|Year : 2021 | Volume
| Issue : 2 | Page : 160-166
Ocular biometric parameters of children with refractive errors in the age group of 6–15 years
P Thanusree1, V Mallika1, Suma Unnikrishnan2
1 Department of Ophthalmology, Government Medical College, Thrissur, Kerala, India
2 Department of Ophthalmology, Government Medical College, Kozhikode, Kerala, India
|Date of Submission||26-Oct-2020|
|Date of Acceptance||08-Nov-2020|
|Date of Web Publication||21-Aug-2021|
Dr. P Thanusree
Thandassery House, GNDA 5, Gandhinagar 3rd Street, Cheroor Road, Peringavu, Thrissur - 680 008, Kerala
Source of Support: None, Conflict of Interest: None
Background: Refractive errors are one of the leading causes of visual impairment in children. Studies on the association between refractive errors and ocular biometrics have shown inconclusive results; hence, this study aims to examine this relationship. Objectives: The objective of this study is to investigate the association between ocular biometrics such as axial length (AL), anterior chamber depth (ACD), lens thickness, vitreous chamber depth (VCD), and corneal curvature (CC) with different refractive errors in children aged 6–15 years. Materials and Methods: This was a cross-sectional study and studied 130 eyes of children. Children with congenital and acquired anterior or posterior segment diseases were excluded. All underwent detailed ocular examination, visual acuity measurement, and cyclopegic refraction. Children were divided into emmetropia, myopia, and hypermetropia. Ocular biometrics measured using A-scan and automated keratometer. Results: AL, ACD, and VCD significantly increased in the higher levels of myopia (P ≤ 0.0001), (P = 0.04), and (P ≤ 0.0001), respectively, whereas hypermetropes had the lowest. Spherical equivalence was significantly correlated with AL in myopes (ρ= −0.624; P < 0.0001) and hypermetropes (ρ = −0.803; P < 0.001). It was also significantly correlated with ACD more strongly for hypermetropes (ρ = −−0.58; P = 0.002) and VCD more strongly for myopes (ρ = −0.59; P < 0.0001). There was a significant difference between the age group of 6–10 years and 11–15 years for AL (P = 0.001), ACD (P ≤≤ 0.0001), VCD (P = 0.001), and CC (P = 0.03). Conclusion: AL and VCD make the greatest contribution to refractive errors. ACD has more important role in hypermetropes and VCD in myopes. A relative higher AL, ACD, VCD, and CC were found in the age group of 11–15 years.
Keywords: Anterior chamber depth, axial length, corneal curvature, lens thickness, refractive errors, spherical equivalence, vitreous chamber depth
|How to cite this article:|
Thanusree P, Mallika V, Unnikrishnan S. Ocular biometric parameters of children with refractive errors in the age group of 6–15 years. Kerala J Ophthalmol 2021;33:160-6
|How to cite this URL:|
Thanusree P, Mallika V, Unnikrishnan S. Ocular biometric parameters of children with refractive errors in the age group of 6–15 years. Kerala J Ophthalmol [serial online] 2021 [cited 2021 Nov 30];33:160-6. Available from: http://www.kjophthal.com/text.asp?2021/33/2/160/324220
| Introduction|| |
Ocular biometrics such as axial length (AL), anterior chamber depth (ACD), vitreous chamber depth (VCD), lens thickness (LT), and corneal curvature (CC) are among the most important factors affecting in refractive errors, and emmetropization is a result of a balance among these biometric components. The studies on the relationship between refractive errors and ocular biometrics have shown inconclusive results, and no such study has been conducted in children from South India. Therefore, this study aims to examine the relationship between the various ocular biometric parameters such as AL, ACD, VCD, LT, and CC with different refractive errors in the age group of 6–15 years.
| Materials and Methods|| |
- Study design: Cross-sectional study
- Study setting: Department of ophthalmology of a tertiary care center in Central Kerala
- Study participants: Children of the age group of 6–15 years attending the ophthalmology outpatient department (OPD), for their eye check-up during a period of 1 year from May 2018 to April 2019
- Study period: 1 year
- Sample size: 130 eyes.
The sample size was determined and calculated using the following formula (according to Bueno-Gimeno et al.):
Where, SD = standard deviation of the variable (AL), d = precision of study = 0.02 mm.
A total of 130 eyes of 71 children who came for their eye check-up were evaluated after obtaining consent from parent/guardian.
