Agreement of Ocular Parameters and Calculated Intraocular Lens between Three Biometric Devices and a Corneal Topographer

doi:10.21203/rs.3.rs-1644515/v1

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Agreement of Ocular Parameters and Calculated Intraocular Lens between Three Biometric Devices and a Corneal Topographer

https://doi.org/10.21203/rs.3.rs-1644515/v1

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Cataract surgery is among the most common medical procedures, and accurate ocular biometry measurements are key for successful visual outcome. The current study evaluated agreement between the Eyestar 900, Anterion, IOLMaster700 biometers and the Pentacam corneal topographer. Clinical impact was assessed based on the calculated intraocular lens (IOL) of each biometry device. Compared values were axial length (AL), anterior chamber depth (ACD), steep and flat K, cylinder and axis. IOL was calculated for each biometry device using the mean values of every parameter and the Barrett and Kane formulas. This study included 196 eyes (98 participants) of cataract surgery candidates. When comparing the IOLMaster to the Eyestar 900 (157 eyes), no difference was found in mean AL or ACD measurements (P > 0.05). Steep K measurements differed between these devices and the Pentacam (P = 0.01). AL and ACD measurements differed between the IOLMaster and Anterion (38 eyes; P < 0.05). Strong correlations (range 0.72–0.99) were found between all four devices. Bland-Altman analysis demonstrated excellent agreement between biometry devices other than ACD between the IOLMaster and Eyestar 900. Spherical equivalent (SE) of the calculated IOL tended to be 0.50D lower with the IOLMaster, which could impact the residual refraction.

Cataract surgery, in which the opaque crystalline lens is replaced with an artificial intraocular lens (IOL), is one of the most common and successful medical procedures performed worldwide.^1,2 Ocular biometric parameters are measured before surgery in order to calculate the optimal IOL for the individual patient. The axial length (AL) of the eye, anterior chamber depth (ACD) and corneal curvature (K) measurements strongly impact the calculated IOL.³ Accurate pre-operative biometric measurements are considered one of the most important factors for successful surgical⁴, especially with the evolution of toric and multifocal IOLs which require the utmost surgical precision. As new or updated biometric devices are brought into clinical practice, it is important to thoroughly understand their capabilities, agreement with existing devices, and impact on IOL selection.

Swept-source optical coherence tomography (SS-OCT) is a non-invasive imaging modality that scans biological structures at high resolution, speed and sensitivity. The output volume of scans enables three-dimensional analysis of the given structure.⁵ Anterior segment OCT (ASOCT) scans the cornea, sclera and lens, thereby providing vital information for IOL selection in cataract surgeries. The Eyestar 900(Haag Streit Diagnostics, Koeniz, Switzerland) and Anterion (Heidelberg Engineering, Heidelberg, Germany) are two recently developed biometers based on the SS-ASOCT technology. In contrast, the Pentacam corneal tomographer (Oculus Inc., Wetzlar, Germany) measures the K values using a rotating Sheimpflug camera that acquires cross-sectional scans of the cornea.⁶ While several studies evaluating the ocular measurements have already shown good repeatability and agreement with established biometers^7,8, differences in specific parameters such as anterior chamber depth (ACD) and corneal curvatures (K) have been reported relative to SS-ASOCT devices such as the IOLMaster 700 and corneal tomographers such as the Pentacam. ^9–11 Additionally, there is limited data in the literature as to whether these differences have any clinical impact, i.e., whether they affect the final selection of IOL.^12,13 The purpose of this study was therefore to compare the ocular parameters measured by these two recent biometers to those measured by the IOLMaster 700 (Carl Zeiss Meditec, Jena, Germany), the first SS-OCT-based biometric device and one of the most commonly used devices for pre-cataract surgery measurements.¹⁴ To further investigate the accuracy of SS-OCT corneal measurements, these values were also compared to those obtained by the Pentacam (Oculus, Wetzlar, Germany) topographer. The final lens calculations based on the measurements of each biometric device were compared to examine the clinical impact.

This retrospective study followed the tenants of the Helsinki declaration and was approved by the institutional Helsinki Committee of Hadassah Medical Center (study number HMO-0459-18). The committee exempts retrospective research from informed consent by the participants. Data was collected from the Ophthalmology Department database and anonymized before analysis. Before biometric measurements, each participant underwent ophthalmic examination including best-corrected visual acuity (BCVA) with and without pinhole and full slit-lamp evaluation.

