Comparison of a new optical biometry with an optical low-coherence reflectometry for ocular biometry

Accuracy comparison of tomography devices for ray tracing-based intraocular lens calculation

PURPOSE

To evaluate the interchangeability of different tomography devices used for ray tracing-based intraocular lens (IOL) calculation.

SETTING

Eye clinic, Castrop-Rauxel, Germany.

DESIGN

Retrospective analysis.

METHOD

Measurements from 3 Placido-Scheimpflug devices and 3 optical coherence tomography (OCT) devices were compared in 83 and 161 other eyes after cataract surgery, respectively. 2-dimensional matrices of anterior local corneal curvature and local corneal thickness are transferred to the ray-tracing software OKULIX. Calculations are performed with the same IOL in the same position of an eye with the same axial length. Differences in spherical equivalent (SE), astigmatism, and spherical aberration are evaluated. Furthermore, the influence of the size of the matrices (optical zone) on the accuracy is quantified.

RESULTS

For the Placido-Scheimpflug devices, the deviations from the average of three measurements taken for each eye in SE (mean ± SD) were 0.17 ± 0.24 diopters (D), -0.26 ± 0.29 D, and 0.08 ± 0.39 D ( P < .001, analysis of variance [ANOVA]), for the centroids of the astigmatic differences 0.04 D/173 degrees, 0.14 D/93 degrees, and 0.10 D/7 degrees, and for the median of the absolute values of the vector differences 0.31 D, 0.33 D, and 0.29 D. For OCT devices, the corresponding results were 0.01 ± 0.21 D, -0.03 ± 0.21 D, and 0.02 ± 0.20 D ( P = .005, ANOVA); 0.18 D/120 degrees, 0.07 D/70 degrees, and 0.22 D/4 degrees; and 0.26 D, 0.30 D, and 0.33 D. The accuracy of the calculated spherical aberrations allows for an individual selection of the best fitting IOL model in most cases.

CONCLUSIONS

The differences are small enough to make the devices interchangeable regarding astigmatism and spherical aberration. Although there are significant differences in SE between Scheimpflug and OCT devices, the differences between OCT devices are also small enough to make them interchangeable, but the differences between Placido-Scheimpflug devices are too large to make these devices interchangeable.

Double peak axial length measurement signal in cataract patients with epiretinal membrane

PURPOSE

To evaluate the accuracy of axial length (AL) measurement for intraocular lens (IOL) calculation in patients with cataract and epiretinal membrane (ERM).

METHODS

This prospective, cross-sectional study was performed in cataract patients with ERM. All subjects were sent for standard optical biometry, prepared for cataract surgery. Signals of AL measurement were detected as double peaks and recorded as AL1 (first peak), and AL2 (second peak). The IOL power was calculated from AL1 and AL2, and reported as IOL1 and IOL2. The IOL2 was chosen for cataract surgery in all cases. Postoperative predictive errors were compared between IOL1 and IOL2.

RESULTS

Thirty-seven eyes from 37 patients were included. Mean AL1 was significantly shorter than AL2 (23.13 ± 1.28 vs. 23.60 ± 1.34 mm, p < 0.001), resulting in higher power of IOL1 than IOL2 (mean difference was 1.53 ± 0.96 diopters, p < 0.001). At 3-months post-operation, twenty-nine eyes (78.4%) (95% CI 62.8%-88.6%) showed refractive error within ± 0.5 diopter and all eyes were within ± 1.0 diopter. Postoperative predictive errors including mean arithmetic error (ME) and mean absolute error (MAE) of IOL2 were significantly lower than those of IOL1 (ME: IOL1 vs. IOL2, -0.94 ± 0.91 vs. 0.08 ± 0.51; MAE: 0.97 ± 0.88 vs. 0.39 ± 0.33 diopter, all p < 0.001).

CONCLUSIONS

AL measurement in ERM can be detected as a double peak signal during biometric measurement. The IOL power calculated from the first and second peak signals is significantly different. However, the IOL power derived from the second peak signal provides better refractive outcomes. The results suggest that the second peak signal represents an accurate AL measurement.

