|Year : 2022 | Volume
| Issue : 1 | Page : 148-153
Relationship between central corneal thickness and axial eye length using partial coherence interferometry
Wafaa A.E Abdelkhalek1, Hanan S Hegazy2, Mohamed I El-Kasaby2
1 Department of Ophthalmology, Imbaba Eye Hospital, Imbaba, Egypt
2 Department of Ophthalmology, Faculty of Medicine (for Girls), Al-Azhar University, Cairo, Egypt
|Date of Submission||07-Dec-2021|
|Date of Decision||22-Dec-2021|
|Date of Acceptance||26-Dec-2021|
|Date of Web Publication||4-Mar-2022|
MBBC Wafaa A.E Abdelkhalek
Department of Ophthalmology, 6th October, Giza
Source of Support: None, Conflict of Interest: None
Background and aim Several studies have shown the relationship between axial length (AL) of the eye and central corneal thickness (CCT). Since genetics, ethnicity, and race can affect these factors, their differences between different societies can probably explain refractive error variance. We present the ocular parameter values in 154 eyes of different refractive error groups to investigate the correlation between AL of the eye and CCT in Egyptians with refractive errors.
Patients and methods In all, 154 patients were classified into emmetropic, hypermetropic, simple myopic, congenital myopic, and malignant myopic groups. Most ocular parameters were achieved using IOLMaster 700 and stratified according to AL and CCT.
Results The CCT means in the studied groups was 537±34, 523±31, 541±40, 524±40, and 524±27 μm in emmetropic, hypermetropic, simple myopic, congenital myopic, and malignant myopic groups, respectively. The AL was 23±0.76, 22±1.1, 25±1.3, 26±1.4, and 29±1.6 mm, respectively. Regarding the correlation between AL of the eye and CCT (r=−0.01, P=0.92, confidence interval=−0.17 to 0.15).
Conclusion This study provided valued measurements of ocular parameters of the Egyptians with refractive errors. Besides, there is no significant correlation between AL of the eye and its CCT in Egyptians with errors of refraction.
Keywords: axial length, central corneal thickness, IOLMaster 700
|How to cite this article:|
Abdelkhalek WA, Hegazy HS, El-Kasaby MI. Relationship between central corneal thickness and axial eye length using partial coherence interferometry. Al-Azhar Assiut Med J 2022;20:148-53
|How to cite this URL:|
Abdelkhalek WA, Hegazy HS, El-Kasaby MI. Relationship between central corneal thickness and axial eye length using partial coherence interferometry. Al-Azhar Assiut Med J [serial online] 2022 [cited 2022 Jun 29];20:148-53. Available from: http://www.azmj.eg.net/text.asp?2022/20/1/148/339065
| Introduction|| |
Several studies indicated that errors of refraction are the first cause of visual impairment and the second reason of visual loss globally, as refractive errors are the cause of 43% of visual impairment cases . With the current advances in refractive surgeries, there is a great interest in understanding the relationship between central corneal thickness (CCT) with other optical biometric parameters such as axial length (AL), which is the distance from the retina to the anterior corneal surface , and refraction . Despite several researches, the relationship remains indescribable, as the results are quite inconstant. The relationship between different parameters differs with the societies studied. Since these factors can be affected by genetics, race, and ethnicity, their variances between different societies can probably explain the differences in errors of refraction, and it would be helpful to determine the distribution of biometric parameters in different world areas . Dual-beam partial coherence interferometry was reported to yield fast, noncontact measurements of the CCT with precision better than 1 μm .
Based on this requirement, it is important for our society to quantify and analyze the presence of a relationship between CCT and axial errors of refraction in Egyptians. So, we aimed at exploring the presence of a correlation between AL and CCT in Egyptians subjects with errors of refraction.
| Methods|| |
An informed written consent was taken from each participant (or his parents in case of children) after illustrating the study purpose and had the right to accept or not. All procedures were conducted in accordance with Helsinki standards as revised in 2013 and approved by ethics committee of Al-Azhar University.
