An Evaluation of Keratometry in 6-Year-Old Children

Refractive development I: Biometric changes during emmetropisation

PURPOSE

Although there are many reports on ocular growth, these data are often fragmented into separate parameters or for limited age ranges. This work intends to create an overview of normal eye growth (i.e., in absence of myopisation) for the period before birth until 18 years of age.

METHODS

The data for this analysis were taken from a search of six literature databases using keywords such as "[Parameter] & [age group]", with [Parameter] the ocular parameter under study and [age group] an indication of age. This yielded 34,409 references that, after screening of title, abstract and text, left 294 references with usable data. Where possible, additional parameters were calculated, such as the Bennett crystalline lens power, whole eye power and axial power.

RESULTS

There were 3422 average values for 17 parameters, calculated over a combined total of 679,398 individually measured or calculated values. The age-related change in refractive error was best fitted by a sum of four exponentials (r²  = 0.58), while all other biometric parameters could be fitted well by a sum of two exponentials and a linear term ('bi-exponential function'; r² range: 0.64-0.99). The first exponential of the bi-exponential fits typically reached 95% of its end value before 18 months, suggesting that these reached genetically pre-programmed passive growth. The second exponentials reached this point between 4 years of age for the anterior curvature and well past adulthood for most lenticular dimensions, suggesting that this part represents the active control underlying emmetropisation. The ocular components each have different growth rates, but growth rate changes occur simultaneously at first and then act independently after birth.

CONCLUSIONS

Most biometric parameters grow according to a bi-exponential pattern associated with passive and actively modulated eye growth. This may form an interesting reference to understand myopisation.

Preterm refraction and ocular biometry in children with and without retinopathy of prematurity in the first year of life

PURPOSE

To determine ocular biometric and refractive profiles of premature children at risk of retinopathy of prematurity (ROP), comparing those who did and did not require laser treatment.

METHODS

In this prospective study, premature infants underwent biometry and refraction with their first ROP examination. Study parameters were assessed again at 3 months, 6 months, and 1 year. The main outcome measures were spherical equivalent, axial length, and keratometry.

RESULTS

A total of 122 infants (243 eyes) were included. At baseline, infants without ROP, those with ROP who never needed treatment, and those who later needed treatment had overall comparable axial length (P = 0.53) and myopia (P = 0.05); the highest severity group had higher corneal steepness and more myopia at baseline. At 1 year, children with laser-treated ROP had the shortest axial lengths, with the least decrease in keratometry, and the greatest increase in myopia (-2.0 D; P = 0.001). Anisometropia, if present initially, persisted through the 1-year examination. Mean refractive error was more myopic in zone 1 disease (P = 0.3) and in aggressive posterior ROP (P = 0.15).

CONCLUSIONS

Severe ROP is associated with disruption of emmetropization, and steeper corneas and more myopia at the first ROP examination, before any intervention. In our study cohort, these differences became more marked over the course of 1 year after laser therapy. The myopia in these cases was not axial. Laser therapy did not induce new anisometropia.

Feasibility and repeatability of ocular biometry measured with Lenstar LS 900 in a large group of children and adolescents

PURPOSE

To evaluate the feasibility and repeatability of Lenstar LS 900 biometry measurements in a paediatric population.

METHODS

Children were examined as part of the LIFE Child Study (Leipzig Research Centre for Civilization Diseases), a population-based study in Leipzig, Germany. Altogether, 1917 children, aged from 3.5 to 17.5 years, were assessed with the Haag Streit Lenstar LS 900. Three consecutive measurements of the right eye were analysed for axial length, central corneal thickness, anterior chamber depth, aqueous depth, lens thickness and flat and steep corneal radii. The number of successful measurements and repeatability were evaluated for each parameter and three age bands (3.5 to 6.5 years, 6.5 to 10.5 years and 10.5 to 17.5 years).

