Abstract
PURPOSE: To investigate the change in corneal toricity and associated refractive astigmatism after discontinuation of long-term orthokeratology (ortho-k) lens wear. METHODS: This study investigated 136 subjects aged between 6 and 14 (9.1 ± 1.5) years old at the commencement of ortho-k treatment, who had been undergoing overnight ortho-k treatment for 24 to 72 (37.4 ± 11.9) months. Corneal refractive power and manifest refraction were measured and compared before ortho-k and 1 month after discontinuation of ortho-k lens wear. Changes in corneal curvature were analyzed. