Comparison of anterior segment measurements with rotating Scheimpflug photography and partial coherence reflectometry

Comparison of keratometric values and anterior segment parameters measured using Scheimpflug Sirius topography and Lenstar biometry

PURPOSE

This study aimed to evaluate the consistency of preoperative keratometric values, anterior segment, and intraocular lens (IOL) power measurements in patients with cataract and no comorbidities using the Sirius topography device (CSO, Italy) and Lenstar LS 900 (Haag-Streit AG, Köeniz, Switzerland).

METHODS

Patients with grade 2 and 3 cataracts who applied to Ophthalmology Clinic of Dışkapı Yıldırım Beyazıt Education and Research Hospital, University of Health Sciences and planned for cataract surgery were included the study. Forty eyes with cataract from 40 patients were taken in the study. All patients underwent preoperative assessment using a combined Scheimpflug-Placido disc-based tomography device (Sirius) and Lenstar before cataract surgery. Keratometric measurements, such as flat keratometry (K1), steep keratometry (K2), and maximum keratometry (Kmax), and anterior segment parameters, white-to-white (WTW) distance, IOL power, astigmatism (AST), anterior chamber depth (ACD), aqueous depth (AD), and central cornea thickness (CCT), were recorded.

RESULTS

There were significant differences between K1Lenstar and K1Sirius, K2Lenstar and K2Sirius, KmaxLenstar and KmaxSirius, WTWLenstar and WTWSirius, and IOL powerLenstar versus IOL powerSirius. However, there were insignificant differences between ASTLenstar and ASTSirius, ACDLenstar versus ACDSirius, ADLenstar and ADSirius, and CCTLenstar and CCTSirius variables. Furthermore, it was found that Sirius measured significantly higher than Lenstar, especially in terms of IOL power.

CONCLUSION

Significant differences were observed between Lenstar and Sirius in terms of keratometric values, WTW distance, and IOL power. The IOL power value measured with Sirius was found to be higher than the IOL power value measured with Lenstar.

Comprehensive comparisons of ocular biometry: A network-based big data analysis

PURPOSE

To systematically compare and rank ocular measurements with optical and ultrasound biometers based on big data.

METHODS

PubMed, Embase, the Cochrane Library and the US trial registry ( www.

CLINICALTRIAL

gov ) were used to systematically search trials published up to October 22nd, 2020. We included comparative studies reporting the following parameters measured by at least two devices: axial length (AL), flattest meridian keratometry (Kf), steepest meridian keratometry (Ks), mean keratometry (Km), astigmatism (AST), astigmatism vectors J₀ and J₄₅, anterior chamber depth (ACD), aqueous depth (AQD), central corneal thickness (CCT), corneal diameter (CD) and lens thickness (LT). A network-based big data analysis was conducted using STATA version 13.1.

RESULTS

Across 129 studies involving 17,181 eyes, 12 optical biometers and two ultrasound biometers (with both contact and immersion techniques) were identified. A network meta-analysis for AL and ACD measurements found that statistically significant differences existed when contact ultrasound biometry was compared with the optical biometers. There were no statistically significant differences among the four swept-source optical coherence tomography (SS-OCT) based devices (IOLMaster 700, OA-2000, Argos and ANTERION). As for Ks, Km and CD, statistically significant differences were found when the Pentacam AXL was compared with the IOLMaster and IOLMaster 500. There were statistically significant differences for CCT when the OA-2000 was compared to Pentacam AXL, IOLMaster 700, Lenstar, AL-Scan and Galilei G6.

CONCLUSION

For AL and ACD, contact ultrasound biometry obtains the lower values compared with optical biometers. The Pentacam AXL achieves the lowest values for keratometry and CD. The smallest value for CCT measurement is found with the OA-2000.

Comparison of Anterior Segment Measurements with a New Multifunctional Unit and Five Other Devices

Purpose

To evaluate the clinical availability of a multifunctional ocular biometric unit, MR-6000, for simultaneous keratometry, tonometry, topography, and pachymetry evaluation, and compare anterior segment measurements with five other devices: autokeratometer (KR-1), Scheimpflug camera (Pentacam HR), swept-source optical coherence tomography (IOLMaster 700), Placido disk scanning-slit topography (Orbscan II), and noncontact tonometry (FT-1000).

Methods

Thirty eyes from thirty patients who visited Severance Hospital for cataract surgery were examined using MR-6000 and the other devices. The mean keratometry, central corneal thickness (CCT), white-to-white (WTW) distance, and intraocular pressure (IOP) values were compared. Repeated measures analysis of variance, Wilcoxon signed-rank test, intraclass correlation coefficient (ICC), and Bland-Altman plot were used to assess the correlation and agreement between devices.

Results

Thirty eyes of thirty patients were evaluated. Statistically significant differences in mean keratometry between MR-6000, KR-1, Pentacam HR, and IOLMaster 700 were not observed (p > 0.05). All five devices, including Orbscan II, had almost perfect agreement in measuring keratometry (ICC > 0.80, p < 0.05). CCT measured by MR-6000 was significantly different from that of Pentacam HR and Orbscan II measurements (p < 0.05) but correlated with that of Pentacam HR and Orbscan II measurements (ICC > 0.60, p < 0.05). The WTW distance measured by MR-6000 was not significantly different from that measured by IOLMaster 700 but was different from that measured by Orbscan II. IOP measured by MR-6000 was not correlated with FT-1000.

Conclusions

Keratometric values obtained through MR-6000 can be used interchangeably with other devices based on good correlation and agreement. However, the CCT, WTW, and IOP values were not interchangeable with a single multifunctional unit for cataract surgery preoperative examination.

Agreement analysis of Lenstar with other four techniques of biometry before cataract surgery

PURPOSE

To test whether some biometry measurements provided by the Lenstar LS900 compared well with the AL-Scan, Pentacam rotating Scheimpflug camera, Ultrasound Biomicroscopy (UBM) and Tomey EM-3000.

METHODS

Two hundred and one patients having routine cataract surgery had standard preoperative assessment. In this clinical study, the axis length (AL) and lens thickness (LT) were taken by Lenstar LS900 and AL-Scan; anterior chamber depth (ACD) was taken by Lenstar LS900, A-Scan, Pentacam and UBM; central corneal thickness (CCT) was taken by Lenstar LS900, Pentacam and Tomey EM-3000. The results were compared using a Wilcoxon-Mann-Whitney U test and Pearson correlation calculations. Agreement was assessed through intraclass correlation coefficients and Bland-Altman plots.

