Laser vs ultrasound biometry—a study of intra- and interobserver variability

Evaluation of biometric formulas in the calculation of intraocular lens according to axial length and type of the lens

To compare the accuracy of the modern biometric formulas in cataract surgery according to axial length and lens type. It is a Cross-sectional design from 365 patients who underwent cataract surgery. The SRK/T, Hoffer Q, Haigis, and Holladay I formulas were extracted from the IOLMaster 500 biometer. Barret formulas and the Kane were obtained from the online calculator. Patients are classified according to axial length (AL) into three groups: AL ≤ 22 mm, 22 < AL < 25 mm, and AL ≥ 25 mm. In addition, implanted intraocular lenses are classified as Monofocal, extended focus, and Multifocal. There are no significant differences between the formulas. In short, the Kane formula was more accurate than the other biometric formulas. Kane and SRK/T were the most accurate in monofocal lenses, with the lowest residual refractive error. The Holladay I formula obtained the lowest mean absolute error with the highest number of eyes with minimum residual ± 0.5Dp in the multifocal lenses in the 22 < AL < 25 mm eyes. In the long AL eyes, SRK/T and Kane's obtained the lowest mean absolute error and the best percentage of eyes with ± 0.5Dp of residual refractive error. There are no significant differences between the formulas. However Kane's formula has shown high accuracy, especially in short and long eyes with monofocal lenses.

Ocular biometry in dense cataracts: Comparison of partial-coherence interferometry, swept-source optical coherence tomography and immersion ultrasound

Purpose:

To assess the axial length (AL) measurement failure rate using partial-coherence interferometry (PCI) and swept-source optical coherence tomography (SS-OCT) in dense cataracts. As a secondary outcome, the SS-OCT biometry was compared to immersion ultrasound.

Methods:

This is a prospective cross-sectional and comparative study. Seventy eyes from 70 patients with dense cataracts were enrolled in this study. Dense cataract was defined according to the Lens Opacities Classification System III (LOCS III) scores equal to or more than NO4, NC4, C4, and P3. The failure rate of AL measurement was evaluated using PCI and SS-OCT. Anterior chamber depth (ACD), lens thickness (LT), and AL measurements obtained by SS-OCT were compared with IUS.

Results:

AL measurement failure rate with PCI was 68.57% and 21.43% with SS-OCT (P = 0.007). AL measurement was achieved in 69.23% of NO4, 66.6% of P3, and 15.3% of mixed cataracts using PCI, while SS-OCT was achieved in 100% of NO4, NO5, P3, and P5 and 76.9% of mixed cataracts. Cortical cataracts alone did not influence AL measurement. Biometric data of ACD, LT, and AL were statistically different comparing US and SS-OCT with a good correlation of AL.

Conclusion:

SS-OCT significantly improves the rate of successful AL measurements when compared to PCI in dense cataracts. The LOCS III clinical cut-off for the use of SS-OCT ocular biometry may well be up to P4 and NO5.

Immersion Ultrasound Biometry vs. Optical Biometry

ABSTRACT

PurposeAxial length (AL) measurements are routinely obtained by optical biometry (OB). Sometimes, however, immersion ultrasound (IUS) is required. Due to the small discrepancies between the two methods, it is unknown if optimized constants for OB are accurate for IUS. We compared these techniques and found how to use OB constants for eyes with AL by IUS.SettingMulticenter studyDesignRetrospective observational case seriesMethodsAgreement between OB and IUS ALs was investigated in 4 subsets. Also, in a test database, the prediction error for IUS AL was assessed with four methods: 1) data-optimized constants; 2) User group for Laser Interference Biometry (ULIB) constants with IUS biometry; 3) with recalibrated AL; and 4) ULIB A-constant-0.23.ResultsIn the combined 1,970 eyes, OB mean ALs was 0.0873 mm longer than IUS AL. The latter was made equivalent to OB ALs with this equation: Recalibrated IUS AL = 1.0228 × IUS AL - 0.4556. In a fifth database (n=1,079) with OB AL measurements only, after AL was artificially shortened by 0.0873 mm, the original A-constant had to be reduced by 0.23 to maintain a zero prediction error. In a sixth database (n = 127) with IUS AL, the original ULIB A-constant provided the poorest outcomes. Using either Recalibrated IUS AL or ULIB A-constant - 0.23 zeroed out the mean PE and achieved the lowest MedAE.ConclusionAL measurements by IUS can be used with ULIB constants for OB by subtracting 0.23 from the A-constant; alternatively, the IUS AL may be recalibrated. The recalibrated IUS AL should be treated as AL measurements obtained by OB. It is longer than IUS AL in long eyes.

