Assessment of Central Corneal Thickness Using OCT, Ultrasound, Optical Low Coherence Reflectometry and Scheimpflug Pachymetry

Comparison of central corneal thickness measurements using three different imaging devices

PURPOSE

The purpose of this study was to compare central corneal thickness (CCT) values and evaluate the agreement obtained with three different devices in healthy eyes.

METHODS

A total of 120 eyes of 60 healthy individuals (36 men and 24 women) were enrolled in this retrospective study. CCT measurements were performed using an optical biometer (AL-Scan), spectral-domain optical coherence tomography (SD-OCT) (Topcon 3D) and ultrasonic pachymetry (UP) (Accupach VI), and the results were compared. Bland-Altman analysis was used to quantify the agreement between methods.

MAIN RESULTS

The mean patient age was 28±5.73years (18-40years). The mean CCT values obtained by AL-Scan, UP, and SD-OCT were 532.4μm±29.7, 549μm±30.4, and 547μm±30.6, respectively. The mean differences in CCT were 15.30±9.52μm between AL-Scan and OCT (P<0.01), 17.15±8.42μm between AL-Scan and UP (P<0.01), and 1.85± 8.78μm between UP and OCT (P=0.067). All three methods of CCT measurement were closely correlated with each other.

CONCLUSION

The present study results suggest that, despite good agreement between the three devices, AL-Scan significantly underestimated CCT compared to UP and OCT. Therefore, clinicians should be aware that different results can be obtained using different devices for CCT measurements. It would be a better approach not to use them as interchangeable in clinical practice. CCT examination and follow-up should be performed using the same device, especially for patients who will undergo refractive surgery.

Central corneal thickness and its associations in a Russian population. The Ural eye and Medical Study

BACKGROUND

To assess central corneal thickness (CCT) and its associations in a Russian population.

METHODS

The population-based Ural Eye and Medical Study included 5899 (80.5%) out of 7328 eligible individuals. As part of an ophthalmological and general examination, CCT was measured by Scheimflug imaging.

RESULTS

The study included 5792 (98.2%) participants (age:58.8 ± 10.6 years;range: 40-94 years) with available bilateral CCT measurements. Mean CCT was larger in Russians than non-Russians (549.5 ± 32.8 µm versus 539.2 ± 33.9 µm; P < 0.001). In multivariable analysis, thicker CCT was associated (regression coefficient r:0.43) with younger age (standardized regression coefficient beta:-0.09; non-standardized regression coefficient B:-0.29;95% confidence interval (CI):-0.39,-0.20; P < 0.001), male sex (beta:0.05; B:3.10; 95%CI:1.18,5.03; P = 0.002), urban region of habitation (beta:0.10; B:6.83; 95%CI:4.61, 9.05; P < 0.001), Russian ethnicity (beta:0.04; B:3.48; 95%CI:1.04, 5.91; P = 0.005), higher level of education (beta:0.04; B:0.97;95%CI:0.29,1.66; P = 0.006), higher serum bilirubin concentration (beta:0.05;B:0.15; 95%CI:0.07,0.23;P < 0.001), lower corneal refractive power (beta:-0.09;B:11.92; 95%CI:-2.50,-1.35; P < 0.001), smaller anterior chamber angle (beta:-0.07;B:-0.38;95%CI:-0.52,-0.24;P < 0.001), higher IOP readings (beta:0.38; B:3.47; 95%CI:3.21,3.73; P < 0.001), and higher rise in IOP readings by medical mydriasis (beta:0.07; B:0.88;95%CI:0.54,1.22;P < 0.001). In that model, CCT was not associated with body height (P = 0.14), previous cataract surgery (P = 0.10), axial length (P = 0.18) or prevalence of glaucoma (P = 0.11). The mean inter-eye difference in CCT was 8.52 ± 13.9 µm (median:6.0;95CI:8.16,8.88). A higher inter-eye CCT difference was associated with older age (beta:0.08; B:0.11;95%CI:0.07,0.15; P = 0.01), lower level of education (beta:-0.04;B:-0.34; 95%CI:-0.60,-0.08; P < 0.001) and status after cataract surgery (beta:0.04; B:2.92;95%CI:1.02,4.83; P = 0.003).

INTRODUCTION CONCLUSIONS

In this ethnically mixed population from Russia with an age of 40+ years, mean CCT (541.7 ± 33.7 µm) was associated with parameters such as younger age, male sex, Russian ethnicity, and higher educational level. These associations may be taken into account when the dependence of IOP readings on CCT are considered. Glaucoma prevalence was unrelated to CCT.

Comparison of central corneal thickness measurements obtained by OrbscanIIz® and ultrasound pachymetry: A concordance study in the usual clinical practice

PURPOSE

The objective of this study was to assess the concordance between the values obtained in measuring central corneal thickness using the OrbscanIIz^® and the contact ultrasonic pachymeter available in our public ophthalmology service.

METHODS

Measurements were taken from 88 eyes of 44 patients using the two instruments. The data obtained were statistically analyzed using version 22 of the IBM SPSS^® program.