RESULTS

The highest correlation was found between Lenstar and AL-Scan for AL (r = 0.975; P < 0.001). For LT measurements, the correlation between these two devices was also good (r = 0.699; P < 0.001). Excellent correlations were showed between Lenstar and Pentacam or UBM for ACD (r = 0.948, 0.704, respectively, both P < 0.001), but not between Lenstar and AL-Scan (r = 0.453, P < 0.001). The correlations of CCT between Lenstar and Pentacam or Tomey EM-3000 were both excellent (r = 0.817, 0.882, respectively, both P < 0.001).

CONCLUSIONS

In phakic eyes of cataract patients, measurements of AL, LT, ACD and CCT from Lenstar LS900 yielded results that correlated very well with other clinical instruments.

Evaluation of the agreement of optical biometry and Scheimpflug corneal topography with different axial lengths

PURPOSE

To compare anterior segment parameters evaluated with optical low coherence reflectometry and combined Scheimpflug-Placido disc topography in eyes with different axial lengths.

METHODS

Deux cent quatre patients were divided into 3 groups according to their axial lengths. Central corneal thickness (CCT), anterior chamber depth (AD), mean keratometry value (K mean) and white-to-white distances (WTW) obtained from both devices were compared. All measurements were performed 3 times and averaged.

RESULTS

In group 1, a significant difference was detected between the two devices for CCT, WTW and Kmean measurements (P<0.001, P<0.001, p:0.005 respectively). In group 2, a significant difference was detected between the two devices for WTW measurement (P<0.001). In group 3, a significant difference was detected between the two devices for CCT and WTW measurement (P<0.001, P<0.001 respectively). In the Bland-Altman analysis, there was no match for Kmean obtained with both devices in group 1. In group 2, there was no agreement for AD obtained with both devices. In group 3, there was no match for AD, WTW or Kmean values obtained with both devices.

CONCLUSION

Some anterior segment parameters are not suitable for interchangeability in eyes with different axial lengths evaluated by Lenstar and Sirius anterior segment imaging systems. When planning critical surgery and treatment, more attention should be paid to measurements in eyes of different axial lengths.

Anterior chamber depth measurement using Pentacam and Biograph in children

CLINICAL RELEVANCE

Accurate measurement of the anterior chamber depth is very important. There is no report regarding the agreement between rotating Scheimpflug imaging (Pentacam HR) and biograph (Lenstar LS 900) in children. This study therefore explores the agreement between Pentacam and Biograph in measuring anterior chamber depth in children.

BACKGROUND

This study aims to determine the agreement between Pentacam and Biograph in measuring anterior chamber depth in children.

METHODS

The participants were students living in urban and rural areas of Shahroud, Iran, selected through cluster sampling. The students were transported to the examination site to undergo imaging and optometric tests. Pentacam imaging was then conducted, and biograph was used to measure biometric components. In this report, the anterior chamber depth was calculated from the corneal endothelium.

RESULTS

Of 6624 students selected randomly, 5620 participated in the study. After applying the exclusion criteria, 4882 eyes were included in the final analysis. The mean anterior chamber depth measured by the Pentacam (3.09 ± 0.26 mm) was higher than that of biograph (3.04 ± 0.24 mm) (p < 0.001). The 95% limit of agreement (LOA) between the two devices was -0.19 to 0.09 mm. The variation of the difference between the two devices decreased, LOA became narrower, and the correlation coefficient of the devices increased with ageing. The highest intraclass correlation coefficient was seen among myopic (0.974) participants. The 95% LOA was -0.20 to 0.12 mm in hyperopic, -0.17 to 0.07 mm in myopic and -0.19 to 0.09 mm in emmetropic participants.

CONCLUSION

The Pentacam and Biograph can be used interchangeably for measuring the anterior chamber depth in children.

Agreement of keratometric readings measured using rotating Scheimpflug imaging, auto-refractokeratometer, and biograph in eyes with keratoconus

AIM

To determine agreement in keratometric readings obtained using rotating Scheimpflug imaging with Pentacam, biograph with Lenstar LS900, and Topcon KR-8100P auto-keratorefractometer in eyes with different stages of keratoconus.

METHODS

A total of 89 eyes of 58 patients with keratoconus were examined in this study, retrospectively. The eyes were divided into two groups: mild group (group 1: 42 eyes) (Amsler-Krumeich stage 1) and moderate-to-severe group (group 2: 47 eyes) (Amsler-Krumeich stage 2, 3, 4). The keratometric readings measured using the Pentacam Scheimpflug system, Lenstar LS900, and Topcon KR-8100P auto-keratorefractometer were compared between the groups. The effects of the measurements of anterior chamber depth, Q value, axial length, central corneal thickness (CCT), and maximum value of keratometry (Kmax) on the differences of devices for keratometric readings were investigated.

RESULTS

The mean values of the keratometric readings obtained using the Lenstar were steeper than with the Pentacam and Topcon, especially in group 2. In group 1, the mean K2 values measured using the Lenstar were significantly steeper than with the Topcon (p < 0.05); however, the devices were accordant for the other keratometric readings. In group 2, there was an agreement between the Pentacam and Topcon for the mean K1 and Km values; however, there were significant differences between the devices for the other values. The Q value and CCT had a negative correlation, and Kmax had a positive correlation with the differences of Lenstar-Pentacam and Lenstar-Topcon (p < 0.01).

CONCLUSION

According to our results, Pentacam-Topcon and Pentacam-Lenstar can be used interchangeably for keratometry in mild stages of keratoconus. The keratometric readings of Lenstar were found steeper than the other devices with increasing grades of keratoconus. None of these devices can be used interchangeably in moderate-to-severe stages of keratoconus.

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 a new Scheimpflug imaging combined with partial coherence interferometry biometer and a low-coherence reflectometry biometer

PURPOSE

To evaluate the repeatability of a new biometer using Scheimpflug technology combined with partial coherence interferometry (PCI) (Pentacam AXL) and its agreement with a device based on optical low-coherence reflectometry (OLCR), the Allegro Biograph.

SETTING

Oftalvist Centro Integral Ocular Jerez, Jerez de la Frontera, Spain.

DESIGN

Evaluation of a diagnostic test.

METHODS

The mean keratometry (K), central corneal thickness (CCT), anterior chamber depth (ACD), and axial length (AL) were measured with the 2 devices 3 times by the same examiner in 2 groups (patients with cataract and patients without cataract). The repeatability was determined using the within-subject standard deviation, test-retest repeatability, coefficient of variation, and intraclass correlation coefficient. The correlation was evaluated with the Pearson coefficient and interchangeability with the Bland-Altman plot.