Ocular Measurements

Identical ocular parameters were measured using three different ocular biometry devices: the The Eyestar 900 (Haag Streit Diagnostics, Koeniz, Switzerland), the Anterion (Heidelberg Engineering, Heidelberg, Germany) and the IOLMaster 700 (Carl Zeiss Meditec, Jena, Germany). The parameters compared were axial length (AL), anterior chamber depth (ACD), anterior corneal values (steep- and flat-K), cylinder (cyl) and axis. Additionally, K values were compared to those obtained by the Pentacam corneal tomographer (Oculus Inc., Wetzlar, Germany). Measurements in all four devices were performed by optometrists with both the participants’ eyes open during each measurement. In cases where more than one measurement was performed for a single participant using the same instrument, only the most recent complete measurement was included in the final analysis.

The parameters included in this study have the greatest impact on IOL calculation. Therefore, in order to assess whether any discrepancies between the different devices would result in differences in the recommended IOL, the mean values of every parameter for each biometry device were entered in the Barrett Toric Calculator ¹⁵ and Kane Formula ¹⁶ and the final IOLs compared.

Participants

All participants included in this study were cataract surgery candidates who presented at the clinic for standard biometric measurements before surgery. Excluded were participants under age 40, with missing study parameters, and/or whose ocular measurements had a standard deviation greater than 0.05 (mm or D). Participants were measured using the Eyestar 900 and IOLMaster 700 (Group A) or the Anterion and IOLMaster 700 (Group B). A subset of each group had corneal values measured also with the Pentacam.

Statistical analysis

The normality of the data was confirmed using the Shapiro-Wilk test. AL, ACD, flat- and steep-K, cylinder and axis were compared using paired sample t-test or Friedman test. Cohen's d was performed on values that were significantly different in pairwise analysis in order to examine effect size and clinical significance. Correlation between parameters measured by different devices was evaluated with Pearson's coefficient. Mean values of AL, ACD and K’s of each device were used to calculate the recommended IOL by Barrett Toric and the Kane calculators. Bland and Altman analysis was used to identify systematic agreement between the measurements by the different devices and to identify outliers. Linear regression was used to assess the significance of agreement level between biometry devices. The analysis was performed using SPSS software (IBM SPSS Statistics, Version 27.0, Chicago. Armonk, NY: IBM Corp).

Patient characteristics

Records of 238 eyes (119 participants) were extracted from the Eyestar 900 and Anterion devices. This data was filtered for the current study based on age and data completeness, resulting in the exclusion of 42 eyes (17.6%). Ultimately, a total of 196 eyes (98 participants, 47.9% female, mean age 68.8 ± 9.7 years, range 42–88 years) were included in this study. Participants were divided to two groups: Group A consisted of 157 eyes (79 participants, 80.6%)) measured with the Eyestar and IOLMaster, with 48 eyes (24.4%) also measured by Pentacam. Group B consisted of 38 eyes (19 participants, 19.3%) measured with the Anterion and IOLMaster, with 22 eyes (11.22%) also measured by Pentacam. Table 1 describes the demographic characteristics of the study population.

Table 1

**Basic characteristics of study population.** ^aChi-Square; ^bIndependent sample t-test
	Group A	Group B	P
N eyes (participants)	157 (79)	38 (19)	NA
Female N (%)	78 (49.0)	16 (42.1)	0.42^a
Mean age ± SD (Y)	68.7 ± 10.0	69.1 ± 8.7	0.80^b
Age range (Y)	42.0–88.0	48.0–82.0	NA
Eyestar 900	157 eyes	NA	NA
IOLmaster 700	157 eyes	38 eyes	NA
Anterion	NA	38 eyes	NA
Pentacam	48 eyes	22 eyes	NA

Biometry results

In Group A there was no difference in mean AL values when comparing the IOLMaster (24.22 ± 2.0mm) to the Eyestar 900 (24.2 ± 2.04mm; P = 0.79; Cohen’s d 0.009). Mean ACD was also similar (3.34 ± 0.56mm vs. 3.36 ± 0.56mm, respectively; P = 0.09; Cohen’s d 0.03). No differences were found in mean flat and steep K values or in cylinder axis (Table 2). A sub-group of 48 eyes in Group A were also measured using the Pentacam. In this comparison, a difference was found in mean steep K measurements between the IOLMaster (45.02 ± 1.84D), the Eyestar (44.99 ± 1.85D) and the Pentacam (44.88 ± 1.76D) (P = 0.01). No differences were found in mean flat K values or in cylinder axis. (Table 2)