RESULTS

The mean of central corneal thickness measurements obtained from OrbscanIIz^® was significantly higher than that obtained from ultrasound pachymetry. However, the mean of differences between both instruments was only 7.22 μ, which could be considered a clinically insignificant result when considering the good concordance obtained between both systems.

CONCLUSION

OrbscanIIz^® and ultrasound pachymetry can be interchangeable in the usual public clinical practice when measuring central corneal thickness. This is the first research found in the literature that uses a concordance study to compare the data resulting from central corneal thickness measurements obtained by an OrbscanIIz^® and an OcuScan^® pachymeter in our environment.

Reproducibility, Repeatability, and Correlation of Central Corneal Thickness Measurement with the Pentacam Scheimpflug System and Ultrasound Pachymetry

BACKGROUND/AIM

The importance of an accurate determination of central corneal thickness (CCT) relies on its diagnostic and therapeutic implications in glaucoma, corneal ectasias, corneal edema and endothelial function monitoring, and refractive surgery suitability, among others. We aimed to analyze the repeatability, reproducibility, correlation, and laterality variations of CCT measurements performed with the Pentacam HR and the standard of care ultrasound A-scan (USP).

METHODS

A cross-sectional study including CCT measurements of healthy individuals was performed by three independent examiners with the Pentacam HR and USP. Intra-observer and inter-observer variations were calculated with intra-class correlation coefficients (ICCs). Bland-Altman plots and 95% limits of agreement (95% LoA) were used to assess the agreement between devices. Linear correlation was calculated with Pearson's coefficient.

RESULTS

Thirty individuals (60 eyes), including 10 (33.3%) men and 20 (66.6%) women, with a mean age of 30.0 ± 9.1 years, were studied. No statistical differences were found in CCT measurements between Pentacam HR (range 500 - 609 µm) and USP (range 498 - 628 µm). There was a high degree of correlation in repeatability and reproducibility of each independent device (ICC > 0.90). Pearson's correlation between 1 vs. 2, 2 vs. 3, and 3 vs. 1 Pentacam HR attempts were 0.914, 0.958, and 0.925, respectively (p < 0.001). Corresponding results for USP were 0.957, 0.957, and 0.943 (p < 0.001). The Pentacam HR tended to overestimate CCT by a mean difference of 3.77 µm (95% LoA, - 24.9 - 18.4). Right eyes were also overestimated (- 3.6 ± 14.1 µm) with the Pentacam HR device, whereas left eyes were underestimated (1.3 ± 11.1 µm).

CONCLUSIONS

The Pentacam HR device provides reliable operator-independent estimates of CCT. Right eyes exhibited a tendency to overestimate with the Pentacam HR. We suspect this difference is due to USP underestimation related to patients' position while performing the study. In clinically relevant scenarios, performing a third measurement and cautiously measuring right eyes can provide higher accuracy.

Comparison of central corneal thickness measurements with three different optical devices

Purpose:

The purpose of this study was to compare and evaluate the agreement of central corneal thickness (CCT) values obtained with three different devices working according to optical principle in healthy eyes.

Methods:

60 eyes of 60 individuals (30 men and 30 women) were enrolled in this study. CCT measurements performed with Scheimpflug–Placido topographer (Sirius), spectral-domain optical coherence tomography (RTVue) with an anterior segment module, and optical biometer (AL-Scan) were compared. Bland–Altman analysis was used to demonstrate agreement between methods.

Results:

The mean age was 30.07 ± 7.313 years (range, 18–47 years). The mean CCT values obtained by RTVue, Sirius, and AL-Scan were 518.25 ± 36.38 µm, 526.08 ± 36.33 µm, and 513.50 ± 39.09 µm, respectively. The mean differences in CCT were 7.83 ± 14.15 µm between Sirius and RTVue, 12.58 ± 11.87 µm between Sirius and AL-Scan, and 4.75 ± 4.50 µm between RTVue and AL-Scan. The mean CCT was statistically different among the three groups (p < 0.05). All three modalities of CCT measurements correlated closely with each other, with Pearson’s correlation coefficients ranging from 0.924 to 0.961. The 95% limits of agreement were −19.90 to 35.56 µm between Sirius and RTVue, −10.69 to 35.85 µm between Sirius and AL-Scan, and −4.07 to 13.58 µm between RTVue and AL-Scan.

Conclusion:

Different results could be obtained through different noncontact devices in CCT measurements. Although the measurement values obtained by these devices show a high level of correlation, it would be a more correct approach to not use them directly interchangeably in clinical practice. Evaluation and follow-up of CCT should be performed using the same device.

Comparison of central corneal thickness and intraocular pressure measured with two different tono/pachymeter devices in non-glaucomatouse children

PURPOSE

The goal of this research is to compare the intraocular pressure (IOP) and the mean central corneal thickness (CCT) values obtained from the measurements with Nidek NT-530P and Canon TX-20P devices with the values obtained by ultrasound pachymetry (UP) and Goldmann applanation tonometry (GAT) in children.