RESULTS

Eighty eyes (40 eyes in each group) of 80 patients were analyzed. Significant differences were found between the Scheimpflug-PCI device and the OLCR device for mean K in the normal group (P < .001) and for CCT in the normal group (P < .05) and the cataract group (P < .001). There were no differences between devices in ACD and AL in either group. The repeatability between devices was similar. Although a significant correlation between devices was found for all measurements (all P < .001), wide limits of agreement were found in both groups for all biometric parameters.

CONCLUSIONS

The Scheimpflug-PCI and OLCR devices showed excellent intravisit repeatability and high correlation for mean K, CCT, ACD, and AL in healthy and cataractous eyes. No differences were found in AL; however, the 2 devices might not be interchangeable.

Correlations between ocular biometrics and refractive error: A systematic review and meta-analysis

The understanding of correlations between different biometric parameters is essential for personalized eye care in the field of cataract and refractive surgery. This systematic review offers a clear overview of the previous literature assessing these correlations including a meta-analysis. The review is focused on the following five correlations: (1) axial length and refractive error; (2) anterior chamber depth and refractive error; (3) axial length and anterior chamber depth; (4) corneal power and refractive error; (5) corneal power and axial length. An expected strong correlation between axial length and refractive error was found. Correlations including corneal power were weak and might be clinically insignificant.

Keratometry in children: Comparison between auto-refractokeratometer, rotating scheimpflug imaging, and biograph

PURPOSE

To determine the agreement and validity of keratometric measurements in children with the Nidek ARK-510A auto-refractokeratometer compared to rotating Scheimpflug imaging with Pentacam and biograph with Lenstar LS 900.

METHODS

This study was conducted on 5620 schoolchildren aged 6-12 years in Shahroud, Iran. Minimum and maximum keratometry values and corneal astigmatism magnitude were compared by calculation of Paired difference, interclass correlation coefficient, and 95% limits of agreement (LoA) between devices.

RESULTS

After applying the exclusion criteria, 4215 right eyes were enrolled into the study. Mean minimum keratometry with Nidek ARK-510A, Pentacam, and Lenstar was 43.13±1.51, 43.14±1.48, and 42.87±1.46 diopters (D), respectively, and mean maximum keratometry was 43.97±1.59, 44.00±1.56, and 43.75±1.54D, respectively. Nidek ARK-510A overestimated minimum and maximum keratometry by 0.25±0.37 and 0.22±0.41, respectively, compared to Penatcam. The LoA between Nidek ARK-510A and Pentacam for minimum and maximum keratometry measurements were -0.98 to 0.47D and -1.02 to 0.57D, respectively. The LoA between Nidek ARK-510A and Lenstar for minimum and maximum keratometry measurements were -0.70 to 0.72D and -0.79 to 0.85D, respectively. The agreement between devices was best in emmetropes, worst in hyperopes. For astigmatic vector components, the agreements between devices were poor but best agreement was between Nidek ARK-510A and Pentacam.

CONCLUSIONS

Keratometry measurement with Nidek ARK-510A was not significantly different from Pentacam and Lenstar, and this device can be used in screening programs in emmetropes.

Lenstar® LS 900 vs Pentacam®-AXL: Comparative study of ocular biometric measurements and intraocular lens power calculation

Purpose:

Comparison of biometric measurements and calculation of intraocular lens with a new biometer (Pentacam®-AXL, Oculus, Germany) and a reference biometer (Lenstar LS 900®, Haag-Streit AG, Switzerland), in order to assess the agreement between these two devices.

Setting:

Centro Hospitalar de Leiria, Portugal

Materials and methods:

Prospective, institutional study, in which measurements of axial length, anterior chamber depth from the corneal epithelium and endothelium to the anterior surface of the lens (anterior chamber depth ext and anterior chamber depth int), central corneal thickness and keratometry readings of the flattest and steepest meridians (K1 and K2) were obtained with the two systems. Intraocular lens calculation was also performed, using the Haigis, SRK/T and HofferQ formulas.

Results:

The study sample included 136 eyes of 79 patients. Of these, 42 were women and 37 were men. Statistically significant differences were found (p < 0.05, paired T test) in K1, K2 and central corneal thickness between the 2 biometers. Intraocular lens calculation with the Lenstar® and the Pentacam® with Haigis, SRK/T and HofferQ formulas showed statistically significant differences (p < 0.05 Paired T test).

Conclusion:

Axial length measurements obtained with the Pentacam® and Lenstar® appear to be interchangeable, while measurements of anterior chamber depth, K1 and K2, and central corneal thickness do not appear to be interchangeable between different devices. Statistically significant differences were found in the calculation of intraocular lenses in all formulas used.

Repeatability of Ophtha Top topography and comparison with IOL-Master and LenstarLS900 in cataract patients

AIM

To determine the repeatability of Ophtha Top topography and assess the consistency with intraocular lens (IOL)-Master and LenstarLS900 (Lenstar) in measuring corneal parameters among cataract patients.

METHODS

Totally 125 eyes were enrolled. Corneas were successively measured with Ophtha Top, IOL-Master and Lenstar at least three times. The flattest meridian power (Kf), the steepest meridian power (Ks), mean power (Km), J0 and J45 were recorded. Intra-class correlation coefficients (ICCs), the coefficient of variance (COV), within subject standard deviation (Sw), and test-retest repeatability (2.77Sw) were adopted to determine the repeatability. The 95% limit of agreement (95%LOA) and Bland-Altman plots were used to assess comparability.

RESULTS

Repeatability of Ophtha Top topography for measuring corneal parameters showed the ICCs were all above 0.93, 2.77Sw was lower than 0.31, and the COV of the Kf and Ks was lower than 0.25. The keratometric readings with Ophtha Top topography were flatter than with the IOL-Master and Lenstar devices, while the Pearson correlation coefficients were over 0.97. The J0 and J45 with Ophtha Top topography were smaller compared with Lenstar and IOL-Master, while was comparable between Lenstar and IOL-Master.

CONCLUSION

Ophtha Top topography shows excellent repeatability for measuring corneal parameters. However, differences between the Ophtha TOP topography and Lenstar, IOL-Master both in cornea curvature and the astigmatism should be noted clinically.

