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| ORIGINAL ARTICLE |
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| Year : 2020 | Volume
: 32
| Issue : 3 | Page : 252-257 |
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Ocular biometry in an adult Ghanaian population
Samuel Kyei1, Frank Assiamah2, Michael Agyemang Kwarteng3, Victor Kwesi Ansah4
1 Department of Optometry and Vision Science, School of Allied Health Sciences, College of Health and Allied Sciences, University of Cape Coast, Cape Coast, Ghana
2 Inter-Star Eye Clinic and Laser Center, Accra, Ghana
3 Discipline of Optometry, College of Health Sciences, University of KwaZulu-Natal, Durban, South Africa
4 Bishop Ackon Memorial Christian Eye Centre, Cape Coast, Ghana
| Date of Submission | 07-Apr-2020 |
| Date of Decision | 13-Apr-2020 |
| Date of Acceptance | 16-Apr-2020 |
| Date of Web Publication | 23-Dec-2020 |
Correspondence Address:
Dr. Michael Agyemang Kwarteng
Discipline of Optometry, College of Health Sciences, University of KwaZulu-Natal, Durban
South Africa
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/kjo.kjo_38_20
Purpose: To measure ocular biometry and its correlates in an adult population. Materials and Methods: The measured biometric data included central corneal thickness (CCT), corneal power (K), anterior chamber depth (ACD), lens thickness (LT), vitreous chamber depth (VCD), axial length (AL), and spherical refractive error (SER) in 162 adult eyes. Results: The mean CCT was 506.7 ± 39.2 μm, mean K was: K1 = 42.50 ± 2.00 D, K2 = 43.50 ± 2.44 D, the mean AL was 24.2 ± 1.3 mm, ACD had a mean of 3.5 ± 0.6 mm, LT (mean of 3.9 ± 0.8 mm), VCD (mean of 16.4 ± 1.39 mm), and SER ranged from -10.00 D – +8.00 D. There were no significant correlations between the CCT and SER (r = 0.06, P = 0.44), LT (r = 0.06, P = 0.59), ACD (r = −0.12, P = 0.12), AL (r = −0.02, P = 0.98), and VCD (r = −0.05, P = 0.68). Pearson's correlation coefficient tests showed that AL was significantly positively correlated with ACD (r = 0.4, P < 0.001) and VCD (r = 0.73, P < 0.001) and negatively correlated with LT (r = −0.22, P < 0.05). A significant negative weak correlation was found between LT and ACD values (r = −0.22, P < 0.05). Conclusion: A thin CCT was observed among an adult Ghanaian population. CCT was found to be independent of AL. Correlation among ocular biometry showed that AL positively correlated with ACD and negatively correlated with LT.
Keywords: Anterior chamber depth, axial length, central corneal thickness, Ghana, spherical refractive error
How to cite this article:
Kyei S, Assiamah F, Kwarteng MA, Ansah VK. Ocular biometry in an adult Ghanaian population. Kerala J Ophthalmol 2020;32:252-7 |
| Introduction | |  |
Biometric data of the eye are important clinical parameters due to the influence of these measures on the calculation of intraocular lens implant, refractive errors and intraocular pressure measurements among patients with glaucoma.[1],[2],[3],[4],[5],[6],[7] Parameters such as anterior chamber depth (ACD), vitreous chamber depth (VCD), axial length (AL), corneal curvature (CC) or astigmatism, and lenticular thickness (LT) may help explain the pathophysiological dynamics of common eye disorders.[8],[9] Biometric studies have shown that ALs account for differences in refractive status among age groups.[10],[11],[12],[13],[14],[15],[16],[17],[18],[19]
The AL refers to the distance between the anterior pole and the posterior pole of the eye which ranges from 23 to 25 mm in an adult eye (mean of 23.30 mm).[20],[21] Age, gender, refractive error, corneal curvature, and racial and ethnic variations have been observed in reported studies in Africa and African Americans.[7],[19],[22],[23],[24],[25],[26],[27],[28],[29],[30]
A study by Ntim-Amponsah et al.[31] compared the central corneal thickness (CCT) among glaucomatous (cases) and nonglaucomatous (controls) population in Ghana and found no significant difference between mean CCT of cases and controls. Another study by Ntim-Amponsah et al.,[32] normative CCT among 169 Ghanaians were found to be different from neighboring countries and as such cannot be generalized as representative of Ghanaians. This highlights the need for geographic-specific studies on ocular biometry and how they correlate with common ocular disorders.
