AIM: To compare the changes of corneal refractive power before and after wearing defocus rigid gas permeable contact lens(RGPCL)in children with high myopia, and to analyze its influence on corneal refractive power and astigmatism after wearing glasses.

METHODS: Self-controlled before-after study. A total of 30 cases(60 eyes)of children aged 8-12, with high myopia who were treated and fitted with defocus RGPCL in the Optometry Center of Xi'an First Hospital from June 2019 to June 2020 were collected. Using TMS-4N corneal topography instrument to measure the corneal tangential refractive power at baseline and wearing lens for 0.5 and 1a, and analyze the nasal side(N), temporal side(T), superior(S)and inferior(I)of the maximum corneal refractive power values at the 4 axial directions and the changes of the corneal refractive power at the center were collected at the same time at 1 mm intervals. The changes of corneal refractive power at each point before and after wearing glasses were analyzed. The axial length, diopter and corneal topography were required to be measured after 0.5 and 1a, and the changes in axial length, spherical equivalent, astigmatism and corneal refraction compared with baseline were analyzed.

RESULTS: The maximum corneal refractive power of nasal(N), temporal(T), superior(S)and inferior(I)side was significantly increased at 0.5 and 1a when wearing defocus RGPCL compared with that before wearing glasses, which all showed positive relative refractive power compared with the corneal refractive power at center and was significantly different from the negative relative refractive power before wearing lenses. The relative peripheral refractive power of the cornea changed in the direction of positive refractive power when the lenses were worn for 0.5 and 1a. Except for the increase in the peripheral negative refractive power at the T1 point, the peripheral refractive power at all points in the other axes increased significantly. After wearing for 0.5a, the corneal steep K value became flat by 0.11±0.10D, the simK value decreased by 0.20±0.18D, the corneal steep K value became flat by 0.10±0.12D after 1a, the average K value became flat by 0.02±0.05D, and the simK value decreased by 0.16±0.13D. There was no significant difference in corneal level K from the baseline after wearing glasses for 0.5 and 1a.

CONCLUSIONS: The maximum refractive power of the cornea in the state of wearing defocus RGPCL is positive relative refractive power compared with the vertex of cornea, and the relative peripheral negative refractive power of the cornea at each point on the 4 axes changes from negative value to positive value. Within 1a of wearing glasses, the axial length and spherical equivalent increased compared with the baseline, while the amount of astigmatism decreased, and the corneal refractive power showed a trend of steep K and flattening.