Table 2

Biometric parameters - mean differences (Group A)
	IOLmaster700 mean ± SD	Eyestar900 mean ± SD	Pentacam mean ± SD	P^a	Cohen's d
N	157	157	N/A
AL (mm)	24.22 ± 2.00	24.20 ± 2.04	N/A	0.79	0.009
ACD (mm)	3.34 ± 0.56	3.36 ± 0.56	N/A	0.09	0.03
Flat K (D)	43.23 ± 2.07	43.22 ± 2.09	N/A	0.64	0.004
Steep K (D)	44.52 ± 1.92	44.51 ± 1.95	N/A	0.65	0.005
Cyl (D)	1.31 ± 1.34	1.32 ± 1.33	N/A	0.61	0.007
N	48	48	48	P^b
Flat K (D)	43.12 ± 1.79	43.14 ± 188	43.17 ± 1.71	0.67	N/A
Steep K (D)	45.02 ± 1.84	44.99 ± 1.85	44.88 ± 1.76	0.01*	N/A
Cyl (D)	1.93 ± 1.66	1.92 ± 1.68	1.72 ± 1.50	0.16	N/A
Flat K axis (°)	83.17 ± 59.92	79.91 ± 57.74	89.59 ± 55.80	0.67	N/A
Steep K axis (°)	76.12 ± 54.12	80.47 ± 53.56	89.91 ± 58.51	0.25	N/A
ACD: anterior chamber depth; AL: Axial length; Cyl: cylinder
a: paired sample t-test
b: Friedman test

In Group B, mean AL values were different when comparing the IOLMaster to the Anterion (23.68 ± 1.27mm vs. 23.57 ± 1.27mm, respectively; P = 0.006; Cohen’s d 0.08). Mean ACD was also different (3.27 ± 0.73mm vs. 3.38 ± 0.78mm; P = 0.04; Cohen’s d 0.14). No differences were found in mean flat and steep K values or in cylinder axis. (Table 3) A sub-group of 22 eyes in Group B were also measured using the Pentacam. No significant differences were found in any corneal parameter between the IOMaster, Anterion and Pentacam. (Table 3)

Table 3

Biometric parameters - mean differences (Group B)
	IOLmaster700 mean ± SD	Anterion mean ± SD	Pentacam mean ± SD	P^a	Cohen's d
N	38	38	N/A
AL (mm)	23.68 ± 1.27	23.57 ± 1.27	N/A	0.006*	0.08
ACD (mm)	3.27 ± 0.73	3.38 ± 0.78	N/A	0.04*	0.14
Flat K (D)	43.73 ± 1.94	43.61 ± 1.83	N/A	0.19	0.06
Steep K (D)	45.51 ± 1.75	45.40 ± 1.97	N/A	0.51	0.05
Cyl (D)	1.77 ± 1.64	1.78 ± 1.79	N/A	0.94	0.005
N	22	22	22	P^b
Flat K (D)	43.33 ± 2.02	43.30 ± 1.96	43.45 ± 2.10	0.46	N/A
Steep K (D)	45.30 ± 2.11	45.33 ± 2.38	45.33 ± 2.38	0.23	N/A
Cyl (D)	1.96 ± 1.64	2.08 ± 1.88	1.82 ± 1.77	0.59	N/A
Flat K axis (°)	104.13 ± 61.34	90.81 ± 62.48	108.22 ± 59.62	0.31	N/A
Steep K axis (°)	79.59 ± 45.66	74.45 ± 45.17	73.63 ± 44.44	0.09	N/A
ACD: anterior chamber depth; AL: Axial length; Cyl: cylinder
a: paired sample t-test
b: Friedman test

Analysis of correlations and agreements across devices

When testing the correlations between the different devices, strong correlations were found between all four devices in AL, ACD, flat and steep K values and cylinder, ranging from R = 0.72 to 0.99. (Table 4) Comparison of cylinder axes between the different devices yielded weaker correlations, ranging from R = 0.32 to 0.95. (Table 4)

