The Role of Axial Length-Corneal Radius of Curvature Ratio in Refractive State Categorization in a Nigerian Population

Eghosasere Iyamu,Joy Iyamu,Christian Izuchukwu Obiakor

doi:10.5402/2011/138941

Abstract

The aim of this study was to investigate the association of axial length (AL)/corneal radius of curvature (CRC) ratio (AL/CRC) with spherical equivalent refractive state (SER) in young adults. A total of seventy (n = 70) subjects consisting of 31 males and 39 females participated in this study. Subjects were categorized into emmetropia, hyperopia and myopia using the spherical equivalent refraction. The axial length was measured with I-2100 A-Scan ultrasonography/Biometer (CIMA Technology, USA), the corneal radius of curvature with Bausch & Lomb H-135A (Bausch & Lomb Corp., USA), and the refractive state by static retinoscopy and subjective refraction. The mean AL, CRC and AL/CRC ratio of all subjects were 23.74 ± 0.70 mm, 7.84 ± 0.19 mm, and 3.03 ± 0.14, respectively. Myopes had significantly longer AL, steeper CRC and higher AL/CRC ratio than the emmetropes and hyperopes. There was statistically significant inverse correlation between AL and CRC (r = −0.53, P < 0.0001), SER (r = −0.64, P < 0.0001), and between SER and AL/CRC (r = −0.78, P < 0.0001). A significant positive correlation was found between CRC and SER (r = −0.69, P < 0.0001). The categorization of the refractive state of an individual is better done by using the AL/CRC ratio index.

Highlights

The refractive state of the eye is determined by refractive components which are interdependent rather than independent variables, and that the eye grows during the early years in life in such a manner that the refractive state tends towards emmetropia [1, 2]
The axial length has been found to be one of the key variables used in assessing the refractive status of the eye, and the interaction between it and corneal radius of curvature play a major role in the emmetropization process
Numerous studies [3, 8, 9] have shown that axial length and corneal radius of curvature are interdependent variables and that the true refractive state can be assessed based on axial lengthcorneal radius of curvature index expressed as axial length-corneal radius of curvature (AL/CRC) ratio

Summary

Introduction

The refractive state of the eye is determined by refractive components (corneal power, lens power, anterior chamber depth, and axial length) which are interdependent rather than independent variables, and that the eye grows during the early years in life in such a manner that the refractive state tends towards emmetropia [1, 2]. Overall the changes in axial length appear to outweigh the progressive corneal flattening with age in normal eyes; the majority of axial length elongation takes place in the first three to 6 months of life and a gradual reducing rate of growth over the two years [7], and by three years the adult eye size is attained [8]. The interaction between axial length and corneal radius of curvature (CRC) has played a major role in the compensatory adjustments of the optical components of the eye towards attaining emmetropic state [8]. The aim of this study is to determine the role of axial length-corneal radius of curvature (AL/CRC) ratio in refractive state categorization in Nigerians

Objectives

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Results

Conclusion