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Research

Anterior chamber depth measurement using Pentacam and Biograph in children

ORCID Icon, ORCID Icon, ORCID Icon, ORCID Icon, ORCID Icon & ORCID Icon
Pages 582-586 | Received 27 Nov 2019, Accepted 23 Jun 2021, Published online: 06 Sep 2021

ABSTRACT

Clinical relevance

Accurate measurement of the anterior chamber depth is very important. There is no report regarding the agreement between rotating Scheimpflug imaging (Pentacam HR) and biograph (Lenstar LS 900) in children. This study therefore explores the agreement between Pentacam and Biograph in measuring anterior chamber depth in children.

Background

This study aims to determine the agreement between Pentacam and Biograph in measuring anterior chamber depth in children.

Methods

The participants were students living in urban and rural areas of Shahroud, Iran, selected through cluster sampling. The students were transported to the examination site to undergo imaging and optometric tests. Pentacam imaging was then conducted, and biograph was used to measure biometric components. In this report, the anterior chamber depth was calculated from the corneal endothelium.

Results

Of 6624 students selected randomly, 5620 participated in the study. After applying the exclusion criteria, 4882 eyes were included in the final analysis. The mean anterior chamber depth measured by the Pentacam (3.09 ± 0.26 mm) was higher than that of biograph (3.04 ± 0.24 mm) (p < 0.001). The 95% limit of agreement (LOA) between the two devices was −0.19 to 0.09 mm. The variation of the difference between the two devices decreased, LOA became narrower, and the correlation coefficient of the devices increased with ageing. The highest intraclass correlation coefficient was seen among myopic (0.974) participants. The 95% LOA was −0.20 to 0.12 mm in hyperopic, −0.17 to 0.07 mm in myopic and −0.19 to 0.09 mm in emmetropic participants.

Conclusion

The Pentacam and Biograph can be used interchangeably for measuring the anterior chamber depth in children.

Introduction

Accurate measurement of the anterior chamber depth (ACD) is very important in children. ACD measurement is used for evaluation of the emmetropization process,Citation1 changes of biometric components with age,Citation2 ACD changes with accommodation,Citation2,Citation3 intraocular lens (IOL) power calculation using new formulas,Citation4 IOL vault calculation,Citation5 prediction of the risk of injury to the corneal endothelium in cases requiring phakic-IOL implantation,Citation6 and in the diagnosis, monitoring and treatment of glaucoma.Citation7 Different methods for measuring the ACD are available, which include ultrasonic, optical and photographic techniques.Citation8,Citation9 The ultrasound method has been used as a gold standard method of ACD measurement but it may produce incorrect results because of corneal indentation due to the need for a direct contact with the cornea.Citation10,Citation11 Moreover, accurate measurements depend on the experience of the operator in placing the probe on the corneal centre and also patient cooperation. This method may also cause discomfort in patients and injury to the corneal epithelium.Citation8 Therefore, considering the disadvantages of the contact methods, non-contact technologies are preferred, especially in children. Rotating Scheimpflug imaging (Pentacam HR) and Biograph (Lenstar LS 900) are among non-contact techniques of ACD measurement in children that are easy to apply and require minimal training.Citation12 The Lenstar 900 with optical low coherence reflectometry is one of the most reliable and repeatable biometric methods. The advantages of Biograph include its high precision, non-contact application, ease of use, and brevity because it provides all parameters needed for IOL power calculation in one measurement.Citation13 Some studies have recommended its use in difficult situations, like paediatric biometric measurements.Citation14,Citation15

The Pentacam uses the Scheimpflug imaging technique for anterior chamber analysis and measuring parameters like the depth and angle of the anterior chamber. This method is easy to use in children because of its non-contact nature and short duration.Citation16

Different studies have compared the available tools and methods for measurement of anterior segment parameters, including ACD,Citation9,Citation17–20 but a limited number of studiesCitation12,Citation21,Citation22 have compared the Lenstar and Pentacam, and there are no reports of their agreement in children. Moreover, the results of studies investigating the agreement between the Pentacam and Lenstar in adults are contradictory. However, it may be concluded that these devices cannot be used interchangeably for ACD measurement for vault calculation but their ACD readings can be used interchangeably for IOL power calculation.Citation23 The aim of the present study was to assess the agreement between ACD measurements of the Pentacam and Lenstar in children and to investigate the determinants of this agreement.

