (14, 10.5%), corneal edema (14, 10.5%), and postkeratoplasty eyes (8, 6%). Thirty-five (26.5%) eyes had no known ophthalmic diseases. There was an overall agreement of 86.5% in qualifying CCT into each of the 3 groups (kappa 0.76). The sensitivity and specificity of clinical estimation of CCT were found to be 96.26% (95% confidence interval [CI], 76.1%-94.2%) and 92.31% (95% CI, 78.7%-92.2%), respectively. The agreement was highest in patients with corneal edema (100%, kappa 1.00) and postkeratoplasty eyes (100%, kappa 1.00). The agreement was 82.9% (kappa 0.3) in normal eyes. Estimation of CCT by slitlamp examination is a reliable tool in clinical practice. In our study, there was a substantial agreement between clinically estimated CCT and ultrasonic pachymetry. This agreement was higher in eyes with abnormal corneal thickness compared with normal eyes.

Comparison of intraoperative ultrasound pachymetry and postoperative optical coherence tomography of anterior segment in the measurement of flap thickness in eyes receiving laser in situ keratomileusis.

To compare the measurement of flap thickness using intraoperative ultrasound pachymetry and postoperative Visante anterior segment optical coherence tomography (Visante-OCT) in eyes receiving laser in situ keratomileusis (LASIK). Seventeen patients (34 eyes) received LASIK using a Technolas-217Z100 laser and AMADEUSⅡ mechanical microkeratome (140μm head). Flap thickness was assessed with an ultrasound pachymeter intraoperatively and a Visante -OCT postoperatively at 1 week and 1 month. The intraoperative mean flap thickness by ultrasound pachymetry was (124±13.9) μm (range: 96.5 to 160 μm), and mean flap thickness by Visante-OCT was (145±7.13) μm (range: 130 to 158 μm) and (143±5.32) μm (range: 132 to 155 μm) postoperatively at 1 week and 1 month respectively (F =63.52, P<0.01). Intraoperative subtraction pachymetry underestimated flap thickness compared with postoperative Visante-OCT (P<0.01). There was no significant difference between postoperative Visante-OCT measurements at 1 week and 1 month after LASIK (P=0.16). The 95% limit of agreement (LoA) of flap thickness between ultrasound Visante-OCT and pachymetry was -5.40 to 42.10 μm. OCT overestimates flap thickness compared with intraoperative ultrasound pachymetry when using the AMADEUSⅡ mechanical microkeratome.

Accuracy and Repeatability of a New Tono-Pachymeter for Measuring Central Corneal Thickness

The recently developed noncontact tonopachymeter Tonopachy NT-530 P provides intraocular pressure values corrected for central corneal thickness (CCT). The purpose of this study was to assess the accuracy and repeatability of its CCT measurements. The CCT measurements were obtained in 64 right eyes of 64 young healthy subjects using the Orbscan corneal topography system followed by the Tonopachy and then by ultrasound pachymetry (UP). Another sample of 31 subjects was used to test the repeatability of the tonopachy measurements in 2 separate sessions 1 week apart. To compare the tonometers and determine intersession repeatability for the tonopachymeter, differences in the readings provided by pairs of the instruments or obtained in the two sessions were plotted against mean differences. The hypothesis of zero bias was examined by a paired t-test. The coefficient of repeatability was calculated as the 95% limits of agreement (LoAs) of differences between the 2 sessions. Measurements made using the three instruments were significantly correlated (P<0.001). Mean CCTs (±SD) measured using the Tonopachy, Orbscan (acoustic factor set at 0.92) and ultrasound pachymeter were 530.42 ± 34.96, 526.73 ± 39.53, and 550.69 ± 37.26 μm, respectively. The differences between modalities (±95% LoAs) were -3.68 ± 24.36 for Orbscan versus Tonopachy, 20.66 ± 14.69 for UP versus Tonopachy, and 23.95 ± 24.21 for UP versus Orbscan. The coefficient of repeatability for the tonopachymeter was ±15.11 μm. The Tonopachy offers similar CCT measurements to those provided by conventional pachymeters with good repeatability.

