Central Corneal Thickness: Ultrasound Pachymetry Verus Anterior Segment Optical Coherence Tomography

Purpose: To determine the mean difference in central corneal thickness between ultrasound pachymetry and anterior segment optical coherence tomography in patients visiting tertiary care hospital of Karachi Study design: Cross sectional study Place and Duration of Study: Department of Ophthalmology, Liaquat National Hospital, Karachi from 27th December 2018 to 26th June 2019. Methods: Total 216 eyes of 108 patients were divided into two groups. Central corneal thickness was measured using ultrasound pachymeters in group A and with anterior segment optical coherence tomography in group B. Data was collected and analyzed using SPSS version 21. Mean central corneal thickness was compared between the two methods. Stratification was done on gender, age and post-stratification independent sample t-test was applied for mean difference CCT and P-value ? 0.05 was taken as significant. Results: Total 108 patients were equally divided into two groups. Mean age was 48.70±7.82 years in group A and 50.66±6.88 years in group B. In group A, there were 74.1% males and 25.9% females while in group B, there were 75.9% males and 24.1% females. There was statistically significant difference between the mean central corneal thickness of group A and group B for right and left eyes (p<0.001). Mean difference was also compared for gender and age groups. We found statistically significant differences in central corneal thickness in between the two methods in both age groups (?45 years and > 45 years). Conclusion: Central corneal thickness was more with pachymeters as compared to the AS-OCT (p value < 0.05) Key Words: Central Corneal Thickness, Anterior Segment Optical Coherence Tomography, Ultrasound Pachymetry.

Comparison of Central Corneal Thickness Measured by Tono-pachymetry and Ultrasound Pachymetry

Purpose: We compared the accuracy of central corneal thickness (CCT) measurements according to CCT measured by noncontact Tono-pachymetry and ultrasound pachymetry (USP). Methods: CCT was measured in 90 eyes of 90 subjects by two optometrists. The CCT measurements were compared and the correlations between the measurements were analyzed. To evaluate whether the measurements varied depending on CCT, the subjects were classified into three groups according to CCT (group 1: thin thickness group; group 2: medium thickness group; and group 3: thick thickness group). The differences in CCT obtained by the two devices (△CCT = Tono-pachymetry-USP) were compared and analyzed among the three groups. Results: The average CCT measurements by Tono-pachymetry and USP were 523.26 ± 32.93 μm and 527.08 ± 37.33 μm, respectively. CCT by Tono-pachymetry was significantly thinner than by USP (△CCT= -3.82 ± 15.34, p = 0.020). The two measurements were strongly correlated (r = 0.912, p < 0.001). The △CCT values were 5.40 ± 12.13 μm in group 1, -6.37 ± 15.07 μm in group 2, and -10.50 ± 14.39 μm in group 3 (p < 0.001). Conclusions: CCT measured by tono-pachymetry was thinner on average compared to the value measured by USP and the differences in measurements between the two devices were different according to CCT. The thinner the CCT, the thicker the measurement, and the thicker the CCT, the thinner the measurement. Therefore, this trend should be considered when interpreting tono- pachymetry results in clinical practice.

Central corneal thickness measurements in phakic, pseudophakic, and aphakic children with ultrasound pachymetry and different non-contact devices

Aims: Evidence for choosing a satisfactory device for central corneal thickness (CCT) measurement in children particularly pseudophakic and aphakic ones is insufficient. The aim of this study is to compare four differently-measured CCTs obtained using ultrasound pachymetry (UP), Pentacam, partial coherence interferometry (PCI), and specular microscopy (SM) in phakic, pseudophakic, and aphakic children and assess the agreement between the six pairs of the methods. Methods: Children with history of cataract surgery at age six or younger and phakic children were recruited into this study. CCT was measured using UP (Optikon 2000, Rome, Italy), Pentacam (Oculus Inc, Wetzlar, Germany), PCI (IOLMaster 700, Carl Zeiss Meditec AG, Jena, Germany), and SM (Topcon SP-3000P; Topcon Corporation, Japan).Results: One-hundred two eyes (53 phakic, 29 pseudophakic, and 20 aphakic eyes) were included. The mean ages (±SD) of phakic, pseudophakic, and aphakic cases were 9.75 (±3.3), 9.9 (±2.3), and 8.2 (±2.8) years respectively. The mean CCTs (±SE) for phakic children using Pentacam, PCI, UP, and SM were 549.7 (±5.0), 546.5 (±4.5), 565.9 (±5.5), and 506.2 (±4.4) mm respectively, for pseudophakic cases were 570.1 (±6.4), 565.0 (±6.1), 571.9 (±6.3), and 524.3 (±6.3) mm respectively, and for aphakic participants were 635.3 (±14.2), 635.4 (±14.5), 649.0 (±13.5), and 589.1 (±13.3) mm respectively. Conclusion: Compared to Pentacam and PCI, SM underestimated CCT particularly in phakic and pseudophakic children, whereas UP slightly overestimated CCT especially in phakic and aphakic children. Furthermore, Pentacam and PCI had the closest agreement. By contrast, SM had the poorest agreement with the other three methods.