Methods

This cross-sectional study, which was part of phase one of Shahroud Eye Cohort Study, was conducted in Shahroud, northeast of Iran in 2015. The target population of this study was primary school students of rural and urban areas of Shahroud. The methodology of this study was reported earlier, but it is also briefly presented in the following section.Citation24 All primary school students living in villages (n = 1214) were invited to take part in the study while cluster sampling was done in urban areas. There were 473 classrooms in primary schools in urban areas, of which 200 were selected through systematic randomisation to access an adequate number of samples. Informed consent was obtained from the parents of the students, and they were transported to the examination site free of charge. Students underwent optometric and ophthalmologic examinations and ocular imaging.

Examinations

First, uncorrected distance visual acuity was measured at three metres using the Nidek CP-770 chart projector (Nidek Co. Ltd, Gammagori, Aichi, Japan). Then, non-cycloplegic refraction was performed using the Nidek ARK-510A auto-refractometer (Nidek Co. Ltd, Gammagori, Aichi, Japan) and its results were refined with retinoscopy. Finally, the students underwent subjective refraction. The Pentacam HR (Oculus optikgeräte GmbH, Wetzlar, Germany) was used for ACD measurement (Oculus software version 6.03r19/ 1.18r08). Examinations were performed between 9 am and 3 pm at least 2 h after waking up to avoid diurnal variation.Citation25 Moreover, all students were also examined using the Lenstar LS 900 (WaveLight AG, Erlangen, Germany) as well.

All measurements with two devices were done in the same room. In most cases, first biometry and then tomography was done, and there was no specific order for the two tests. The interval between the two tests was about 10 min and both eyes were open during tests. In order to ensure data repeatability, an average of three measurements were considered for the biograph. In the case of Pentacam, test was performed once unless an error occurred.

Finally, cycloplegic refraction was conducted 30 min after instilling 3 drops of cyclopentolate 1.0% with 5 min apart.

The exclusion criteria were a history of ocular surgery, tropia, ptosis, congenital cataracts, pterygium, measurement errors in Pentacam (blinking error, unsteady fixation, lid closure, alignment (XY) error, 3D model deviation and data gaps), trauma and lack of Pentacam data.

Definitions

Both devices measured the ACD from the corneal endothelium. A spherical equivalent (SE) of ≤-0.5 dioptre (D) and ≥2 D according to cycloplegic refraction was considered myopia and hyperopia, respectively.

Statistical analysis

Given the high correlation between the two eyes (correlation of coefficient between two eyes for ACD was 0.973), only data related to right eye was considered for analysis. Paired t test was applied to compare the mean of ACD measured by the Lenstar and Pentacam and their intraclass correlation coefficient for agreement (ICC) was reported. The 95% limit of agreement (LOA) and Bland-Altman plot were used to show the agreement between the two devices. To remove potentially wrong measurements, 14 outlier Pentacam data that were defined as an ACD greater or lesser than 3 standard deviation from the mean, were excluded from analysis. The mean, standard deviation and data range for ACD in mm by Pentacam were 3.091, 0.263, 1.820–4.660 and 3.091, 0.258, 2.010–4.290; before and after the removing of outlier data, respectively.

Ethical consideration

The study was conducted in accordance with the Helsinki Declaration. All procedures involving children were approved by the Ethics Committee of Shahroud University of Medical Sciences.

Written informed consent was obtained from all parents or students’ legal guardians and also oral consent obtained from all the students.

Results

Of 6624 selected students, 5620 (response rate: 84.8%) participated in the study. The final analysis was performed in 4882 (investigated rate: 73.7%) students after applying the exclusion criteria, of whom 2594 (53.1%) were boys. The mean age of the students was 9.2 ± 1.7 years (range: 6-12 years). The mean SE was 0.86 ± 0.81 (range: 5.75 to −8.13) in the participants.

presents the mean ACD measured by the two devices together with their mean difference and 95% LOA. According to the results, the mean ACD measured by the Lenstar and Pentacam was 3.04 ± 0.24 and 3.09 ± 0.26 mm, respectively (p < 0.001). shows the correlation of the Lenstar and Pentacam in ACD measurement (Pearson Correlation = 0.961). The Bland-Altman plot showed a 95% LOA of −0.194 (−0.197 to −0.190) to 0.086 (0.083 to 0.089) mm between the two devices (). According to , the 95% LOA was almost same in both sexes; however, analysis according to age showed that the variation of difference between the two devices decreased, LOA became narrower, and the ICC of the devices increased with ageing. Comparison of the devices according to refractive error showed the widest and narrowest LOA in hyperopic and myopic subjects, respectively ().

