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Relationship between anterior corneal asphericity and refractive variables

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Abstract

Background

The anterior corneal surface is closely modelled by a conic section that is fully described by asphericity (Q) and the apical radius of curvature. Computerized corneal topographers have allowed for more accurate and complete descriptions of corneal shape. Our objective was to compare anterior corneal asphericity (Q) values determined for different corneal diameters in eyes of different refractive state.

Methods

Q-values were determined in 118 eyes of 118 subjects using both a videokeratoscope (Atlas Mastervue, Humphrey Instruments-Zeiss) and Vol-CT 6.89 software (Sarver & Associates Inc.), which estimates Q-values for several corneal diameters (3.0 mm, 4.0 mm, 5.0 mm, 6.0 mm, 7.0 mm and 8.0 mm) using topographic data obtained with the instrument. For comparisons, Q-values were stratified three ways: by refractive error (myopic, emmetropic or hyperopic eyes), corneal power (low, intermediate and high) and corneal astigmatism (low, intermediate and high).

Results

Mean corneal asphericity was −0.35 ± 0.03, differing significantly from reported data (Student’s t-test). Asphericities determined using both methods did not vary significantly withh regard to refractive error or corneal power, but did differ among the corneal astigmatism groups (p < 0.01). A trend was observed towards more negative Q-values with increasing corneal diameter, but differences in corneal asphericity according to corneal diameter were only significant in the astigmatism group (p < 0.01).

Conclusion

Q-values varied according to the refractive properties examined. However, the relationship between refractive state and corneal asphericity was found to be determined more by the geometric properties of the eye (corneal power and axial length) than by manifest refraction.

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Authors and Affiliations

  1. Department of Optics II, University School of Optics, University Complutense of Madrid, Arcos de Jalon s/n, Madrid, 28040, Spain

    Amelia Nieto-Bona & Amalia Lorente-Velázquez

  2. Department of Optics, University of Valencia, Valencia, Spain

    Robert Mòntes-Micó

Authors
  1. Amelia Nieto-Bona
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  2. Amalia Lorente-Velázquez
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  3. Robert Mòntes-Micó
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Correspondence to Amelia Nieto-Bona.

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The authors declare no financial or proprietary interests in any materials or methods mentioned. No sources of public and private financial support declared

Human sujects and informed consent

The authors declare that this research was performed following the tenets of the Declaration of Helsinki, and that informed consent was obtained from the subjects after the nature of the study had been explained to them in detail. The study protocol was approved by the Clinical Research Ethics Committee of the School of Optometry.

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Nieto-Bona, A., Lorente-Velázquez, A. & Mòntes-Micó, R. Relationship between anterior corneal asphericity and refractive variables. Graefes Arch Clin Exp Ophthalmol 247, 815–820 (2009). https://doi.org/10.1007/s00417-008-1013-2

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  • DOI: https://doi.org/10.1007/s00417-008-1013-2

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