Table 4

Matrix of correlations
Parameter	Devices	r	P
AL	IOLMaster700-Anterion	0.99	< 0.001
AL	IOLMaster 700-Eyestar900	0.88	< 0.001
ACD	IOLMaster700-Anterion	0.93	< 0.001
ACD	IOLMaster 700-Eyestar900	0.90	< 0.001
Flat K	IOLMaster700-Eyestar	0.97	< 0.001
	IOLMaster700-Anterion	0.95	< 0.001
	IOLMaster700-Pentacam	0.95	< 0.001
	Eyestar-Pentacam	0.91	< 0.001
	Anterion-Pentacam	0.89	< 0.001
Flat K axis	IOLMaster700-Eyestar	0.67	< 0.001
	IOLMaster700-Anterion	0.39	0.01
	IOLMaster700-Pentacam	0.65	< 0.001
	Eyestar-Pentacam	0.51	< 0.001
	Anterion-Pentacam	0.32	0.13
Steep K	IOLMaster700-Eyestar	0.99	< 0.001
	IOLMaster700-Anterion	0.86	< 0.001
	IOLMaster700-Pentacam	0.97	< 0.001
	Eyestar-Pentacam	0.98	< 0.001
	Anterion-Pentacam	0.85	< 0.001
Steep K axis	IOLMaster700-Eyestar	0.64	< 0.001
	IOLMaster700-Anterion	0.88	< 0.001
	IOLMaster700-Pentacam	0.39	0.001
	Eyestar-Pentacam	0.36	0.01
	Anterion-Pentacam	0.95	< 0.001
Cyl	IOLMaster700-Eyestar	0.96	< 0.001
	IOLMaster700-Anterion	0.82	< 0.001
	IOLMaster700-Pentacam	0.95	< 0.001
	Eyestar-Pentacam	0.97	< 0.001
	Anterion-Pentacam	0.72	< 0.001
ACD: anterior chamber depth; AL: Axial length; Cyl: cylinder

Bland and Altman analysis was performed in order to assess the agreement between the biometry devices. A preliminary analysis demonstrated no difference between the IOLMaster and Eyestar and therefore AL, ACD, and flat and steep K values were all included in the agreement analysis. However, a difference between the IOLMaster and Anterion in mean AL and ACD values (P = 0.006, P = 0.04; respectively) was observed. Because these parameters did not show a useful level of agreement, there were not included in the Bland and Altman analysis.

When analyzing the linear regression line of the Bland and Altman scatter plot, IOLMaster and Eyestar values demonstrated no difference of proportional bias of scatter dots above and below the mean difference line for AL and flat and steep K values (P = 0.54, P = 0.69, P = 0.21, respectively). These devices differed in ACD values (P < 0.001), with a higher amount of ACD observations above the mean difference line. IOLmaster and Anterion flat and steep K plots were equally distributed above and below the mean difference line (P = 0.23, P = 0.18, respectively). (Fig. 1)

Effect of biometry measurements on IOL power calculation

In order to investigate whether the minor differences observed between the devices impacted the suggested IOL power, the mean output values of each biometry device (Tables 2 and 3) were inserted to the Barrett and Kane toric online calculators. Parameters were consistent between calculators: Bausch & Lomb MX60T lens, A-Constant 119.15, surgical induced astigmatism (SIA) 0, target refraction plano, and incision location at 100° for right eye of each IOL calculation. When comparing the IOLMaster and Eyestar (Group A) using the Barrett calculator, the calculated IOLs were 18.50/2.00 and 19.00/2.00, respectively. Using the Kane calculator, both IOLs were 19.00/2.25. In Group B, comparison of the IOLMaster and Anterion with the Barrett calculator yielded calculated IOLs of 19.50/2.75 and 20.00/2.75, respectively, and with the Kane calculator 20.00/2.25 and 20.50/2.25, respectively. It can be seen that the spherical equivalent (SE) of the suggested IOL based on the Barrett calculator was 0.50D lower in the IOLMaster relative to the Eyestar, but no difference was found using the Kane calculator. This same 0.50D difference was again found with both calculators when comparing the IOLMaster and Anterion.

This study aimed to compare the ocular parameters measured by two newly developed SS-OCT devices with an established biometer, and to compare the corneal measurements of all three devices to a Scheimpflug-based corneal topographer.

When comparing AL and ACD measurements, a statistically significant difference was found between IOLMaster and Anterion but not between the IOLMaster and Eyestar. However, Cohen’s d analysis demonstrated that these differences were not clinically significant, and all values were highly correlated. These results are in line with recent findings by Fişuş and collaborators, which revealed discrepancies between measurements of the Anterion and IOLMaster.⁹ Similarly, Tañá-Rivero et et al. also reported shorter ACD measurements with the IOLMaster relative to the Anterion.¹⁰ Like in the current study, the differences in measurements were found to be statistically significant but were minor enough to most likely be clinically insignificant.

