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First Author: J.Calvache SPAIN
Co Author(s): S. Fernández E. Tomás I. Signes
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To study a mathematical function that provides an ocular refraction theoretical value in function of corneal power and axial length in myopic eyes.
Clínica Baviera, Palma de Mallorca, Spain.
Based on paraxial optic method and ammetropia definition, a two variables mathematical function has been deduced with the aim of predict the spherical equivalent of the subjective refraction (SESR), from corneal power and axial length values.This function is called refractive function (RF). To verify FRs predictive capacity in myopia, it will be applied to 55 healthy, myopic eyes of 27 patients aged between 10 and 43 years old (average 28,82 + 8,06 years), with the condition that they have no previous eye surgery. For each patient, non cycloplegic subjective refraction, automatic keratometry (Topcon KR-8800) and ocular immersion biometry (Ocuscan RxP, Alcon) was performed. From these measurements, spherical equivalent of subjetive refraction (SESR), average corneal power (Ka) and axial length (AL) was obtained. From AL and Ka data a value of spherical equivalent of theoretical refraction (SETR) was calculated for each patient by applying the RF. SESR and SETR values were compared.
The average values of SERS, Ka and AL was -9,75 + 3,93 D (range -18,50 to -2,00 D), 44,26 + 1,19 D (range 42,25 to 47,75 D) and 27,11 + 1,69 mm (range 23,52 to 31,16 mm) respectively. The average values of SETR calculated from Ka and AL values with the RF was -9,73 + 3,79 D. The average difference in absolute values between SESR and SETR was 0,79 + 0,66 D (range 0 to 2,95 D). The R2 coefficient of linear correlation obtained for EERS and SETR data was 0,93.
RF can predict the SESR from Ka and AL values with a good aproximation in myopic eyes for the age range included in this study. This function relates refraction, corneal power and axial length values, therefore knowing two of them, a good aproximation to the other unknown value can be obtained for myopic eyes.