Rigid Contact Lens Research, The Role And Mechanism Of Peripheral Refraction On Children's Eye

Part 1 Effects of rigid gas-permeable contact lens on ocular peripheral refraction in childrenPurpose To investigate the effects of rigid gas-permeable contact lens (RGPCL) on ocular peripheral refraction in children. Methods Fifteen children were enrolled in the self-controlled study. They were required to focus on seven successive targets at a distance of 5m from 30°nasal to 30°temporal, without correction or with spectacle and RGPCL correction, respectively. An infra-red autorefractor was used to obtain six peripheral refractions and one central refraction. The difference between peripheral refraction and central refraction was stated as relative peripheral refraction (RPR). RPRs were compared in each direction between the three corrective methods using one-way ANOVA, and a Bonferroni post-hoc test was employed. Results RPRs were all hyperopic without correction or with spectacle and RGPCL correction(except 10°nasal), showing asymmetry between nasal and temporal visual fields, with higher hyperopia in the peripheral and temporal visual field. However, RPRs with RGPCL correction were relatively myopic in the temporal visual field, compared to the other two corrective methods. Differences were more evident in the periphery. RPR values reached (1.69±1.03)D, (1.84±0.99)D and (0.81±1.28)D at 30°temporal, respectively. Statistically significant differences were found between the three corrective methods(F=3.79, P=0.031) and between the spectacle and RGPCL corrective method by Bonferroni test(P=0.043). Conclusion RGPCL has an effect of altering temporal peripheral refraction to relative myopia in children.Part 2 Effects of orthokeratology on ocular peripheral refraction in children and the mechanism studyPurpose To investigate the effects of orthokeratology on ocular peripheral refraction in children and its working mechanism. Methods Eleven children were enrolled in the self-controlled study. They underwent subjective refraction, topography and peripheral refraction measurement before and one month after ortho-k lens wearing. Only right eyes were tested. During peripheral refraction measurement, children were required to focus on seven successive targets at a distance of 5m from 30°nasal to 30°temporal. An infra-red autorefractor was used to obtain six peripheral refractions and one central refraction. The difference between peripheral refraction and central refraction was stated as relative peripheral refraction (RPR). RPR values and corneal refractive powers before and after lens wearing were compared using paired t test. Seven corneal positions related to each angle were estimated by simulating the Gaussian Optic System. Changes in their sagittal refractive powers were compared with corresponding RPR changes using Pearson correlation analysis. Results RPR values were hyperopic in all peripheral angles before ortho-k lens wearing (except 10°nasal), showing asymmetry between nasal and temporal visual fields, with higher hyperopia in the peripheral and temporal visual field. RPR values reversed to myopia at all peripheral angles after lens wearing for one month, with higher myopia in the peripheral and temporal visual field. When compared to baseline values, differences were statistically significant at 30°nasal and 10°,20°,30°temporal (p=0.043, p=0.013, p<0.001, p<0.001, respectively). Peripheral refractive changes were significantly correlated to changes in corneal sagittal refractive power (R2=0.7083, p=0.018). Conclusion Orthokeratology has an effect of altering peripheral refraction to myopia in children, which was closely related to corneal anterior surface reshaping by orthokeratology.Part 3 Effects of orthokeratology on ocular axial growth in myopic childrenPurpose To investigate the effects of orthokeratology on ocular axial growth in myopic children. Methods Sixty children were enrolled in the prospective controlled study and divided into two groups. Thirty were assigned to wear ortho-k (OK), and the other thirty single vision lens (SVL). Children in both groups underwent refraction and axial length (AL) measurement at 6th,12th and 18th month after treatment. Background data including refractive history, parental myopia and working schedules were tracked. Baseline and follow-up data concerning AL, anterior chamber depth (ACD), spherical equivalent of refractive error (SER), corneal radius and background data between two groups were compared using independent t test. Nonparametric tests were employed for unequal variances. Results Baseline SER for SVL and OK group was (-2.68±0.73)D and (-2.91±0.72)D, respectively. The difference was not statistically significant (p=0.305). However, myopia progression was significantly faster in OK group than SVL group in the past two years (p=0.022). The odds ratio of parental myopia to emmetropia between OK and SVL group was 7.89. Differences of axial growth between SVL and OK group were not statistically significant at 6th,12th or 18th month visit (p=0.666, p=0.375, p=0.650). Conclusions Effect of Orthokeratology on the control of axial growth in myopic children was not significant. Its potential validity for myopic control needs further investigation.