METHODS

This prospective study was conducted with 119 healthy children. The measurements were repeated three times for each eye. The intraclass correlation coefficient (ICC) was used to assess the correlation between the measurements obtained from different devices. The Bland-Altman plot was used to analyze the agreement between two different devices graphically. The measurements were taken in the same order in all subjects: TX-20P, NT-530P, UP, and GAT.

RESULTS

The mean age of the children was 10.1 ± 3.2 (6-17) years. The mean CCT values for the eyes were 568.90 and 569.68 (TX-20P), 571.44 and 566.37 (NT-530P), 564.77 and 564.67 μm UP, (right and left, respectively). The highest correspondence observed for CCT was between UP and NT-530P devices (ICC, 0.982, the left eye). The mean IOP measurements for Canon TX-20P, NT-530P, and GAT were 16.5 ± 3.2, 16.3 ± 3.2, and 16.8 ± 3.6 mmHg for the right eyes, respectively, while those for the left eyes were 16.6 ± 3.1, 16.2 ± 3.3, and 16.8 ± 3.7 mmHg. The highest correspondence was noted between measurements obtained using GAT and Nidek NT-530P devices (ICC, 0.945, in the left eye).

CONCLUSION

Tono/pachymetry devices in the healthy children are provides significant agreements with the gold standard methods for IOP and CCT measurements.Clinical Trial Registration number: 2016-94.

Repeatability and reproducibility of post-mortem central corneal thickness measurements using a portable optical coherence tomography system in humans: a prospective multicenter study

To assess the repeatability and reproducibility of post-mortem central corneal thickness (CCT) measurements made by the portable iVue spectra-domain (SD) optical coherence tomography OCT (Optovue Inc, Fremont, CA) system in humans, and to prospectively establish the time-course of CCT after death. In a prospective multicenter setting, CCT measurements were obtained from 58 human eyes at the following 16 time-points after death: immediately (within 2 h), and at each hour by the next 17 h. The range of CCT values for each subject was determined and longitudinal data were used to illustrate the variation in open and close eye mode. All measurements were made by two independent and well-trained examiners for session. Main outcome measures were intraclass correlation coefficients (ICC), repeatability and reproducibility coefficients, and coefficients of variation of the average central (0–2 mm). Overall, a total of 5,568 OCT measurements were performed by examiners. The repeatability coefficient varied from 0.3 to 1.7% and the reproducibility coefficient varied from 0.3 to 1.6% throughout the entire experimental time frame. Furthermore, the values of the different ICCs were also high during the different postmortem intervals, thus demonstrating the excellent repeatability and reproducibility of the present OCT approach. When CCT measurements were analyzed longitudinally, corneal thickness showed different behavior based on the open or close eye mode. The present study demonstrates that portable OCT imaging can be reliably used for corneal pachymetric measurements in supine subjects and during the post mortem period, i.e. without visual fixation and normal physiology/architecture of examined tissues.

Agreement of Central Corneal Thickness Measurements between Scheimpflug Photography and Optical Low-Coherence Reflectometry in Children

PURPOSE

Central corneal thickness (CCT) is a key indicator of the corneal health status and is therefore of clinical importance. The aim of the present study was to determine the agreement between Scheimpflug photography (SP) and optical low-coherence reflectometry (OLCR) systems in measuring the CCT in children.

METHODS

In this cross-sectional study, the samples were selected from Shahroud schoolchildren using cluster sampling. The samples then underwent optometric examinations, including the measurement of visual acuity and refraction. CCT measurements were done by the SP and OLCR systems between 8 am and 4 pm. To evaluate the agreement between these devices, 95% limits of agreement (LoA) and interclass correlation coefficient (ICC) were reported.

RESULTS

After applying the exclusion criteria, 4890 right eyes (53.2% male) were analyzed. The mean age of the students was 9.22 ± 1.72 years (range: 6-12 years). The mean CCT by the SP and OLCR systems was 555.30 ± 34.15 and 550.23 ± 35.11 µm, respectively. The 95% LoA between the two devices was -19.81 to 9.66 µm, and the ICC was 0.983. The CCT difference between the SP and OLCR systems was 5.61 µm in boys and 3.36 µm in girls. The CCT difference between the two devices was 6.41 µm in 6-year-old and 3.54 µm in 12-year-old children. The 95% LoA was -17.96 to 9.58 µm and -18.89 to 8.47 µm and the ICC was 0.987 and 0.984 in myopic and hyperopic subjects, respectively.

CONCLUSION

The results of this study showed a high agreement between OLCR and SP measurements of CCT in children.

Comparison of central corneal thickness measurements using different imaging devices and ultrasound pachymetry

Purpose:

To compare central corneal thickness (CCT) measurements obtained by the AL-Scan, Lenstar LS900, Galilei, and ultrasound pachymetry (UP) in normal and cataractous eyes.

Methods:

Eighty eyes of healthy subjects were included in the study. Each subject was assessed by four different methods of measurements using the AL-Scan, Lenstar LS900, Galilei, and UP by a single examiner. To assess the intraobserver repeatability, three consecutive measurements were taken for the AL-Scan.