Evaluation of intra-operative aphakic axial eye length measurements using swept source optical coherence tomography

PURPOSE

Evaluation of intra-operative aphakic axial eye length (AL) measurements using swept source optical coherence tomography.

SETTING

Hanusch Hospital, Vienna, Austria.

DESIGN

Prospective single-center study.

METHODS

Patients scheduled for cataract surgery were measured using swept-source optical coherence tomography (ss-OCT, IOLMaster 700, Carl Zeiss Meditec AG, Jena, Germany) to assess the axial eye length. Intra-operatively, swept source optical coherence tomography (ss-OCT) measurements were performed with a prototype device (IOLMaster 700 connected to an OPMI Lumera 700 microscope, CZM) at the beginning of cataract surgery furthermore of the aphakic eye and 2 months after surgery.

RESULTS

Of the 59 eyes of 59 patients, the phakic median AL pre-operatively (pre-OP) and intra operatively (intra-OP) were 23.61 mm ± 0.96 (SD) and 23.51 mm ± 0.96 (SD). Absolute median difference was 0.028 ± 0.02 (SD) (p=0.049). Median phakic AL intra-OP versus 2 months post operatively (post-OP) was 23.51 mm ± 0.97 (SD) vs 23.49 mm ± 0.95 (SD). Absolute median difference was 0.049 ± 0.04 (SD) (p=0.000).Median AL intra-OP aphakic versus vs 2 months post-Op pseudophakic were 23.42 mm ± 0.97 (SD) versus 23.42 mm ± 0.97 (SD). Absolute median difference was 0.038 ± 0.04 (SD) (p=0.379).

CONCLUSIONS

Intra-OP swept source OCT technology of the phakic and aphakic eye shows excellent comparability to pre- and post-operative measurements. This technique allows axial eye length measurements with high precision in cases where pre-op biometric measurements are not possible.

Preoperative measurements for cataract surgery: a comparison of ultrasound and optical biometric devices

PURPOSE

To evaluate differences in preoperative measurements and refractive outcomes between ultrasound and optical biometry when using the Barrett Universal II intraocular lens (IOL) power formula.

METHODS

In this consecutive case series, cataract extraction and IOL implantation cases from two surgical centers in Toronto, Canada, were recruited between January 2015 and July 2017. Differences between ultrasound (applanation or immersion A-scan) and optical biometry (IOLMaster 500) were compared for axial length (AL), anterior chamber depth and refractive outcomes. The primary outcome was the percentage of cases in each cohort within ± 0.50D of refractive error.

RESULTS

In total, 527 cataract cases underwent IOLMaster testing. Of these, 329 eyes (62.4%) were also measured by applanation A-scan, and the other 198 eyes (37.6%) received immersion A-scan testing. Applanation ultrasound led to 5.8%, 16.0% and 46.4% of eyes within ± 0.25D, ± 0.50D and ± 1.00D of refractive error, respectively, whereas the IOLMaster 500 led to 48.5%, 77.1% and 94.9%, respectively (n = 293, ± 0.50D: p < 0.001). Immersion ultrasound led to 31.2%, 57.6% and 91.2% of eyes within ± 0.25D, ± 0.50D and ± 1.00D of refractive error, respectively, whereas the IOLMaster 500 led to 42.4%, 72.0% and 92.0%, respectively (n = 125, ± 0.50D: p = 0.001). Applanation (n = 329, A-scan AL: 23.64 ± 1.67 mm, IOLMaster AL: 24.20 ± 1.70 mm, p < 0.001) and immersion ultrasound (n = 198, A-scan AL: 25.01 ± 2.06 mm, IOLMaster AL: 25.08 ± 2.13 mm, p = 0.002) yielded significantly lower AL values compared to optical biometry measurements.

