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Effects of error in radius of curvature on the corneal power measurement before and after laser refractive surgery for myopia
Author(s) -
Liu Yongji,
Wang Yan,
Wang Zhaoqi,
Zuo Tong
Publication year - 2012
Publication title -
ophthalmic and physiological optics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.147
H-Index - 66
eISSN - 1475-1313
pISSN - 0275-5408
DOI - 10.1111/j.1475-1313.2012.00921.x
Subject(s) - scheimpflug principle , radius of curvature , refractive error , radius , ophthalmology , curvature , cornea , refractive surgery , optics , corneal topography , keratometer , optical power , mathematics , medicine , laser , physics , geometry , mean curvature , visual acuity , computer security , computer science , mean curvature flow
Citation information: Liu Y, Wang Y, Wang Z & Zuo T. Effects of error in radius of curvature on the corneal power measurement before and after laser refractive surgery for myopia. Ophthalmic Physiol Opt 2012, 32 , 355–361. doi: 10.1111/j.1475‐1313.2012.00921.x Abstract Purpose: To investigate the sources of error in corneal power measurement before and after corneal refractive surgery for myopia. Methods: The study comprised 28 eyes of six males and eight females with a mean age of 26 (range 18–39 years). The radius of curvature of anterior and posterior corneal surface, Q ‐Values of anterior and posterior corneal surface and corneal central thickness were measured by rotating Scheimpflug imaging (Pentacam). The true net power F g , back vertex power F v , and keratometric power SimK , were calculated respectively at the apex and at a paracentral area on the 3 mm ring. Results: For virgin eyes, the overestimation (0.53 ± 0.11 D) of the corneal power by using a keratometric index of 1.3375 was balanced by the underestimation (−0.21 ± 0.09 D) of the corneal power by the error in the radius of curvature, resulting in a relatively small corneal power error with a mean value of 0.33 ± 0.11 D. With the Q ‐value changing from −0.09 to −0.41, the percentage balanced by the error in radius of curvature increased from 16% to 73%. However, for eyes after laser refractive surgery, the radius of curvature error lead to an overestimation (0.54 ± 0.16 D) of the corneal power and the keratometric index of 1.3375 again overestimated (1.59 ± 0.26 D) the corneal power, resulting in a large measurement error with a mean value of 2.12 ± 0.40 D. With the Q ‐value changing from 0.35 to 1.89, the percentage added by the error in radius of curvature increased from 14% to 32%. Conclusions: For virgin eyes, the overestimation of the corneal power by using a keratometric index of 1.3375 is balanced by the underestimation of the corneal power by the error in the radius of curvature, resulting in a relatively small corneal power error. However, for eyes after laser refractive surgery, the flatter anterior corneal surface means that the use of a keratometric index of 1.3375 significantly overestimates the corneal power and the radius of curvature error now adds to this overestimation and results in a large measurement error.