RESULTS

Best measurement feasibility was found for axial length and central corneal thickness (91% to 100%), followed by flat and steep corneal radii (86% to 100%), anterior chamber and aqueous depth (76% to 92%) and lens thickness (50% to 81%), with higher numbers for older children. Repeatability values (in mm) were: axial length 0.025 to 0.035; central corneal thickness 0.003 to 0.027; aqueous depth 0.024 to 0.058; anterior chamber 0.024 to 0.054; lens thickness 0.034 to 0.067. An overall trend showed better repeatability for older children, especially for central corneal thickness, aqueous depth and lens thickness.

CONCLUSIONS

For ocular biometry in the paediatric population, axial length, central corneal thickness, flat and steep corneal radii can be measured very reliably even in children from 4 years old onward using the Lenstar LS 900. Lens thickness can be quantified in a limited number of younger children. Repeatability was high for all variables investigated. Repeatability improved with age, reaching adult values in the adolescent age band. Established repeatability limits can be applied in future studies as a quality parameter.

Agreement between Pentacam and handheld Auto-Refractor/Keratometer for keratometry measurement

OBJECTIVE

This study was conducted to evaluate the level of agreement in keratometry measurements between a rotating Scheimpflug imaging-based system (Pentacam) and a handheld auto-refractokeratometer (handheld NIDEK ARK-30).

METHOD

This analytical cross-sectional study was conducted in the right eyes of 579 subjects. Keratometry measurements were conducted with the Pentacam and the handheld NIDEK ARK-30 systems. The SPSS Software version 22 and MedCalc V3 were applied to estimate descriptive statistics using paired t-test, Pearson correlation coefficient, 95% limits of agreement (LoA), and Bland-Altman plot.

RESULTS

In the total sample, the inter-device difference in the mean flat and steep keratometry values was -0.266 diopter (D) (P-value<0.001) and 0.052D (P-value=0.093), respectively. There was a significant difference in mean flat keratometry between the two devices in all groups of refractive errors (paired difference <0.5D and P-value<0.001). The difference in mean steep keratometry was significant only in myopic subjects (P-value=0.046). The 95% LoA between the two devices measurements was 2.51D, 3.98D, and 6.37D for flat keratometry and 2.6D, 3.2D, and 3.9D for steep keratometry in emmetropic, myopic, and hyperopic subjects, respectively.

CONCLUSION

Our study showed relatively wide limits of agreement between handheld NIDEK ARK-30 and Pentacam; therefore, these devices cannot be used interchangeably for measuring corneal curvature.

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.

Agreement between Keratometric readings by VERION image guided System, Galilei G4 and Pentacam

Objective:

To study Agreement between Keratometric readings by VERION image guided System, Galilei G4 and Pentacam.

Methods:

The quasi experimental study was conducted at Armed Forces Institute of Ophthalmology, Rawalpindi, Pakistan from August 2016 to December 2016. Twenty five patients fulfilling the inclusion criteria participated in the study. All Patients were subjected to Keratometric assessment using Galilei G4 Dual Scheimpflug analyzer (Ziemer, Switzerland), Wavelight Oculyzer II (Pentacam, Germany) and Verion image guided system (Alcon). Steep and flat meridian and diopter of astigmatism by three systems were recorded and endorsed. All readings were taken by the same observer. Statistical Program for Social Sciences (SPSS) version 22.0 was used for statistical analysis. Results analyzed for significance by t-tests and Interclass correlation analysis. In t tests, P values of <0.05 was considered statistically significant while interclass coefficient of >0.7 was considered acceptable.

Results:

Fifty eyes of twenty-five patients (22 male, 28 female) with mean age of 29.50 ± 3.46 years were studied. Flat K, steep K and dioptric power of astigmatism were measured with verion, pentacam and Galilei G4. Interclass correlation analysis showed agreement between individual variables measured by the three devices, while one sample t test showed no significant difference between dioptric power of astigmatism between Verion-Pentacam and Verion- Galilei group. (p 0.178 for former and 0.622 for later group).

Conclusion:

Verion image guided system is comparable to other instruments used currently for keratometry. Verion can be interchangeably used with Pentacam and Galilee G4 in assessing corneal astigmatism.