Comparison of Central Corneal Thickness Measurements by Galilei Dual-Scheimpflug Analyzer ® and Ultrasound Pachymeter in Myopic Eyes

To compare the central corneal thickness (CCT) measurements by Galilei Dual-Scheimpflug analyzer (GSA) (Ziemer Group, Port, Switzerland) and ultrasound pachymeter (UP) in myopic eyes. In this prospective study, CCT of 161 myopic eyes of 81 refractive surgery candidates (35 female, 46 male; mean age: 23.18 ± 4.08 years) were measured by GSA and UP consecutively. The data were analyzed statistically by paired t test, Bland-Altman plot, and Pearson correlation test to assess the agreement of the measurements. The mean CCTs obtained by GSA and UP were 559.85 ± 30.87 and 560.41 ± 34.45 μm, respectively. No significant difference was found between the measurements (P = .684) and regression analysis showed a high correlation between the measurements obtained with both devices (r = 0.86; P < .001). A strong agreement between the two methods was also found by Bland-Altman plot. In myopic eyes, the CCT measurements of GSA and UP are similar and highly correlated. Because of high agreement between these devices, the GSA is a non-contact method that may be an alternative to UP for measurement of CCT.

Comparison of central corneal thickness measurements using ultrasound pachymetry, ultrasound biomicroscopy, and the Artemis-2 VHF scanner in normal eyes

PurposeTo compare the precision of central corneal thickness (CCT) measurements taken with the handheld ultrasound pachymeter (USP), ultrasound biomicroscopy (UBM), and the Artemis-2 very high frequency ultrasound scanner (VHFUS) on normal subjects.DesignProspective study.MethodsOne eye from each of 61 normal subjects was randomly selected for this study. The measurements of the CCT were taken with the USP, VHFUS, and UBM. Results were compared statistically using repeated-measures analysis of variance (ANOVA), Pearson’s correlation coefficient, and limits of agreement.ResultsThe average CCT (± standard deviation) was 530.1 ± 30.5 μm, 554.9 ± 31.7 μm, and 559.5 ± 30.7 μm for UBM, VHFUS, and USP respectively. The intraobserver repeatability analyses of variance are not significant for USP, UBM, and VHFUS. P-values were 0.17, 0.19, and 0.37 respectively. Repeated-measures ANOVA showed a significant difference between the three different methods of measuring CCT (P = 0.0001). The ANOVA test revealed no statistically significant difference between USP and VHFUS (P > 0.05), yet statistical significant differences with UBM versus USP and UBM versus VHFUS (P < 0.001). There were high correlations between the three instruments (P < 0.0001). The mean differences (and upper/lower limits of agreement) for CCT measurements were 29.4 ± 14.3 (2.7/56), 4.6 ± 8.6 (−14.7/23.8), and −24.8 ± 13.1 (−50.4/0.8) for USP versus UBM, USP versus VHFUS, and UBM versus VHFUS, respectively.ConclusionThe UBM produces CCT measurements that vary significantly from those returned by the USP and the VHFUS, suggesting that the UBM may not be used interchangeably with either equipment for monitoring the CCT in the clinical setting.

Corneal endothelium after deep anterior lamellar keratoplasty and penetrating keratoplasty for keratoconus: A four-year comparative study