Case–control prospective observational study.
This study included 154 eyes of 154 subjects presented in AL-Zahraa Ophthalmic Outpatient Clinic.
These eyes were classified into five groups as follows:
- Group 1: included 31 emmetropic eyes as a control group.
- Group 2: included 32 hypermetropic eyes.
- Group 3: included 30 simple myopic eyes.
- Groups 4: included 30 congenital myopic eyes.
- Group 5: included 31 malignant myopic eyes.
Subjects with clear cornea and clear lens aged 5–60 years.
Subjects with corneal opacity, contact lens, diabetes, cataract, pregnancy, and prior ocular surgery.
Study tools and procedures
History taking (name, age, sex, occupation, past medical history, ophthalmic history), complete ocular examination including refractive status using TOPCON RM-800 (Topcon, Tokyo, Japan) autorefractometer, best-corrected visual acuity, visual acuity using Snellen’s chart, slit-lamp microscopic examination including full examination of the anterior eye segment, fundus examination by slit-lamp biomicroscopy using 90⁺ lens, CCT, AL, keratometry, and anterior chamber depth (ACD) values were assessed by ZEISS IOLMaster 700 (ZEISS, Jena, Germany), and intraocular pressure (IOP) by TOPCON CT-80 computerized tonometer.
Statistics was achieved using IBM SPSS software, version 23 (IBM SPSS Incorp., New York, USA). One-way analysis of variance test was used for the comparison between five groups; group 1 included 31 emmetropic eyes as a control group, group 2 included 32 hypermetropic eyes, group 3 included 30 simple myopic eyes, groups 4 included 30 congenital myopic eyes, and finally group 5 included 31 malignant myopic eyes. The confidence interval was set to 95% and the accepted error limit was set to 0.05. The P value was considered significant as in the following:
- P value more than 0.05 means nonstatistical significance.
- P value less than 0.05 means statistical significance.
- P value less than 0.01 means high statistical significance.
| Results|| |
A total of 154 eyes from 154 participants were included in this study. Their demographic data are included in [Table 1].
In our study we noted that CCT did not show significant difference between the studied groups.
Regarding AL we noted that AL of hypermetropic subjects was significantly lower than other groups. Also, in the congenital myopic group, AL was significantly higher than emmetropic, hypermetropic, and simple myopic groups. Finally, AL of malignant myopic group was significantly higher than all other groups ([Table 2]).
|Table 2 Central corneal thickness, axial length, intraocular pressure, anterior chamber depth, refraction, and best-corrected visual acuity of the studied groups|
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In our study, IOP ranges from 15 to 18 mmHg. There is no significant difference between emmetropic, hypermetropic, simple myopic, and congenital myopic groups but the malignant myopic group showed significant increased IOP compared with previous groups ([Table 2]).
The range of ACD was from 3 to 3.6 mM among the studied groups. It was noted that ACD of the hypermetropic group is significantly lower than that of emmetropic and myopic groups ([Table 2]).
It was noted that refraction of the emmetrope group was −0.2±0.45, hypermetrope group was 3.1±2, simple myopia group was −3.4±1.9, congenital myopia group was −8.3±1.6, and malignant myopia group was −14±3.9 ([Table 2]).
Regarding spherical equivalence of cornea (SE), K1, K2, and ΔD of the studied groups, it was noted that K1 was 43 in all groups while K2 ranged from 44 to 54, SE from 43 to 44, and finally ΔD from −2.15 to −0.75. We also found that there is no significant difference between groups regarding K1, K2, and SE ([Table 3]).
|Table 3 Spherical equivalent of cornea, K1, K2, and ΔD of studied groups|
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Regarding correlation between AL and CCT, ACD, SE and age, it was found that there is no significant correlation between AL with CCT [Figure 1] nor age ([Table 4]) in the studied groups. On the other hand, AL had a significant positive correlation with ACD in hypermetrope subjects and also in overall combined subjects ([Table 4]). Regarding SE, it was negatively correlated with AL ([Table 4]).
