Evaluation The Corneal Aspherity In Chinese Children

Purpose: The axial length is known to vary with refractive error , but the relation between cornea] topography of the anterior surface of the cornea and ametropia is less concerned about. The current study was conducted to determine the cornea! topographic characteristics of normal children and the relation between cornea! asphericity and refractive error.Method: Using computerized videokeratography (Humphrey ALTAS Cornea! Topography System) , the topographic parameters in 291 eyes of 164 nomal children aged from 5 to 17 years old (spherical equivalent refractive error -14.75diopter [D] to 8.13 D ) were analyzed ,which included the shape factor (SF), cornea! irregular measure (CIM) , the average power of zone of apex ,3mm,5mm,7rnm in diameter and the simulated keratoscopic reading (SimK) . Refraction was measured with retinoscopy and autorefractor with cycloplegia. The relations between the shape factor (SF) and the corneal power , the shape factor (SF) and refractive error , the comeal power and the refractive error were analyzed.Result: 1) the corneal shape factor (SF) is 0.281?.105 with normal distribution ,the comeal irregular measure (CIM) is 0.64?.16 with normal distribution. The average power of zone apex ,3mm,5mm,7mm jn diameter ,the simulated keratoscopic reading (SimK) is 43.91 ?.44, 43.86+1.42, 43.62 + 1.45, 43.15 ?1.40, 43.61 ?1.43 diopter(D) respectively.2) The SF of the children with myopia is lower a little. The SF of the children with hyperopia is higher a little. 3) A low but statistically significant positive correlation is found between comeal shape factor (SF) and spherical equivalent refractive error (r2 = 0.027 P = 0.003) . A statistically significant positive correlation is also found between comeal shape factor (SF) and the average power of zone 5mm,7mm in diameter (^=0.264 P=0.000 ). Eyes with higher levels of myopia have steeper corneal curvatures especially periphery. Conclusion: 1) The children's corneal surface from center to periphery show an oblate ellipse to correct spherical aberration.2) A tendency for cornea to flatten less rapidly in the periphery with increasing myopia or decreasing hyperopia is shown .3) The cornea! irregular measure (CIM) of myopia , emmetropia , hyperopia is no difference .