Comparison of ocular biometric measurements between a new swept-source optical coherence tomography and a common optical low coherence reflectometry

The purpose of the current study was to compare the measurements between a new optical biometer based on swept-source optical coherence tomography (SS-OCT), the OA-2000 (Tomey, Japan), and an optical biometer based on optical low coherence reflectometry (OLCR), the Lenstar (Haag-Streit, Switzerland). Ninety-nine eyes of 99 healthy subjects were included. The axial length (AL), central corneal thickness (CCT), anterior chamber depth (ACD), aqueous depth (AD), lens thickness (LT), keratometry (K) readings, including flat K (Kf), steep K (Ks), mean K (Km), astigmatism vectors J₀, J₄₅ at diameters of 2.5 and 3.0 mm, and white-to-white diameter (WTW) were measured three times each using both biometer in normal eyes by random sequence. Bland-Altman analysis showed good agreement between the SS-OCT and OLCR devices for AL, AD, ACD, LT, with narrow 95% LoA (−0.05 to 0.07 mm, −0.09 to 0.10 mm, −0.10 to 0.09 mm, and −0.06 to 0.22 mm, respectively), and the P values of ACD were both >0.05. The CCT, Kf, Ks, Km, J₀, J₄₅ and WTW values provided by the OA-2000 were in good agreement with the Lenstar, and statistically significant differences were detected for some of them but not clinical differences. The agreement was excellent especially for AL.

Repeatability and Agreement of Central Corneal Thickness and Keratometry Measurements between Four Different Devices

Background. To estimate repeatability and comparability of central corneal thickness (CCT) and keratometry measurements obtained by four different devices in healthy eyes. Methods. Fifty-five healthy eyes from 55 volunteers were enrolled in this study. CCT (IOLMaster 700, Pentacam HR, and Cirrus HD-OCT) and keratometry readings (IOLMaster 700, Pentacam HR, and iDesign) were measured. For statistical analysis, the corneal spherocylinder was converted into power vectors (J0, J45). Repeatability was assessed by intraclass correlation coefficient (ICC). Agreement of measurements between the devices was evaluated by the Bland-Altman method. Results. The analysis of repeatability of CCT data of IOLMaster 700, Pentacam HR, and Cirrus HD-OCT showed high ICCs (range 0.995 to 0.999). The comparison of CCT measurements revealed statistically significant differences between Pentacam HR versus IOLMaster 700 (p < 0.0001) and Pentacam HR versus Cirrus HD-OCT (p < 0.0001), respectively. There was no difference in CCT measurements between IOLMaster 700 and Cirrus HD-OCT (p = 0.519). The repeatability of keratometry readings (J0 and J45) of IOLMaster 700, Pentacam HR, and iDesign was also high with ICCs ranging from 0.974 to 0.999. The Pentacam HR revealed significantly higher J0 in comparison to IOLMaster 700 (p = 0.009) and iDesign (p = 0.041); however, no significant difference was between IOLMaster 700 and iDesign (p = 0.426). Comparison of J45 showed no significant difference between IOLMaster 700, Pentacam HR, and iDesign. These results were in accordance with Bland-Altman plots. Conclusion. In clinical practice, the devices analyzed should not be used interchangeably due to low agreement regarding CCT as well as keratometry readings.

Comparison of Anterior Segment Measurements with Optical Low-coherence Reflectometry and Partial-coherence Interferometry Optical Biometers

AIMS

To evaluate a new noncontact optical biometer using partial-coherence interferometry and to compare the clinical measurements with those obtained from the device using optical low-coherence reflectometry (OLCR).

SETTING AND DESIGN

Ondokuz Mayis University, Samsun, Turkey. Nonrandomized, prospective clinical trial.

SUBJECTS AND METHODS

The study was performed on the healthy phakic eyes of volunteers in the year 2014. Measurements of axial length (AL), anterior chamber depth (ACD), central corneal thickness (CCT), mean keratometry (K), and white-to-white (WTW) measurements obtained with the low-time coherence interferometry (LTCI) were compared with those obtained with the OLCR.

STATISTICAL ANALYSIS USED

The results were evaluated using Bland-Altman analyses. The differences between both methods were assessed using the paired t-test, and its correlation was evaluated by Pearson's coefficient.

RESULTS

We examined seventy participants with a mean age of 33.06 (±9.7) (range: 19-53) years. AL measurements with LTCI and OLCR were 23.7 (±1.08) mm and 23.7 (±1.1) mm, respectively. ACD was 3.6 (±0.4) mm and 3.5 (±0.4) mm for LTCI and OLCR, respectively. The mean CCT measurements for both devices were 533 (±28) mm and 522 (±28) mm, respectively. The mean K readings measurements for LTCI and OLCR were 43.3 (±1.5) D and 43.3 (±1.5) D, respectively. The mean WTW distance measurements for both devices were 12.0 (±0.5) mm and 12.1 (±0.5) mm, respectively.

CONCLUSIONS

Measurements with LTCI correlated well with those with the OLCR. These two devices showed good agreement for the measurement of all parameters.

Effect of posterior corneal astigmatism on power calculation and alignment of toric intraocular lenses: Comparison of methodologies

PURPOSE

To compare the accuracy of different methods that consider posterior corneal curvature in toric intraocular lens (IOL) calculations.

SETTING

Ein-Tal Eye Center, Tel-Aviv, Israel.

DESIGN

Retrospective comparative case series.

METHODS

Consecutive cases of toric IOL implantation and preoperative measurements by optical biometry with optical low-coherence reflectometry (OLCR) (Lenstar LS 900) and a Scheimpflug camera (Pentacam) were retrospectively reviewed. Five methods of toric IOL calculation were compared as follows: (1) anterior corneal astigmatism using OLCR, (2) application of the Baylor nomogram, (3) posterior tomography combined with anterior corneal measurements using vector summation, (4) the Scheimpflug camera's true net power, and (5) total corneal refractive power. Toric IOL astigmatic power and axis, aiming for the lowest residual astigmatism, were selected according to these methods. Simulated residual refraction was calculated for each method based on manifest refraction and measured IOL alignment more than 3 weeks after surgery.

RESULTS

The study included 115 eyes of 92 patients. The median simulated residual astigmatism was lower when based on vector summation of anterior and posterior astigmatisms than with calculations based on anterior corneal measurements only, application of the Baylor nomogram, true net power, and total corneal refractive power readings (0.49 diopters [D] versus 0.70 D, 0.60 D, 0.64 D, and 0.76 D, respectively) (P < .001).

CONCLUSIONS

Residual astigmatism after toric IOL implantation can be reduced by appropriate consideration of the posterior corneal astigmatism. Using methods that take into account the effect of the posterior cornea in toric IOL calculations is suggested.