Purpose:To compare the status of corneal endothelium and central corneal thickness within the first four postoperative years after deep anterior lamellar keratoplasty (DALK) and penetrating keratoplasty (PK) in patients with keratoconus.Materials and Methods:Thirty-nine eyes (Group A) which had PK and 44 eyes (Group B) which had DALK for the treatment of keratoconus were included in this retrospective study. The endothelial cell density (ECD), the mean endothelial cell area and the coefficient of variation of cell area were assessed with a non-contact specular microscope, and the central corneal thickness (CCT) was measured with an ultrasound pachymeter.Results:Mean ECD loss rate at two years was 36.24% in Group A and 18.12% in Group B (P<0.001). Mean ECD loss rate at four years was 47.82% in Group A and 21.62% in Group B (P<0.001). Mean annual ECD loss rate was calculated 14.12% per year in Group A and 5.78% per year in Group B. In the PK group, increase in mean CCT was 15.60% in two years and 15.03% in four years, while in the DALK group, mean CCT increased by 8.05% in two years and 9.31% in four years.Conclusions:As the majority of ectatic disorders such as keratoconus occur in young people, long-term endothelial cell survival following treatment with keratoplasty is essential for the long-term visual ability. Our finding that corneal endothelial cell loss in the DALK group occurs at a slower rate than in the PK group suggests DALK as a safer alternative to PK in these selected patients.

Repeatability and interobserver reproducibility of Artemis-2 high-frequency ultrasound in determination of human corneal thickness

BackgroundThe purpose of this study was to assess the repeatability and limits of agreement of corneal thickness values measured by a high-frequency ultrasound (Artemis-2), hand-held ultrasound pachymeter (DGH-500) and a specular microscope (SP-3000P).MethodsCentral corneal thickness (CCT) was analyzed in this prospective randomized study that included 32 patients (18 men and 14 women) aged 21–24 years. Measurements were obtained in two sessions, one week apart, by two examiners with three devices in a randomized order. Nine measurements were taken (three with each device) on one randomly selected eye of each patient in each measurement session. The coefficient of repeatability and interobserver reproducibility for the values of each method were calculated. The limits of agreement between techniques were also evaluated.ResultsThere were no significant differences in CCT values between sessions for each of the three devices (P > 0.05). The repeatability coefficients for the Artemis-2 (±8 μm/±9 μm) were superior to those of the SP-3000P (±9 μm/±11 μm) and DGH 500 (±12 μm/±12 μm) in session 1/session 2 respectively, while the interobserver reproducibility index (differences between session 1 and session 2) was superior for the SP-3000P (±17 μm) with respect to DHG-500 (±29 μm) and the Artemis-2 (±31 μm). In session 1 and session 2, the limits of agreement between the techniques were 35 μm to −31 μm and 34 to −20 μm, respectively, for DGH-500 versus Artemis-2, 73 μm to 3 μm and 60 μm to 9 μm for Artemis-2 versus SP-3000P, and 58 μm to 22 μm and 72 μm to 10 μm for DGH-500 versus SP-3000P comparisons. The DGH-500 and Artemis-2 gave similar values (P > 0.05) in both sessions, but both (Artemis-2 and DGH-500) values were significantly greater than that of the SP-3000P (P < 0.05) in both sessions.ConclusionRepeatability was comparably good for the three techniques. However, interobserver reproducibility was approximately twice as good with the SP-3000P compared with the other two devices. The Artemis-2 CCT values consistently agreed with the DGH-500 and less so with the SP-3000P. The Artemis-2 provided CCT values that were, on average, 38 μm and 34 μm greater than that of the SP-3000P in session 1 and session 2, respectively.

Blue-on-yellow perimetry and corneal thickness in patients with ocular hypertension.

To evaluate the frequency of blue-on-yellow perimetry (B/YP) deficits in ocular hypertension (OHT) patients and to correlate these findings with central corneal thickness (CCT), and to investigate the influence of age, refraction and gender on the B/YP results in OHT patients. The B/YP and CCT were checked respectively in 72 OHT patients with normal white-on-white perimetry(W/WP) and normal optic nerve head. The B/YP was tested by Octopus 101 automated perimetry using G2 strategy, while the CCT was checked with DGH-550 ultrasound pachymeter. All patients were chosen randomly one eye for statistical analysis, a binary regression model was used to determine the independent contribution of variables included in the model, and the differences of the intraocular pressure (IOP), CCT, age, refraction and gender between the normal B/YP group and abnormal B/YP group were compared. Forty-nine out of 72 patients with OHT showed normal B/YP results, whereas 23 of 72 patients(31.9%) demonstrated abnormal B/YP results. CCT showed a correlation with the B/YP results (B=-0.038, SE=0.019, P=0.044), whereas none of the IOP, age, refraction and gender was found to be correlated with the B/YP results. The mean CCT in OHT patients with abnormal B/YP group was lower than that with normal B/YP group (t=2.066, P=0.043).There was a significant positive correlation between IOP and CCT (R(2)=0.513, P=0.000). The mean CCT in OHT patients with abnormal B/YP results was lower than that with normal B/YP results. There was a significant positive correlation between IOP and CCT in OHT patients. The age, refraction and gender didn't influence the B/YP results in OHT patients.