Prediction of residual astigmatism in cataract surgery at different diameter zones using optical biometry measurement

The studies for astigmatism prediction error at different diameters using optical biometry are scant. We investigated patients who underwent cataract surgery with monofocal, nontoric intraocular lens (IOL) from 2017 through 2019 in a medical center. Patients with prior refractive surgeries, corneal opacity, or surgical complications were excluded. Corneal astigmatism (CA) was measured using AL-Scan at 2.4- and 3.3-mm diameter zones and calculated using the Barrett toric calculator preoperatively and postoperatively. The mean absolute error and centroid prediction error for the two zones were computed using double-angle plots. In total, 101 eyes of 76 patients were analyzed. Mean patient age was 68.7 ± 9.3 years and mean preoperative CA power was 0.7 ± 0.5 D. The overall centroid prediction error a 3.3 mm (0.09 ± 0.58 D@25) was significantly lower than that at 2.4 mm (0.09 ± 0.68 D@87) on the X-axis (P = 0.003). The 3.3-mm measurement also had a lower centroid prediction error than the 2.4-mm did for eyes with against-the-rule (ATR) and oblique astigmatism (P = 0.024; 0.002 on X-axis, respectively). The 3.3-mm measurement provided a more accurate CA estimation than the 2.4-mm did, particularly for ATR astigmatism. Diameter zone and astigmatism type should be considered crucial to precise astigmatism calculation.

Comparison of a New Optical Biometer That Combines Scheimpflug Imaging With Partial Coherence Interferometry With That of an Optical Biometer Based on Swept-Source Optical Coherence Tomography and Placido-Disk Topography

PURPOSE

To evaluate measurement precision and to compare the Pentacam AXL (Oculus Optikgeräte, Wetzlar, German), a new optical biometer based on Scheimpflug imaging and partial coherence interferometry (PCI) with that of the OA-2000 biometer (Tomey, Nagoya, Japan), which combines swept-source optical coherence tomography (SS-OCT) and Placido-disk topography.

METHODS

Axial length (AL), central corneal thickness (CCT), anterior chamber depth (ACD), aqueous depth (AQD), mean keratometry (Km), astigmatism vectors J0, J45, and corneal diameter (CD) were measured in triplicate by two technical operators. Within-subject standard deviation (Sw), repeatability and reproducibility (2.77 Sw), coefficient of variation (CoV), and intraclass correlation coefficient (ICC) were used to assess the Pentacam AXL intra-observer repeatability and inter-observer reproducibility. Paired t-test and Bland-Altman plots were used to determine the agreement between the two biometers.

RESULTS

The new optical biometer had high intra-observer repeatability [all parameters evaluated had low CoV (<0.71%) and high ICC (>0.88)]. Inter-observer reproducibility was also excellent, with high ICC (>0.95) and low CoV (<0.52%). The 95% LoA between the new biometer and OA-2000 were insignificant for most of the parameters evaluated, especially for AL. However, the measurement agreement was moderate for CCT.

CONCLUSIONS

Intra-observer repeatability and inter-observer reproducibility were excellent for all parameters evaluated using the new optical biometer based on Scheimpflug imaging and PCI. There was a high agreement between the two devices and hence could be clinically interchangeable for the measurement of most ocular parameters.

Evaluation of 6 biometers based on different optical technologies

PURPOSE

To evaluate repeatability and agreement between various biometric parameters using 6 biometers based on different optical technologies.

SETTING

University of Valencia, Spain.

DESIGN

Prospective, comparative case series.

METHODS

150 eyes were measured using the Aladdin, AL-Scan, Argos, IOLMaster700, Lenstar LS900, and OA-2000 biometers. Keratometry (K1 and K2), J0 and J45, central corneal thickness (CCT), anterior chamber depth (ACD), lens thickness (LT), axial length (AL), white to white (WTW), and pupil size (PS) were measured 5 times with each device. Intrasubject SD, coefficient of variability (CoV), coefficient of repeatability, intraclass correlation coefficient, and Bland -Altman graphs were analyzed.

RESULTS

CoV values were <0.30% for K1, K2, and AL and up to 1.61% for CCT, ACD, LT, and WTW. PS values were higher (from 4.2% to 7.68%). There was statistically significant differences between biometers for all parameters evaluated (P < .001), and these differences varied as a function of the parameter analyzed. The limit of agreement (LoA) width of some comparisons for K1 and the majority for K2 were >0.50 diopter. A similar pattern was found for J0/J45. For CCT, many comparisons showed LoA width values of >25 μm. The LoA width for ACD ranged from 0.366 mm to 0.175 mm and for LT was about 0.2 mm. AL showed a highest LoA width of 0.225 mm. The LoA width for WTW was, in most cases, about ≥0.50 mm. The LoA width for PS ranged from 1.578 mm to 3.541 mm.