FINANCIAL DISCLOSURES

Drs. Assia and Kleinmann are consultants to Hanita Lenses, Israel. Dr. Abulafia received a speaker's fee from Haag-Streit AG. No other author has a financial or proprietary interest in any material or method mentioned.

Agreement Between Swept-Source Optical Biometry and Scheimpflug-based Topography Measurements of Anterior Segment Parameters

PURPOSE

To estimate the agreement of anterior segment parameters between a swept-source optical biometry (IOLMaster 700; Carl Zeiss Meditec AG, Jena, Germany) and a Scheimpflug-based topography with high resolution (Pentacam HR; OCULUS, Wetzlar, Germany).

DESIGN

Interinstrument reliability analysis.

METHODS

A total of 62 eyes from 62 young adults were included in the study. Average keratometry (AveK) and simulated keratometry (SimK) along 2.0-mm-ring measurements provided by Pentacam HR, keratometry readings provided by IOLMaster 700, and central corneal thickness (CCT) and anterior chamber depth (ACD) values obtained from both devices were recorded. J0 and J45 vectoral components of astigmatism were obtained using power vector analysis. Mean keratometry (Km) values of IOLMaster 700 were compared for each type of Km value from Pentacam HR, while other parameters were compared between devices. To assess the agreement between measurements of the devices, Bland-Altman analysis was performed.

RESULTS

The Pentacam HR exhibited significantly lower Km and CCT measurements (P < .001, for all); however, no significant difference emerged in J0, J45, and ACD measurements (P = .057, P = .574, and P = .64, respectively). The mean difference between AveK, SimK 2.0 mm, and the IOLMaster 700 Km was -0.20 diopter (D) and -0.14 D, respectively, while the mean difference between J0, J45, CCT, and ACD measurements was 0.07 D, -0.016 D, -5.05 μm, and 0.004 mm, respectively.

CONCLUSION

In clinical practice, Pentacam HR and IOLMaster 700 can be used interchangeably to measure J0 and J45 vectoral components of astigmatism for SimK 2.0 mm and IOLMaster keratometry values, as well as ACD and CCT measurements. However, SimK 2.0 mm and AveK values can be not interchangeable, as the devices have clinical and statistical differences in measurements.

Device interchangeability on anterior chamber depth and white-to-white measurements: a thorough literature review

We have reviewed a set of recently published studies that compared the anterior chamber depth (ACD) and/or white-to-white (WTW) distance obtained by means of different measuring devices. Since some of those studies reached contradictory conclusions regarding device interchangeability, this review was carried out in attempting to clarify which clinical devices can or cannot be considered as interchangeable in clinical practice to measure ACD and/or WTW distance, among these devices: A-scan, ultrasound biomicroscopy, Orbscan and Orbscan II (Bausch&Lomb Surgical Inc., San Dimas, California, USA), Pentacam and Pentacam HR (Oculus, Wetzlar, Germany), Galilei (Ziemer, Switzerland), Visante optical coherence tomography (Visante OCT, Carl Zeiss Meditec Inc., Dublin, California, USA), IOLMaster (Carl Zeiss Meditec, Jena, Germany), and Lenstar LS 900/Biograph (Haag-Streit AG, Koeniz, Switzerland/Alcon Laboratories Inc., Ft Worth, Texas, USA).

Pupil Dilation with Intracameral Epinephrine Hydrochloride during Phacoemulsification and Intraocular Lens Implantation

Objective. To investigate mydriatic effect of intracamerally injected epinephrine hydrochloride during phacoemulsification and intraocular lens (IOL) implantation. Methods. Eighteen cataract patients for bilateral phacoemulsification were enrolled. To dilate pupil, one eye was randomly selected to receive intracamerally 1 mL epinephrine hydrochloride 0.001% for 1 minute after corneal incision (intracameral group), and the contralateral eye received 3 drops of compound tropicamide 0.5% and phenylephrine 0.5% at 5-minute intervals 30 minutes before surgery (topical group). Pupil diameters were measured before corneal incision, before ophthalmic viscoelastic device (OVD) injection, after OVD injection, before IOL implantation, and at the end of surgery. Results. At each time point, the mean pupil diameter in the intracameral group was 2.20 ± 0.08, 5.09 ± 0.20, 6.76 ± 0.19, 6.48 ± 0.18, and 5.97 ± 0.24 mm, respectively, and in the topical group it was 7.98 ± 0.15, 7.98 ± 0.15, 8.53 ± 0.14, 8.27 ± 0.16, and 7.93 ± 0.20 mm, respectively. The topical group consistently had larger mydriatic effects than the intracameral group (P < 0.05). The onset of mydriatic effect was rapid in the intracameral group. There was no difference in surgical performance or other parameters between groups. Conclusions. Intracameral epinephrine hydrochloride appears to be an alternative to the mydriatic modalities for phacoemulsification and IOL implantation. In comparison with topical mydriatics, intracameral epinephrine hydrochloride offers easier preoperative preparation, more rapid pupil dilation, and comparable surgical performance.

Precision (Repeatability and Reproducibility) and Agreement of Corneal Power Measurements Obtained by Topcon KR-1W and iTrace

Purpose

To evaluate the repeatability and reproducibility of corneal power measurements obtained by Topcon KR-1W and iTrace, and assess the agreement with measurements obtained by Allegro Topolyzer and IOLMaster.

Methods

The right eyes of 100 normal subjects were prospectively scanned 3 times using all the 4 devices. Another observer performed additional 3 consecutive scans using the Topcon KR-1W and iTrace in the same session. About one week later, the first observer repeated the measurements using the Topcon KR-1W and iTrace. The steep keratometry (Ks), flat keratometry (Kf), mean keratometry (Km), J0 and J45 were analyzed. Repeatability and reproducibility of measurements were evaluated by the within-subject standard deviation (Sw), coefficient of variation (CoV), test-retest repeatability (2.77Sw), and intraclass correlation coefficient (ICC). Agreements between devices were assessed using Bland-Altman analysis and 95% limits of agreement (LoA).

Results

Intraobserver repeatability and interobserver and intersession reproducibility of the Ks, Kf and Km showed a CoV of no more than 0.5%, a 2.77Sw of 0.70 D or less, and an ICC of no less than 0.99. However, J0 and J45 showed poor intraobserver repeatability and interobserver and intersession reproducibility (all ICCs not greater than 0.446). Statistically significant differences existed between Topcon KR-1W and IOLMaster, Topcon KR-1W and iTrace, Topcon KR-1W and Topolyzer, iTrace and Topolyzer, iTrace and IOLMaster for Ks, Kf and Km measurements (all P < 0.05). The mean differences between Topcon KR-1W, iTrace, and the other 2 devices were small. The 95% LoA were approximately 1.0 D to 1.5 D for all measurements.

