The relation between central corneal thickness and axial length in a sample of Erbil population

Abstract

IntroductionThe axial length (AL) of the eye is the distance between the anterior and posterior poles of the eye, 1 and it is typically defined as the distance from the anterior corneal surface to the anterior surface of the retina. 2,3 In vivo, it is measured either by ultrasonography or by partial coherence interferometry. The AL of the eye at birth is approximately 17 mm and reaches approximately 24 mm in adulthood. It is typically longer than 24 mm in myopes and shorter than 24 mm in hyperopes. Each one millimeter of change in AL of the eye corresponds to approximately 2.5 diopters (D) change in refractive power of the eye. 4 From birth to age six years, the AL of the eye grows by approximately 5 mm, and one might expect from this a high prevalence of myopia in infants. However, most children are actually emmetropic, with only a 2% incidence of myopia at six years. This phenomenon is due to a still undetermined mechanism called emmetropization. During that first six years of life, a compensatory loss of 4 D of corneal power and 2 D of lens power keeps most eyes close to emmetropia. It appears that the immature human eye develops so as to reduce refractive errors. The cornea is a transparent, avascular tissue that measures 11-12 mm horizontally and 10-11 mm vertically. Its refractive index is 1.376, although, in calibrating a keratometer, a refractive index of 1.3375 is used to account for the combined optical power of the anterior and posterior curvatures of the cornea. The average radius of curvature of the central cornea is 7.8 mm. The cornea thus contributes 74%, or 43.25 D, of the total 58.60 dioptric power of a normal human eye.5 Normal central Background and objective:A thin central corneal thickness has been reported to be a risk factor for developing primary open-angle glaucoma. This has led to a hypothesis that thinning of the cornea may be an indication of generalized weakness of the ocular integument. This study was conducted to explore the relationship between central corneal thickness and axial length in a sample of Erbil population. Methods: This is an observational cross sectional prospective study that was conducted from October 2012 to March 2013 and included 260 eyes of 130 patients. The mean age (± SD) was 37.8 ± 17.7 years for males and 35.4 ± 15.5 years for females. Axial length was measured with A-scan ultrasound biometry and central corneal thickness with ultrasonic Pachymeter. Results:The mean central corneal thickness (± SD) was 542.8 ± 36 µm in male eyes and 530.1 ± 32.5 µm in female eyes. The mean axial length (± SD) was 23.38 ± 1.1 mm in male eyes, 23.15 ± 1.2 mm in female eyes. Central corneal thickness was not correlated with axial length (Pearson correlation coefficient r = 0.037, P = 0.558). Conclusion:Central corneal thickness and axial length of the eye are two independent measurements. Thin corneas are not related to longer eye.

Clinical Profile of Primary Open-angle Glaucoma Patients at an Eye Center in Nigeria

“… 25 , 32 , 33 According to these studies, there is a drop in the density of keratocytes, a reduction in inter-collagen fiber lengths, and denaturing of collagen fibers as a person advances in age with resultant alteration in CCT. 34 , 35 Studies conducted in Nigeria and Africa at large have borne this out in studies quite similar to ours in which the authors reported that aging was associated with corneal thinning. 15 , 25 , 36 , 37 Although our study did not reveal significant clinical profiles that are typical of patients developing POAG that can be used as early indicators for the disease, apart from the usual monitoring of IOP, it is clear that individuals who require evaluation and management of glaucoma can be identified more readily through the provision of screening services and health education in communities, work, and religious institutions 38 so that patients at risk of glaucoma can be identified early and treated to avoid late presentation to the eye clinic with glaucoma and its associated complications.…”