No differences were found in the current study between any of the biometers in flat and steep K values or axes, yet when comparing these values to the Pentacam measurements, a statistically significant difference was observed between the IOLMaster, Eyestar and Pentacam in steep K values. Interestingly, the flat and steep K values were strongly correlated between all devices while axis values demonstrated low to medium correlations. Fişuş et al. did report significant differences in flat and steep K values⁹, but this may be due to differences in sample size. This is supported by the results presented by Tañá-Rivero et al., which did not find significant differences in K values and were based on a sample size similar to that of the current study.¹⁰ The matter of K axes has not yet been sufficiently studied and must be further investigated, as accurate axis measurements are vital for successful toric lens implantation.

In order to establish interchangeability of the devices, Bland and Altman analysis was performed. Our results indicated good agreement between all three biometers on most parameters, with a minor offset in ACD measurements between the IOLMaster and the Eyestar. Although Fişuş et al. advised against using the Anterion and IOLMaster interchangeably,⁹ the lack of clinically significant differences between the devices leads us to suggest that these two devices can be used interchangeably, between themselves as well as with the Eyestar.

The second aim of this study was to evaluate the clinical impact of the differences between the biometry devices. This was achieved by calculation of the suggested IOL based on the mean values of each device. Applying two commonly used IOL calculators, the IOLMaster tended to yield a suggested IOL with lower power relative to the Eyestar and Anterion. However, the difference found was 0.50 diopter, which is difficult to consider clinically significant as half a diopter is an acceptable surgical deviation. Similarly, Tañá-Sanz et al. and Shetty et al. reported differences in the calculated IOL between the IOLMaster and Anterion which were statistically significant but clinically insignificant.^12,13 It is important to take these results into account when selecting monofocal and premium IOLs, as clinicians seek to avoid hyperopic residual refraction post cataract surgery in the majority of cases.

This study had several limitations, primarily due to the retrospective study design which strongly influenced the data available for analysis and caused unequal sample sizes between groups. Additionally, because the study was not built prospectively, many viable measurements could not be included in the study since the patients had only undergone measurements by one biometric device. An even smaller sample size had measurements taken by two biometers and a corneal topographer, resulting in the small sub-groups with Pentacam data. The main strength of this study, however, is the comparison of three biometry devices, two of which are quite recent with limited data in the literature. Moreover, the comparison of corneal measurements between SS-OCT devices and a Scheimpflug-based device further validates both technologies and also provides a standard for comparison in cases of disagreement between the biometry devices.

In conclusion, all three biometers compared in this study demonstrated strong agreement and interchangeability, with corneal measurements correlating well to the Pentacam. However, it is important to note that the Eyestar was more similar to the IOLMaster in both AL and ACD, which are critical features in IOL calculation. Additionally, the devices differed slightly in the suggested IOL. While these differences were not found to be clinically significant in the current study, further investigation is needed in order to assess the impact on residual refraction post cataract surgery.

Acknowledgments

The authors thank Heidelberg Engineering and Haag Streit Diagnostics for the loan of the Anterion and Eyestar devices, and ARVO for the presentation of parts of this manuscript as an Annual Meeting abstract.

Author contribution

R.L. and H.B. wrote the main manuscript text. H.B. performed the statistical analysis and RL prepared the figures and tables. R.G., Z.B., L.B., I.N. and S.S. operated the instruments and performed the measurements. D.M. and C.K. collected the data and performed data entry. I.C. provided the design of the study and reviewed the manuscript.

Data availability statement

The data set generated during the current study is available from the corresponding authors on reasonable request.

Competing interests

The authors declare no competing interests

Ethical considerations

The institutional Helsinki committee exempts retrospective research from informed consent by the participants.

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No competing interests reported.

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You are reading this latest preprint version

Agreement of Ocular Parameters and Calculated Intraocular Lens between Three Biometric Devices and a Corneal Topographer

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Version 1

Abstract

Figures

Introduction

Methods

Ocular Measurements

Participants

Statistical analysis

Results

Patient characteristics

Biometry results

Analysis of correlations and agreements across devices

Effect of biometry measurements on IOL power calculation

Discussion

Declarations

References

Additional Declarations

Status:

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