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Agreement between lens thickness measurements by ultrasound immersion biometry and optical biometry
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ARTICLE
Agreement between lens thickness measurements by ultrasound immersion biometry and optical biometry Giacomo Savini, MD, Kenneth J. Hoffer, MD, Domenico Schiano-Lomoriello, MD
Purpose: To compare lens thickness measurements provided by immersion ultrasound (US) biometry and optical biometry. Setting: IRCCS-Fondazione Bietti, Rome, Italy. Design: Evaluation of diagnostic technology. Methods: Immersion US biometry and optical biometry were performed in a consecutive series of eyes having cataract surgery. Three optical biometers (OA-2000, Aladdin, and Galilei G6) were used. To assess how the differences in lens thickness measurements influenced intraocular lens (IOL) power calculation, the lens thickness values were entered into the Olsen formula. Results: Eighty-eight eyes were analyzed. Ultrasound immersion biometry yielded significantly higher lens thickness values than all of the optical biometers (P < .0001). The mean difference ranged
F
or many years, immersion ultrasound (US) biometry has been regarded as the gold standard for measuring the axial length (AL) of the eye.1–4 Since the IOLMaster (Carl Zeiss Meditec AG) was introduced in 1999, optical biometry has gradually gained popularity and is now considered the state of the art when dealing with axial eye measurements. Optical biometry offers two main advantages over US biometry; that is, it does not require water bath setup and it is based on automatic measurements requiring minimal skill. However, previous studies have not shown that optical biometry yields more accurate results in intraocular lens (IOL) power calculation because the few studies comparing the two techniques4–6 did not find one to be better than the other. The apparent equivalence of US immersion biometry and optical biometry in terms of accuracy is not surprising if we consider that optical biometry measurements were initially calibrated
between 0.29 mm and 0.43 mm. Although the differences between the 3 optical biometers were smaller, they were still statistically significant (P < .001). With respect to the immersion US biometry, lens thickness measurements using the optical biometric measurements would have resulted in the selection of a lower IOL power in between 43.2% and 62.5% of eyes, depending on the optical biometer. Comparison of the measurements of the 3 optical biometers showed that a different IOL power would have been selected in between 9.1% and 19.3% of eyes.
Conclusions: Lens thickness measurements by immersion US biometry and optical biometry cannot be considered interchangeable. Minor, but still significant, differences between the 3 optical biometers tested were also found. J Cataract Refract Surg 2018; -:-–- Q 2018 ASCRS and ESCRS
against US immersion biometry to obtain the same AL values and thus maintain the same formula lens constants.3 When comparing measurements by US immersion and optical biometry, most researchers have focused their attention on the AL and, to a lesser extent, the anterior chamber depth (ACD) (ie, the distance from the corneal epithelium to the anterior lens surface) because the AL is required by the most commonly used formulas, such as the Haigis,3 Hoffer Q,7,8 Holladay 1,9 and SRK/T,10 and the ACD is required by the Haigis formula. Newer formulas, however, also rely on lens thickness. Examples of this approach are the Olsen,11 Holladay 2,A and Barrett Universal IIB formulas. Lens thickness measurements have received little attention over the past two decades, and we are not sure whether the same values are provided by US immersion and optical biometry or whether difference exists between
Submitted: May 5, 2018 | Final revision submitted: June 26, 2018 | Accepted: July 19, 2018 From IRCCS-Fondazione Bietti (Savini, Schiano-Lomoriello), Rome, Italy; Stein Eye Institute (Hoffer), University of California, Los Angeles, and St. Mary’s Eye Center (Hoffer), Santa Monica, California, USA. Contribution of IRCCS-Fondazione Bietti supported by the Italian Ministry of Health and Fondazione Roma. Corresponding author: Giacomo Savini, MD, Fondazione G.B. Bietti - IRCCS Via Livenza, 3–Rome, Italy. Email: [email protected]. Q 2018 ASCRS and ESCRS Published by Elsevier Inc.
0886-3350/$ - see frontmatter https://doi.org/10.1016/j.jcrs.2018.07.057
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the measurements obtained with different optical biometers. Hence, the aim of this study was to compare axial measurements of lens thickness as well as of AL and ACD provided by US immersion biometry and 3 optical biometers based on different technologies as follows: optical low-coherence interferometry (OLCI), partial coherence interferometry (PCI), and swept-source optical coherence tomography (SS-OCT). PATIENTS AND METHODS This prospective observational study included consecutive adult patients scheduled for cataract surgery from January to December 2017 performed by the same surgeon (G.S.). One eye of each patient was analyzed. The Ethics Committee, G.B. Bietti Foundation IRCCS, approved the study. All patients provided informed consent, and the study complied with the tenets of the Declaration of Helsinki. Exclusion criteria were previous corneal or intraocular surgery, corneal disease (eg, keratoconus or marginal pellucid degeneration), previous contact lens wear in the past month, and retinal or optic nerve pathology that would affect postoperative visual acuity. Only eyes with a postoperative corrected distance visual acuity of 20/40 or better were enrolled. Instruments Three parameters (AL, ACD, and lens thickness) were measured by immersion US biometry (Ocuscan RX, Alcon Laboratories, Inc.) and 3 optical biometers: Aladdin (Topcon Europe Medical B.V.), Galilei G6 (Ziemer Ophthalmic Systems AG) and OA2000 (Tomey Corp.). Different US velocities were used for the aqueous and vitreous (1532 m/sec) and the cornea and lens (1641 m/sec). The 3 optical biometers use different technologies for measurements. The Aladdin (software version 1.6.0, Topcon Europe Medical B.V., Visia Imaging S.r.l.) combines an optical biometer and a Placido-ring topographer.12,13 Optical biometry relies on OLCI, based on an 830 nm superluminescent diode that is used to measure the AL, ACD, and lens thickness of the eye. Optical distances are converted into geometric distances using a group refractive index. As suggested by the manufacturer, each patient had 3 scans for a total of 18 AL, 3 ACD, and 3 lens thickness measurements, whose values were averaged. The Galilei G6 (software version 2.3.1, Ziemer Ophthalmic Systems AG) combines an optical biometer and a dual Scheimpflug analyzer.14 Optical biometry relies on PCI, based on an 880 nm A-scan interferometer that is used to measure the AL and lens thickness of the eye; optical distances are converted into geometric distances using a group refractive index. The ACD is measured by 2 oppositely rotating Scheimpflug cameras. Each patient had 1 scan, which produced a total of 1 ACD, 3 AL, and 3 lens thickness measurements. The averaged AL and lens thickness values provided in the final printout were analyzed. The OA-2000 (software version 1.0 R, Tomey Corp.) combines an optical biometer, based on SS-OCT, and a Placido-ring topographer.15,16 Swept-source OCT uses a wavelength of 1060 nm to measure AL, ACD, and lens thickness; a group refractive index is used to convert the optical path length into geometric distances. Each patient had 1 acquisition, for a total of 10 AL, 10 ACD, and 10 lens thickness measurements. The data provided in the final printout represented the average of the measurements of each parameter. Influence of Lens Thickness Measurement Differences on Intraocular Lens Power Calculation To assess how the differences in lens thickness measurements influenced IOL power calculation, the lens thickness values Volume - Issue - - 2018