CONCLUSIONS

Optical biometry yielded a significantly larger percentage of cases within ± 0.50D of refractive error compared to ultrasound biometry when using the Barrett Universal II IOL power formula.

Enhanced Penetration for Axial Length Measurement of Eyes with Dense Cataracts Using Swept Source Optical Coherence Tomography: A Consecutive Observational Study

Introduction

The aim of this study was to find cases in which the axial eye length could not be measured with partial coherence interferometry (PCI) technology and to assess if it could be measured using swept source optical coherence tomography (ss-OCT) technology.

Methods

All patients were measured at their pre-assessment visit 1 week prior to cataract surgery using conventional optical biometry (PCI technology, IOLMaster 500, Carl Zeiss Meditec AG, Jena, Germany). Patients in whom one or both eyes could not be measured using PCI technology were invited to participate in the study and to be measured with the ss-OCT (IOL Master 700, Carl Zeiss Meditec AG, Jena, Germany) device.

Results

Altogether, 1226 eyes of 613 patients were measured consecutively, and 78 eyes were not measured successfully with PCI technology. Among those with unsuccessfully measured eyes, 23 patients were willing to participate in the study, and two of those were also unsuccessfully measured with the ss-OCT device (8.7%, 2/23). However, 91.3% (21/23) of the eyes that were unsuccessfully scanned with PCI technology were measurable with the ss-OCT device. The estimated overall rate of unsuccessful scans with the ss-OCT device was 0.5% (6/1226) (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ p_{{\chi^{2} }} $$\end{document}pχ2 < 0.01).

Conclusion

ss-OCT technology significantly improves the rate of attainable axial eye length measurements, especially in eyes with posterior subcapsular cataracts, but also in eyes with dense nuclear cataracts, except for white cataracts.

Refractive Results Using a New Optical Biometry Device: Comparison With Ultrasound Biometry Data

The aim of the study was to compare the measurements of optical (AL-Scan; Nidek Co., Ltd.) and ultrasonic (Echo Scan US-800; Nidek Co., Ltd.) biometry devices and to assess refractive results after cataract surgery. Eighty-one cataractous eyes of 81 patients were included in this study. Biometry was performed using the AL-Scan and an ultrasonic biometer (USB). Axial length (AL), keratometry (K) data, and intraocular lens (IOL) power calculations using the SRK/T formula were compared. Bland-Altman analysis was used to assess the extent of agreement between AL-Scan and USB data in terms of AL measurement and IOL power calculation. The K measurements of the AL-Scan were compared to autorefractor data (Canon Autorefractor RK-F1). The AL-Scan assessed the AL as longer (average difference 0.06 ± 0.18 mm; ICC = 0.987; P < 0.001) and the IOL power as greater (average difference 0.19 ± 0.66 D; ICC = 0.964; P < 0.001) than the USB. The AL-Scan also measured average K values (average difference 0.25 ± 0.25 D; ICC = 0.985; P < 0.001) greater than those given by the autorefractor. The postoperative mean absolute error was +0.30 ± 0.04 D (minimum: -0.51 D, maximum +1.04 D). The postoperative mean K value change was 0.36 ± 0.29 D (P < 0.05). The differences between measurements afforded by the AL-Scan and USB may be clinically acceptable. Keratometric changes that develop after cataract operations compromise the attainment of good refractive outcomes.

Comparison of Optical versus Ultrasonic Biometry in Keratoconic Eyes

Purpose. To compare the measurements of optical versus ultrasonic biometry devices in keratoconic eyes. Materials and Methods. Forty-two eyes of 42 keratoconus (KC) patients enrolled in the study were examined. Clinical and demographic characteristics of the patients were noted, and detailed ophthalmological examination was performed. Following Pentacam measurements, central corneal thickness (CCT), anterior chamber depth (ACD), lens thickness (LT), and axial length (AL) were obtained using the Lenstar and US biometer to determine the reproducibility of the measurements between the two devices in keratoconic eyes. The Bland-Altman method was used to describe the agreement between the two devices. Results. The Lenstar could not measure at least one of the biometric properties in one eye and did not automatically give the corrected ACD in 2/3 of our study population. The Lenstar measured CCT (average difference 5.4 ± 19.6 µm; ICC = 0.90; P < 0.001), LT (average difference 0.13 ± 0.17 mm; ICC = 0.67; P < 0.001), and AL (average difference 0.10 ± 0.76 mm; ICC = 0.75; P < 0.001) thinner than US biometer, whereas it measured ACD (average difference 0.18 ± 0.17 mm; ICC = 0.85; P < 0.001) deeper than US biometer in keratoconic eyes. Conclusion. Although the difference between the measurements obtained using the two devices might be clinically acceptable, US biometry and Lenstar should not be used interchangeably for biometric measurements in KC patients.