Results:

The mean CCT [± standard deviation (SD)] for the AL-Scan, Lenstar LS900, Galilei, and UP were 554.6 ± 30.9 μm, 542.9 ± 31.3 μm, 570.7 ± 30 μm, and 552.7 ± 32.8 μm, respectively. The differences between pairs of mean CCT for the methods are statistically significant for the pairs of Galilei–UP, AL-Scan–Galilei, and Lenstar LS900–Galilei. Bland–Altman plots showed that AL-Scan–UP have the closest agreement, followed by Lenstar–UP and AL-Scan–Lenstar. Galilei was found to have the poorest agreement with the other three methods. The intraobserver repeatability of the AL-Scan was very good with an intraclass correlation coefficient (ICC) of 0.980.

Conclusion:

We found that CCT measurements between the AL-Scan–UP, Lenstar LS900–UP, and AL-Scan–Lenstar LS900 showed very strong correlation and comparable agreement. AL-Scan–UP showed the closest agreement and these devices can be used interchangeably in clinical practice. Galilei significantly showed higher value of CCT compared to other methods. It was also observed that the Al-Scan had excellent intraobserver repeatability.

Central corneal thickness measurement using ultrasonic pachymeter, optical coherence tomography, and TMS-5 topographer

AIM:

This study aimed to compare the central corneal thickness (CCT) measurements using Optical Coherence Tomography (OCT) and TMS-5 topographer with that taken with the gold standard digital Ultrasonic pachymeter (USP).

MATERIALS AND METHODS:

A total of 61 subjects (122 eyes) were prospectively and consecutively studied in a period from June 2016 to June 2017 at Sudan Eye Centre (SEC), Khartoum, Sudan. Besides the visual and refractive data, measurements of CCT were taken using OCT, TMS-5 and USP. Data analyzed using SPSS software for windows (IBM SPSS 20, IBM Corp., Armonk, NY).

RESULTS:

A statistically significant differences in mean CCT was detected between the three instruments (P < 0.001). USP was found to measure the CCT 29μm thicker than OCT and 22μm thicker than TMS-5 topographer. A significant difference was also found between OCT and TMS-5. OCT found to give the lower values of CCT compared to both USP and TMS-5 topographer. Further analysis showed that the three procedures were significantly and strongly correlated to each other (USP vs OCT, r = 0.77), (USP vs TMS-5, r = 0.78) and (OCT vs TMS-5, r = 0.80).

CONCLUSION:

Mean central corneal thicknesses (CCT) were comparable among OCT, TMS-5 topographer and the gold standard USP. However, there is a reproducible systematic difference between CCT measurements taken with the three devices. It is important to note in clinical practice, that measurements acquired by these three modalities are not directly interchangeable.

Agreement and repeatability of central corneal thickness measurements by four different optical devices and an ultrasound pachymeter

PURPOSE

To compare the repeatability and agreement of central corneal thickness (CCT) measurements by spectral-domain optical coherence tomography (OCT), corneal topography (CT) with a combined Scheimpflug-Placido system, optical biometry (OB), specular microscopy (SM), and ultrasound pachymetry (UP).

METHODS

A single observer measured CCT twice in 150 eyes of 150 subjects with each of five devices: Nidek RS-3000 Advance OCT, CSO Sirius combined Scheimpflug-Placido disc system CT, Nidek AL-Scan partial coherence interferometry-based OB, Tomey EM-3000 SM, and Reichert iPac ultrasonic pachymeter. Pachymetry values corrected by the SM device software were also recorded. Levels of agreement between devices were evaluated by Bland-Altman plots with 95% limits of agreement, and repeatability for each device was analysed with intraclass correlation coefficients.

RESULTS

The mean CCTs measured by OCT, CT, OB, SM, corrected SM, and UP were 544.60 ± 29.56, 536.19 ± 32.14, 528.29 ± 29.45, 524.88 ± 32.38, 537.88 ± 32.38, and 545.29 ± 30.75 μm, respectively. Mean CCT differed significantly between the devices (p < 0.05) apart from between OCT and UP, and between CT and corrected SM. Mean paired differences between devices ranged between 0.68 and 20.41 μm. Repeatability with all devices was excellent (> 0.99). The range of limits of agreement was the least between OCT and UP.

CONCLUSIONS

Different CCT measurement techniques produce quite different results, so CCT evaluation and follow-up should be performed using the same device or devices with close compatibility.

Accuracy of Cirrus HD-OCT and Topcon SP-3000P for measuring central corneal thickness

PURPOSE

To compare and analyze the interchangeability of three measuring systems, each based on a different technique, for central corneal thickness (CCT) analysis.

METHODS

CCT measurements were measured using optical coherence tomography (OCT), non-contact specular microscopy (NCSM), and ultrasonic pachymetry (USP) in 60 eyes of 60 healthy patients with a mean age of 66.5±15.0 years and a mean spherical equivalent of 0.43±1.14 D. Analysis of variations in measurement concordance and correlation among the three different methods were performed. Comparison of CCT measurements were done using Bland-Altman plots (with bias and 95% confidence intervals), intraclass correlation coefficient (ICC), and paired t-student analysis.