measured by each instrument for each patient were entered into the Olsen formula.11 Phacooptics software (version 1.10.100.2032, IOL Innovations ApS) was used and two approaches were followed. In the first approach, the aim was to evaluate the influence of lens thickness alone; therefore, arbitrary keratometry (K) (43.00 diopters [D]), ACD (3.00 mm), and AL (23.00 mm) values were used in all eyes. In the second approach, the aim was to evaluate the influence of the combination of AL, ACD, and lens thickness; therefore, the individual AL and ACD values measured by each instrument were entered and a K value of 43.00 D was maintained in all cases. In both analyses, the IOL power to be selected for a given eye was the one with the lowest predicted myopic refraction. Statistical Analysis All statistical analyses were performed with Instat software (version 3.1, Graphpad Inc.). Normal distribution of data was assessed with the Kolmogorov-Smirnov test. Repeated-measures analysis of variance (ANOVA) with a Bonferroni posttest was used to compare AL and ACD measurements, which were normally distributed with all instruments. The Friedman test (nonparametric ANOVA) with the Dunn posttest was used to compare lens thickness measurements, which were not normally distributed. Linear regression was used to correlate age and lens thickness measurements. A P value less than .05 was considered statistically significant. Based on power and sample-size calculations performed using PS Power and Sample Size Calculations (version 3.0),C it was estimated that a sample size of 3 eyes would be necessary to detect a difference of 0.1 mm in lens thickness between any pair of biometers with a power of 95% at a significance level of 5%, given a within-subject standard deviation for lens thickness equal to 0.02 mm.16 Agreement was evaluated using 95% limits of agreement (LoA).17
RESULTS One hundred eyes of 100 consecutive patients having cataract surgery were enrolled. Five cases were excluded because of myopic staphyloma, which precluded a correct AL measurement by immersion US biometry. Seven more cases were excluded for failed acquisition by one or more devices because of subcapsular or very dense cataract (4 cases with the OLCI biometer; 5 cases with the PCI biometer). Hence, 88 eyes of 88 patients 47 women [53%]) were analyzed. The mean age of the patients was 68.3 years G 10.0 (SD) (range 39 to 90 years). Table 1 shows the mean values, standard deviations, and ranges of the measured parameters. Lens Thickness
Ultrasound immersion biometry yielded significantly higher lens thickness values than all 3 optical biometers (P ! .0001); the mean difference ranged from 0.29 mm (SS-OCT biometer) to 0.43 mm (PCI biometer). Although the differences between the 3 optical biometers were smaller, they were statistically significant according to the Dunn posttest (P ! .001). The SS-OCT biometer higher mean value was higher than the values of the other two optical biometers. Table 2 shows the 95% LoA for the lens thickness measurements. Linear regression found a positive correlation between age and lens thickness measurements by US immersion biometry (P Z .0001, r Z 0.4022, r2 Z 0.1618), SS-OCT biometry (P Z .0001, r Z 0.3952, r2 Z 0.1562), OLCI
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Table 1. Axial measurements provided by the 4 technologies. Parameter LT (mm) Mean G SD Range ACD (mm) Mean G SD Range AL (mm) Mean G SD Range
US Immersion
OLCI
PCI
SS-OCT
P Value
4.94 G 0.40 3.99, 5.74
4.59 G 0.42 3.64, 5.52
4.51 G 0.38 3.59, 5.26
4.66 G 0.39 3.68, 5.46
!.0001
3.29 G 0.37 2.26, 4.26
3.23 G 0.36 2.25, 4.27
3.26 G 0.37 2.24, 4.26
3.23 G 0.35 2.37, 4.26
!.0001
23.96 G 1.43 20.17, 28.47
24.02 G 1.46 20.21, 28.72
24.03 G 1.48 20.23, 28.79
24.02 G 1.46 20.25, 28.69
!.0001
ACD Z anterior chamber depth (epithelium to lens); AL Z axial length; LT Z lens thickness; OLCI Z optical low-coherence interferometry; PCI Z partial coherence interferometry; SS-OCT Z swept-source optical coherence tomography; US Z ultrasound
biometry (P ! .0001, r Z 0.4285, r2 Z 0.1836), and PCI biometry (P Z .0002, r Z 0.3863, r2 Z 0.1493). Anterior Chamber Depth
Although repeated-measures ANOVA showed a statistically significant difference between the 4 techniques (P ! .0001), the differences would have no clinical significance because they ranged between 0.03 mm and 0.06 mm. The highest mean value was provided by US immersion biometry. According to the Bonferroni posttest, the difference was significant between US immersion biometry and OLCI biometry, US immersion biometry, and SSOCT biometry, OLCI biometry and PCI biometry, and between PCI biometry and SS-OCT biometry. Axial Length
Again, repeated-measures ANOVA showed a statistically significant difference between the 4 techniques (P ! .0001). Ultrasound immersion biometry gave the lowest mean value, which was significantly different than those provided by the 3 optical biometers according to the Bonferroni posttest (P ! .001) (Table 1). The same test found there were no statistically significant differences in AL measurements between the 3 optical biometers. Intraocular Lens Power Calculation
When the lens thickness measurement provided by immersion US immersion biometry was entered into the Olsen formula and the eye model with constant AL, K, and ACD values, a mean IOL power of 21.75 G 0.37 D (range 21.00 to 22.50 D) was calculated. Using the optical biometric measurements of lens thickness would have resulted in the selection of a lower IOL power in 38 eyes (43.2%) with the SS-OCT biometer, 46 eyes (52.3%) with the OLCI biometer, and 55 eyes (62.5%) with the PCI biometer. In all cases, the difference would have been 0.50 D, the only
exception being 2 eyes in which the PCI biometer would have calculated an IOL with a 1.0 D difference. A different IOL power would have also been selected on the basis of the lens thickness measurements of the 3 optical biometers. More specifically, the OLCI biometer and the PCI biometer would have calculated an IOL with a lower power than the SS-OCT biometer in 8 cases (9.1%) and 17 cases (19.3%), respectively. When the individual ACD, lens thickness, and AL measurement provided by immersion US biometry were entered into the Olsen formula, a mean IOL power of 21.40 G 4.72 D (range 8.50 to 36.00 D) was calculated. A lower mean IOL power was calculated with the optical biometers. The mean IOL power was 20.89 G 4.68 D for the OLCI biometer, 20.83 G 4.74 D for the PCI biometer, and 20.90 G 4.72 D for the SS-OCT biometer; the range was 7.50 to 35.00 D for all optical biometers. The ANOVA shows that the difference between immersion US biometry and optical biometry was statistically significant (P ! .0001). Using the optical biometry measurements would have resulted in the selection of an IOL power lower than that using US immersion biometry in 69 eyes (78.4%) with the SS-OCT biometer, 71 eyes (80.7%) with the OLCI biometer, and in 70 eyes (79.6%) with the PCI biometer. In most cases the difference was 0.50 D, with a maximum value of 1.50 D. Different IOL powers would have been selected also when comparing the 3 optical biometers. With the OLCI biometer, an IOL with a different power than with the SS-OCT biometer and the PCI biometer would have been selected in 18 eyes (20.4%) and 35 eyes (40.91%), respectively. With the SS-OCT biometer, an IOL with a different power than with the PCI biometer would have been selected in 29 eyes (32.9%). In these cases, the maximum difference was 1.00 D. DISCUSSION Optical biometry was introduced in 1999; however, the first optical biometer able to measure lens thickness became
Table 2. Agreement between the 3 optical biometers in measuring lens thickness. Parameter
OLCI L PCI
Mean difference (mm) GSD 95% limits of agreement (mm)
0.08 G 0.12 0.16, 0.32
OLCI L SS-OCT 0.06 G 0.09 0.24, 0.11
PCI L SS-OCT 0.15 G 0.09 0.33, 0.03
OLCI Z optical low-coherence interferometry; PCI Z partial coherence interferometry; SS-OCT Z swept-source optical coherence tomography