CONCLUSIONS

The 6 biometers provided repeatable measurements for the different parameters analyzed. The LoA obtained for each comparison should be analyzed carefully to consider the interchangeability of these devices.

Repeatability of 2 swept-source OCT biometers and 1 optical low-coherence reflectometry biometer

AIM

To compare the repeatability of 2 swept-source optical coherence tomography (SS-OCT) biometers, IOLMaster 700 (biometer A, Carl Zeiss Meditec AG) and ANTERION (biometer B, Heidelberg Engineering GmbH) and 1 optical low-coherence reflectometry (OLCR) device (biometer C, LENSTAR, LS900; Haag-Streit AG).

SETTING

Department of Ophthalmology, Hanusch Hospital, Vienna Institute for Research in Ocular Surgery-Karl Landsteiner Institute, Vienna, Austria.

DESIGN

Prospective study that included patients scheduled for cataract surgery.

METHOD

Three consecutive measurements were performed with 2 SS-OCT devices and 1 OLCR device. The repeatability of the following biometry variables was compared: keratometry, central corneal thickness, anterior chamber depth (ACD), lens thickness (LT), and axial eye length (AL). To assess the repeatability of each parameter, the within-subject SD (Sw) and coefficient of variation (CoV) were calculated.

RESULT

Fifty eyes of 50 patients were included. The CoV values were below 0.5 for all variables, except for ACD and LT for biometer C. The Sw values for mean keratometry were 0.018 for biometer A, 0.083 for biometer B, and 0.137 for biometer C. For the ACD, the Sw values were 0.039 and 0.004 for biometer A and biometer B, respectively, and 0.134 for biometer C. For the AL, the values were 0.006 for biometer A, 0.008 for biometer B, and 0.012 for biometer C.

CONCLUSIONS

All biometry devices included in the analysis presented a high repeatability. The SS-OCT devices showed a higher repeatability performance compared with the OLCR device.

Sources of Error in Toric Intraocular Lens Power Calculation

PURPOSE

To evaluate the influencing factors on remaining astigmatism after implanting a toric intraocular lens (IOL) during cataract surgery.

METHODS

This retrospective study included parameters that were considered to have an influence on toric IOL power calculation. Therefore, data from the literature and the authors' own data were used. This included axial eye length, anterior chamber depth, central corneal thickness, corneal radii (anterior and posterior), diurnal changes of the cornea, inter-device differences, rotational misalignment of the IOL, tilt and decentration of the IOL, pupil size, angle kappa, and surgically induced astigmatism. Ray-tracing and Gaussian error propagation analysis was performed to quantify the sources of error.

RESULTS

In total, 4,949 eyes (4,365 eyes of 42 studies and 584 eyes of retrospectively analyzed study data) were included in the study and the difference vector between aimed and calculated remaining astigmatism was 0.81 diopters (D). The main source of error was the preoperative measurement of the cornea (27%), followed by IOL misalignment (14.4%) and IOL tilt (11.3%). Other factors, such as angle kappa (10.9%), pupil size (8.1%), surgically induced astigmatism (7.8%), anterior chamber depth (7.5%), axial eye length (7.5%), and decentration (5.6%), also contributed to the refractive astigmatic error.

CONCLUSIONS

The main source of error in toric IOL power calculation is the preoperative corneal measurement followed by IOL misalignment and tilt. [J Refract Surg. 2020;36(10):646-652.].

Efficacy of Swept-source Optical Coherence Tomography in Axial Length Measurement for Advanced Cataract Patients

SIGNIFICANCE

A major limitation of standard time-domain optical coherence tomography-based biometers (TD-OCT) is an inability to measure the axial length (AL) in advanced cataract. A new device that uses swept-source optical coherence tomography (SS-OCT) allows better light penetration. Hence, a considerable number of cataract patients who failed AL measurement by TD-OCT can be recovered by SS-OCT.

PURPOSE

The purposes of this study were to evaluate the efficacy of an SS-OCT for AL measurement in advanced cataract patients and to identify characteristics of lens opacity that impede the AL measurement.

METHODS

Advanced cataract patients who were unable to obtain AL measurement using a standard TD-OCT-based optical biometer (IOLMaster500; Carl Zeiss Meditec, Jena, Germany) were recruited in this study. The AL was remeasured using SS-OCT (IOLMaster700), followed by measurement with immersion ultrasonography (IU). The percentage of patients who achieved AL measurement by SS-OCT was recorded. The AL obtained from SS-OCT was then verified by comparing with the AL derived from IU. The cataract type of each patient was classified according to standard Lens Opacity Classification III score. The association between characteristics of cataract and successful AL measurement by SS-OCT was analyzed.