Conclusions

The Ks, Kf and Km obtained by Topcon KR-1W and iTrace showed excellent intraobserver repeatability and interobserver and intersession reproducibility in normal eyes. The agreement between Topcon KR-1W and Topolyzer, Topcon KR-1W and IOLMaster, iTrace and Topolyzer, iTrace and IOLMaster, Topcon KR-1W and iTrace were not so good, they should not be interchangeable in clinical application. Given that the intraobserver repeatability and interobserver and intersession reproducibility of corneal astigmatism measurements obtained by Topcon KR-1W and iTrace were poor, it should be cautious that Topcon KR-1W and iTrace were applied for the preparation of toric lens implantation.

Evaluation of keratometry with a novel Color-LED corneal topographer

PURPOSE

To assess the performance of a novel keratometer based on reflections of colored light-emitting diodes (LEDs) and compare it with devices based on Placido rings, monochromatic LEDs, and Scheimpflug images.

METHODS

Sixty-three eyes of 63 patients with virgin corneas underwent keratometry with color-LED corneal topography (Cassini; i-Optics, The Hague, The Netherlands) and with devices based on Placido ring reflections (Keratron; Optikon, Rome, Italy), monochromatic LED reflections (Lenstar; Haag-Streit, Koeniz, Switzerland), and Scheimpflug imaging (Pentacam; Oculus Optikgeräte, Wetzlar, Germany). Three repeated measurements were performed with each device. Comparability and repeatability of corneal power and cylinder measurements were assessed. The Bonferroni-corrected α-threshold for statistical significance was 0.016.

RESULTS

Corneal power measurements with the Cassini topographer were not statistically significantly different from those with the Pentacam (P = .64). They were statistically significantly lower than those with the Keratron and Lenstar (P < .01), but the differences were of negligible clinical relevance. Cylinder measurements with the Cassini topographer were not statistically significantly different from those with any other device (P = .46). Repeatability of Cassini corneal power measurements was not statistically significantly different from that of the Keratron (P = .02), but was statistically significantly lower than that of the Lenstar and Pentacam (P < .001). Repeatability of Cassini cylinder measurements was statistically significantly higher than that of the Pentacam and Keratron (P < .001), but was not statistically significantly different from that of the Lenstar (P > .05).

CONCLUSIONS

Corneal power and cylinder measurements with color-LED corneal topography yielded values that were comparable to those of other commonly used devices. Repeatability of corneal power measurements was lower compared to some devices, but repeatability of cylinder measurements was relatively high. This may be of particular interest when using toric intraocular lenses.

Comparison of keratometry and white-to-white measurements obtained by Lenstar with those obtained by autokeratometry and corneal topography

PURPOSE

To compare anterior eye segment measurements obtained using low optical coherence reflectometry (LENSTAR LS900, Haag-Streit), autokeratometry (RC-5000, Tomey) and corneal topography (Topolyzer, Wavelight).

METHODS

In 46 healthy subjects, flat keratometry (Kf), steep keratometry (Ks), mean keratometry (Km) and white-to-white (WTW) distance were measured by Lenstar, Tomey RC-5000 and Topolyzer.

RESULTS

Kf and Km measurements of Lenstar were significantly steeper than Tomey RC-5000 (both p<0.001), but the 95% LoA of them were narrow (-0.22 to 0.46D, -0.16 to 0.36D, respectively). There were no significant differences between the Kf and Km measurements of Lenstar and Topolyzer, with a narrow 95% LoA. There were no significant differences between the Ks measurements of Lenstar and Tomey RC-5000, and Lenstar and Topolyzer. A good agreement was found between them with 95% LoA of -0.40 to 0.56D, and -0.56 to 0.64D, respectively. WTW measurements with Lenstar were greater than those with Tomey RC-5000 and Topolyzer (p=0.042, p<0.01, respectively). A good agreement existed between the WTW obtained by Lenstar and Topolyzer, Tomey RC-5000, with 95% LoA ranging from -0.13 to 0.74mm and -0.33 to 0.51mm.

CONCLUSIONS

Generally good agreement was found between the Lenstar and Tomey RC-5000, Topolyzer for K and WTW measurements. In clinical practice, K and WTW measurements obtained by Lenstar and Tomey RC-5000, Topolyzer can be used interchangeably.

Comparison of anterior chamber depth measurements of Nidek AL-Scan and Galilei Dual Scheimpflug Analyzer

PURPOSE

We aimed to compare anterior chamber depth (ACD) measurements between the Nidek AL-Scan and the Galilei Dual Scheimpflug Analyzer.

SETTING

Turgut Ozal University Medical Faculty, Ankara, Turkey.

DESIGN

Prospective masked bilateral randomized study.

METHODS

Sixty-three individual patient eyes with normal ocular examination findings and no prior ocular surgery were analyzed. Paired two-tailed t-test was used to evaluate agreement between devices. Interobserver repeatability was evaluated in 22 patients using intraclass correlation coefficient (ICC) and Bland-Altman analysis.

RESULTS

The mean ± standard deviation (SD) ACD for Nidek and Galilei was 3.57 ± 0.29 (range from 2.92 to 4.32) and 3.65 ± 0.29 (range from 3.01 to 4.40), respectively. Comparing the two instruments using paired samples t-test, a statistically significant difference was found between the measurements obtained for ACD (P = 0). Two observers' intraclass correlation coefficients (ICC) were 0.996 for Nidek and 0.968 for Galilei. For Nidek, ACD mean difference was 0mm (P < 0.001); 95% limits of agreement was from -0.05 to 0.05. For Galilei ACD mean difference was -0.01 mm (P < 0.001); 95% limits of agreement was from -0.14 to 0.12. The Galilei Dual Scheimpflug Analyzer measured longer ACD values than the Nidek AL-Scan.

CONCLUSION

This comparative study showed that the difference in ACD between the measurements of the Nidek AL-Scan and the Galilei Dual Scheimpflug Analyzer was statistically significant but clinically it was negligible. Further studies are needed, especially on IOL calculation formulas that include ACD and its effect on postoperative spherical equivalent values.