Children attending the ophthalmology OPD for their eye check-up in the age group of 6–15 years were included in the study.
- Children with congenital anterior or posterior segment disease
- Children with acquired anterior or posterior segment disease
- Children with a history of ocular surgery, trauma, or on any long-term ocular medication were excluded from the study.
After obtaining the ethical clearance from the institutional research board, we started the data collection. Informed consent from the parents or guardians of the children fulfilling the inclusion criteria was obtained, and a detailed history was taken. It included the chief complaints, previous ocular and medical history. All children then underwent a detailed ocular examination, and any anterior or posterior segment diseases were ruled out. Anterior segment was first assessed by a torch light and then followed by a slit-lamp examination. Visual acuity measurement was done by a Snellen's chart (or E chart or picture chart). It was followed by a cyclopegic refraction test after instilling Homatropine 2% eye drop (1 drop every 10 min for three times). After 1 h, pupils were fully dilated. The child was then subjected to retinoscopy and autorefraction. Following this, a detailed dilated fundus examination was also performed using a direct ophthalmoscope.
After 1 week, the participants were again reviewed for a post mydriatic test and ocular biometry. Children underwent subjective refraction, and then, the type of refractive error along with the spherical equivalent (SE) was calculated (SE = sphere + cylinder/2). The sample was divided into three main groups of emmetropic eyes (as control), myopic eyes and hypermetropic eyes. Emmetropia was defined as the presence of a SE between +0.75D and −0.25 D. The myopic group was further divided into low (SE of −0.5D to −3D), moderate (SE of −3.25 D to −6D), and high (SE of more than − 6D). The hypermetropic group was similarly divided into three subgroups as low (SE of +1D to +3D), moderate (SE of +3.25D to +6D), and high (SE of more than +6D); (however moderate and high hypermetropic samples were not obtained in this study). In order to assess the relationship between age and ocular biometry, the participants were subgrouped into 6–10 years and 11–15 years also.
Measurement of ocular biometrics was performed after the above-mentioned tests and procedures. For AL, ACD, LT, and VCD measurement, an A-scan ultrasound (Sonomed 300-A) was used (even though immersion, indentation technique was accepted for this study). After instilling 1 drop of local anesthethic, proparacaine drop in the eye, readings were taken with the child seated. The onscreen settings were set to phakic and while measuring, the probe was perpendicular to the cornea and did not indent it. The AL, ACD, and LT were displayed in the monitor, whereas VCD was calculated by subtracting the total of ACD and LT from the AL. The CC was measured using an automated keratometer (Canon RK-5). Finally, the total number of eyes studied was correlated with their ocular biometry.
Statistical analysis was performed using the SPSS version 21.0 software (SPSS software Trial version from IBM). The mean and standard deviation were calculated in different levels of refractive errors, and the ocular biometric parameters were assessed using one-way ANOVA test and Bonferroni post hoc test. Correlations were examined using Spearman's rho. Mann–Whitney U-test was used to assess the ocular biometric components between the two age groups. P < 0.05 was considered statistically significant in all statistical tests.
| Results|| |
In total of 130 eyes of 71 children, 42% of the total sample was myopic [Figure 1].
The mean age of the whole sample was 8.7 years (range, 6–15 years). The mean of spherical equivalence (SE) was −1.06±(3.04) D (range, −11.5D–D) [Figure 2].
|Figure 2: Frequency distribution of spherical equivalence of the whole sample|
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The mean AL, ACD, VCD, LT, and CC of the whole sample were 22.75± (1.35) mm, 3.38± (0.33) mm, 15.76± (1.25) mm, 3.59± (0.26) mm, and 43.94± (1.17) D, respectively.
[Table 1] summarizes the mean ocular biometric measurements such as AL, ACD, LT, VCD, and CC at different levels of refractive error [Table 1]. AL, ACD, and VCD significantly increased at higher levels of myopia (P ≤ 0.0001), (P = 0.04), and (P ≤ 0.0001), respectively, and hypermetropes had the lowest. LT was the highest for hypermetropes (3.66 ± 0.36) mm and high myopes (3.79 ± 0.28) mm.
|Table 1: Mean and standard deviation of spherical equivalence, axial length, anterior chamber depth, lens thickness, vitreous chamber depth and corneal curvature in different levels of refractive errors|
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One-way ANOVA showed significant differences of the mean between the three main groups (emmetropia, myopia, and hypermetropia) for AL (P < 0.0001), ACD (P = 0.03), and VCD (p=<0.0001), but not for LT and CC [Table 2].