Figure 1. Scatterplot between Pentacam and Lenstar LS 900 measurements of anterior chamber depth.

Figure 1. Scatterplot between Pentacam and Lenstar LS 900 measurements of anterior chamber depth.

Figure 2. Agreement between Pentacam and Lenstar LS 900 measurements of the anterior chamber depth. The middle line indicates the mean difference and the two dashed side lines show the 95% limits of agreement.

Figure 2. Agreement between Pentacam and Lenstar LS 900 measurements of the anterior chamber depth. The middle line indicates the mean difference and the two dashed side lines show the 95% limits of agreement.

Table 1. Mean, standard deviation (SD), paired differences, 95% limit of agreement (LOA) and intraclass correlation coefficient (ICC) of anterior chamber depth measured with Pentacam and Lenstar, Shahroud, Iran, 2015.

Discussion

The results of the present study showed a relatively good agreement between ACD measurements of the Pentacam and Lenstar in children. The mean difference between the two devices in the total participants was only 0.05 mm and in different subgroups it varied between 0.04 and 0.06. Although this difference was statistically significant due to the high sample size, it did not appear to be clinically remarkable. Holladay et al.Citation26 found that ACD was not related to axial length of the globe, however, there are studies that reported a significant linear correlation between ACD and axial length (correlation coefficient 0.531) and an inverse relationship between ACD and SE (correlation coefficient −0.625).Citation27 Whether or not ACD has an effect on axial length and consequently refractive error, it has been proven that it is an important indicator of effective lens position and helpful in predicting postoperative refractive error.Citation28 It is reported that a difference of 1 mm in IOL position leads to 1.25 D change in refractive error.Citation29–31So, 0.05 mm difference in measuring ACD, which directly affects lens position, could lead to 0.0625 D change in refractive error, which is negligible in clinic. On the other hand, shows that there is a good agreement between two methods (the values of the difference between the two devices are on either side of the bias line and are mostly between +1.96 and −1.96 standard deviation) and although this agreement is mostly in ACD sizes above 3 mm, there is no proportional bias.

Considering a narrow LOA between the two devices, it could be concluded that these two devices can be used interchangeably for ACD measurement in children aged 6-12 years.

Similarly, based on the ICC results, it can be seen that the ICC in all individuals and all groups were above 0.95 which indicates an excellent agreement between the two devices and high similarity of them.

Several studiesCitation9,Citation17–20 have assessed the agreement between different devices used for ACD measurement but a limited number of studies with small sample sizes have investigated the agreement between ACD measurements of the Pentacam and Lenstar.Citation12,Citation21,Citation22 An advantage of the present study was its population-based design and large sample size of children aged 6-12 years. According to the search in literature, no studies evaluated the agreement between these devices in children. Since biometric measurements using contact methods are difficult in children, evaluation of the agreement between devices like the Pentacam and Lenstar, which are capable of measuring ACD using non-contact methods in a short time, is of great importance.

Three studies evaluated the agreement between ACD measurements of the Lenstar and Pentacam in adults and reported contradictory results.Citation12,Citation21,Citation22 The results of the studies investigating the agreement between Pentacam and Lenstar measurements of the ACD conducted by Uchakhan et alCitation22 (2013) and Huang et alCitation21 (2011) were similar to current findings, although Pentacam measurements were slightly larger than Lenstar readings; however, the Bland-Altman test results showed the devices had a relatively good agreement and could be used interchangeably. O Donell et alCitation12 compared the Pentacam, optical coherence tomography (OCT), and Lenstar and reported the highest agreement between the Pentacam and Lenstar readings. However, according to this study, these devices could not be used interchangeably. The above studies were conducted in small samples of adults, and therefore their results cannot be compared with current findings. Nonetheless, previous studies suggest that these two devices are not interchangeable for ACD measurement in adults for vault calculation but their ACD measurements can be used interchangeably for IOL power calculation.Citation23

In this study, the ACD measured by the Pentacam was 3.09 mm, which was slightly larger than the value obtained by the Lenstar (3.04 mm). Since children have an active accommodation and Lenstar measurements are done in illuminated rooms and take a longer time than Pentacam measurements, the chances of accommodation, increased lens thickness, and its forward displacement are higher, leading to a decreased ACD value when measured by the Lenstar.Citation32

