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The relationship between the sagitta of the anterior corneal surface and refractive error of the eye

Garner, Leon F.; Owens, Helen

Authors

Leon F. Garner



Abstract

Changes in the sagitta of the anterior corneal surface associated with a change in the corneal radius of curvature have been used to calculate the change in refractive error of the eye in two areas: the ablation depth for laser surgery, and the change in corneal thickness associated with orthokeratology lens wear. An approximate formula known as Munnerlyn's formula is commonly used to calculate the refractive error change from sagittal data. This article compares the change in refraction calculated using the approximate formulae with the change calculated from a formula based on an elliptical corneal section. The approximate formula underestimates the ablation depth for a given refractive change and overestimates the refractive change for a given change in corneal thickness, assuming a constant asphericity. When the corneal asphericity increases together with an increase in radius of curvature, a suggested mechanism in orthokeratology, the approximate formula underestimates the change in ocular refraction.

Journal Article Type Article
Publication Date Aug 1, 2004
Journal Optometry and Vision Science
Print ISSN 1040-5488
Publisher Lippincott, Williams & Wilkins
Peer Reviewed Peer Reviewed
Volume 81
Issue 8
Pages 636-639
APA6 Citation Garner, L. F., Garner, L. F., & Owens, H. (2004). The relationship between the sagitta of the anterior corneal surface and refractive error of the eye. Optometry and Vision Science, 81(8), 636-639. https://doi.org/10.1097/01.opx.0000141798.41340.8b
DOI https://doi.org/10.1097/01.opx.0000141798.41340.8b
Keywords corneal topography, refraction, orthokeratology
Publisher URL http://dx.doi.org/10.1097/01.opx.0000141798.41340.8b
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