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available only 10 years later with the introduction of the Lenstar 900 (Haag-Streit AG), which is based on OLCR. Since then, several optical biometers have been introduced, and most of them measure lens thickness. However, lens thickness measurements have received little attention, despite the increasing use of this parameter for IOL power calculation. The only two studies comparing lens thickness measurements by US biometry and optical biometry found opposite results. In 1998, Drexler et al.18 reported that lens thickness measurements by applanation US biometry were lower than those provided by a PCI prototype (4.53 G 0.56 mm versus 4.65 G 0.48 mm). In 2016, Aydin et al.19 reported the opposite; namely, that lens thickness measurements by applanation US biometry were higher than those obtained by OLCR (4.33 G 0.49 mm versus 4.20 G 0.44 mm). Our findings are closer to those reported by Aydin et al. because we found that lens thickness measurements obtained using immersion US biometry are significantly higher than those given by any optical biometer. This difference has a clinical impact on IOL power calculation because it would have led to the selection of a different IOL power in a high percentage of cases when using a formula such as Olsen’s,11 which predicts the IOL position on the basis of lens thickness and was developed using optical biometry. In the first eye model, in which we used fixed AL, K, and ACD values to highlight the influence of lens thickness measurements, a different IOL power would have been recommended in about half of the eyes. In the second eye model, in which we used individual AL and ACD values, the percentage was close to 80% of cases. In this model, a different IOL power would have also been selected in a relevant percentage of cases (between 20% and 40%) when using optical biometry measurements only. Future studies are needed to assess which technique of measuring lens thickness leads to more accurate results with the Olsen formula.11 The difference between the lens thickness measurements provided by US immersion biometry and optical biometry is most likely because of the different ability of the two technologies to detect the anterior and posterior edges of the lenses. We initially thought that it might further depend on the fact that US biometry separately measures each segment with a specific sound velocity, although the 1641 m/sec value selected for the lens US velocity is an average and large variations can occur according to the density of the cataract.20,21 In contrast, optical biometers are known to use a single group refractive index to calculate the geometric distances from the optical path length (as originally proposed by Haigis for the IOLMaster3). However, all manufacturers have told us that their device uses a specific refractive index when calculating the lens thickness. Hence, the use of a group refractive index cannot be considered an explanation of the difference in lens thickness between US biometry and optical biometry. Other studies have evaluated the agreement in lens thickness measurements between different optical biometers. In Volume - Issue - - 2018
a previous study,22 our group did not find a statistically significant difference between the values provided by the IOLMaster 700 biometer (Carl Zeiss Meditec AG) and the Lenstar biometer, whose measurements (4.59 G 0.43 and 4.62 G 0.44 mm, respectively) were close to those for the Aladdin biometer and OA-2000 biometer in our study. Similarly, no statistically significant differences were detected between the IOLMaster 700 biometer and the Aladdin and Galilei G6 biometers.23,24 In contrast, Shammas et al.25 found a mean difference of 0.22 mm between the Argos biometer (Movu, Inc.) and the Lenstar 900 biometer. In the present study, although the differences between the 3 optical biometers were small, they were statistically significant and would have led to the choice of different IOL powers in a significant number of eyes. Therefore, we recommend that the lens thickness measurements of different optical biometers not be considered interchangeable. The mean lens thickness value measured by immersion US biometry in the present study (4.94 G 0.40 mm) is higher than the value reported by Drexler et al.18 (4.53 G 0.56 mm) and Olsen and Thorwest26 (4.67 G 0.55 mm), who used contact US biometry. We cannot attribute this discrepancy to a difference in the age of patients because the mean age of our cohort (68.3 years) was only slightly lower (4 to 8 years) than the mean age of the samples in the Drexler et al. and Olsen and Thorwest studies (76.0 years and 74.1 years, respectively) and lens thickness is known to increase with age.27 Moreover, the mean value of lens thickness using immersion US biometry in our study is higher than the mean value (4.63 mm) reported by Hoffer27 in any age group. The use of different instruments is the most likely explanation because the indentation required for contact biometry should not play a role in lens thickness measurement. Racial and ethnic differences might also be involved, as suggested in a recent review that reported notable differences in lens thickness between ethnic groups.28 We believe that ours is the first study of lens thickness performed on western hemisphere patients from southern Europe. The ACD measurements were minimally (although statistically significantly) different between the 4 techniques, with US immersion biometry yielding a slightly higher mean value. Such discrepancies were 0.06 mm or less and are unlikely to influence IOL power calculation. Comparison with previous studies is difficult because in most cases contact applanation US biometry was used and this method is known to produce falsely low ACD measurements because of corneal indentation. Few studies have assessed ACD measurements by immersion US biometry in phakic eyes. Landers and Goggins29 found that similar mean measurements were provided by immersion US biometry (3.05 G 0.37) and the IOLMaster biometer (3.02 G 0.44). Other studies compared ACD measurements by immersion US biometry with those obtained using different techniques, such as optical pachymetry30 or anterior segment OCT31; thus, their findings cannot be matched against our results. On the other hand, ACD
LENS THICKNESS MEASUREMENTS
measurements by the Galilei G6 biometer have been reported to be similar to those provided by other optical biometers, such as the Lenstar32 and the IOLMaster 500.14 Finally, the AL measurements provided by the 3 optical biometers were not statistically different, whereas the ALs measured by immersion US biometry were slightly shorter, with a mean difference of 0.06 to 0.07 mm, which is sufficient to require specific constant optimization with any formula for calculating IOL power. Although the lack of a significant difference between the 3 biometers is not surprising given the large number of studies that found similar results,14,15,33,34 the difference compared with immersion US biometry was unexpected because optical biometry was originally calibrated to match immersion US biometry.3 We can postulate that the difference observed in the present study is related to a systematic difference in the measurements provided by our US biometer and the biometer originally used by Haigis et al.3 This study has limitations. We did not evaluate all available optical biometers, and we did not enroll healthy eyes with clear lenses, for which the results may be different. We did not assess the repeatability of lens thickness measurements because previous studies have reported that repeatability is high for all measurements by two of the tested optical biometers13,16 as well for measurements by a previous version of the dual Scheimpflug analyzer.35 However repeatability for lens thickness data are lacking for Galilei G6 biometer and for US immersion biometry and will be the target of future studies. In conclusion, we found that lens thickness measurements by immersion US biometry and optical biometry cannot be considered interchangeable and might lead to different results when entered into IOL power formulas requiring this parameter to estimate the position of the IOL.
WHAT WAS KNOWN Lens thickness is used by several formulas to estimate the IOL position and calculate its power. Lens thickness measurements obtained using US-based and optical methods have been compared in few studies with conflicting results.
WHAT THIS PAPER ADDS In older patients with cataract, lens thickness measurements obtained using immersion US biometry and 3 different optical biometry techniques showed significant differences and therefore cannot be considered interchangeable.