The relationship between central corneal thickness and corneal curvature in adult Nigerians

Purpose: The aim of this study was to provide average values for central corneal thickness (CCT) and corneal curvature (CC) and also to determine a regression model for the relationship between CCT and CC in adult Nigerians without glaucoma.Methods: A total of 95 subjects consisting of 56 males and 39 females aged between 20 and 69 years with mean age of 47.1 ± 14.1 years were recruited for the study. Central corneal thickness was measured by ultrasound pachymetry (SW-1000P ultrasound pachymeter, Tianjin Suowei Electronic Technology, China) and corneal curvature was measured by keratometry (Bausch &amp; Lomb keratometer H-135A, USA).Results: The average values of 550.1 ± 33.1µm and 43.0 ± 1.1 D were obtained for CCT and CC respectively. CCT significantly correlated with age (p=0.01), and the regression model predicts a decrease of 6.0 µm in CCT per decade. No significant association was found between CC and age (p=0.56). Also, no significant association was found between CCT and CC (p=0.07). Female subjects had significantly steeper corneas than their male counterparts.Conclusion: Central corneal thickness decreases with increasing age. Neither CCT nor age appear to be significantly correlated with corneal curvature. (S Afr Optom 2011 70(1) 44-50)

Repeatability of intraoperative central corneal and residual stromal thickness measurement using a handheld ultrasound pachymeter

To determine and compare the repeatability of intraoperative central corneal thickness (CCT) and residual stromal bed thickness measurements using a handheld ultrasound (US) pachymeter. London Vision Clinic, London, United Kingdom. Comparative evaluation of a diagnostic test or technology. This study comprised eyes that had laser in situ keratomileusis retreatment by flap lift in which handheld US pachymetry (Corneo-Gage Plus 50 MHz) had been performed intraoperatively. In each case, 5 consecutive measurements were obtained centrally immediately before and after the flap was lifted. The within-eye repeatability was calculated as the standard deviation of the 5 repeated measurements for the CCT measurements and the central residual stromal thickness (RST) measurements. The study evaluated 134 eyes (79 patients). The mean CCT was 467 μm ± 40 (SD) (range 393 to 577 μm). The repeatability of CCT measurements was 6.83 μm, the coefficient of repeatability was 13.40 μm, and the coefficient of variation (CoV) was 1.46%. The mean central RST was 335 ± 46 μm (range 259 to 465 μm). The repeatability of central RST measurements was 4.91 μm, the coefficient of repeatability was 9.62 μm, and the CoV was 1.46%. The repeatability of intraoperative handheld US pachymetry was similar between measurements of CCT and measurements of central RST; the CoV was 1.46% in both cases.