Sirius Scheimpflug–Placido versus ultrasound pachymetry for central corneal thickness: meta-analysis

Background To compare the difference in central corneal thickness (CCT) measurements in normal eyes between a rotating Scheimpflug camera combined with a Placido-disk corneal topographer (Sirius, CSO, Italy) and ultrasound pachymetry (USP). Methods A systematic literature search was conducted for relevant studies published on PubMed, Medline, EMBASE, and the Cochrane Library and ClinicalTrials.gov from inception to August 1st, 2019. Primary outcome measures were CCT measurements between Sirius and USP. A random effects model was used to pool CCT measurements. Results A total of twelve studies involving 862 eyes were included in this meta-analysis. The meta-analysis found CCT measurements between Sirius and USP to be statistically significantly different (P < 0.0001). The mean difference between Sirius and USP was −11.26 μm with a 95% confidence interval (CI) (−16.92 μm, −5.60 μm). The heterogeneity was I2 = 60% (P = 0.004). Conclusion CCT measurements with the Sirius Scheimpflug-Placido topographer were statistically significantly lower than USP. However, it may be argued that the mean difference of 11.26 μm is not a clinically significant difference.

Comparison of Central Corneal Thickness Measurements between Angiovue Optical Coherence Tomography, Ultrasound Pachymetry and Ocular Biometry

Purpose: To compare central corneal thickness (CCT) measurements and their reproducibility when taken by Ultrasound Pachymetry, Ocular Biometry and Angiovue Optical Coherence Tomography (OCT). Methods: Twenty-five healthy volunteers were recruited creating a sample size of 50 eyes. All subjects had pachymetric measurements by Ultrasound pachymetry (PachPen Handheld Pachymeter, Keeler Instruments Inc), Ocular biometry (IOL Master 700 Swept Source Biometry, Zeiss) and Angiovue Optical Coherence Tomography (Optovue Avanti RTVue XR Angiovue). The measurements of central corneal thickness for the three devices were taken by the same examiner twice for more accuracy. Results: The average measurements of central corneal thickness by Ultrasound pachymetry (PachPen Handheld Pachymeter, Keeler Instruments Inc), Ocular biometry (IOL Master 700 Swept Source Biometry, Zeiss) and Angiovue Optical Coherence Tomography (Optovue Avanti RTVue XR Angiovue) were 547.26 μm, 551.36 μm, and 536.42 μm, respectively. The mean standard deviation (SD) of repeated measurements by Ocular biometry was 48.87 μm, which was greater than the mean SD of 44.24 μm and 40.35 μm (P < 0.001) by ultrasound pachymetry and Angiovue optical coherence tomography, respectively. There were statistically significant differences in the measurement results among the 3 methods (Ultrasound pachymetry vs. Ocular biometry P = 0.019; Ultrasound pachymetry vs. Angiovue Optical Coherence Tomography; P < 0.001; Ocular biometry vs. Angiovue Optical Coherence Tomography P < 0.001). There was a significant linear correlation between the Ultrasound pachymetry and Ocular biometry (r = 0.945, P<0.001), Ultrasound pachymetry and Angiovue Optical Coherence Tomography (r = 0.895, P<0.001), and Ocular biometry and Angiovue Optical Coherence Tomography (r = 0.902, P<0.001). Conclusion: Central corneal thickness readings were comparable between PachPen Handheld Pachymeter, IOL Master 700 Biometry and Angiovue Optical Coherence Tomography; Angiovue optical coherence tomography gave significantly smaller values. The measurements of the 3 methods showed significant linear correlations with one another. All methods provided acceptable repeatability of measurements.