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4. Packer M, Fine IH, Hoffman RS, Coffman PG, Brown LK. Immersion A-scan compared with partial coherence interferometry; outcomes analysis. J Cataract Refract Surg 2002; 28:239–242 5. Kiss B, Findl O, Menapace R, Wirtitsch M, Petternel V, Drexler W, Rainer G, Georgopoulos M, Hitzenberger CK, Fercher AF. Refractive outcome of cataract surgery using partial coherence interferometry and ultrasound biometry: clinical feasibility study of a commercial prototype II. J Cataract Refract Surg 2002; 28:230–234 ez J, Cherwek DH, Stulting RD, Waldron R, Zimmerman GJ, 6. Narva Wessels IE, Waring GO III. Comparing immersion ultrasound with partial coherence interferometry for intraocular lens power calculation. Ophthalmic Surg Lasers Imaging 2008; 39:30–34 7. Hoffer KJ. The Hoffer Q formula: a comparison of theoretic and regression formulas. J Cataract Refract Surg 1993; 19:700–712; errata, 1994; 20:677 8. Zuberbuhler B, Morrell AJ. Errata in printed Hoffer Q formula [letter]. J Cataract Refract Surg 2007; 33:2; reply by KJ Hoffer, 2–3 9. Holladay JT, Prager TC, Chandler TY, Musgrove KH, Lewis JW, Ruiz RS. A three-part system for refining intraocular lens power calculations. J Cataract Refract Surg 1988; 14:17–24 10. Retzlaff JA, Sanders DR, Kraff MC. Development of the SRK/T intraocular lens power calculation formula. J Cataract Refract Surg 1990; 16:333– 340; erratum, 528 11. Olsen T, Hoffmann P. C constant: new concept for ray tracing–assisted intraocular lens power calculation. J Cataract Refract Surg 2014; 40:764–773 12. Mandal P, Berrow EJ, Naroo SA, Wolffsohn JS, Uthoff D, Holland D, Shah S. Validity and repeatability of the Aladdin ocular biometer. Br J Ophthalmol 2014; 98:256–258 13. Huang J, Savini G, Wu F, Yu X, Yang J, Yu A, Yu Y, Wang Q. Repeatability and reproducibility of ocular biometry using a new noncontact optical lowcoherence interferometer. J Cataract Refract Surg 2015; 41:2233–2241 14. Ventura BV, Ventura MC, Wang L, Koch DD, Weikert MP. Comparison of biometry and intraocular lens power calculation performed by a new optical biometry device and a reference biometer. J Cataract Refract Surg 2017; 43:74–79 15. Savini G, Hoffer KJ, Shammas HJ, Aramberri J, Huang J, Barboni P. Accuracy of a new swept-source optical coherence tomography biometer for IOL power calculation and comparison to IOLMaster. J Refract Surg 2017; 33:690–695 16. Huang J, Savini G, Hoffer KJ, Chen H, Lu W, Hu Q, Bao F, Wang Q. Repeatability and interobserver reproducibility of a new optical biometer based on swept-source optical coherence tomography and comparison with IOLMaster. Br J Ophthalmol 2017; 101:493–498 17. Bland JM, Altman DG. Measurement error [Statistics notes]. BMJ 1996; 313:744 18. Drexler W, Findl O, Menapace R, Rainer G, Vass C, Hitzenberger CK, Fercher AF. Partial coherence interferometry: a novel approach to biometry in cataract surgery. Am J Ophthalmol 1998; 126:524–534 19. Aydin R, Karaman Erdur S, Serefoglu Cabuk K, Karahan E, Kaynak S. Comparison of optical low coherence reflectometry versus ultrasonic biometry in high hypermetropia. Eye Contact Lens 2016 [Epub ahead of print] 20. Pallikaris I, Gruber H. Determination of sound velocity in different forms of cataracts. In: Thijssen JM, Verbeek AM, eds, Ultrasonography in Ophthalmology. Proceedings of the 8th SIDUO Congress, Nijmegen, The Netherlands, 1980. Doc Ophthalmol Proc Ser, , 1981; 29:165–169 21. Massin M, Lambrinakis I. In vivo determination of the speed of ultrasound in cataracted lenses. In: Sampaolesi R, ed, Ultrasonography in Ophthal Falls, Argentina, mology. Proceedings of the 12th SIDUO Congress, Iguazu 1988. Doc Ophthalmol Proc Ser, , 1990; 12:131–134 22. Hoffer KJ, Hoffmann PC, Savini G. Comparison of a new optical biometer using swept-source optical coherence tomography and a biometer using optical low-coherence reflectometry. J Cataract Refract Surg 2016; 42:1165–1172 23. Calvo-Sanz JA, Portero-Benito A, Arias-Puente A. Efficiency and measurements agreement between swept-source OCT and low-coherence interferometry biometry systems. Graefes Arch Clin Exp Ophthalmol 2018; 256:559–566 24. Jung S, Chin HS, Kim NR, Lee KW, Jung JW. Comparison of repeatability and agreement between swept-source optical biometry and dualScheimpflug topography. J Ophthalmol 2017 article ID1516395 25. Shammas HJ, Ortiz S, Shammas MC, Kim SH, Chong C. Biometry measurements using a new large-coherence–length swept-source optical coherence tomographer. J Cataract Refract Surg 2016; 42:50–61 26. Olsen T, Thorwest M. Calibration of axial length measurements with the Zeiss IOLMaster. J Cataract Refract Surg 2005; 31:1345–1350 27. Hoffer KJ. Axial dimension of the human cataractous lens. Arch Ophthalmol 1993; 111:914–918; correction, 1626
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28. Hoffer KJ, Savini G. Effect of gender and race on ocular biometry. Int Ophthalmol Clin 2017; 57 (3):137–142 29. Landers J, Goggin M. Comparison of refractive outcomes using immersion ultrasound biometry and IOLMaster biometry. Clin Exp Ophthalmol 2009; 37:566–569 30. Hoffer KJ, Savini G. Anterior chamber depth studies. J Cataract Refract Surg 2015; 41:1898–1904 31. Nemeth G, Vajas A, Tsorbatzoglou A, Kolozsvari B, Modis L Jr, Berta A. Assessment and reproducibility of anterior chamber depth measurement with anterior segment optical coherence tomography compared with immersion ultrasonography. J Cataract Refract Surg 2007; 33:443–447 32. Shin MC, Chung SY, Hwang HS, Han KE. Comparison of two optical biometers. Optom Vis Sci 2016; 93:259–265 33. Hoffer KJ, Shammas HJ, Savini G. Comparison of 2 laser instruments for measuring axial length. J Cataract Refract Surg 2010; 36:644–648; erratum, 1066 34. Hoffer KJ, Shammas HJ, Savini G, Huang J. Multicenter study of optical low-coherence interferometry and partial-coherence interferometry optical biometers with patients from the United States and China. J Cataract Refract Surg 2016; 42:62–67 35. Savini G, Carbonelli M, Barboni P, Hoffer KJ. Repeatability of automatic measurements performed by a dual Scheimpflug analyzer in unoperated and post-refractive surgery eyes. J Cataract Refract Surg 2011; 37:302–309
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OTHER CITED MATERIAL A. Holladay JT. Holladay IOL Consultant Software & Surgical Outcomes Assessment. Bellaire, TX, Holladay Consulting, 2015; Available at: http: //www.hicsoap.com. Accessed August 13, 2018 B. Barrett GD. Barrett Universal II Formula. Singapore, Asia-Pacific Association of Cataract and Refractive Surgeons. Available at: http://www.apacrs .org/barrett_universal2/. Accessed August 13, 2018 C. Dupont WD, Plummer WDJr PS. Power and Sample Size Calculation. Nashville, TN, Department of Biostatistics, Vanderbilt University, 2014; Available at: http://biostat.mc.vanderbilt.edu/wiki/Main/PowerSampleSize. Accessed August 13, 2018
Disclosures: Dr. Hoffer licenses the registered trademark name Hoffer to ensure accurate programming of his formulas to Carl Zeiss Meditec AG (IOLMasters), Haag-Streit AG (Lenstar), Oculus €te GmbH (Pentacam AXL), Movu, Inc. (Argos), Nidek Co., Optikgera Ltd. (AL-Scan), Tomey Corp. (OA-2000), Topcon Europe Medical B.V./Visia Imaging S.r.l. (Aladdin), Ziemer Ophthalmic Systems AG (Galilei G6), and all A-scan biometer manufacturers except Alcon Laboratories, Inc. (Verion). Neither of the other authors has a financial or proprietary interest in any material or method mentioned.