Central Corneal Thickness Measurements: Using an Ultrasonic Instrument and 4 Optical Instruments

Both between-session and within-session repeatability were determined for measurement of corneal thickness with the following techniques: ultrasound pachymetry (UP), confocal microscopy (CS), Orbscan pachymetry (ORB), spectral oscillation interferometry (SOI), and optical coherence tomography (OCT). The right eyes of 20 normal subjects were tested on 2 different days. For each session, 2 central corneal thickness measurements were determined using the ConfoScan 3 microscope, the Orbscan system, and the Stratus OCT system; 5 measurements were found with the Sonogage ultrasound pachymeter; and between 2 and 10 measurements were found with the SOI system. This study showed that SOI had the best repeatability, whereas CS had the worst repeatability for both within-session and between-session repeatability. Based on 95% limits of agreement (LoA), the within-session repeatability can be ranked as: (1) SOI; (2) UP; (3) OCT; (4) Orbscan pachymetry; and (5) CS. SOI had a bias of 0.13 and 95% LoA of -1.07 to 1.33, whereas UP had a bias of -0.98 and 95% LoA of -7.35 to 5.40. The between-session repeatability of the instruments can be ranked as: (1) SOI; (2) OCT; (3) UP; (4) Orbscan pachymetry; and (5) CS. Of the optical methods, SOI had the best repeatability with a bias of 1.26 and 95% LoA of -6.14 to 8.66, followed by OCT with a bias of 0.75 and 95% LoA of -16.22 to 17.27. Of the 4 instruments that are commercially available, the UP was the most repeatable for within sessions, and the OCT was the most repeatable for between sessions.

The relationship between corneal biomechanical properties and intraocular pressure

AbstractPurpose To determine the relationship between the biomechanical properties and the intraocular pressure (IOP) measured with the Goldmann applanation Tonometer (GAT) and a noncontact tonometer (NCT). Repeatability of corneal biomechanical properties was also assessed.Methods One randomly selected eye of 106 healthy subjects was assessed using the Ocular Response Analyzer (ORA), a noncontact tonometer, an ultrasound pachymeter and the Goldmann tonometer, on two separate days. The order of measurement was randomized between the ORA and the NCT, followed by measurements of central corneal thickness (CCT) and IOP with the GAT. The main outcome measures were corneal hysteresis (CH), corneal resistance factor (CRF), central corneal thickness (CCT) &amp; IOP.Results The Pearson correlation coefficients between the GAT IOP on one hand and CH, CRF &amp; CCT on the other, respectively, were: 0.323(P &lt; 0.0001), 0.579 (p &lt; 0.0001), &amp; 0.421 (P &lt; 0.0001) in session 1. The corresponding values for the NCT were: 0.565 (P &lt; 0.0001), 0.772 (P &lt; 0.0001) &amp; 0.681 (P &lt; 0.0001) respectively. The highest correlation coefficients obtained (with both tonometers) when IOP was plot against ‘CCT + CRF’, were: 0.562 (P&lt;0.001) and 0.788 (P&lt;0.0001), for the GAT and the NCT, respectively in session 1. Repeatability indices in the first session were ±2.91mmHg, ±2.51mmHg, and ±0.01μm, respectively, for CH, CRF, &amp; CCT. Reproducibility indices were ±3.11mmHg, ±2.78mmHg and ±0.03μm for CH, CRF and CCT, respectively.Conclusion CH, CRF, and CCT are all significantly correlated with IOP, more so when the IOP is measured with a NCT. When plot together, CCT &amp;CRF were best able to explain the variation of IOP. All three corneal biomechanical properties showed good repeatability and reproducibility indices.

Evaluation of the corneal pachymetry and biomechanical parameters changes in patients treated by prostaglandins topical medication

AbstractPurpose To assess the possible corneal changes after topical prostoglandins treatment.Methods Prospective study including 15 patients newly diagnosed with OHT or POAG needed to be treated. The patients had complete basic ophthalmological examination before treatment (D0). IOP was measured with Goldmann aplanation tonometer, Pascal contour tonometry and ocular response analysis (ORA). The corneal biomechanical parameters, CRF and CH were measured as well with ORA. Axiale length and the anterior chamber depth were measured using IOL master. The pachymetry was performed using an ultrasound pachymeter. These examinations were repeated on D42 and D90. Anova test for repeated measurements was used for statistical analysisResults The mean CCT was 552.6 ± 30 µ on D0, 548.8 ± 32 µ on D42 and 542.6 ± 31µ on D90. There was a significant difference between the CCT measurements on D0 and D90 (p= 0.006). The mean CRF on D0, D42 and D90 was: 11.8 ± 2.3 mmHg, 10.6 ± 1.7 mmHg and 10.7 ± 1.8 mmHg respectively. There were no significant differences between these values. The mean CH on D0, D42 and D90 was: 8.8 ± 2.1 mmHg, 9.6 ± 1.6 mmHg and 10 ± 2 mmHg respectively. There were no significant differences between these values.Conclusion In this study we found a significant decrease of CCT after topical prostaglandins treatment. We didn’t find any significant change in corneal biomechanic parameters after treatment.

