Agreement of Ocular Biometry Measured by LenStar LS 900 and CASIA2 Optical Coherence Tomography

Document Type : Original article

Authors

1 1. Refractive Errors Research Centre, Mashhad university of Medical Sciences, Mashhad, Iran. 2. Student Research Committee, Mashhad University of Medical Sciences, Mashhad, Iran.

2 Retina Research Center, Mashhad University of Medical Sciences, Mashhad, Iran.

3 1. Refractive Errors Research Centre, Mashhad university of Medical Sciences, Mashhad, Iran. 2. Department of Optometry, Mashhad University of Medical Sciences, Mashhad, Iran.

Abstract

Introduction:The present study aimed to compare the anterior segment measurements between optical low-coherence reflectometry (LenStar LS900) and anterior segment optical coherence tomography (CASIA2 OCT).
Methods:A total of 198 right eyes of 198 healthy participants were used for the current study, according to the inclusion and exclusion criteria. Ocular biometry parameters, such as central corneal thickness (CCT), anterior chamber depth (ACD), keratometry, and anterior chamber width (ACW), were measured usingLenStar LS 900 and CASIA2 OCT. The differences and correlations were assessed between these two instruments. The agreement was calculated as the 95% limits of agreement (LoA).
Results: Among 198 subjects with a mean age of 29.39±7.88 years who enrolled in the study, 106 individuals (53.5%) were women. The mean CCT values were 531.7±35.25 and 527.3±37.82 µm for LenStar and OCT, respectively (P˂0.0001). The ACD measurements showed 2.92±0.40 and 2.95±0.43 mm for LenStar and OCT, respectively (P=0.0549). The ACW mean values were 12.04±0.52 and 11.79±0.49 mm by LenStar and OCT (P˂0.0001). The 95% LoA between the two instruments were within the ranges of -20.79 to 29.43 µm, -0.50 to -0.43 mm, -0.32 to 0.82 mm, and -0.70 to 0.87 D for CCT, ACD, ACW, and astigmatism, respectively.
Conclusion: LenStar and OCT showed to have interchangeable ACD measurements; however, the results of CCT, ACW, and corneal astigmatism measured by these two instruments demonstrated clinically significant differences

Keywords


Introduction
With recent advances in ocular surgeries, the accuracy of ocular biometry becomes important in order to satisfy patients’ expectations (1).
Axial length (AL), corneal power, and anterior chamber depth (ACD) are essential elements for intraocular lens (IOL) calculations in cataract surgery. The assessment of central corneal thickness (CCT) is also an important

factor in refractive surgeries, corneal diseases, and glaucoma (2).
Several methods have been developed for biometry evaluations, such as slit-lamp biomicroscopy, scheimflug imaging, A-scan ultrasounds, ultrasound biomicroscopy, (UBM) and Purkinje reflexes (3).
Since the advent of IOL Master, optical biometry has been the gold standard for ocular biometric parameters (4).
LenStar has been designed according to Optical Low Coherence Reflectometry technology using a broadband light (wavelength: 820 µm) (5). It can simultaneously measure nine parameters, including AL, ACD, CCT, lens thickness (LT), keratometry, retinal thickness, white-to-white (WTW) and optical line eccentricity, (6) in approximately 20 seconds for each measurement (7).
The Tomey CASIA2 is a swept-source spectral domain (SD) optical coherence tomography (OCT) employing low-coherence interferometry technology to provide high-resolution cross-sectional images of the anterior ocular segment by a 1310 nm wavelength light as an earlier time domain OCT device. It can also measure CCT, ACD, keratometry, and anterior chamber width (ACW)(8,9).
Both LenStar and CASIA2 OCT devices have previously shown repeatable measures of anterior segment dimensions (8,10); however, their measurements may not be necessarily interchangeable. The main advantage of these two instruments over ultrasound devices is non-contact property measurement (11).
With this background in mind, the purpose of the current study was to compare the ocular biometric parameters between CAIA2 OCT and LenStar in a normal population and assess the agreement of these parameters between the two devices.