ARTICLE
Agreement between lens thickness measurements by ultrasound immersion biometry and optical biometry Giacomo Savini, MD, Kenneth J. Hoffer, MD, Domenico Schiano-Lomoriello, MD
Purpose: To compare lens thickness measurements provided by immersion ultrasound (US) biometry and optical biometry. Setting: IRCCS-Fondazione Bietti, Rome, Italy. Design: Evaluation of diagnostic technology. Methods: Immersion US biometry and optical biometry were performed in a consecutive series of eyes having cataract surgery. Three optical biometers (OA-2000, Aladdin, and Galilei G6) were used. To assess how the differences in lens thickness measurements influenced intraocular lens (IOL) power calculation, the lens thickness values were entered into the Olsen formula. Results: Eighty-eight eyes were analyzed. Ultrasound immersion biometry yielded significantly higher lens thickness values than all of the optical biometers (P < .0001). The mean difference ranged
F
or many years, immersion ultrasound (US) biometry has been regarded as the gold standard for measuring the axial length (AL) of the eye.1–4 Since the IOLMaster (Carl Zeiss Meditec AG) was introduced in 1999, optical biometry has gradually gained popularity and is now considered the state of the art when dealing with axial eye measurements. Optical biometry offers two main advantages over US biometry; that is, it does not require water bath setup and it is based on automatic measurements requiring minimal skill. However, previous studies have not shown that optical biometry yields more accurate results in intraocular lens (IOL) power calculation because the few studies comparing the two techniques4–6 did not find one to be better than the other. The apparent equivalence of US immersion biometry and optical biometry in terms of accuracy is not surprising if we consider that optical biometry measurements were initially calibrated
between 0.29 mm and 0.43 mm. Although the differences between the 3 optical biometers were smaller, they were still statistically significant (P < .001). With respect to the immersion US biometry, lens thickness measurements using the optical biometric measurements would have resulted in the selection of a lower IOL power in between 43.2% and 62.5% of eyes, depending on the optical biometer. Comparison of the measurements of the 3 optical biometers showed that a different IOL power would have been selected in between 9.1% and 19.3% of eyes.
Conclusions: Lens thickness measurements by immersion US biometry and optical biometry cannot be considered interchangeable. Minor, but still significant, differences between the 3 optical biometers tested were also found. J Cataract Refract Surg 2018; -:-–- Q 2018 ASCRS and ESCRS
against US immersion biometry to obtain the same AL values and thus maintain the same formula lens constants.3 When comparing measurements by US immersion and optical biometry, most researchers have focused their attention on the AL and, to a lesser extent, the anterior chamber depth (ACD) (ie, the distance from the corneal epithelium to the anterior lens surface) because the AL is required by the most commonly used formulas, such as the Haigis,3 Hoffer Q,7,8 Holladay 1,9 and SRK/T,10 and the ACD is required by the Haigis formula. Newer formulas, however, also rely on lens thickness. Examples of this approach are the Olsen,11 Holladay 2,A and Barrett Universal IIB formulas. Lens thickness measurements have received little attention over the past two decades, and we are not sure whether the same values are provided by US immersion and optical biometry or whether difference exists between
Submitted: May 5, 2018 | Final revision submitted: June 26, 2018 | Accepted: July 19, 2018 From IRCCS-Fondazione Bietti (Savini, Schiano-Lomoriello), Rome, Italy; Stein Eye Institute (Hoffer), University of California, Los Angeles, and St. Mary’s Eye Center (Hoffer), Santa Monica, California, USA. Contribution of IRCCS-Fondazione Bietti supported by the Italian Ministry of Health and Fondazione Roma. Corresponding author: Giacomo Savini, MD, Fondazione G.B. Bietti - IRCCS Via Livenza, 3–Rome, Italy. Email: [email protected]. Q 2018 ASCRS and ESCRS Published by Elsevier Inc.
0886-3350/$ - see frontmatter https://doi.org/10.1016/j.jcrs.2018.07.057
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the measurements obtained with different optical biometers. Hence, the aim of this study was to compare axial measurements of lens thickness as well as of AL and ACD provided by US immersion biometry and 3 optical biometers based on different technologies as follows: optical low-coherence interferometry (OLCI), partial coherence interferometry (PCI), and swept-source optical coherence tomography (SS-OCT). PATIENTS AND METHODS This prospective observational study included consecutive adult patients scheduled for cataract surgery from January to December 2017 performed by the same surgeon (G.S.). One eye of each patient was analyzed. The Ethics Committee, G.B. Bietti Foundation IRCCS, approved the study. All patients provided informed consent, and the study complied with the tenets of the Declaration of Helsinki. Exclusion criteria were previous corneal or intraocular surgery, corneal disease (eg, keratoconus or marginal pellucid degeneration), previous contact lens wear in the past month, and retinal or optic nerve pathology that would affect postoperative visual acuity. Only eyes with a postoperative corrected distance visual acuity of 20/40 or better were enrolled. Instruments Three parameters (AL, ACD, and lens thickness) were measured by immersion US biometry (Ocuscan RX, Alcon Laboratories, Inc.) and 3 optical biometers: Aladdin (Topcon Europe Medical B.V.), Galilei G6 (Ziemer Ophthalmic Systems AG) and OA2000 (Tomey Corp.). Different US velocities were used for the aqueous and vitreous (1532 m/sec) and the cornea and lens (1641 m/sec). The 3 optical biometers use different technologies for measurements. The Aladdin (software version 1.6.0, Topcon Europe Medical B.V., Visia Imaging S.r.l.) combines an optical biometer and a Placido-ring topographer.12,13 Optical biometry relies on OLCI, based on an 830 nm superluminescent diode that is used to measure the AL, ACD, and lens thickness of the eye. Optical distances are converted into geometric distances using a group refractive index. As suggested by the manufacturer, each patient had 3 scans for a total of 18 AL, 3 ACD, and 3 lens thickness measurements, whose values were averaged. The Galilei G6 (software version 2.3.1, Ziemer Ophthalmic Systems AG) combines an optical biometer and a dual Scheimpflug analyzer.14 Optical biometry relies on PCI, based on an 880 nm A-scan interferometer that is used to measure the AL and lens thickness of the eye; optical distances are converted into geometric distances using a group refractive index. The ACD is measured by 2 oppositely rotating Scheimpflug cameras. Each patient had 1 scan, which produced a total of 1 ACD, 3 AL, and 3 lens thickness measurements. The averaged AL and lens thickness values provided in the final printout were analyzed. The OA-2000 (software version 1.0 R, Tomey Corp.) combines an optical biometer, based on SS-OCT, and a Placido-ring topographer.15,16 Swept-source OCT uses a wavelength of 1060 nm to measure AL, ACD, and lens thickness; a group refractive index is used to convert the optical path length into geometric distances. Each patient had 1 acquisition, for a total of 10 AL, 10 ACD, and 10 lens thickness measurements. The data provided in the final printout represented the average of the measurements of each parameter. Influence of Lens Thickness Measurement Differences on Intraocular Lens Power Calculation To assess how the differences in lens thickness measurements influenced IOL power calculation, the lens thickness values Volume - Issue - - 2018
