Abstract
PURPOSE: The study analyzed the changes in corneal surface shape after replacing orthokeratology lenses carrying a small base curve (BC) diameter. METHODS: In this retrospective study, we included ~54 right eyes belonging to 54 myopic children who insisted on wearing an orthokeratology (ortho-k BC 6.0 mm) lens for more than 12 months and then replaced the second ortho-k (BC 6.0 mm or BC 5.0 mm) lens ~12 months. The children were categorized into two groups based on the design of the BC of the replaced ortho-k lens 6.0/5.0 and 6.0/6.0. RESULTS: The ratio of axial length (AL) elongation in the 6.0/5.0 group was significantly less than in the 6.0/6.0 group (-0.015 ± 0.014 mm/M vs. -0.005 ± 0.012 mm/M, t = -2.672, P = 0.010). After replacing the BC 5.0 ortho-k lens, the optical zone (8.19 ± 2.60 mm(2) vs. 9.64 ± 1.57 mm(2), t = -2.345, p = 0.023), reverse zone (31.64 ± 5.80 mm(2) vs. 34.86 ± 4.61 mm(2), t = -2.169, p = 0.035), and treatment zone (17.16 ± 3.94 mm(2) vs. 22.96 ± 2.59 mm(2), t = -6.049, p < 0.001) were all smaller than those in the 6.0/6.0 group. In the 6.0/5.0 group, the optical zone (wearing more than 1 month as first: 11.16 ± 2.12 mm(2), the last inspection before replacing lens as before: 10.87 ± 1.90 mm(2)), reverse curve zone (first: 22.03 ± 3.11 mm(2), before: 26.24 ± 5.06 mm(2)), and treatment zone (first: 35.97 ± 5.54 mm(2), before: 37.11 ± 6.04 mm(2)) were all greater than these after replacing ortho-k lens (all P < 0.001). CONCLUSION: Replacing an ortho-k lens with a smaller BC resulted in a larger decrease in the mean central corneal zone and a substantial increase in the paracentral corneal zone. In addition, the ortho-k lens with a smaller BC does not increase the decentration distance and contributes to effective myopia control.