RESULTS

Mean CCT values were: 549.20±26.91μm for USP (range 503-618μm), 514.20±27.49μm for NCSM (range 456-586μm) and 542.80±25.56μm for OCT (range 486-605μm). CCT values obtained with NCMS were significantly lower than those obtained with OCT and USP methods. NCMS CCT value was 36.08±10.72μm lower than USP value (p<0.05), and NCMS CCT value was 7.88±8.86μm lower than OCT value (p<0.05). ICC between USP-NCSM pair was 0.488 and 0.909 between USP-OCT pair.

CONCLUSION

OCT and UPS offered highly comparable results, whereas NCSM offered lower mean CCT values compared to the other two methods. Therefore, NCSM should not be considered a reliable method for measuring CCT and should rather be considered for assessing longitudinal changes in the same patient.

Comparison of central corneal thickness with four noncontact devices: An agreement analysis of swept-source technology

Purpose:

The purpose of this study was to compare the central corneal thickness (CCT) measurements of four noncontact devices in healthy eyes.

Materials and Methods:

In a sample of 45 healthy controls, CCT was measured using an optical biometer (IOLMaster 700) based on swept-source optical coherence tomography (SS-OCT), high-resolution rotating Scheimpflug camera system (Pentacam HR), spectral-domain OCT (SD-OCT) device with an anterior segment module (Spectralis), and noncontact pachymetry (NCP) device (Topcon TRK-2P). Agreement among the devices was analyzed using mean differences (i.e., bias) and Bland–Altman analysis with 95% limits of agreement (LoA).

Results:

Mean CCT measurements were 537.5 ± 47.5 μm for SS-OCT optical biometer, 532.3 ± 43.8 μm for Scheimpflug system, 521.3 ± 44.7 μm for SD-OCT device, and 518.0 ± 43.1 μm for NCP (P < 0.001). The SD-OCT device and NCP showed the closest agreement, with a bias of 2.6 μm (95% LoA, −3.6–8.8 μm), whereas the SS-OCT optical biometer and NCP showed the least agreement, with a bias of 18.7 μm (95% LoA, −2.1–39.5 μm). Bias was 16.1 μm (95% LoA, −3.1–35.3 μm) for SS-OCT optical biometer and SD-OCT, 5.1 μm (95% LoA, −6.8–17.0 μm) for SS-OCT optical biometer and Scheimpflug system, 10.9 μm (95% LoA, −15.1–36.9 μm) for SD-OCT device and Scheimpflug system, and 13.6 μm (95% LoA, −5–32.2 μm) for Scheimpflug system and NCP.

Conclusions:

SS-OCT optical biometer overestimates CCT measurements compared to Scheimpflug system, SD-OCT device, and NCP. Given mean differences and range variations in CCT measurements between devices, SS-OCT optical biometer and Scheimpflug system are interchangeable as are SD-OCT and NCP.

Repeatability of Central Corneal Thickness Measurement Using Rotating Scheimpflug Camera in Dry and Normal Eyes

PURPOSE

To compare the repeatability of central corneal thickness (CCT) measurement using the Pentacam between dry eyes and healthy eyes, as well as to investigate the effect of artificial tears on CCT measurement.

METHODS

The corneal thicknesses of 34 patients with dry eye and 28 healthy subjects were measured using the Pentacam. One eye from each subject was assigned randomly to a repeatability test, wherein a single operator performed three successive CCT measurements time points-before and 5 min after instillation of one artificial teardrop. The repeatability of measurements was assessed using the coefficient of repeatability and the intraclass correlation coefficient.

RESULTS

The coefficient of repeatability values of the CCT measurements in dry and healthy eyes were 24.36 and 10.69 μm before instillation, and 16.85 and 9.72 μm after instillation, respectively. The intraclass correlation coefficient was higher in healthy eyes than that of in dry eyes (0.987 vs. 0.891), and it had improved significantly in dry eyes (0.948) after instillation of one artificial teardrop. The CCT measurement fluctuated in dry eyes (repeated-measures analysis of variance, P<0.001), whereas no significant changes were detected in healthy eyes, either before or after artificial tear instillation.

CONCLUSIONS

Central corneal thickness measurement is less repeatable in dry eyes than in healthy eyes. Artificial tears improve the repeatability of CCT measurements obtained using the Pentacam in dry eyes.

[Effect of donor graft characteristics on clinical outcomes in Descemet stripping automated endothelial keratoplasty (DSAEK)]

INTRODUCTION

The purpose of our study was to evaluate the progression of lamellar corneal grafts after endothelial keratoplasty by Descemet stripping automated endothelial keratoplasty (DSAEK) and the effect of their characteristics on the clinical and functional results.

MATERIALS AND METHODS

This was a prospective study in which 74 patients who had undergone endothelial keratoplasty by DSAEK were included. The corneal grafts were obtained from a French tissue bank and were delivered in a preservation medium containing a deturgescent agent (Corneajet^® or Stemalpha 3^®). Pachymetry of the corneal graft was measured ex vivo by ultrasonic pachymetry prior to dissection, then after the 1st or 2^nd cut as necessary. Corrected visual acuity in logMAR, total graft pachymetry, measured by anterior segment OCT (Spectralis^® HRA+SDOCT, Heidelberg engineering, Inc., Heidelberg, Germany) and corneal density (Pentacam^®, Oculus, Inc., Wetzlar, Germany) were obtained for each patient preoperatively, at D5, M1, M3, M6, M9 and M12.