Methods
A total of 198 right eyes of 198 participants (92 male and 106 female subjects) with best-corrected visual acuity of 6/6 or better were recruited for the current study. The participants with any history of ocular diseases or surgery were excluded from the study population. Written consent was obtained from all the study subjects after a complete explanation of the study.
The study followed the principles of the Declaration of Helsinki and was approved by the Research Ethics Committee of Mashhad university of medical sciences with an approval code of 941712.
All the subjects underwent anterior segment OCT (AS-OCT) imaging using Tomey CASIA2 and non-contact biometry using LenStar LS 900. Five consecutive scans were performed on the CASIA2 in “Anterior Chamber” mode. The cornea was centered for each scan session producing 128 cross-sectional images. The CASIA software automatically specified intraocular structures and showed measurement values after defining scleral spurs.
For LenStar, the device was aligned to ensure that all readings were taken on the visual axis. Blinking and loss of fixation were automatically detected. Sixteen consecutive scans were obtained by LenStar per measurement without realignment, and five serial measurements were automatically averaged to be displayed on the monitor.
The CCT, ACD, keratometry, and ACW measurements were obtained for the right eye using both devices. This allocation was regardless of the ocular dominance, refraction, or aberrations. The order of the measurement of instruments was randomized, and all the measurements for each subject were performed at a single session.
All the statistical analyses were performed using GraphPad Prism software (version 6). The quantitative data are expressed as mean± standard deviation (SD). A paired t-test was used for the determination of the differences in biometry parameters between the two instruments. The Pearson correlation coefficient was utilized to evaluate the correlation between the measurements of the two instruments.
The 95% limits of agreement (LoA) that are the mean difference ± 1.96 times the SD of the differences were detected by the Bland-Altman plot. These limits showed the level of agreement between the measurements of the two devices to be interchangeably used. A p-value of less than 0.05 was considered statistically significant.

Results
Among 198 participants with a mean age of 29.39±7.88 years (range: 18-50 years) who enrolled in the study, 106 (53.5%) individuals were female. The mean spherical equivalent (MSE) was -0.80±1.68 D (range: -4.50 to +3.98 D). Table 1 shows six different parameters measured by LenStar and CASIA2 OCT.
A paired t-test analysis indicated significantly smaller values of CCT and ACW measured by CASIA2 OCT, compared to those reported for LenStar (P<0.0001 and P<0.0001, respectively). The Pearson correlation coefficient results revealed high correlations in all the reported parameters between the two devices (P<0.0001).
Bland-Altman plot showed a clinical agreement of ACD measurements between the two devices. Figures 1-3 illustrate the Bland-Altman plots of agreement between the two instruments. Figure 1 depicts 95% LoA of ACD measurements within the range of -0.50 to -0.43.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


cantly higher than that of the neonates who did not recover (2141.7 ± 755.2 g) (p < 0.01). There was also a significant relationship between the TSH level and birth weight (p < 0.01). Moreover, the mean age of mothers in participants was 26.9 ± 3.7 years, with a minimum and maximum of 12 and 35 years, and did not have any significant relation with the level of TSH and with the recovery rate (p > 0.05).
The mean level of TSH in neonates who recovered within three-month was 9.4 ± 3 mIU/L, and in neonates who did not recover was 22 ± 6.5 mIU/L. The relation between the recovery and TSH level

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Discussion
The present study showed that the prevalence of febrile seizures was associated with gender, living place, temperature, family history of seizure, and the serum level of zinc. In this regard, the frequency of zinc deficiency was higher in patients with febrile seizures compared to febrile patients without seizure, before and after adjusting for gender.
Zinc plays a vital role in the neuronal terminals of the hippocampus and amygdala by producing pyridoxal phosphate and affecting glutamatergic, gamma-aminobutyric acidergic (GABAergic), and glycinergic synapses (13).
Glutamic acid decarboxylase (GAD) acts as a major inhibitory neurotransmitter in the synthesis of gamma-aminobutyric acid (GABA) (14). A study by Ganesh R. and Janakiraman L. on 38 children with febrile convulsion and 38 children as a control group, aged between 3 months and 5 years, indicated that a serum zinc deficiency was significantly more prevalent in their case group than in the control group (15). Another study has reported that there is a correlation between disruption in Zn2+ homeostasis and fever seizure (16).
In studies by Papierkowski A., Mollah M.A., and Gündüz Z. et al., the mean serum zinc level in the febrile convulsion group was significantly lower than in the control group, which indicates the role of zinc in febrile seizure. Comparing the groups in terms of age and gender, no significant difference was found, similar to our study (17-19). Abdel Hameed Z.A. et al. (20), in a study on 100 infants in Egypt, observed that temperature had no significant difference between the case and control groups. But Berg A.T. (21), Ahmed B.W. (22), and our study showed the importance of temperature in febrile seizure. The geographic area can be the cause of this difference. Duangpetsang J. in a study from 2014 to 2017 reported that a high fever with electrolyte disturbance hyponatremia has an important role in FS (23). Sharifi R. et al., in a study in 2007-2014, showed the importance of family history in febrile seizure (24), which is similar to our results.

Conclusion
The findings of this study show that zinc deficiency is significantly associated with the occurrence of febrile seizures. Zinc supplementation in children can therefore be helpful for the prevention and treatment of FS.

Conflict of interest
The authors declare no conflicts of interest. 

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