DETERMINATION OF NORMATIVE VALUES FOR CENTRAL CORNEAL THICKNESS IN GHANAIAN CHILDREN IN THE ABLEKUMA SOUTH SUB-METROPOLITAN AREA

Abstract

Background The thickness of the cornea has importance in ocular health. Several studies including the work done by the Ocular Hypertension Treatment Study (OHTS) have demonstrated the significance of Central Corneal Thickness (CCT) measurements in the accurate assessment of intraocular pressure (IOP), accurate diagnosis and prognosis of glaucoma. The variation of CCT with age, gender and race have also been confirmed in studies. CCT has been shown to increase gradually with age in children stabilizing after the age of 10 years and has been shown to be thinner in African/Americans compared to whites. In the adult population, CCT values have been shown to affect the accurate diagnosis and management of glaucoma resulting in the need for assessment of the normal CCT values for any given population. The racial and ethnic variation in CCT values does not support extrapolation of normal population values from one geographic location to the other. In Ghana, data on normal CCT values in children is lacking, resulting in assessment of intraocular pressure based on reference values from populations with potentially different CCT values. It is therefore imperative that CCT values be assessed in healthy Ghanaian children to determine normal values for our population. This will provide baseline data for assessment of deviations from the mean values in the Ghanaian population in future studies to better correlate CCT with IOP values in Ghana. Aim

The overall aim of this study was to measure the CCT in healthy Ghanaian children and determine the normal values of defined age-groups. Materials and methods A prospective cross-sectional study was conducted to measure the CCT of 420 children (840 eyes) aged 6 to 15 years. Informed written consent was obtained from parents/ guardians and assent obtained from children aged 8 years and above. An interviewer-administered questionnaire was used to obtain demographic data followed by an anterior and posterior ocular exam. One drop of 0.5% amethocaine was instilled in the eye 1 minute prior to measurement after which a hand-held pachymeter was used to take 3 measurements from the central 3mm of the cornea of the eye. Data handling and statistical analysis plan Statistically significant differences were assessed with the independent t-test for differences in continuous variables such as CCT, analysis of variance (ANOVA) for differences between groups such as age and gender and linear regression for differences in trends. Statistical significance was set at a p value of less than 0.05. Results: The overall mean CCT was 538.8 ± 27 µm (420 children, 840 eyes) and among children aged 6-8 years was 541.4±24.9 µm., for children aged 8-10 years 534.9±25.8 µm and those 10-15 years 538.3±28.6 µm. ANOVA (Analysis of variance with the F statistics) with the Post Hoc tests showed no significant difference in mean CCT among the age groups for both eyes. There was found to be a weak negative correlation between CCT and age. Thus, CCT decreased with age. Though CCT was higher in males, the difference was not statistically significant. Our study also demonstrated that there was a weak positive correlation between CCT and IOP. CCT was higher in hyperopes compared to emmetropes and thinnest in myopes and the difference was statistically significant. Conclusion: CCT in healthy Ghanaian children was found to be 538.8 ± 27 µm and did not vary significantly among age groups or sex. Results of this study provide baseline data for larger national studies that could ultimately lead to the development of national reference ranges for CCT values in the Ghanaian paediatric population. Secondary benefits of this study include improvement in the diagnosis, prognostic prediction, and management of glaucoma in children.