Comparison of keratometric measurements obtained by the Verion Image Guided System with optical biometry and auto-keratorefractometer

The aim of this study was to compare the keratometric measurements of Verion Image Guided System with an optical biometer (Zeiss IOLMaster 500, Carl Zeiss Meditec, Jena, Germany) and an automated keratorefractometer (AKR) (Topcon KR-8900, Topcon, Japan). In this prospective clinical trial, the right eyes of 52 patients with cataract were examined (mean age 62.25 ± 12.16 years). The measurements were taken by the three systems in a random order. Keratometric data, magnitude of astigmatism, and astigmatic axis measurements from all three instruments were compared. The results were evaluated using, intraclass correlation coefficients (ICC), Bland-Altman plots, and paired samples t tests. The mean flat/steep K of Verion, IOLMaster, and AKR were 43.22 ± 1.38D/44.23 ± 1.46D, 43.07 ± 1.26D/44.05 ± 1.34D, and 43.07 ± 1.31D/43.89 ± 1.42D, respectively. Flat K readings of Verion were higher than IOLMaster and AKR (p < 0.05 for both). Steep K readings were different for all three (p < 0.05). The magnitude of astigmatism by Verion and IOLMaster were 0.98 ± 0.65D and 0.98 ± 0.59D (p = 0.88). The mean astigmatism measured by the AKR was 0.82 ± 0.62D, less than the other two instruments (p < 0.001). Astigmatic axis measurements of Verion and AKR differed <10° in 38, between 10° and 20° in 5, and >20° in 9 eyes; the same difference was 30, 11, and 11 eyes, respectively, between Verion and IOLMaster. Although, keratometric and astigmatic results obtained from Verion were not completely interchangeable with IOLMaster and AKR, especially the agreement between Verion and IOLMaster was excellent with ICCs close to one. However, there were pronounced astigmatic axis measurement differences between three instruments.

Assessment of corneal curvature using verion optical imaging system: a comparative study

BACKGROUND

Keratometry is a critical determinant of the postoperative refractive outcome. This study evaluates the comparability of keratometry measurements obtained using the Verion Optical Imaging System with devices used in current clinical practice. Further, it determines the interobserver reliability of the Verion Optical Imaging System.

DESIGN

Retrospective analysis of patient data

PARTICIPANTS

Keratometric data was obtained from 100 patients presenting for pre-operative evaluation. Furthermore, repeatability and reproducibility were assessed using 15 healthy volunteers.

METHODS

Corneal curvature values acquired by the Verion Optical Imaging System were compared with existing keratometry devices including autokeratometry, partial coherence interferometry (IOLMaster) and Scheimpflug corneal topography (Pentacam).

MAIN OUTCOME MEASURES

Direct comparison of corneal power, cylinder, axis of astigmatism and vector analysis were performed using correlation and Bland-Altman analyses. Reproducibility and reliability of the device were assessed using within-subject standard deviation and intraclass correlation coefficients for experienced and inexperienced technicians.

RESULTS

There was no statistically significant difference between Verion values and those obtained by other methods in relation to mean keratometry, corneal astigmatism, steep meridian and vector analyses (P > 0.05). Bland-Altman plots showed narrow limits of agreement for keratometry and astigmatism and wider agreement for steep meridian. Intraoperator reliability for both experienced and inexperienced operators and interoperator reproducibility showed no statistically significant differences between values.

CONCLUSION

Measurements show no significant difference from those obtained by the other devices. This suggests the Verion system is en par with instruments used in current clinical practice. The Verion Optical Imaging System produces repeatable data with no difference related to operator experience.