In the present study, as expected and in line with previous investigations, ACD measurements of the Pentacam were slightly larger than Lenstar readings.Citation12,Citation21,Citation22 Several studies have investigated ACD changes due to accommodation during measurement with different devices.Citation32–34 Some of these studies were performed in the child age group,Citation32 and some among youngCitation34–36and presbyopicCitation35 populations. As for the Lenstar and Pentacam, studies found a decrease of about 0.22 mm with the Lenstar and about 0.11 with the Pentacam for each −5.00 D stimulus of accommodation.Citation35,Citation37 Moreover, most studies have shown a slight increase in ACD following the use of cycloplegic drops.Citation32,Citation36 Furthermore, differences in the measurement mechanisms of the Pentacam and Lenstar may also explain the slight difference between their measurements, because the Lenstar uses the partial coherence interferometry (PCI) for measurement in precise on-axis and central conditions, while Pentacam is a Scheimpflug imaging technique that may be a little off-axis. The mean ACD by the Lenstar in children aged 6–14 years was 3.14 mm in a study by Gursoy et al. In this study, measurements were done after instillation of cycloplegic drops, and as expected, the mean ACD was slightly larger than the ACD reported in this study.Citation14 Therefore, as mentioned earlier, not using cycloplegia before measurement and the possibility of accommodation during measurement could be the reason for the slight difference between the results of these two studies, although ethnic differences (Turkish Vs. Persian) may also explain part of the difference as well. Previous studies have shown the high heritability of ACD and the role of genetics in this parameter.Citation38 A few studies have evaluated ACD measurements of the Pentacam in children, and most of them were done in small sample sizes.Citation39,Citation40 Wang et al conducted the only study in a relatively large sample size of healthy Chinese children (n = 1321). In this study, the Pentacam was used to measure the ACD and other anterior chamber parameters under cycloplegia. The mean ACD was 3.22 mm in this study, which was slightly higher than the mean ACD measured by the Pentacam in the current study. Differences in the measurement method (use of cycloplegia before examination), and ethnic differences between the study populations could be the reason for this small difference.Citation40

The results of this study showed that the mean ACD measured by both devices was higher in boys compared to girls and increased by age from 6 years to 12 years, which was similar to the results of previous studies.Citation40,Citation41Several studies found larger biometric parameters in men than in women.Citation40,Citation42,Citation43 Similar findings have also been reported in a few studies conducted in similar paediatric age groups.Citation40–42 In general, it seems that ACD and anterior chamber volume (ACV) have an increasing trend in the first years of life, and then gradually slowdown with increasing age.Citation40 On the other hand, according to , the LOA of the two devices for ACD measurement became narrower with an increase in age, which could be due to better accommodation control during measurement and more cooperation of children as they grow older.

The results of this study showed a direct relationship between ACD and refractive errors, which was consistent with previous reports.Citation40,Citation44 The results of both devices indicated a smaller ACD in hyperopic individuals compared to emmetropic and myopic subjects. Studies have found that people with myopia have a larger axial length, posterior chamber depth, and ACD compared to hyperopic subjects.Citation27,Citation45 On the other hand, a more active accommodation in hyperopia compared to myopia and emmetropia may be another reason for the smaller ACD in this group.Citation46 Furthermore, considering a more active accommodation in hyperopia, current results show that hyperopic subjects had the widest LOA and myopic individuals had the narrowest LOA.

In general, according to the results of the present study, the Pentacam and Lenstar can be used interchangeably for ACD measurement in children.

A limitation of the present study was the lack of accommodation control during measurements. Several studies have shown the effect of cycloplegia on ACD measurement in different methods.Citation32,Citation36 Considering a more active accommodation in this age group and since accommodation causes changes in the lens dimensions and position and therefore in the anterior chamber depth, the agreement between the two devices should be investigated with and without cycloplegia. In this study, the order of examination with Pentacam and Lenstar was not random and most of the participants were examined Lenstar first. To avoid possible bias in future studies, the examination by devices should be ordered randomly.

Acknowledgements

Shahroud schoolchildren eye cohort study was supported by the Noor Ophthalmology Research Center and Shahroud University of Medical Sciences (grant numbers: 9329 and 960351).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Shahroud University of Medical Sciences [9329,960351].

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