|Table 2: Significance values for each biometric component between emmetropia, myopia, and hypermetropia by one-way ANOVA|
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Correlations by refractive state-spearmans correlation:
- AL and CC - Significant correlation was found between AL and CC (ρ = −0.174, P = 0.04) and strongly correlated in the emmetropic group (P ≤ 0.0001) [Table 3] and [Figure 3]
- AL and LT - No correlation was found between AL and LT (ρ = −0.02; P = 0.80) [Table 4] and [Figure 4]
- SE and AL - SE was significantly correlated with AL in myopes (ρ = −0.62, P. 0.0001) and hypermetropes (ρ = −0.80: P <0.0001) [Figure 5]
- SE and ACD - Statistically significant differences were found between SE and ACD (ρ = −0.179; P = 0.04). SE was more strongly correlated with ACD in hypermetropes (P = 0.002) than myopes (P = 0.01) [Table 5] and [Figure 6]
- SE and VCD - Significant correlation between SE and VCD was noted (ρ = −0.628; P ≤ 0.0001). SE was more strongly correlated with VCD in myopes (P y 0.0001). However, this study could not find any correlation between degree of myopia and change in VCD [Table 6] and [Figure 7]. When we calculated ACD/VCD ratio, as the degree of myopia increases, the ACD/VCD ratio decreases [Table 7]
- No significant differences were found between SE and LT (ρ = −0.109; P = 0.21) [Figure 8], nor between SE and CC (ρ = −0.127 P = 0.14) [Figure 9].
|Table 5: Correlation between spherical equivalence and anterior chamber depth|
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|Figure 6: Scatter graph of spherical equivalence and anterior chamber depth|
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|Table 6: Correlation between spherical equivalence and vitreous chamber depth|
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|Figure 7: Scatter graph of spherical equivalence and vitreous chamber depth|
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|Table 7: Anterior chamber depth/vitreous chamber depth ratio in different levels of refractive error|
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When we divided the children into two groups 6 to10 years and 11–15 years, the mean and standard deviation values of ocular biometric parameters by age are shown in [Table 8]. Mann–Whitney test revealed significant difference between the two age groups for AL (P = 0.001), ACD (P ≤ 0.0001), VCD (P = 0.001), and CC (P = 0.03), but not for LT (P = 0.06).
|Table 8: Mean and standard deviation values of ocular biometric components between 6-10 years and 11-15 years age group|
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| Discussion|| |
The refractive error of the eye is governed by the multifactorial condition which involves AL, corneal and lens power, ACD, and VCD of the eye, due to its variations of these biometric components during the growth of the eye. It has been demonstrated that for the progression of myopia, an increase in the AL of the eyeball is the principal morphological factor related to it in children,,, and similarly, shorter AL is the main morphological factor which is related to hypermetropia. Furthermore, in certain studies, part of refractive errors has also been attributed to ocular biometrics such as ACD, LT, VCD, and CC.,
In this study, we described the relationship between refractive status and biometric components in different types and levels of refractive errors in children between the age group of 6–15 years. Forty-two percent of the total sample was myopic which agrees with the information that myopia is the most prevalent refractive error worldwide. The mean age of the whole sample was 8.7 years (range, 6–15 years). The mean of SE was −1.06± (3.04) D (range, −11.5D–3D). The mean AL, ACD, VCD, LT, and CC of the whole sample were 22.75 (1.35) mm, 3.38± (0.33) mm, 15.76± (1.25) mm, 3.59± (0.26) mm, and 43.94± (1.17) D, respectively.
Significant differences between the three main groups, i.e., myopia, emmetropia, and hypermetropia were found for AL (P < 0.0001), ACD (P = 0.03), and VCD (P ≤ 0.0001). Among the different components, AL, ACD, and VCD made the most contribution to changes in refractive errors whilst LT (P = 0.10) and CC (P = 0.45) showed less variation, similar to study made by Hashemi et al. In most of the previous studies, AL and VCD were the most important components in relation to refractive errors,, which is similar to our results.
Previous reports such as Warrier et al. and Mallen et al. also discussed about having a longer AL and its components such as VCD and ACD in myopes and reverse in hyperopes which is in accordance with our results. AL, ACD, and VCD significantly increased at higher levels of myopia (P ≤ 0.0001), (P = 0.04), (P ≤ 0.0001), respectively, in our study and hypermetropes had the least values.