Agreement analysis of LENSTAR with other techniques of biometry

PURPOSE

To assess the agreement of the optical low-coherence reflectometry (OLCR) device LENSTAR LS900 with partial coherence interferometry (PCI) device IOLMaster and applanation and immersion ultrasound biometry.

METHODS

We conducted the study at the Ophthalmology Clinic, University of Malaya Medical Center, Malaysia. Phakic eyes of 76 consecutive cataract patients were measured using four different methods: IOLMaster, LENSTAR and A-scan applanation and immersion ultrasound biometry. We assessed the method agreement in the LENSTAR-IOLMaster, LENSTAR-applanation, and LENSTAR-immersion comparisons for axial length (AL) and intraocular lens (IOL) power using Bland-Altman plots. For average K, we compared LENSTAR with IOLMaster and the TOPCON KR-8100 autorefractor-keratometer. SRK/T formula was used to compute IOL power, with emmetropia as the target refractive outcome.

RESULTS

For all the variables studied, LENSTAR agreement with IOLMaster is strongest, followed by those with immersion and applanation. For the LENSTAR-IOLMaster comparison, the estimated proportion of differences falling within 0.33 mm from zero AL and within 1D from zero IOL power is 100%. The estimated proportion of differences falling within 0.5 D from zero average K is almost 100% in the LENSTAR-IOLMaster comparison but 88% in the LENSTAR-TOPCON comparison. The proportion of differences falling within 0.10 mm (AL) and within 1D (IOL power) in the LENSTAR-IOLMaster comparison has practically significant discrepancy with that of LENSTAR-applanation and LENSTAR-immersion comparisons.

CONCLUSIONS

In phakic eyes of cataract patients, measurements of AL, average K, and IOL power calculated using the SRK/T formula from LENSTAR are biometrically equivalent to those from IOLMaster, but not with those from applanation and immersion ultrasound biometry.

Learning curve and interobserver reproducibility evaluation of liver stiffness measurement by transient elastography

BACKGROUND/AIMS

Fibroscan allows liver stiffness examination (LSE) that is well correlated with fibrosis stages. Our main objective was to evaluate LSE learning curve.

METHODS

LSE results of five novice observers with different medical status were compared with those of five expert observers (physicians with >100 examinations) in 250 patients with chronic liver disease. Each novice-expert pair had to blindly examine 50 consecutive patients divided into five consecutive subgroups of 10 patients.

RESULTS

In each observer group, novice-expert agreement [intraclass correlation coefficient (Ric)] for LSE results was excellent from the first to the last subgroup. Novice-expert agreement for LSE results varied with liver stiffness level: <9 kPa: Ric=0.49; >or=9 kPa: Ric=0.87. Relative difference (%) between novice and expert LSE results was independently associated with the number of valid LSE measurements, and stabilizes around 20-30% after the fourth valid measurement. In each observer group, novice-expert agreement (Ric) for LSE success rate progressively increased as a function of time.

CONCLUSION

LSE requires no learning curve: a novice is able to obtain a reliable result after a single training session, whatever the professional status. However, success rate will progressively increase. An LSE with less than four valid measurements should not be considered as reliable.

Corneal Radii and Anterior Chamber Depth Measurements Using the IOLMaster Versus the Pentacam

PURPOSE

Corneal radii (R1, R2) and anterior chamber depth are important parameters for biometry and refractive surgery. This study aimed to investigate whether the IOLMaster, a biometric device, and the Pentacam, a rotating Scheimpflug camera, provide comparable results.