The validity and reliability of the handheld SW-100 autokeratometer

Background: The agreement of new instruments or clinical tests with other instruments or tests defines the possibility of these being used interchangeably.Aim: To investigate the validity and reliability of the SW-100 autokeratometer using a Bausch & Lomb (B&L) keratometer as the ‘gold standard’. Methods: Eighty subjects (80 right eyes) aged between 21 and 38 years were recruited. For intra-test repeatability, two measurements of the corneal radius of curvature were taken with the SW-100 and B&L keratometers. Forty of the 80 subjects participated in the inter-test repeatability measurement.Results: Corneal radius of curvature was found to be statistically different between the two instruments (p < 0.001), with the SW-100 providing slightly flatter values of 0.11 mm and 0.05 mm for the horizontal and vertical meridians, respectively, than the B&L keratometer. The average corneal curvature was 0.07 mm flatter with the SW-100 autokeratometer than with the B&L device. Agreement between the SW-100 and B&L keratometers’ axes was 45% within ± 5°, 60.3% within ± 10°, 78.8% within ± 15°, 80.3% within ± 20°, and 88.7% within ± 40°. Intertest repeatability was better for the B&L device than the SW-100 and showed no significant difference between the two sessions. Both instruments demonstrated comparable intrasession repeatability. As such, both instruments were comparatively reliable (per coefficients of repeatability). The range of limits of agreement of ± 0.14 mm (horizontal meridian) and ± 0.17 mm (vertical meridian) between the SW-100 and B&L devices showed good agreement.Conclusion: The results suggest that the SW-100 autokeratometer is a reliable and objective instrument that, however, provides flatter radii of curvature measurements than the B&L keratometer. A compensating factor incorporated into the instrument could reduce the difference between the two instruments and make them more interchangeable. 

Precision and agreement of corneal power measurements obtained using a new corneal topographer OphthaTOP

Purpose

To evaluate repeatability and reproducibility of anterior corneal power measurements obtained with a new corneal topographer OphthaTOP (Hummel AG, Germany) and agreement with measurements by a rotating Scheimpflug camera (Pentacam HR, Oculus, Germany) and an automated keratometer (IOLMaster, Carl Zeiss Meditec, Germany).

Methods

The right eyes of 79 healthy subjects were prospectively measured three times with all three devices. Another examiner performed three additional scans with the OphthaTOP in the same session. Within one week, the first examiner repeated the measurements using the OphthaTOP. The flat simulated keratometry (Kf), steep K (Ks), mean K (Km), J₀, and J₄₅ were noted. Repeatability and reproducibility of measurements were assessed by within-subject standard deviation (Sw), repeatability (2.77 Sw), coefficient of variation (CoV), and intraclass correlation coefficient (ICC). Agreement between devices was assessed using 95% limits of agreement (LoA).

Results

Intraobserver repeatability and interobserver and intersession reproducibility of all measured parameters showed a 2.77 Sw of 0.29 diopter or less, a CoV of less than 0.24%, and an ICC of more than 0.906. Statistically significant differences (P<0.001) were found between the parameters analyzed by the three devices, except J₀ and J₄₅. The mean differences between OphthaTOP and the other two devices were small, and the 95% LoA was narrow for all results.

Conclusions

The OphthaTOP showed excellent intraobserver repeatability and interobserver and intersession reproducibility of corneal power measurements. Good agreements with the other two devices in these parameters were found in healthy eyes.

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.

Comparison of automated and partial coherence keratometry and resulting choice of toric IOL

PURPOSE

Consistent astigmatism correction with implantation of a toric intraocular lens (IOL) requires accurate preoperative keratometry. This article compares corneal astigmatism determined by an autokeratometer (Topcon KR-7100) and a partial coherence interferometry keratometer (IOLMaster 500) and considers if any discrepancy ultimately alters in final cylindrical power of the toric IOL for implantation.

METHODS

Keratometry of 235 eyes was performed using both instruments. Corneal astigmatism was transformed into vector components J0 and J45 and cylindrical power at the IOL plane calculated. Comparisons were made using paired t test and correlation and Bland-Altman analyses.

RESULTS

Although interinstrument differences for J0 (p = 0.013), J45 (p = 0.012), and toric IOL cylindrical power (p < 0.001) were statistically significant, a high correlation for these (R = 0.96, 0.90, and 0.90, respectively) was observed. IOLMaster tended to overestimate corneal astigmatism by 0.13 (±0.31) diopters and toric IOL cylinder by 0.11 (±0.18) diopters. Difference in calculated toric IOL cylindrical power correlated poorly with corneal curvature (R = 0.007) and astigmatism (R = -0.004).