To fill this gap, there is a need for current studies on ocular biometry among the Ghanaian population. Hence, this prospective study aimed to determine ocular biometry and its correlates in a sample population of native adult Ghanaians attending a referral eye clinic in Ghana.
| Materials and Methods | | |
Study setting
This study was carried out at the premises of the Christian Eye Center, Cape Coast. The center is the most utilized eye care institution in the Central region of Ghana serving other regions due to the use of advanced technology for cataract and glaucoma surgery among others.
Study design
This was a hospital-based prospective study of patients visiting the center. The study involved measuring and collating biometric data from patients. It sought to explore the relationship between biometric parameters and refractive error.
Sampling technique
The sampling method was nonprobability convenience sampling. The sampling method was based on the fact that the study involved all clients at the center during the study period.
Inclusion and exclusion criteria
The study included all clients who had no ocular disease other than refractive error and those aged 18 and older. Patients below the age of 18 years and patients with steep corneas (keratometric [K] readings of more than 48 D [diopter]) or abnormally thin or thick corneas (CCT <350 μm or CCT > 650 μm), previous contact lens use, along with known glaucomatous individuals were excluded from the study.
Ethical review
The study adhered to the tenets of the Declaration of Helsinki and approval was sought from the “Institutional Review Board of the University of Cape Coast (UCCIRB/CHAS/2018/65). The informed consent of the participants was obtained. There were no risks and/or discomfort associated with participating in the study, and no financial remunerations were offered to the participants. Participation in this study was voluntary, and participants were informed that they could withdraw their participation at any point and that in the event of refusal/withdrawal of participation, they will not incur penalty or loss of treatment or other benefits to which they would normally be entitled.
Data collection procedure
Data collection involved the use of a data extraction sheet to collect data on demographics, and ocular biometry data.
The data extracted included:
- The examination of the anterior segment was performed on each participant using a slit-lamp biomicroscope
- The examination of the posterior segment was conducted with an ophthalmoscope and slit-lamp biomicroscope
- Ocular biometry was measured among participants: Wavelight oculyzer II (Alcon surgical, Fort Worth, Texas, USA) for central cornea readings and keratometry, ultrasound device: US4000 EchoScan (Nidek Co., Ltd., Japan) for biometry, and KR 9000 Auto REF (Perlong Medical Equipment Co., Ltd., Jiangsu, China) for autorefraction
- Refractive error was calculated in diopters as the spherical equivalent of spherical refractive error plus half of the cylindrical refractive error
- The two major corneal radii separated by 90° were averaged to give corneal curvature and power.
Data analysis
Data were analyzed using the IBM SPSS version 21 (SPSS Inc, Chicago, USA). Categorical data were presented as frequencies. Pearson's correlation coefficient was used to determine the association between ocular biometric variables. P < 0.05 was considered statistically significant.
| Results | | |
Demographics
One hundred and sixty-two eyes of 100 participants were involved in the study. Their ages ranged from 21 to 91 years (mean age = 63.75; standard deviation ± 12.84 years) [Table 1].
Ocular biometry
In this study, ocular biometry was evaluated among participants. The median of AL was 24.1 mm, the median of ACD was 3.5 mm, LT with a median of 4.0 mm, VCD had a median of 16.3 mm, and a median CCT of 505.5 μm (409 μm–593 μm) [Table 2].
Corneal astigmatism
Corneal astigmatism was determined among the participants, 83 (51.2%) had astigmatism >1.00 D, while the remaining 79 (48.8%) had astigmatism of 1.00 D and below [Table 3].
Spherical refractive error
The dominant error of refraction in this study was myopia (57.4%) followed by hypermetropia (31.5%) [Table 4].
Correlations between biometric parameters, refractive error, and central corneal thickness
A Pearson product-moment correlation coefficient was computed to assess the relationship between ocular biometry variables and refractive error. There was a strong positive correlation coefficient between AL and VCD (r = 0.73, n = 162, P < 0.001). The correlations between CCT, SRE, and other biometric parameters are shown in [Table 5] as well as [Figure 1]. | Figure 1: A scatter plot showing the correlation between axial length and central corneal thickness
Click here to view |
| Discussion | | |
This study provides the first ocular biometry data among healthy Ghanaian adults. The study participants were mainly the elderly. A thin mean central corneal thickness (CCT) was recorded in this study due to age factor. This is consistent with other studies, which have reported that age is an important factor in corneal thickness.[33],[34] They reported that the thinner cornea is associated with old age. Hence, as one age, CCT decreases. This cornea thinning is a result of a reduction in the density of keratocytes, collagen fiber degeneration, and a decrease in the distance between fibers in the cornea.[33],[34] A similar study by Mashige and Oduntan[7] reported an average CCT of 493. 05 ± 33.2 μm among the Black South African population. Also, a study by Bagus et al.[3] reported a similar finding of 494 μm in the same population with a median age of 67 years. Furthermore, in a study by Ntim-Amponsah et al.[32] they reported that a sample of participants aged >50 years had a thin CCT of 516 μm which continues to decrease with age. In contrast, a study in Ghana by Ntim-Amponsah et al.,[32] reported a higher mean CCT of 533.3 μm among a healthy population with a mean age of 34.09 ± 12.14. The difference in the means of CCT in these studies is the aging factor associated with corneal thinning.
