To investigate the long-term clinical control effects of orthokeratology (Ortho-K) lenses in low myopia children and its factors.

One hunderd and sixty nine low myopia patients (294 eyes) with an average age of (9.5±1.6) years old (ranged from 8 to 14 years old) who were checked in at Department of Ophthalmology, Renji Hospital affiliated to Shanghai Jiaotong University School of Medicine from January 2016 to December 2021. All patients were divided into 2 years, 3 years and 4 to 5 years groups according to the period of their wearing Ortho-K lenses. The spherical diopters (SD), corneal curvature and axial length (AL) of patients were prospectively analyzed and compared before and after wearing. The changes of spherical diopters (△SD) and AL (△AL) were used to evaluate the controlling myopia progression. The age, SD, cylinder diopters, AL and corneal curvature were expressed by (±s), and compared by paired t test. The different gender, age, the based SD, AL and other indices of patients were compared △SD and △AL after wearing Ortho-K lenses using univariate, respectively. The multiplelinear regression analysis was performed if variables with statistical significance for differences and its relevance determined.

The average corneal curvature of patients before and after wearing in 3 groups was (43.39±1.36)D, (43.21±1.32)D, (43.32±1.40)D, (42.91±2.09)D, (42.85±1.30)D, (42.98±1.37)D, with a significant difference between groups (F=3.319, 5.348, 6.613; P<0.05). The △SD of patients in 3 groups was (-0.71±0.56)D, (-0.74±0.59)D, (-1.15±0.88)D.One-way ANOVA showed that there was a significant difference between the age, the average corneal curvature, AL, respectively and the △SD after wearing Ortho-K lenses for 2 years (F=6.578, 3.279, 7.815; P<0.05), and between the age, the based SD, corneal astigmatism, AL, respectively and △AL (F=17.389, 6.994, 3.566, 5.708; P<0.05). After wearing Ortho-K lenses for 3 years, there was a significant difference between the age, the based SD, AL, respectively and △SD (F=6.639, 13.785, 5.443; P<0.05), and between the age, the based AL, respectively and △AL (F=17.280, 3.170; P<0.05). After wearing Ortho-K lenses for 4 to 5 years, there was a significant difference between the age, the based SD, respectively and △SD (F=19.328, 4.175; P<0.05), and between the age, the based SD and △AL (F=50.146, 4.813; P<0.05). The variables with a significant difference after one-way ANOVA were performed by multiplelinear regression analysis. The age was correlated with △SD in 3 groups with a significant difference (β=0.183, 0.231, 0.508; P<0.05); the age correlated with △SD in 3 groups with a significant difference (β=-0.326, -0.488, -0.697; P<0.05). The based SD, increase of AL was correlated with △SD after wearing Ortho-K lenses for 3 years with a significant difference (β=0.400, 0.181; P<0.05); the based SD and the based AL correlated with △AL after wearing Ortho-K lenses for 2 or 3 years with a significant difference, respectively (β=-0.172, -0.184; P<0.05).

During observation periods for 5 years, corneal curvature tended to flatter and remained stable. Ortho-K lenses has a capacity of effectively controlling progression of low myopia, especially axial myopia. Age, spherical diopters and AL were factors that affect its progression.