CONCLUSIONS

The two keratometers were generally concordant in measuring corneal astigmatism. However, the resultant choice of toric IOL cylinder power differed appreciably in 40% of eyes examined. Therefore, postoperative visual outcome with toric IOL implantation may be optimized by a thorough analysis of biometry data before IOL selection, paying special attention to any difference in corneal astigmatism as measured by more than one instrument.

Comparison of refractive outcomes using five devices for the assessment of preoperative corneal power

BACKGROUND

  To compare keratometric values obtained with a manual keratometer (Topcon), an automated keratometer (Canon), an Orbscan II (Bausch & Lomb), the IOLMaster keratometer (Carl-Zeiss) and the Pentacam rotating Scheimpflug camera (Oculus) in cataract surgery, and to characterize the refractive outcomes generated using each device.

DESIGN

  Retrospective study conducted at a tertiary university hospital.

PARTICIPANTS

Sixty-nine eyes of 69 patients were analysed.

METHODS

  The keratometric values obtained with different devices (manual keratometer, automated keratometer, corneal topography, IOLMaster keratometer and Scheimpflug camera) were employed for intraocular lens power calculation. Multiple comparisons of averaged keratometric value were conducted, and the averaged keratometric value was used to calculate the predicted refraction. The absolute values of corneal astigmatism were calculated and also compared.

MAIN OUTCOME MEASURES

  Mean keratometric value, absolute value of astigmatism, mean error and mean absolute error from each device.

RESULTS

  The mean keratometric values generated by manual keratometer, automated keratometry, corneal topography, IOLMaster keratometer and the Pentacam Scheimpflug system were 43.95 ± 1.39, 43.91 ± 1.39, 44.67 ± 1.53, 44.03 ± 1.41 and 42.96 ± 1.39 diopter, respectively. The absolute value of astigmatism determined via manual keratometer, automated keratometer, corneal topography, IOLMaster keratometer and the Pentacam Scheimpflug system were 0.95 ± 0.60, 0.99 ± 0.69, 1.14 ± 0.74, 1.11 ± 0.65 and 1.03 ± 0.73 diopter, respectively. The corneal topography showed statistically significant differences with other devices and produced the greater value in mean absolute errors (all P < 0.05).

CONCLUSION

  Keratometric values with standard devices are a good choice for cataract surgery, whereas the corneal topography is not an appropriate method for the assessment of preoperative keratometric values.

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

Validation of keratometric measurements obtained with a new integrated aberrometry-topography system

Purpose

A clinical evaluation of the L80 videokeratographer (Visionix Luneau, Chartres, France) was performed to assess its validity and repeatability compared with a traditional Bausch and Lomb (B & L) keratometer.

Methods

87 right eyes of 87 subjects, (mean age 23.72 ± 3.62 years old, 70 women and 17 men), participated in this study. Corneal curvature was measured using the L80 instrument by one practitioner and the manual B & L keratometer by a different practitioner. Intratest and intertest repeatability were assessed.

Results

Corneal curvature was found to be statistically different between the two instruments (p < 0.001), with the L80 providing a slightly steeper bias of 0.05 mm and 0.07 mm for the horizontal and vertical meridians, respectively than the B & L keratometer. 78.2% and 86.2% of the L80 results were within ±0.1 mm (±0.06 D) and 95.4% and 97.7% within ±0.2 mm (±0.11 D) of the readings obtained with the B & L keratometer along the horizontal and the vertical meridians, respectively. The agreement between the L80 and B & L keratometers axes was 31.0% within ±5°, 54.0% within ±10°, 60.9% within ±15°, 71.3% within ±20° and 87.4% within ±40°. Intratest repeatability was the same for both instruments. Intertest repeatability was better for the L80 videokeratographer compared to the B & L keratometer and showed no significant difference between the two sessions.