RESULTS

Overall, 74 corneal grafts, from donors of mean age 69.7±13.3 years (37 to 92 years) were transplanted into 67 patients aged 70.3±12.1 years. Predissection pachymetry was statistically significantly thicker in the case of short deturgescence time (r=-0.383, P=0.001). For the same deturgescence time, predissection pachymetry was statistically significantly thicker in the Stemalpha 3^® medium (691±89μm for Corneajet^® vs. 760±100μm for Stemalpha 3^®, P=0.01), with the same final pachymetry (168±31μm vs. 166±25μm, P=0.833). Graft pachymetry and total corneal pachymetry decreased significantly between the preoperative measurement and M12 (168±29μm vs. 92±57μm, P=0.0008 et 665±124μm vs. 566±73μm, P=0.027 respectively). Preoperative endothelial cell density (2938±418 cells/mm²) did not correlate with postoperative visual acuity. There was a positive correlation between visual acuity at D5 and donor age (r=0.3, P=0.04). Postoperative visual acuity correlated positively with preoperative visual acuity (P<0.05). Corneal densitometry was statically higher than normal postoperative densitometry. Corneal density at M1 correlated positively with time since obtaining the donor tissue (r=0.373, P=0.043). There was no significant difference between the sub-groups of over or under 130μm. Seven patients experienced graft failure with no statistically significant graft risk factor.

DISCUSSION

The preservation medium affects predissection pachymetry with no consequence on clinical results. In our study, preoperative visual acuity and donor age were correlated with visual acuity after DSAEK.

CONCLUSION

Although donor age was associated with better visual acuity at D5, the other donor characteristics had no effect on clinical results.

Comparison of central corneal thickness: ultrasound pachymetry versus slit-lamp optical coherence tomography, specular microscopy, and Orbscan

Background

Central corneal thickness (CCT) can be measured by using contact and non-contact methods. Ultrasound pachymetry (US pachymetry) is a contact method for measuring CCT and is perhaps the most commonly used method. However, non-contact methods like scanning slit topography (Orbscan II), slit-lamp optical coherence tomography (SL-OCT), and specular microscopy are also used. Not many studies have correlated the measurement of CCT with all four modalities. The purpose of this study was to compare and correlate the CCT measurements obtained by US pachymetry with SL-OCT, specular microscopy, and Orbscan.

Method

This is a prospective, comparative study done in an institutional setting. Thirty-two eyes of 32 subjects with no known ocular disease and best-corrected visual acuity of 20/20 were enrolled. CCT measurements were obtained using SL-OCT, specular microscopy, scanning slit topography (Orbscan), and US pachymetry. Three measurements were made with each instrument by the same operator. Mean, standard deviation, and coefficient of variation were calculated for CCT measurements acquired by the four measurement devices. Bland–Altman plot was constructed to determine the agreements between the CCT measurements obtained by different equipment.

Results

The mean CCT was 548.16±48.68 μm by US pachymetry. In comparison, CCT averaged 546.36±44.17 μm by SL-OCT, 557.61±49.92 μm by specular microscopy, and 551.03±48.96 μm by Orbscan for all subjects. Measurements by the various modalities were strongly correlated. Correlations (r²) of CCT, as measured by US pachymetry compared with other modalities, were: SL-OCT (r²=0.98, P<0.0001), specular microscopy (r²=0.98, P<0.0001), and Orbscan (r²=0.96, P<0.0001). All modalities had a linear correlation with US pachymetry measurements.

Conclusion

In subjects with healthy corneas, SL-OCT, specular microscopy, and Orbscan (with correction factor) can be used interchangeably with US pachymetry in certain clinical settings. The four modalities showed significant linear correlations with one another.

Comparison of pachymetry measurements between the Alcon Wavelight EX500 and Sonogage Corneo-Gage plus platforms

PURPOSE

To compare the agreement of intraoperative central corneal thickness (CCT) measurements of the Wavelight EX500 (Alcon Laboratories, Fort Worth, TX) that uses optical low coherence reflectometry to the Corneo-Gage Plus ultrasound pachymetry device (Sonogage, Cleveland, OH).

METHODS

In this retrospective study, 50 eyes of 26 patients undergoing LASIK were evaluated. Following LASIK flap creation, each eye was measured by both optical low coherence reflectometry and ultrasound pachymetry immediately prior to flap lifting and then again after flap lifting.

RESULTS

The mean CCT value before lifting the flap was 556.9 and 557.78 µm as measured by ultrasound pachymetry and optical low coherence reflectometry, respectively. After lifting the flap, the mean ultrasound pachymetry value was 440.96 µm and the mean optical low coherence reflectometry value was 441.7 µm. A two-sample Kolmogorov-Smirnov test demonstrated that the ultrasound pachymetry and the optical low coherence reflectometry distribution of measurements were the same. A Shapiro-Wilk test of normality could not be rejected. Bland-Altman plots showed strong agreement. The correlation between the two tests was 0.98 before flap lifting and 0.97 after flap lifting, both with a 95% confidence interval.