measured by each instrument for each patient were entered into the Olsen formula.11 Phacooptics software (version 1.10.100.2032, IOL Innovations ApS) was used and two approaches were followed. In the first approach, the aim was to evaluate the influence of lens thickness alone; therefore, arbitrary keratometry (K) (43.00 diopters [D]), ACD (3.00 mm), and AL (23.00 mm) values were used in all eyes. In the second approach, the aim was to evaluate the influence of the combination of AL, ACD, and lens thickness; therefore, the individual AL and ACD values measured by each instrument were entered and a K value of 43.00 D was maintained in all cases. In both analyses, the IOL power to be selected for a given eye was the one with the lowest predicted myopic refraction. Statistical Analysis All statistical analyses were performed with Instat software (version 3.1, Graphpad Inc.). Normal distribution of data was assessed with the Kolmogorov-Smirnov test. Repeated-measures analysis of variance (ANOVA) with a Bonferroni posttest was used to compare AL and ACD measurements, which were normally distributed with all instruments. The Friedman test (nonparametric ANOVA) with the Dunn posttest was used to compare lens thickness measurements, which were not normally distributed. Linear regression was used to correlate age and lens thickness measurements. A P value less than .05 was considered statistically significant. Based on power and sample-size calculations performed using PS Power and Sample Size Calculations (version 3.0),C it was estimated that a sample size of 3 eyes would be necessary to detect a difference of 0.1 mm in lens thickness between any pair of biometers with a power of 95% at a significance level of 5%, given a within-subject standard deviation for lens thickness equal to 0.02 mm.16 Agreement was evaluated using 95% limits of agreement (LoA).17
RESULTS One hundred eyes of 100 consecutive patients having cataract surgery were enrolled. Five cases were excluded because of myopic staphyloma, which precluded a correct AL measurement by immersion US biometry. Seven more cases were excluded for failed acquisition by one or more devices because of subcapsular or very dense cataract (4 cases with the OLCI biometer; 5 cases with the PCI biometer). Hence, 88 eyes of 88 patients 47 women [53%]) were analyzed. The mean age of the patients was 68.3 years G 10.0 (SD) (range 39 to 90 years). Table 1 shows the mean values, standard deviations, and ranges of the measured parameters. Lens Thickness
Ultrasound immersion biometry yielded significantly higher lens thickness values than all 3 optical biometers (P ! .0001); the mean difference ranged from 0.29 mm (SS-OCT biometer) to 0.43 mm (PCI biometer). Although the differences between the 3 optical biometers were smaller, they were statistically significant according to the Dunn posttest (P ! .001). The SS-OCT biometer higher mean value was higher than the values of the other two optical biometers. Table 2 shows the 95% LoA for the lens thickness measurements. Linear regression found a positive correlation between age and lens thickness measurements by US immersion biometry (P Z .0001, r Z 0.4022, r2 Z 0.1618), SS-OCT biometry (P Z .0001, r Z 0.3952, r2 Z 0.1562), OLCI
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Table 1. Axial measurements provided by the 4 technologies. Parameter LT (mm) Mean G SD Range ACD (mm) Mean G SD Range AL (mm) Mean G SD Range
US Immersion
OLCI
PCI
SS-OCT
P Value
4.94 G 0.40 3.99, 5.74
4.59 G 0.42 3.64, 5.52
4.51 G 0.38 3.59, 5.26
4.66 G 0.39 3.68, 5.46
!.0001
3.29 G 0.37 2.26, 4.26
3.23 G 0.36 2.25, 4.27
3.26 G 0.37 2.24, 4.26
3.23 G 0.35 2.37, 4.26
!.0001
23.96 G 1.43 20.17, 28.47
24.02 G 1.46 20.21, 28.72
24.03 G 1.48 20.23, 28.79
24.02 G 1.46 20.25, 28.69
!.0001
ACD Z anterior chamber depth (epithelium to lens); AL Z axial length; LT Z lens thickness; OLCI Z optical low-coherence interferometry; PCI Z partial coherence interferometry; SS-OCT Z swept-source optical coherence tomography; US Z ultrasound
biometry (P ! .0001, r Z 0.4285, r2 Z 0.1836), and PCI biometry (P Z .0002, r Z 0.3863, r2 Z 0.1493). Anterior Chamber Depth
Although repeated-measures ANOVA showed a statistically significant difference between the 4 techniques (P ! .0001), the differences would have no clinical significance because they ranged between 0.03 mm and 0.06 mm. The highest mean value was provided by US immersion biometry. According to the Bonferroni posttest, the difference was significant between US immersion biometry and OLCI biometry, US immersion biometry, and SSOCT biometry, OLCI biometry and PCI biometry, and between PCI biometry and SS-OCT biometry. Axial Length
Again, repeated-measures ANOVA showed a statistically significant difference between the 4 techniques (P ! .0001). Ultrasound immersion biometry gave the lowest mean value, which was significantly different than those provided by the 3 optical biometers according to the Bonferroni posttest (P ! .001) (Table 1). The same test found there were no statistically significant differences in AL measurements between the 3 optical biometers. Intraocular Lens Power Calculation
When the lens thickness measurement provided by immersion US immersion biometry was entered into the Olsen formula and the eye model with constant AL, K, and ACD values, a mean IOL power of 21.75 G 0.37 D (range 21.00 to 22.50 D) was calculated. Using the optical biometric measurements of lens thickness would have resulted in the selection of a lower IOL power in 38 eyes (43.2%) with the SS-OCT biometer, 46 eyes (52.3%) with the OLCI biometer, and 55 eyes (62.5%) with the PCI biometer. In all cases, the difference would have been 0.50 D, the only
exception being 2 eyes in which the PCI biometer would have calculated an IOL with a 1.0 D difference. A different IOL power would have also been selected on the basis of the lens thickness measurements of the 3 optical biometers. More specifically, the OLCI biometer and the PCI biometer would have calculated an IOL with a lower power than the SS-OCT biometer in 8 cases (9.1%) and 17 cases (19.3%), respectively. When the individual ACD, lens thickness, and AL measurement provided by immersion US biometry were entered into the Olsen formula, a mean IOL power of 21.40 G 4.72 D (range 8.50 to 36.00 D) was calculated. A lower mean IOL power was calculated with the optical biometers. The mean IOL power was 20.89 G 4.68 D for the OLCI biometer, 20.83 G 4.74 D for the PCI biometer, and 20.90 G 4.72 D for the SS-OCT biometer; the range was 7.50 to 35.00 D for all optical biometers. The ANOVA shows that the difference between immersion US biometry and optical biometry was statistically significant (P ! .0001). Using the optical biometry measurements would have resulted in the selection of an IOL power lower than that using US immersion biometry in 69 eyes (78.4%) with the SS-OCT biometer, 71 eyes (80.7%) with the OLCI biometer, and in 70 eyes (79.6%) with the PCI biometer. In most cases the difference was 0.50 D, with a maximum value of 1.50 D. Different IOL powers would have been selected also when comparing the 3 optical biometers. With the OLCI biometer, an IOL with a different power than with the SS-OCT biometer and the PCI biometer would have been selected in 18 eyes (20.4%) and 35 eyes (40.91%), respectively. With the SS-OCT biometer, an IOL with a different power than with the PCI biometer would have been selected in 29 eyes (32.9%). In these cases, the maximum difference was 1.00 D. DISCUSSION Optical biometry was introduced in 1999; however, the first optical biometer able to measure lens thickness became
Table 2. Agreement between the 3 optical biometers in measuring lens thickness. Parameter
OLCI L PCI
Mean difference (mm) GSD 95% limits of agreement (mm)
0.08 G 0.12 0.16, 0.32
OLCI L SS-OCT 0.06 G 0.09 0.24, 0.11
PCI L SS-OCT 0.15 G 0.09 0.33, 0.03
OLCI Z optical low-coherence interferometry; PCI Z partial coherence interferometry; SS-OCT Z swept-source optical coherence tomography