Conclusion

The L80 videokeratographer is a reliable objective instrument comparable to other autokeratometers which, in addition, combines many other useful clinical features. It provides steeper radii of curvature measurements than the B & L keratometer. An offset incorporated into the instrument could mitigate the difference between the two instruments and make them interchangeable.

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

PURPOSE

To compare central corneal thickness (CCT), anterior chamber depth (ACD), and keratometry (K) readings measured using optical low-coherence reflectometry (OLCR) biometry and high-resolution rotating Scheimpflug photography.

SETTING

Eye Hospital of Wenzhou Medical College, Wenzhou, China.

DESIGN

Comparative case series.

METHODS

The CCT, ACD endothelium to lens, ACD epithelium to lens, and K (mean; in flattest meridian; in steepest meridian) were measured 5 times using the LenStar/Biograph OLCR biometer and 3 times with the Pentacam Scheimpflug system in eyes of healthy volunteers. Concordance was evaluated using paired t tests, the Pearson correlation, and Bland-Altman analyses.

RESULTS

The CCT, ACD endothelium to lens, and ACD epithelium to lens measured with the Scheimpflug system were slightly, albeit significantly, higher than with the OLCR biometer (P<.05); the respective 95% limits of agreement (LoA) were -8.2 μm to 15.7 μm, -0.11 to 0.15 mm, and -0.13 to 0.17 mm. However, the Scheimpflug system gave significantly flatter readings for K in the flattest meridian (95% LoA, -0.54 to 0.32 diopters [D]), K in the steepest meridian (95% LoA, -0.63 to 0.45 D), and mean K (95% LoA, -0.53 to 0.33 D) (P<.001). The CCT, ACD, and K readings were all highly correlated between the 2 devices (r >0.95, P<.001).

CONCLUSIONS

The CCT and ACD measurements with the OLCR biometer and Scheimpflug system can be used interchangeably in healthy young subjects. However, for K measurements, these devices have wide LoA so may not be interchangeable under certain clinical circumstances.

Determinants of corneal biomechanical properties in an adult Chinese population

PURPOSE

To investigate variations in corneal hysteresis (CH) and corneal resistance factor (CRF) and their ocular and systemic associations in Chinese adults.

DESIGN

Population-based, cross-sectional study.

PARTICIPANTS

We included 1136 subjects of Chinese origin from an ongoing population-based study.

METHODS

All subjects in this population-based study underwent a standardized ocular examination including keratometry (corneal radius of curvature), intraocular pressure (IOP) measurement with Goldmann applanation tonometry, central corneal thickness (CCT), and axial length (AL) assessments. The CH and CRF were measured with the Ocular Response Analyzer. Participants underwent a detailed interview and laboratory investigations that included estimation of nonfasting serum glucose, glycosylated hemoglobin, and lipid profile.

MAIN OUTCOME MEASURES

We assessed CH, CRF, and their associations with demographic, ocular, and systemic factors.

RESULTS

The mean age of study subjects was 55.3±8.4 years and 51.2% were females. The mean CH and CRF were 10.6±1.5 and 10.1±1.6 mmHg, respectively. Women had higher mean CH (10.8 vs 10.4 mmHg; P<0.001) and CRF (10.4 vs. 9.8 mmHg; P<0.001) than men. After adjusting for age, gender, IOP, CCT, keratometry, AL, and diabetes, CH was negatively associated with age (β = -0.034; P<0.001), IOP (β = -0.037; P = 0.01), corneal radius of curvature (β = -0.963; P<0.001), and AL (β = -0.106; P = 0.001); and positively associated with female gender (β = 0.308; P<0.001) and CCT (β = 0.020; P<0.001). The CRF showed a negative association with age (β = -0.023; P<0.001) and corneal radius of curvature (β = -0.771; P<0.001), and was positively associated with female gender (β = 0.368; P<0.001), IOP (β = 0.134; P<0.001) and CCT (β = 0.024; P<0.001). Subjects with diabetes had a higher CH (β = 0.324; P<0.001) and CRF (β = 0.396; P = 0.002) compared with those without diabetes.

