Effect of different position of defocus ring on cornea of orthokeratology for myopia control

AIM:To observe the different effect of controlling myopia by orthokeratopraxis with different width between defocus circle and the rim around the cornea.METHODS: A retrospective case-control study. A total of 45 patients(85 eyes)who came to our hospital for orthokeratopraxis lens fitting during January 2014 to December 2015 were selected. The diameter of the orthokeratopraxis lens was 90%-95% of the diameter of the cornea. So the patients were divided into three groups according to the different diameter of the orthokeratopraxis lens. The diameter of the orthokeratopraxis lens for the patients whose corneal diameter was between 12.1 to 13.00mm was 11.0-11.2mm(Group A). The diameter of the orthokeratopraxis lens for the patients whose corneal diameter was between 11.1-12.00mm was 10.5-10.9mm(Group B). The diameter of the orthokeratopraxis lens for the patients whose corneal diameter was between 10.0-11.00mm was 10.0-10.4mm(Group C). The change of the spherical equivalent(SE)and axial length(AL)were analyzed after wearing the lens for 1a and 2a.RESULTS: Before wearing lens, the age, SE(D)and AL(mm)was not statistically significant in the three groups(P>0.05). After wearing lens for 1a and 2a, the change of SE(D)and AL(mm)was not statistically significant in Group A and Group B(P>0.05)and the change was statistically significant in Group C(PPPCONCLUSION: The effect of controlling myopia by orthokeratopraxis with different position of defocus circle on cornea is different. The position of defocus circle is more close to the corneal limbus, the effect is weaker