Correlation of central and peripheral corneal thickness in healthy corneas

To study the thickness profile of the normal cornea in order to establish any correlation between central and peripheral points. Sixty-seven eyes of 40 patients were subjected to central corneal thickness measurement (CCT) with an ultrasound pachymeter (UP) and corneal thickness mapping with the Oculus Pentacam. The corneal apex thickness (CAT), pupil centre thickness (recorded as CCT and corresponded to CCT of UP) and thickness at the thinnest location (CTL) were obtained and compared with each other. Corneal thickness data at 3 mm and 7 mm temporally, nasally, superiorly and inferiorly from the corneal apex were obtained. The mean corneal thickness values along the 2, 4, 6, 8 and 10 mm diameter concentric circles, with the CTL as the centre, were also obtained. The above data at different points were statistically correlated. There was no significant difference between CCT readings measured by UP and Pentacam (P=0.721). There was high positive correlation between the CAT values and the thickness at 3 mm (R≥0.845, P<0.001) and at 7 mm points (R≥0.654, P<0.001). A gradual increase in thickness was noted from the centre to the periphery with a high positive correlation between the CTL values and the mean thickness at the circles of 2, 4, 6, 8 and 10 mm (R≥0.635, P<0.001). The results suggest that central corneal thickness can serve as a good guide for predicting peripheral thickness. For surgical procedures specifically undertaken at mid-peripheral and peripheral zones, the actual measurements at the site of surgery may confer some advantage.

Comparison of intraoperative subtraction pachymetry and postoperative anterior segment optical coherence tomography of laser in situ keratomileusis flaps

To prospectively compare intraoperative subtraction pachymetry flap thickness measurements and postoperative anterior segment optical coherence tomography (AS-OCT) flap thickness measurements in eyes that had laser in situ keratomileusis (LASIK) flap creation with a femtosecond laser or a mechanical microkeratome. Stanford Eye Laser Center, Stanford University School of Medicine, Stanford, California, USA. Comparative case series. Each patient received wavefront-guided LASIK using an Intralase femtosecond laser in 1 eye and a Hansatome mechanical microkeratome in the fellow eye. Flap morphology was assessed with an ultrasound pachymeter intraoperatively and an AS-OCT system postoperatively at 1 year. Thirty-six eyes (18 patients) were enrolled. Intraoperative subtraction pachymetry consistently underestimated mechanical microkeratome flap thickness compared with postoperative AS-OCT (P<.001). There was no significant difference between intraoperative subtraction pachymetry and postoperative AS-OCT measurements for femtosecond flaps (P=.38). The overall mean variation in flap thickness (ie, mean deviation from targeted flap thickness) was 2.6μm (range 3 to 11 μm) with the femtosecond laser and 14.2 μm (range 17 to 52 μm) with the mechanical microkeratome (P<.001). Postoperative AS-OCT measurements showed femtosecond flaps had a planar configuration and mechanical microkeratome flaps had a meniscus-shaped configuration. The femtosecond laser created more uniformly planar flaps than the mechanical microkeratome as measured by intraoperative subtraction pachymetry and postoperative AS-OCT. Postoperative AS-OCT measurements varied less than intraoperative subtraction pachymetry measurements for mechanical microkeratome flaps. Neither author has a financial or proprietary interest in any material or method mentioned.

