The development and progression of myopic eyes is biomechanical and dominated by axial elongation.The biomechanics change of stretching of the fundus and sclera appears to reduce its thickness and elastic modulus, which make eyeballs more susceptible to the distending forces of intraocular pressure (IOP).
This study was to analyz the axial length (AL) and IOP changes in different degree of myopia and investigate the roles of IOP in myopia development and AL elongation.
A prospective cases-controlled study was performed under the informed consent of patients and custodian.Four hundred and twenty-eight eyes of 428 children aged 4-14 years were enrolled in Affilicated Second Hospital of Zhengzhou University from February to December 2014.The patients were divided into 4 groups based on the refractive status.Ninety-three eyes of 93 patients were in the hyperopic-emmetropia group with the spherical equivalent (SE) of (1.81±2.32)D, 192 eyes of 192 patients were in mild myopia group with the SE of (-1.43±0.74)D, 83 eyes of 83 patients were in the moderate myopia group with the SE of (-4.09±0.89)D and 60 eyes of 60 patients were in the high myopia group with the SE of (-8.02±2.61)D.AL was measured by IOL Master system, IOP was measured by iCare tomnometer, and the central corneal thickness (CCT) was measured by OCT.The corrected IOP was calculated based on IOPcorrection =IOPGAT+ (544-CCT)/37.03.The correlations between IOPcorrection and AL or diopter were analyzed.
The AL values were (22.44±1.32)mm, (23.89±1.09)mm, (25.05±0.89)mm and (26.47±1.20)mm in the hyperopic-emmetropia group, mild myopia group, moderate myopia group and the high myopia group, showing a significant difference among the four groups (F=177.336, P=0.000). The IOPcorrection values were (15.24±2.73)mmHg, (17.51±2.98)mmHg, (17.94±2.34)mmHg and (18.49±2.90)mmHg in the hyperopic-emmetropia group, mild myopia group, moderate myopia group and the high myopia group, with a significant difference among the four groups (F=22.104, P=0.000). The IOPcorrection values were significantly lower in the hyperopic-emmetropia group than that in the mild myopia group, moderate myopia group and high myopia group (all at P<0.05), and the mean IOPcorrection value in the high myopia group was significantly higher than that in the mild myopia group (P=0.018). The IOPcorrection was negatively correlated with diopter (r=-0.384, P<0.01) and positively correlated with AL (r =0.377, P<0.01).
As the increase of myopic diopter and elongation of AL, IOPcorrection is considerably elevated in childhood.IOPcorrection rising in childhood probably promotes the progression of myopia and elongation of AL.