Clear-cornea cataract surgery: pupil size and shape changes, along with anterior chamber volume and depth changes. A Scheimpflug imaging study

PURPOSE

To investigate, by high-precision digital analysis of data provided by Scheimpflug imaging, changes in pupil size and shape and anterior chamber (AC) parameters following cataract surgery.

PATIENTS AND METHODS

The study group (86 eyes, patient age 70.58±10.33 years) was subjected to cataract removal surgery with in-the-bag intraocular lens implantation (pseudophakic). A control group of 75 healthy eyes (patient age 51.14±16.27 years) was employed for comparison. Scheimpflug imaging (preoperatively and 3 months postoperatively) was employed to investigate central corneal thickness, AC depth, and AC volume. In addition, by digitally analyzing the black-and-white dotted line pupil edge marking in the Scheimpflug "large maps," the horizontal and vertical pupil diameters were individually measured and the pupil eccentricity was calculated. The correlations between AC depth and pupil shape parameters versus patient age, as well as the postoperative AC and pupil size and shape changes, were investigated.

RESULTS

Compared to preoperative measurements, AC depth and AC volume of the pseudophakic eyes increased by 0.99±0.46 mm (39%; P<0.001) and 43.57±24.59 mm(3) (36%; P<0.001), respectively. Pupil size analysis showed that the horizontal pupil diameter was reduced by -0.27±0.22 mm (-9.7%; P=0.001) and the vertical pupil diameter was reduced by -0.32±0.24 mm (-11%; P<0.001). Pupil eccentricity was reduced by -39.56%; P<0.001.

CONCLUSION

Cataract extraction surgery appears to affect pupil size and shape, possibly in correlation to AC depth increase. This novel investigation based on digital analysis of Scheimpflug imaging data suggests that the cataract postoperative photopic pupil is reduced and more circular. These changes appear to be more significant with increasing patient age.

Agreement study of keratometric values measured by Biograph/LENSTAR, auto-kerato-refractometer and Pentacam: decision for IOL calculation

BACKGROUND

The aim was to determine the agreement in keratometric readings measured with the Biograph/LENSTAR, the Pentacam and an auto-kerato-refractometer in a 40- to 64-year-old population.

METHODS

This report is part of the first phase of the population-based Shahroud Cohort Eye Study. In virgin eyes, agreement among keratometry readings of three devices was examined in 7,260 eyes using the Bland-Altman method. The inter-device 95 per cent limits of agreement (95% LoA) and 95% confidence interval for upper and lower limits of agreement were calculated. Comparisons were made for keratometric readings of the flat and steep meridians as maximum keratometry (max-K), minimum keratometry (min-K) and their average (mean-K).

RESULTS

Based on Biograph/LENSTAR measurements, averages of max-K, min-K and mean-K were 44.70 ± 1.64, 43.87 ± 1.54 and 44.28 ± 1.58 D, respectively. The quantile-quantile plot revealed that all three variables had normal distributions in this population. Agreement between the Biograph/LENSTAR and the auto-kerato-refractometer (max-K difference: -0.03 D, 95% LoA: -0.81 to 0.75; min-K difference: -0.08 D, 95% LoA: -0.85 to 0.68) was better than the agreement between the Biograph/LENSTAR and the Pentacam (max-K difference: 0.50 D, 95% LoA: -3.24 to 4.25; min-K difference: 0.59 D, 95% LoA: -3.00 to 4.17). The agreement between the Pentacam and the auto-kerato-refractometer (max-K difference: 0.54 D, 95% LoA: -3.16 to 4.24; min-K difference: 0.66 D, 95% LoA: -0.77 to 0.53) was worse than the other two pairs.

CONCLUSION

These three devices are not interchangeable in terms of keratometry for calculation of the intraocular lens power. Agreement between the Biograph/LENSTAR and the auto-kerato-refractometer can be increased with regression models but this is not true in case of Biograph/LENSTAR and Pentacam.

A new algorithm and problems in automatic anterior eye chamber volume determining

This study investigates the problem of automatic determination of the anterior eye chamber volume using previously published as well as new algorithms of image analysis and processing proposed by the authors. A new method for determining the anterior eye chamber volume that provides more accurate results has been proposed. The entire algorithm was implemented in Matlab and C language. 60,000 images were obtained using OCT SS-1000 CASIA and Zeiss Visante OCT. The acquired images of the anterior segment of the eye had a resolution of 256×1024 pixels with a measuring range of 8×16mm(2). The images were acquired during routine medical examination at the Clinical Department of Ophthalmology, District Railway Hospital in Katowice, Poland, and were analysed in accordance with the Declaration of Helsinki. The new algorithm uses edge detection, morphological operations, binarization and filtration. The proposed algorithm gave the anterior chamber surface measurement error at the level of 4.3% and the anterior chamber volume measurement error of 12%. For comparison, the surface measurement error of the tomograph software was at 6.7%. Thus the obtained results were better by 2.4%. The proposed algorithm provides reproducible results automatically at a runtime of 3s per patient using a Core i7 PC computer with 8GB of RAM.

Central and midperipheral corneal thickness measured with Scheimpflug imaging and optical coherence tomography

Purpose

To compare corneal thickness measurements using Pentacam (Oculus, Germany), Sirius (CSO, Italy), Galilei (Ziemer, Switzerland), and RTVue-100 OCT (Optovue Inc., USA).

Methods

Sixty-six eyes of 66 healthy volunteers were enrolled. Three consecutive measurements were performed with each device. The mean value of the three measurements was used for subsequent analysis. Central corneal thickness (CCT), thinnest corneal thickness (TCT), and midperipheral corneal thickness (MPCT; measured at superior, inferior, nasal, and temporal locations with a distance of 1 mm (CT_2mm) or 2.5 mm (CT_5mm) from the corneal apex) were analyzed. Differences and agreement between measurements were assessed using the repeated-measures analysis of variance (ANOVA) and Bland-Altman analyses, respectively.

Results

Statistically significant differences (p<0.001) among the four devices were revealed in CCT, TCT and CT_2mmmeasurements. The CCT, TCT, and CT_2mm values were ranked from the thickest to the thinnest as follows: Galilei>Sirius>Pentacam>RTVue OCT. For these measurements, agreement between measurements by Sirius and Pentacam was good, whereas Galilei overestimated and RTVue underestimated corneal thickness compared to Sirius and Pentacam. As regards CT_5mm measurements, Pentacam provided the largest values, whereas RTVue OCT yielded the smallest values. Agreement of the CT_5mm measurements was good between the Pentacam, Sirius, moderate between Galilei and the other two Scheimpflug systems, and poor between the RTVue OCT and the remaining devices.