In this study, the mean AL was greater than that reported among African descends. An average AL of 21.02 mm[35] and 23.50 mm[36] in Nigeria, 23.05 mm in South Africa,[9] 23.09 mm in Sudan,[26] and 23.7 mm in Egypt[37] has been reported. The reason for a longer AL in this study might be due to scleral thinning and eyeball elongation in myopic eyes which happen to be the dominant error of refraction in this study. Our study reported a higher mean age along with a longer AL which is consistent with studies by Yin et al.[38] and Nangia et al.[39] However, it contrasts studies that have reported that AL decreases with age.[9],[35],[40]
The mean ACD in this study was higher than that reported by Mashige and Oduntan,[9] among South Africans but consistent with that of Nagra et al.,[41] who reported ACD of 3.55 mm among Britons. It has been established that accurate ACD measurements potentially prevent refractive errors among patients after intraocular lens implantation more than corneal power or AL measures among patients undergoing cataract surgery.[42] A deep ACD has been observed among myopes, which correspond with a high number of myopic eyes in this study [Table 4].
The mean lens thickness (LT) in this study was consistent with that of Mallen et al.[43] who reported an average LT of 3.85 mm. The LT is this study is higher than that reported by Mashige and Oduntan:[9] 3.69 mm, Osuobeni:[44] 3.72 mm but lower than reports by Hashemi et al.:[45] 4.28 mm, Shufelt et al.:[46] 4.28 mm, He et al.:[47] 4.44 mm and Olsen et al.:[42] 4.68 mm and 4.65 mm in the right and left respectively. A thicker lens observed in this study is due to the higher mean age, since LT increases as one age. Similar studies have reported the effect of age on LT.[42],[45],[46],[47] The anterior lens capsule thickens gradually from the neonatal stage to the seventh decade of life before stabilizing due to the continual addition of lens fibers.[48]
VCD is deeper among myopes than hyperopes and emmetropes as suggested by other researchers[40] which is consistent with VCD findings in this study due to the high number of myopes. A study by Hashemi et al.[44] reported a mean VCD of 15.72 mm as well as a recent study by Takkar et al.,[49] also reported an average VCD of 15.38 mm. The VCD reported in these studies were lower than what is reported in this current study. However, a study by Saka et al.[50] reported an average VCD of 21–22.3 mm among participants with high myopia. It can be concluded that a mean refractive error of approximately-0.75 D might have resulted in an appreciable increase in VCD among the eyes.
Corneal astigmatism had a significant visual effect on the sample population with more than half of the participants having astigmatism of more than 1.00 D [Table 3]. This is similar to a study in Africa by Bagus et al.[3] which reported 45% of Black South Africans with astigmatism of 1.00 D or greater. Information on corneal astigmatism is helpful to surgeons in ensuring a reduction in postoperative astigmatism among patients due to cataract surgery. Hence, the use of toric intraocular lenses as recommended, can be used among the Ghanaian population.
There was a poor correlation between CCT and AL in this study [Figure 1] and [Table 5]. Studies have reported that CCT is not correlated with AL, making them two independent variables in ocular biometry.[2],[33],[34],[51],[52] AL was positively correlated with ACD and negatively correlated with LT. These findings correlate with studies by Chen et al.,[2] Mashige and Oduntan[7],[9] Olsen et al.[42] and Osuobeni.[44] ACD has great effects on the pathogenesis of ocular conditions such as refractive errors and glaucoma.[9] There was a negative association between ACD and LT in this study which correlates with previous studies.[9],[44],[53],[54] The gradual thickening of the anterior capsule of the lens will decrease the ACD since it happens to be in the anterior chamber.
| Conclusion | | |
A biometry profile was established in native Ghanaians for the first time. CCT was found to be independent of AL because there was no significant relationship between the two variables. There was no association between CCT and ACD, LT, VCD, and SRE. Intercorrelation among ocular biometry showed that AL positively correlated with ACD, VCD and negatively correlated with LT.
Acknowledgment
The authors are grateful to the Management of Bishop Ackon Memorial Christian Eye Centre, Cape Coast, Ghana.
Financial support and sponsorship
This study was solely funded by the authors.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]
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