CONCLUSIONS

The pachymetry measurements by the optical low coherence reflectometry correlated with those of the ultrasound pachymetry device. The Wavelight EX500 optical low coherence reflectometry may be used in place of the ultrasound pachymetry device for measuring CCT.

The effect of room illumination on the measurement of anterior segment parameters

OBJECTIVE

To evaluate the effect of room illumination on the measurement of anterior segment parameters.

METHODS

In this comparative study, measurements of anterior segment parameters of 25 eyes of 25 healthy patients were performed by optical low-coherence reflectometry (OLCR). Measurements were taken under photopic conditions (150 lux) and under mesopic conditions (3 lux). Paired t test by SPSS 16.0 was used to compare the anterior segment measurements performed in both conditions. A P value lower than 0.05 was accepted as statistically significant.

RESULTS

The mean age of the patients was 27.09±1.72 years (range, 20-40 years). Of the anterior segment parameters, axial length and keratometry did not show significant difference between photopic and mesopic conditions (P=0.541 and P=0.812, respectively). The mean anterior chamber depth measurements was 3.04±0.35 mm and 3.06±0.35 mm, whereas the mean lens thickness was 3.75±0.36 mm and 3.77±0.36 mm in the mesopic and photopic conditions, respectively. The mean pupil diameter measurement was 4.86±0.70 mm under photopic conditions and 6.36±0.94 mm under mesopic conditions. The anterior chamber depth, lens thickness, and pupil diameter showed significant difference between photopic and mesopic conditions (P=0.01, P=0.006, and P=0.0001, respectively).

CONCLUSION

Anterior chamber depth, lens thickness, and pupil diameter were affected by the changes in luminance while performing measurements with OLCR. Considering the age of the study group, further studies are needed to test the measurement of accommodation amplitude.

Comparison of central corneal thickness measurements with a rotating scheimpflug camera, a specular microscope, optical low-coherence reflectometry, and ultrasound pachymetry in keratoconic eyes

OBJECTIVE

To compare central corneal thickness (CCT) measurements with a rotating Scheimpflug camera (RSC), noncontact specular microscopy (SM), optical low-coherence reflectometry (OLCR), and ultrasonic pachymetry (UP) in keratoconus (KC) patients.

METHOD

In this prospective study, four CCT measurements taken with an RSC, SM, OLCR, and UP were compared in 81 eyes of 44 consecutive KC patients. The KC patients were divided into four subgroups according to Amsler-Krumeich's KC classification.

RESULTS

The RSC and UP measurements of the CCT were not statistically significant in all the groups. Comparison of the SM vs. the OLCR measurements yielded statistically significant differences in all the KC patients and in all KC stages. In all the KC patients, RSC and OLCR showed a high correlation coefficient factor (r = 0.87, p = 0.000).

CONCLUSION

CCT measurements with RSC are comparable to those achieved with UP. Compared with the other devices, according to SM measurements, the central cornea is thicker in all keratoconic eyes and in all KC grades, and it is thinner according to OLCR. RSC, UP, SM, and OLCR should not be used interchangeably in keratoconic eyes.

Central corneal thickness measurements with different imaging devices and ultrasound pachymetry

PURPOSE

The aim of this study was to compare 4 methods of central corneal thickness (CCT) measurements in terms of their agreement, repeatability, and measurement time.

METHODS

CCT was measured in 184 eyes of 92 healthy subjects by the same examiner. The methods used were as follows: noncontact specular microscopy (SM; Topcon SP-3000P; Topcon Corporation, Tokyo, Japan), Pentacam rotating Scheimpflug photography system (Oculus Inc, Wetzlar, Germany), optical low-coherence reflectometry (OLCR; LenStar LS900; Haag-Streit AG, Koeniz, Switzerland), and ultrasound pachymetry (UP; PachPen; Accutome Inc, Malvern, PA). The duration for each examination was measured by an independent observer.

RESULTS

The mean age (±SD) of the subjects was 54.3 (± 15.3) years. The mean CCTs (± SD) for SM, Pentacam, OLCR, and UP were 507.8 (± 30.2), 538.4 (± 31.7), 531.8 (± 31.4), and 528.3 (± 32.9) μm, respectively. The Bland-Altman plots showed closest agreement for OLCR-UP, followed by OLCR-Pentacam and Pentacam-UP. SM had the poorest agreement with the other methods. CCTs measured by SM were on average 20 to 30 μm thinner than those of the other methods. The coefficient of repeatability for SM, Pentacam, OLCR, and UP were 3.14%, 4.23%, 1.51%, and 3.46%, respectively. The mean measurement times (± SD) were 13.5 (± 5.7), 45.7 (± 12.3), 18.5 (± 7.1), and 5.6 (± 1.0) seconds, respectively.

CONCLUSIONS

CCT measurements between OLCR-UP and OLCR-Pentacam are comparable and can be used interchangeably in clinical practice. However, SM underestimates CCT compared with the other methods, whereas Pentacam was found to be the least repeatable and took the longest time.