METHODS

In this prospective study, corneal radii and anterior chamber depth were analyzed in 82 eyes of 41 phakic patients (median age 72 years) using the IOLMaster and Pentacam. Normal distribution was confirmed using the Kolmogorov-Smirnov test. A paired t test was used for statistical analysis.

RESULTS

No statistically significant difference was noted for R2 using the Pentacam versus the IOLMaster (P = .40). There was a small statistical difference of 0.03 mm (P < .01) for R1 (corresponding to 0.08 diopters [D]). The IOLMaster measured a mean R1 of 7.87 mm and R2 of 7.67 mm. The Pentacam measured mean R1 of 7.90 mm and R2 of 7.69 mm. For anterior chamber depth values, a small statistically significant difference of 0.05 mm (P < .001) was found (corresponding to 0.01 D). Mean anterior chamber depth measured from the epithelium was 3.20 mm for the IOLMaster and 3.25 mm for the Pentacam. The Bland-Altman plot showed no distorting trends for either variable.

CONCLUSIONS

Keratometry and anterior chamber depth were comparable for the two devices. If the axial length is known, the Pentacam can be used as a biometric device.

Anterior chamber width measurement by high-speed optical coherence tomography

OBJECTIVE

To measure anterior chamber (AC) width and other dimensions relevant to the sizing of phakic intraocular lenses (IOLs) with a high-speed optical coherence tomography (OCT) system.

DESIGN

Cross-sectional observational study.

PARTICIPANTS

Both eyes of 20 normal volunteers.

METHODS

A novel high-speed (4000 axial scans/second) OCT prototype was developed for anterior segment scanning. The system uses long wavelength (1310 nm) for deeper angle penetration, rectangular scanning for undistorted imaging, and short image acquisition time (0.125 seconds) to reduce motion error. Three horizontal cross-sectional OCT images (15.5 mm wide and 6 mm deep) of the anterior segment were obtained from each eye with real-time image display to guide centration on the corneal apex. Image processing software was developed to correct for image warping resulting from index transitions. Anterior chamber dimensions were measured using computer calipers by 3 expert raters (ophthalmologists). Analysis of variance was used to determine interrater, interimage, right versus left eye, and intersubject standard deviation (SD) of OCT measurements.

MAIN OUTCOME MEASURES

Anterior chamber width (recess to recess), AC depth, and crystalline lens vault as measured by OCT; external white-to-white (WTW) corneal diameter (CD) as measured by Holladay-Godwin gauge.

RESULTS

The mean AC width was 12.53+/-0.47 mm (intereye SD), and the mean corneal diameter was 11.78+/-0.57 mm. Optical coherence tomography measurement of AC width has good repeatability from image to image (SD, 0.134 mm), but there was significant difference between raters (SD, 0.215 mm). Estimation of AC width from WTW CD by linear regression was relatively inaccurate (residual SD, 0.41 mm). The mean AC depth was 2.99+/-0.323 mm (intereye SD), with repeatability of less than 0.001 mm (interimage SD), and the mean crystalline lens vault was 0.39+/-0.27 mm with 0.023 mm repeatability.

CONCLUSIONS

Reproducible OCT AC biometry was demonstrated using a high-speed OCT prototype. Further improvement in reproducibility may be achieved by automating the measurements with a computer. Direct OCT AC width measurement may improve sizing of angle-supported AC IOLs over conventional estimation by WTW CD. The measurement of AC depth and lens vault also may be useful for other types of phakic AC IOLs.

Biometry and intraocular lens power calculation

This article surveys the literature of 1 year, between July 2003 and August 2004, on the topic of biometry and intraocular lens power calculation for cataract surgery. There is an increasing demand for low postoperative refractive error with rising patient expectations, especially with patients who have already undergone refractive surgery, and with developing intraocular lens technologies such as multifocal, accommodating, or toric intraocular lenses. Optical biometry has become an invaluable tool for axial length measurement, especially for a setting with a less experienced biometrist. Introduction of ray tracing for power calculation and new methods of dealing with power calculation in eyes that have undergone previous refractive surgery seem promising. New intraocular lens designs that allow adjusting the axial optic position and therefore the effective refractive power of the intraocular lens have been evaluated in animal studies.