CONCLUSIONS

With advancing age, the CH and CRF in adult Chinese decreased. Women and subjects with diabetes had greater CH and CRF. Corneal biomechanical properties of hysteresis and resistance factor are significantly influenced by IOP, CCT, corneal radius of curvature, and AL.

Comparison of corneal powers obtained from 4 different devices

PURPOSE

To assess the repeatability and comparability of anterior corneal power values obtained from the Galilei Dual Scheimpflug Analyzer (Ziemer, Port, Switzerland), Humphrey Atlas corneal topographer (Carl Zeiss, Jena, Germany), IOLMaster (Carl Zeiss), and a manual keratometer (Bausch & Lomb Inc, Rochester, New York, USA).

DESIGN

Prospective, comparative study.

METHODS

Prospectively, 20 subjects were enrolled. Three sets of corneal power measurements were obtained by a single observer using the Galilei, Atlas topographer, IOLMaster, and manual keratometer. Repeatability of the 3 measurements from each device was evaluated by means of coefficient of variation, standard deviation (SD), and intraclass correlation coefficient. An analysis of variance was used to compare the differences in corneal powers among devices. The Bland and Altman method also was performed to assess agreement in measurements between devices. Vector analysis was used to compare the astigmatism values obtained from different devices.

RESULTS

For each device, the coefficient of variation of repeated measurements was lower than 0.22%. The SD of 3 repeated measurements ranged from 0.042 to 0.096 diopters (D). The intraclass correlation coefficients were higher than 0.99 in all devices. Mean central corneal powers were 43.80 D, 43.88 D, 43.92 D, and 43.76 D for the Galilei, Atlas, IOLMaster, and manual keratometer, respectively. SDs of the differences between devices ranged from 0.07 D for Galilei and IOLMaster to 0.14 D for Galilei and Atlas. For astigmatism, the mean astigmatism values for the Galilei, Atlas, IOLMaster, and manual keratometer were 0.54 D at 84 degrees, 0.51 D at 88 degrees, 0.62 D at 88 degrees, and 0.52 D at 87 degrees, respectively.

CONCLUSIONS

The corneal power measurements from these 4 devices were highly reproducible, comparable, and correlated.

Comparison of different techniques of anterior chamber depth and keratometric measurements

PURPOSE

To compare measurements of anterior chamber depth (ACD) and corneal curvature obtained with the Pentacam to other commonly used devices.

DESIGN

Prospective, nonrandomized clinical trial.

METHODS

Measurements of ACD and keratometry were prospectively obtained in 22 eyes of 11 subjects with the Pentacam compared with measurements of the ultrasound (US) A-scan and IOLMaster (ACD), and with those of automated keratometry (AK) and IOLMaster (keratometry) at the Assaf Harofeh Medical Center.

RESULTS

The mean interdevice differences in keratometry for Pentacam vs AK, Pentacam vs IOLMaster, and AK vs IOLMaster were -0.046 diopters, -0.471 diopters, and -0.424 diopters, respectively. Measurements of keratometry by the IOLMaster differed statistically significantly from those of Pentacam (P < .01) and AK (P < .01). For measurement of keratometry, 95% limits of agreement were -1.321 to 1.229 diopters for the Pentacam and AK, -1.478 to 0.536 diopters for the Pentacam and IOLMaster, and -1.026 to 0.178 diopters for the AK and IOLMaster. The mean interdevice differences in ACD for the Pentacam vs US, Pentacam vs IOLMaster, and US vs IOLMaster were 0.103, 0.099, and -0.004 mm, respectively. Measurements of ACD by the Pentacam differed statistically significantly from those of US (P < .05) and IOLMaster (P < .01). For measurement of ACD, 95% limits of agreement were -0.197 to 0.404 mm for the Pentacam and US, -0.169 to 0.367 mm for the Pentacam and IOLMaster, and -0.332 to 0.324 mm for the US and IOLMaster.

CONCLUSIONS

For some clinical applications, measurements of ACD and corneal curvature with the tested machines may differ greatly and therefore may not be interchangeable.