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available only 10 years later with the introduction of the Lenstar 900 (Haag-Streit AG), which is based on OLCR. Since then, several optical biometers have been introduced, and most of them measure lens thickness. However, lens thickness measurements have received little attention, despite the increasing use of this parameter for IOL power calculation. The only two studies comparing lens thickness measurements by US biometry and optical biometry found opposite results. In 1998, Drexler et al.18 reported that lens thickness measurements by applanation US biometry were lower than those provided by a PCI prototype (4.53 G 0.56 mm versus 4.65 G 0.48 mm). In 2016, Aydin et al.19 reported the opposite; namely, that lens thickness measurements by applanation US biometry were higher than those obtained by OLCR (4.33 G 0.49 mm versus 4.20 G 0.44 mm). Our findings are closer to those reported by Aydin et al. because we found that lens thickness measurements obtained using immersion US biometry are significantly higher than those given by any optical biometer. This difference has a clinical impact on IOL power calculation because it would have led to the selection of a different IOL power in a high percentage of cases when using a formula such as Olsen’s,11 which predicts the IOL position on the basis of lens thickness and was developed using optical biometry. In the first eye model, in which we used fixed AL, K, and ACD values to highlight the influence of lens thickness measurements, a different IOL power would have been recommended in about half of the eyes. In the second eye model, in which we used individual AL and ACD values, the percentage was close to 80% of cases. In this model, a different IOL power would have also been selected in a relevant percentage of cases (between 20% and 40%) when using optical biometry measurements only. Future studies are needed to assess which technique of measuring lens thickness leads to more accurate results with the Olsen formula.11 The difference between the lens thickness measurements provided by US immersion biometry and optical biometry is most likely because of the different ability of the two technologies to detect the anterior and posterior edges of the lenses. We initially thought that it might further depend on the fact that US biometry separately measures each segment with a specific sound velocity, although the 1641 m/sec value selected for the lens US velocity is an average and large variations can occur according to the density of the cataract.20,21 In contrast, optical biometers are known to use a single group refractive index to calculate the geometric distances from the optical path length (as originally proposed by Haigis for the IOLMaster3). However, all manufacturers have told us that their device uses a specific refractive index when calculating the lens thickness. Hence, the use of a group refractive index cannot be considered an explanation of the difference in lens thickness between US biometry and optical biometry. Other studies have evaluated the agreement in lens thickness measurements between different optical biometers. In Volume - Issue - - 2018
a previous study,22 our group did not find a statistically significant difference between the values provided by the IOLMaster 700 biometer (Carl Zeiss Meditec AG) and the Lenstar biometer, whose measurements (4.59 G 0.43 and 4.62 G 0.44 mm, respectively) were close to those for the Aladdin biometer and OA-2000 biometer in our study. Similarly, no statistically significant differences were detected between the IOLMaster 700 biometer and the Aladdin and Galilei G6 biometers.23,24 In contrast, Shammas et al.25 found a mean difference of 0.22 mm between the Argos biometer (Movu, Inc.) and the Lenstar 900 biometer. In the present study, although the differences between the 3 optical biometers were small, they were statistically significant and would have led to the choice of different IOL powers in a significant number of eyes. Therefore, we recommend that the lens thickness measurements of different optical biometers not be considered interchangeable. The mean lens thickness value measured by immersion US biometry in the present study (4.94 G 0.40 mm) is higher than the value reported by Drexler et al.18 (4.53 G 0.56 mm) and Olsen and Thorwest26 (4.67 G 0.55 mm), who used contact US biometry. We cannot attribute this discrepancy to a difference in the age of patients because the mean age of our cohort (68.3 years) was only slightly lower (4 to 8 years) than the mean age of the samples in the Drexler et al. and Olsen and Thorwest studies (76.0 years and 74.1 years, respectively) and lens thickness is known to increase with age.27 Moreover, the mean value of lens thickness using immersion US biometry in our study is higher than the mean value (4.63 mm) reported by Hoffer27 in any age group. The use of different instruments is the most likely explanation because the indentation required for contact biometry should not play a role in lens thickness measurement. Racial and ethnic differences might also be involved, as suggested in a recent review that reported notable differences in lens thickness between ethnic groups.28 We believe that ours is the first study of lens thickness performed on western hemisphere patients from southern Europe. The ACD measurements were minimally (although statistically significantly) different between the 4 techniques, with US immersion biometry yielding a slightly higher mean value. Such discrepancies were 0.06 mm or less and are unlikely to influence IOL power calculation. Comparison with previous studies is difficult because in most cases contact applanation US biometry was used and this method is known to produce falsely low ACD measurements because of corneal indentation. Few studies have assessed ACD measurements by immersion US biometry in phakic eyes. Landers and Goggins29 found that similar mean measurements were provided by immersion US biometry (3.05 G 0.37) and the IOLMaster biometer (3.02 G 0.44). Other studies compared ACD measurements by immersion US biometry with those obtained using different techniques, such as optical pachymetry30 or anterior segment OCT31; thus, their findings cannot be matched against our results. On the other hand, ACD
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measurements by the Galilei G6 biometer have been reported to be similar to those provided by other optical biometers, such as the Lenstar32 and the IOLMaster 500.14 Finally, the AL measurements provided by the 3 optical biometers were not statistically different, whereas the ALs measured by immersion US biometry were slightly shorter, with a mean difference of 0.06 to 0.07 mm, which is sufficient to require specific constant optimization with any formula for calculating IOL power. Although the lack of a significant difference between the 3 biometers is not surprising given the large number of studies that found similar results,14,15,33,34 the difference compared with immersion US biometry was unexpected because optical biometry was originally calibrated to match immersion US biometry.3 We can postulate that the difference observed in the present study is related to a systematic difference in the measurements provided by our US biometer and the biometer originally used by Haigis et al.3 This study has limitations. We did not evaluate all available optical biometers, and we did not enroll healthy eyes with clear lenses, for which the results may be different. We did not assess the repeatability of lens thickness measurements because previous studies have reported that repeatability is high for all measurements by two of the tested optical biometers13,16 as well for measurements by a previous version of the dual Scheimpflug analyzer.35 However repeatability for lens thickness data are lacking for Galilei G6 biometer and for US immersion biometry and will be the target of future studies. In conclusion, we found that lens thickness measurements by immersion US biometry and optical biometry cannot be considered interchangeable and might lead to different results when entered into IOL power formulas requiring this parameter to estimate the position of the IOL.
WHAT WAS KNOWN Lens thickness is used by several formulas to estimate the IOL position and calculate its power. Lens thickness measurements obtained using US-based and optical methods have been compared in few studies with conflicting results.
WHAT THIS PAPER ADDS In older patients with cataract, lens thickness measurements obtained using immersion US biometry and 3 different optical biometry techniques showed significant differences and therefore cannot be considered interchangeable.