RESULTS

Sixty-four eyes that failed AL measurement from TD-OCT were included. Fifty-six eyes (87.5%) were able to be measured by SS-OCT (95% confidence interval, 77.23 to 93.53%). The AL obtained by SS-OCT showed very high agreement with those derived from IU (intraclass correlation coefficient, 0.99). There was no statistically significant correlation between characteristics of lens opacity and the capability of SS-OCT for AL measurement (P > .05). However, there was a trend toward an inability to measure the AL in cataracts with a high grade of lens opacity.

CONCLUSIONS

The efficacy of SS-OCT-based optical biometer was excellent. Of the patients with advanced cataract who failed the AL measurement by TD-OCT, 87.5% could be recovered by SS-OCT. However, there was no specific type of lens opacity associated with a failure of AL measurement using SS-OCT.

Intraocular Lens Power Formulas, Biometry, and Intraoperative Aberrometry: A Review

The refractive outcome of cataract surgery is influenced by the choice of intraocular lens (IOL) power formula and the accuracy of the various devices used to measure the eye (including intraoperative aberrometry [IA]). This review aimed to cover the breadth of literature over the previous 10 years, focusing on 3 main questions: (1) What IOL power formulas currently are available and which is the most accurate? (2) What biometry devices are available, do the measurements they obtain differ from one another, and will this cause a clinically significant change in IOL power selection? and (3) Does IA improve refractive outcomes? A literature review was performed by searching the PubMed database for articles on each of these topics that identified 1313 articles, of which 166 were included in the review. For IOL power formulas, the Kane formula was the most accurate formula over the entire axial length (AL) spectrum and in both the short eye (AL, ≤22.0 mm) and long eye (AL, ≥26.0 mm) subgroups. Other formulas that performed well in the short-eye subgroup were the Olsen (4-factor), Haigis, and Hill-radial basis function (RBF) 1.0. In the long-eye group, the other formulas that performed well included the Barrett Universal II (BUII), Olsen (4-factor), or Holladay 1 with Wang-Koch adjustment. All biometry devices delivered highly reproducible measurements, and most comparative studies showed little difference in the average measures for all the biometric variables between devices. The differences seen resulted in minimal clinically significant effects on IOL power selection. The main difference found between devices was the ability to measure successfully through dense cataracts, with swept-source OCT-based machines performing better than partial coherence interferometry and optical low-coherence reflectometry devices. Intraoperative aberrometry generally improved outcomes for spherical and toric IOLs in eyes both with and without prior refractive surgery when the BUII and Hill-RBF, Barrett toric calculator, or Barrett True-K formulas were not used. When they were used, IA did not result in better outcomes.

Axial length growth and the risk of developing myopia in European children

PURPOSE

To generate percentile curves of axial length (AL) for European children, which can be used to estimate the risk of myopia in adulthood.

METHODS

A total of 12 386 participants from the population-based studies Generation R (Dutch children measured at both 6 and 9 years of age; N = 6934), the Avon Longitudinal Study of Parents and Children (ALSPAC) (British children 15 years of age; N = 2495) and the Rotterdam Study III (RS-III) (Dutch adults 57 years of age; N = 2957) contributed to this study. Axial length (AL) and corneal curvature data were available for all participants; objective cycloplegic refractive error was available only for the Dutch participants. We calculated a percentile score for each Dutch child at 6 and 9 years of age.

RESULTS

Mean (SD) AL was 22.36 (0.75) mm at 6 years, 23.10 (0.84) mm at 9 years, 23.41 (0.86) mm at 15 years and 23.67 (1.26) at adulthood. Axial length (AL) differences after the age of 15 occurred only in the upper 50%, with the highest difference within the 95th percentile and above. A total of 354 children showed accelerated axial growth and increased by more than 10 percentiles from age 6 to 9 years; 162 of these children (45.8%) were myopic at 9 years of age, compared to 4.8% (85/1781) for the children whose AL did not increase by more than 10 percentiles.

CONCLUSION

This study provides normative values for AL that can be used to monitor eye growth in European children. These results can help clinicians detect excessive eye growth at an early age, thereby facilitating decision-making with respect to interventions for preventing and/or controlling myopia.