One of the findings in our study is a higher LT in hyperopes which can be explained by a hyperope accommodating more to focus an image which causes lens to thicken and subsequently leading to a lesser ACD.
In our study, SE was having a correlation with AL in myopes (P ≤ 0.0001) and in hypermetropes (P ≤ 0.0001) which is in accordance with previous reports.,,, SE showed a strong correlation with VCD in myopes (P ≤ 0.0001) which is in agreement to previous study, which states VCD is the main reason for the changes in refraction in case of myopia. When we took ACD/VDC ratio, as the degree of myopia increases, the ratio decreases, which signifies that VCD disproportionately increased at higher levels of myopia also. Zhu et al. state that genetic changes responsible for myopia mostly cause changes in the posterior segment. However, SE had a more important correlation with ACD in hyperopes (P = 0.002), which is to be highlighted as only a few studies have investigated this relationship between anterior segment parameters and hyperopia.
Hashemi et al. conducted a cross-sectional, population-based study with large sample size at Iran, to investigate the association between ocular biometrics with different levels of refractive error in age group of 40–64 years. The study revealed that corneal power and AL make the greatest contribution to SE in high hypermetropia and high myopia. Hashemi et al. in their study found that corneal power increased at higher levels of myopia and decreased at higher levels of hyperopia; but no such correlation was found in our study between AL and CC. The role of cornea in the appearance and progression of refractive errors has been the subject of study since years. Touzeau et al. demonstrated no relationship between refractive errors and CC; although CC has been linked to AL especially in emmetropes. This is in accordance with our study where we obtained similar results (P ≤ 0.0001). This would be expected if we consider that during emmetropization, an increased AL of eye will be counteracted by an increase in the corneal radius to maintain emmetropia. Paradoxically, other authors have found that the most myopic subjects therefore with large AL have small corneal radi., Scott explained this paradox by distinguishing between the normal growth of the eye and abnormal growth that occurs during the development of myopia. In the first case, the cornea becomes flatter as the eye develops and increases in size, whereas in the latter case, the cornea cannot continue to flatten and may even curve because of stretching of the eye. Other authors found no relationship between AL and CC in any levels of myopia., Cornea seems to play at preserving emmetropia.
Bhardwaj and Rajeshbhai conducted a study at Jaipur on 480 eyes with subject's ages ranging from 0 to 60 years to find out the role of AL and ACD in refractive status of the eye in different age groups and the study concluded that myopes have a longer AL and hypermetropes tend to have shorter AL when compared to that of emmetropes. When we divided the participants into two groups (6–10 and 11–15 years), a relative higher AL, ACD, VCD, and CC were found in the latter group. However, no difference in mean noted in LT between the two groups. This also supports the process of emmetropisation. Similar findings were observed by Bhardwaj and Rajeshbhai in their study. Zadnik et al. found that there is a general pattern of ocular growth between the age group of 6–14 years which is found in our study.
| Conclusion|| |
In our study, myopia is the most common refractive error. In children aged 6–15 years, AL and VCD make the greatest contribution to refractive errors. Anterior segment biometric components have a more important role in hypermetropes than myopia and VCD is the most affected in myopes especially at higher myopia. The CC and LT are not determining factors for SE. A relative higher AL, ACD, VCD, and CC were found in the age group of 11–15 years, which thus supports the process of emmetropisation and the general pattern of ocular growth between the ages of 6–15 years.
Limitations of the study
The study was conducted in a small sample size; hence, the results are limited to a small population. We have obtained the ocular biometric parameters by a scan ultrasound; however, immersion technique or the optical technique would have given more accurate results. Moderate and high hypermetropia samples were not obtained; hence, its correlation was not assessed.
We would like to thank the management of Government Medical College, Thrissur, for providing me the facilities to conduct the study in their institution and the entire team of our department for their valuable support. I express my heartfelt gratitude to Dr. Deleep Kumar KV, Professor and HOD, Department of Ophthalmology, Government Medical College, Thrissur, Dr. K. C. Rajini, Professor and HOD, Department of Ophthalmology, Government Medical College, Manjeri (Former HOD, Department of Ophthalmology, Government Medical College, Thrissur) and Dr Sudha V, Professor, Department of Ophthalmology, Government Medical College, Thrissur for their constant supervision, guidance and inspiration. Furthermore, special thanks to Dr Sudhiraj for helping me out with the statistical part of this study.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8]