Transient Corneal Thinning in Eyes Undergoing Corneal Cross-Linking

To report the corneal thinning during and after corneal cross-linking (CXL). Prospective, nonrandomized, single-center observational study. Thirty patients (30 eyes; 9 female, 21 male; age, 38 ± 12 years) were consecutively scheduled for CXL between January 23 and July 6, 2009. Twenty-four eyes had progressive keratoconus, 2 had pellucid marginal degeneration, 3 eyes had progressive keratectasia after a LASIK operation, and 1 eye had pseudophakic bullous keratopathy. Riboflavin-ultraviolet A (UVA)-induced CXL included the instillation of 0.1% riboflavin drops for 30 minutes followed by riboflavin instillation combined with UVA irradiation for another 30 minutes. Corneal thickness was measured preoperatively, during CXL, and after 1 and 6 months using an ultrasound pachymeter. Changes in the endothelial cell count, corneal steepness, refraction, and visual performance are also given. On average, the corneas thinned 87 ± 40 μm (range, 37-206 μm; 19% ± 7%) during a 60-minute CXL treatment. In 1 patient, the cornea did not swell, even with hypotonic solution such that CXL would be safe. After 1 month, the corneal thickness was lower than the preoperative thickness, but after 6 months, the corneas had regained their original thicknesses. The endothelial cell count and corneal steepness were unchanged after CXL. The UCVA (uncorrected visual acuity) and BSCVA (best spectacle-corrected visual acuity) were improved 6 months after CXL. Corneal thickness decreases significantly during CXL, even to a level where the health of the endothelium and cornea is jeopardized. Visual performance is improved 6 months after CXL.

Relationship of Age and Refraction to Central Corneal Thickness

To obtain descriptive statistics of central corneal thickness (CCT) in a large population of normal eyes undergoing refractive surgery and study the relationship of 2 variables, age and refraction, with CCT. Cornea and Laser Eye Institute, Hersh Vision Group, Teaneck, NJ. The CCT of 5158 patients was measured using an ultrasound pachymeter. Age and preoperative spherical equivalent were recorded for all patients. The entire population and subgroups stratified to age and spherical equivalent were analyzed. Mean CCT was 544 μm with an SD of 34 μm and a range of 415-695 μm. CCT did not correlate with either age (r = 0.00645) or refraction (r = 0.00072). This study defines the CCT in a large population of patients undergoing refractive surgery. In this population, age and refraction did not affect CCT.

Reliability of the Corneal Thickness Measurements With the Pentacam HR Imaging System and Ultrasound Pachymetry

To obtain the central corneal thickness (CCT) of healthy eyes using the rotating Scheimpflug imaging system and compare these results with conventional ultrasound pachymetry values. Interoperator reliability and repeatability of the different techniques were also determined. CCT was measured on the right eye of 46 healthy subjects with the Pentacam HR (Pentacam High Resolution; Oculus, Wetzlar, Germany) and contact ultrasound pachymetry (AL-2000; Tomey, Tennenlohe, Germany) by 2 independent investigators. Both observers obtained significantly higher CCT readings with the Pentacam HR imaging system (572 ± 33 and 575 ± 31 μm) than with the ultrasound device (546 ± 27 and 548 ± 28 μm) (P < 0.0001, paired Student t test). Strong and significant correlation was found between the 2 pachymetry techniques regardless of the investigator (r = 0.845 and 0.831, Spearman correlation coefficient) (P < 0.0001). For the Pentacam HR values, statistically significant difference was detected between the observers (P = 0.033). For both pachymetry methods, the degree of agreement between the investigators was reflected by the high interoperator intraclass correlation coefficient value (ICC = 0.96). No significant difference was disclosed between the 3 consecutive readings of either instrument (P > 0.05, analysis of variance). Significant difference in CCT values between the high-resolution Pentacam imaging system and the ultrasound pachymeter suggests that the 2 techniques cannot be used interchangeably in clinical practice.