|Figure 1 Correlation between AL and CCT in the studied groups. AL, axial length; CCT, central corneal thickness.|
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|Table 4 Correlation between central corneal thickness, axial length, spherical equivalent of cornea of cornea, and age in the studied groups|
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Concerning correlation between CCT and ACD, SE and age in the studied groups, we found that CCT did not correlate with ACD, SE, or age. However, emmetropic patients exhibited some sorts of correlation between CCT and SE. Regarding correlation between SE and age in the studied groups, there is no significant correlation between SE and age in most studied groups. However, in malignant myopia we noted a positive correlation between them ([Table 4]).
| Discussion|| |
Measurement of CCT is an important parameter for corneal evaluation before surgery or for diagnosis. IOP is greatly affected by CCT; a thick cornea may explain a falsely elevated IOP .
In our study, CCT did not show a significant difference between emmetrope subjects and others with refractive errors including myopic or hypermetropic subjects. Besides, there is no statistical correlation between CCT and refraction in all studied groups. This result agrees with a previous study reported by Fam et al. . They reported that CCT does not correlate with myopia in myopic Chinese. Moreover, Zhang et al.  reported that CCT was not significantly associated with refractive errors. Although most studies indicated the absent correlation between CCT and refraction, Chang et al.  reported that CCT was thinner in more myopic eyes.
In the development of myopia, eyeballs with longer AL had more myopia, flatter cornea, and longer ACDs . This concept coincides with our results. In our results, AL increases significantly with the degree of myopia, being highest in malignant myopia. As a complement, AL showed a high significant negative correlation with refraction in different studied groups. On the other hand, there is no noticeable relationship between AL and CCT in the different studied groups. This also coincides with the previous report indicated by Chen et al. . Regarding age, Zhang et al.  reported that CCT was not correlated with age. The same result was observed in our study.
In our study, we found that ACD is significantly lower in the hypermetropic group compared to the emmetropic group. Interestingly, although the ACD of the myopic group is higher than the emmetropic one, this relation showed no statistical significance between the two groups. Moreover, there was a statistically significant positive correlation between AL and ACD. This concept might be in accordance with some previous studies. Liu et al.  reported that in axial myopia, there is an increase in AL and ACD, a relation that is proportional to the degree of myopia. In hypermetropia, ACD becomes shallower with a decrease in AL. More hyperopia leads to shallower ACD .
It was reported that IOP plays a critical effect in the development of glaucoma and myopia . Edgar and Rudnicka  reported that myopia was correlated with increased glaucoma risk (about two-fold in low myopia and three-fold in medium and high myopia) at any age compared to those with emmetropia. In our study, malignant myopic patients showed a significantly increased IOP compared with previous four groups. This agrees with previous several studies indicating the increases risk of glaucoma in severe myopia ,.
Several previous reports indicated the significant correlation between corneal curvature and AL. Scheiman et al.  evaluated the correlation between corneal curvature and AL at baseline and at the 3-, 6-, 9-, 12-, and 14-year visits. The overall correlation between corneal curvature and AL at baseline was −0.70 (P<0.0001), that is, more eye length was associated with less corneal curvature at baseline and the correlation reduced monotonically overtime to −0.53 at the 14-year visit (test for linear trend, P=0.0004) .
In our study, we explored the correlation between AL and SE of the cornea. It was found that AL significantly correlated with SE of cornea (P=0.02, r=−19). This result seemed to be in harmony with a previous report indicated by Scheiman et al. .
Limitations: the relatively low number of subjects is the main limitation of our study.
| Conclusion|| |
This study provided valuable measurements of ocular parameters of the Egyptian healthy adults with error of refraction. These parameters can assist researchers and clinicians in refractive surgery screening. Besides, as a general concept, there is no significant correlation between AL and CCT in Egyptians with errors of refraction.
We recommend additional studies with larger groups of participants.
To Dr Elsayed Elsakka, Lecturer of Biochemistry and Molecular Biology, Faculty of Pharmacy (Boys), Al-Azhar University, Cairo, Egypt.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4]