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4. Packer M, Fine IH, Hoffman RS, Coffman PG, Brown LK. Immersion A-scan compared with partial coherence interferometry; outcomes analysis. J Cataract Refract Surg 2002; 28:239–242 5. Kiss B, Findl O, Menapace R, Wirtitsch M, Petternel V, Drexler W, Rainer G, Georgopoulos M, Hitzenberger CK, Fercher AF. Refractive outcome of cataract surgery using partial coherence interferometry and ultrasound biometry: clinical feasibility study of a commercial prototype II. J Cataract Refract Surg 2002; 28:230–234 ez J, Cherwek DH, Stulting RD, Waldron R, Zimmerman GJ, 6. Narva Wessels IE, Waring GO III. Comparing immersion ultrasound with partial coherence interferometry for intraocular lens power calculation. Ophthalmic Surg Lasers Imaging 2008; 39:30–34 7. Hoffer KJ. The Hoffer Q formula: a comparison of theoretic and regression formulas. J Cataract Refract Surg 1993; 19:700–712; errata, 1994; 20:677 8. Zuberbuhler B, Morrell AJ. Errata in printed Hoffer Q formula [letter]. J Cataract Refract Surg 2007; 33:2; reply by KJ Hoffer, 2–3 9. Holladay JT, Prager TC, Chandler TY, Musgrove KH, Lewis JW, Ruiz RS. A three-part system for refining intraocular lens power calculations. J Cataract Refract Surg 1988; 14:17–24 10. Retzlaff JA, Sanders DR, Kraff MC. Development of the SRK/T intraocular lens power calculation formula. J Cataract Refract Surg 1990; 16:333– 340; erratum, 528 11. Olsen T, Hoffmann P. C constant: new concept for ray tracing–assisted intraocular lens power calculation. J Cataract Refract Surg 2014; 40:764–773 12. Mandal P, Berrow EJ, Naroo SA, Wolffsohn JS, Uthoff D, Holland D, Shah S. Validity and repeatability of the Aladdin ocular biometer. Br J Ophthalmol 2014; 98:256–258 13. Huang J, Savini G, Wu F, Yu X, Yang J, Yu A, Yu Y, Wang Q. Repeatability and reproducibility of ocular biometry using a new noncontact optical lowcoherence interferometer. J Cataract Refract Surg 2015; 41:2233–2241 14. Ventura BV, Ventura MC, Wang L, Koch DD, Weikert MP. Comparison of biometry and intraocular lens power calculation performed by a new optical biometry device and a reference biometer. J Cataract Refract Surg 2017; 43:74–79 15. Savini G, Hoffer KJ, Shammas HJ, Aramberri J, Huang J, Barboni P. Accuracy of a new swept-source optical coherence tomography biometer for IOL power calculation and comparison to IOLMaster. J Refract Surg 2017; 33:690–695 16. Huang J, Savini G, Hoffer KJ, Chen H, Lu W, Hu Q, Bao F, Wang Q. Repeatability and interobserver reproducibility of a new optical biometer based on swept-source optical coherence tomography and comparison with IOLMaster. Br J Ophthalmol 2017; 101:493–498 17. Bland JM, Altman DG. Measurement error [Statistics notes]. BMJ 1996; 313:744 18. Drexler W, Findl O, Menapace R, Rainer G, Vass C, Hitzenberger CK, Fercher AF. Partial coherence interferometry: a novel approach to biometry in cataract surgery. Am J Ophthalmol 1998; 126:524–534 19. Aydin R, Karaman Erdur S, Serefoglu Cabuk K, Karahan E, Kaynak S. Comparison of optical low coherence reflectometry versus ultrasonic biometry in high hypermetropia. Eye Contact Lens 2016 [Epub ahead of print] 20. Pallikaris I, Gruber H. Determination of sound velocity in different forms of cataracts. In: Thijssen JM, Verbeek AM, eds, Ultrasonography in Ophthalmology. Proceedings of the 8th SIDUO Congress, Nijmegen, The Netherlands, 1980. Doc Ophthalmol Proc Ser, , 1981; 29:165–169 21. Massin M, Lambrinakis I. In vivo determination of the speed of ultrasound in cataracted lenses. In: Sampaolesi R, ed, Ultrasonography in Ophthal Falls, Argentina, mology. Proceedings of the 12th SIDUO Congress, Iguazu 1988. Doc Ophthalmol Proc Ser, , 1990; 12:131–134 22. Hoffer KJ, Hoffmann PC, Savini G. Comparison of a new optical biometer using swept-source optical coherence tomography and a biometer using optical low-coherence reflectometry. J Cataract Refract Surg 2016; 42:1165–1172 23. Calvo-Sanz JA, Portero-Benito A, Arias-Puente A. Efficiency and measurements agreement between swept-source OCT and low-coherence interferometry biometry systems. Graefes Arch Clin Exp Ophthalmol 2018; 256:559–566 24. Jung S, Chin HS, Kim NR, Lee KW, Jung JW. Comparison of repeatability and agreement between swept-source optical biometry and dualScheimpflug topography. J Ophthalmol 2017 article ID1516395 25. Shammas HJ, Ortiz S, Shammas MC, Kim SH, Chong C. Biometry measurements using a new large-coherence–length swept-source optical coherence tomographer. J Cataract Refract Surg 2016; 42:50–61 26. Olsen T, Thorwest M. Calibration of axial length measurements with the Zeiss IOLMaster. J Cataract Refract Surg 2005; 31:1345–1350 27. Hoffer KJ. Axial dimension of the human cataractous lens. Arch Ophthalmol 1993; 111:914–918; correction, 1626
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28. Hoffer KJ, Savini G. Effect of gender and race on ocular biometry. Int Ophthalmol Clin 2017; 57 (3):137–142 29. Landers J, Goggin M. Comparison of refractive outcomes using immersion ultrasound biometry and IOLMaster biometry. Clin Exp Ophthalmol 2009; 37:566–569 30. Hoffer KJ, Savini G. Anterior chamber depth studies. J Cataract Refract Surg 2015; 41:1898–1904 31. Nemeth G, Vajas A, Tsorbatzoglou A, Kolozsvari B, Modis L Jr, Berta A. Assessment and reproducibility of anterior chamber depth measurement with anterior segment optical coherence tomography compared with immersion ultrasonography. J Cataract Refract Surg 2007; 33:443–447 32. Shin MC, Chung SY, Hwang HS, Han KE. Comparison of two optical biometers. Optom Vis Sci 2016; 93:259–265 33. Hoffer KJ, Shammas HJ, Savini G. Comparison of 2 laser instruments for measuring axial length. J Cataract Refract Surg 2010; 36:644–648; erratum, 1066 34. Hoffer KJ, Shammas HJ, Savini G, Huang J. Multicenter study of optical low-coherence interferometry and partial-coherence interferometry optical biometers with patients from the United States and China. J Cataract Refract Surg 2016; 42:62–67 35. Savini G, Carbonelli M, Barboni P, Hoffer KJ. Repeatability of automatic measurements performed by a dual Scheimpflug analyzer in unoperated and post-refractive surgery eyes. J Cataract Refract Surg 2011; 37:302–309
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OTHER CITED MATERIAL A. Holladay JT. Holladay IOL Consultant Software & Surgical Outcomes Assessment. Bellaire, TX, Holladay Consulting, 2015; Available at: http: //www.hicsoap.com. Accessed August 13, 2018 B. Barrett GD. Barrett Universal II Formula. Singapore, Asia-Pacific Association of Cataract and Refractive Surgeons. Available at: http://www.apacrs .org/barrett_universal2/. Accessed August 13, 2018 C. Dupont WD, Plummer WDJr PS. Power and Sample Size Calculation. Nashville, TN, Department of Biostatistics, Vanderbilt University, 2014; Available at: http://biostat.mc.vanderbilt.edu/wiki/Main/PowerSampleSize. Accessed August 13, 2018
Disclosures: Dr. Hoffer licenses the registered trademark name Hoffer to ensure accurate programming of his formulas to Carl Zeiss Meditec AG (IOLMasters), Haag-Streit AG (Lenstar), Oculus €te GmbH (Pentacam AXL), Movu, Inc. (Argos), Nidek Co., Optikgera Ltd. (AL-Scan), Tomey Corp. (OA-2000), Topcon Europe Medical B.V./Visia Imaging S.r.l. (Aladdin), Ziemer Ophthalmic Systems AG (Galilei G6), and all A-scan biometer manufacturers except Alcon Laboratories, Inc. (Verion). Neither of the other authors has a financial or proprietary interest in any material or method mentioned.