Anterior segment optical coherence tomography versus ultrasound pachymetry to measure corneal thickness in endothelial keratoplasty donor corneas

PURPOSE

To analyze corneal thickness (CT) by anterior segment optical coherence tomography and ultrasound pachymetry in precut endothelial keratoplasty (EK) donor corneas at the eye bank.

METHODS

Thirty-six corneas were analyzed. All corneas were dissected to create lamellar grafts for EK using the standard eye bank protocol. We measured central and peripheral (3 mm from center) CT by ultrasound after lamellar tissue processing and by optical coherence tomography after the tissue was transferred to a viewing chamber. We performed paired t tests and Pearson correlation analyses to compare ultrasound and optical coherence tomography measurements.

RESULTS

Central CT measurements by optical coherence tomography versus ultrasound in donor corneas were not statistically different (mean: 169 vs. 177 µm, respectively, P = 0.09). There was a strong correlation between measurements of central CT (r = 0.73, P < 0.0001). There was a statistically significant difference in mean peripheral CT measurements by optical coherence tomography and ultrasound (mean: 190 vs. 236 µm, respectively, P < 0.0001); at peripheral locations, measurements correlated moderately (r = 0.52, P = 0.002).

CONCLUSIONS

Optical coherence tomography measurements of EK-prepared tissue averaged 8 μm thinner than the ultrasound measurements, similar to clinical measurements of central CT. Given the growing interest in the effect of EK graft thickness on patient outcomes, it is important to understand the differences in measurements obtained by different devices used to assess donor corneas.

Comparison of central corneal thickness measurements with optical low-coherence reflectometry and ultrasound pachymetry and reproducibility of both devices

PURPOSE

To compare the accuracy of optical low-coherence reflectometry (Lenstar LS 900; Haag Streit, Köniz, Switzerland) and conventional ultrasound pachymetry (UP) (US 4000; Nidek, Japan) for measuring central corneal thickness and to assess the interexaminer reproducibilities of both devices.

METHODS

Department of Ophthalmology, Selcuklu Faculty of Medicine, Selcuk University was the study setting. Central corneal thickness (CCT) was measured in both eyes of 65 emmetropic patients by the same examiner using Lenstar LS 900 noncontact biometry and UP. To assess the interexaminer reproducibility, 2 different examiners consecutively obtained CCT measurements in 16 eyes with Lenstar LS 900 noncontact biometry and UP.

RESULTS

Mean CCT measurements with Lenstar LS 900 noncontact biometry and ultrasound biometry were 541.09 ± 33.8 and 545.69 ± 34.0, respectively. Significant correlation was present between these 2 measurements; intraclass correlation coefficient was found to be 95.8% (95% confidence interval: 93.2%-97.4%)(P < 0.001). Interexaminer reproducibility with Lenstar was high, and the intraclass correlation was found to be 99.3% (95% confidence interval: 98.0%-99.7%). We have also investigated the interexaminer reproducibility with UP in these 16 patients, and the results showed a 99.2% (95% confidence interval: 97.7%-99.7%) intraclass correlation.

CONCLUSIONS

The results of Lenstar LS 900 noncontact biometry correlated with the results of UP. It may be used as an alternative method to UP for measuring CCT. Because of the mild underestimation of CCT by Lenstar, the measurements should be carefully evaluated in patients whose intraocular pressure must strictly be monitored.

Comparison of non-contact methods for the measurement of central corneal thickness

BACKGROUND AND OBJECTIVE

This study examined the repeatability of and agreements between central corneal thickness measurements obtained by four different non-contact pachymetry devices.

PATIENTS AND METHODS

Seventy-eight eyes of 39 subjects were included. Central corneal thickness of each eye was measured by Visante optical coherence tomography (OCT) (Carl Zeiss Meditec Inc., Dublin, CA), Pentacam (Oculus Optikgeräte GmbH, Wetzlar, Germany), Orbscan IIz topography (Bausch & Lomb Surgical Inc., San Dimas, CA), and slit-lamp OCT (SL-OCT) (Heidelberg Engineering GmbH, Heidelberg, Germany). Inter-device agreements and correlations and repeatability of each device were examined.

RESULTS

All measurement methods correlated well with each other with a correlation coefficient greater than 0.90 and P value of less than .001 for all comparisons. However, Pentacam overestimated central corneal thickness: 546.7 ± 38.2, 535.5 ± 42.7, 531.7 ± 37.6, and 531.2 ± 36.0 μm for Pentacam, Orbscan IIz, Visante OCT, and SL-OCT, respectively (P < .001 for all comparisons versus Pentacam). Despite good correlation, magnitude of differences was high and this bias was proportional (ie, not constant across a range of corneal thickness values) for the following pairs: Orbscan versus Visante OCT, Orbscan versus SL-OCT, and Orbscan versus Pentacam (P < .001 for all comparisons).

CONCLUSION

Although measurements obtained by various non-contact methods correlate well, numerical agreement of the results may not be sufficient for their interchangeable use in clinical practice.