Conclusions

The Pentacam and Sirius can be used interchangeably for CCT measurements, while the Galilei and RTVue systematically over- and underestimate CCT, respectively. The three Scheimpflug cameras, but not the RTVue, may be used interchangeably for MPCT measurements.

Comparison of corneal curvature and anterior chamber depth measurements using the manual keratometer, Lenstar LS 900 and the Pentacam

Purpose:

The purpose of this study was to compare keratometry and anterior chamber depth (ACD) measurements from the Lenstar LS 900 (Haag-Streit AG, Switzerland) and the Pentacam (Oculus, Weltzar, Germany), and compare the keratometry readings of these two systems to a manual keratometer (MK), (Haag-Streit, Switzerland).

Materials and Methods:

In this prospective study, keratometry and ACD measurements were obtained in 50 eyes of 50 normal subjects with the Lenstar and the Pentacam. Keratometry was also measured using a MK. Correlation, comparison, and interdevice agreement was evaluated using intraclass correlation analysis, Wilcoxon test, and Bland-Altman plots.

Results:

The keratometry and ACD measurements obtained from the Lenstar and the Pentacam showed excellent correlation. The mean interdevice differences in mean keratometry (Km) for the Lenstar and the Pentacam, the Lenstar and the MK, and the Pentacam and the MK were 0.39 D, 0.10 D, and 0.30 D respectively; and the 95% limits of agreement (LoA) for Km were 0.04-0.82 D; −1.90-2.10 D; and −2.30-1.70 D, respectively. The mean interdevice difference in ACD for the Lenstar versus the Pentacam was 0.09 mm, with 95% LoA of 0.23-0.05 mm.

Conclusions:

The ACD measurements obtained using the Lenstar and the Pentacam seem to be interchangeable, whereas, the keratometry measurements obtained using the Lenstar, Pentacam, and MK differ considerably, and are not interchangeable.

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.

Comparison and repeatability of keratometric and corneal power measurements obtained by Orbscan II, Pentacam, and Galilei corneal tomography systems

PURPOSE

To assess the repeatability and comparability of corneal power and central corneal thickness (CCT) measurements obtained using Orbscan II (Bausch & Lomb), Pentacam (Oculus), and Galilei (Ziemer) tomographers.

DESIGN

Prospective, comparative study.

METHODS

setting: Departments of Ophthalmology, University of Auckland and Auckland District Health Board, Auckland, New Zealand. study population: Thirty eyes of 30 healthy participants. observations. CCT and corneal power measured using Orbscan II, Pentacam, and Galilei tomography. main outcome measures: Degree of agreement in and repeatability of CCT and corneal power measures.

RESULTS

Orbscan II measured significantly lower CCT compared with Pentacam (20 μm; P < .0005) and Galilei (18 μm; P < .0005). The Orbscan II had wide limits of agreement when compared with both the Galilei (-11 to 47 μm) and Pentacam (-88 to 47 μm). For each device, the intraclass correlation coefficient for CCT was higher than 0.9. The coefficient of variation ranged from 0.33% to 0.93%. There was no significant difference in mean steep keratometry or mean flat keratometry between instrument pairs. However, there was poor agreement in flat keratometry and steep keratometry obtained by Orbscan II compared with those obtained by the Galilei and Pentacam.

CONCLUSIONS

The keratometry and pachymetry measurements obtained by Orbscan II, Pentcam, and Galilei tomographers were sufficiently disparate that the 3 devices could not be considered equivalent. All 3 devices demonstrated a high level of repeatability, although the Galilei exhibited the best repeatability.

A comprehensive assessment of the precision and agreement of anterior corneal power measurements obtained using 8 different devices

Purpose

To comprehensively assess the precision and agreement of anterior corneal power measurements using 8 different devices.

Methods

Thirty-five eyes from 35 healthy subjects were included in the prospective study. In the first session, a single examiner performed on each subject randomly measurements with the RC-5000 (Tomey Corp., Japan), KR-8000 (Topcon, Japan), IOLMaster (Carl Zeiss Meditec, Germany), E300 (Medmont International, Australia), Allegro Topolyzer (Wavelight AG, Germany), Vista (EyeSys, TX), Pentacam (Oculus, Germany) and Sirius (CSO, Italy). Measurements were repeated in the second session (1 to 2 weeks later). Repeatability and reproducibility of corneal power measurements were assessed based on the intrasession and intersession within-subject standard deviation (Sw), repeatability (2.77Sw), coefficient of variation (COV), and intraclass correlation coefficient (ICC). Agreement was evaluated by 95% limits of agreement (LoA).

Results

All devices demonstrated high repeatability and reproducibility of the keratometric values (2.77Sw<0.36D, COV<0.3%, ICC>0.98). Repeated-measures analysis of variance with Bonferroni post test showed statistically significant differences (P<0.01) among mean keratometric values of most instruments; the largest differences were observed between the EyeSys Vista and Medmont E300. Good agreement (i.e., 95%LoA within ±0.5D) was found between most instruments for flat, steep and mean keratometry, except for EyeSys and Medmont. Repeatability and reproducibility of vectors J₀ and J₄₅ was good, as the ICCs were higher than 0.9, except J₄₅ of Medmont and Pentacam. For the 95% LoAs of J₀ and J₄₅, they were all ≤ ±0.31 among any two paired devices.

Conclusions

The 8 devices showed excellent repeatability and reproducibility. The results obtained using the RC-5000, KR-8000, IOLMaster, Allegro Topolyzer, Pentacam and Sirius were comparable, suggesting that they could be used interchangeably in most clinical settings. Caution is warranted with the measurements of the EyeSys Vista and Medmont E300, which should not be used interchangeably with other devices due to lower agreement.

Trial Registration

ClinicalTrials.gov NCT01587287

Statistical methods for conducting agreement (comparison of clinical tests) and precision (repeatability or reproducibility) studies in optometry and ophthalmology

The ever-expanding choice of ocular metrology and imaging equipment has driven research into the validity of their measurements. Consequently, studies of the agreement between two instruments or clinical tests have proliferated in the ophthalmic literature. It is important that researchers apply the appropriate statistical tests in agreement studies. Correlation coefficients are hazardous and should be avoided. The 'limits of agreement' method originally proposed by Altman and Bland in 1983 is the statistical procedure of choice. Its step-by-step use and practical considerations in relation to optometry and ophthalmology are detailed in addition to sample size considerations and statistical approaches to precision (repeatability or reproducibility) estimates.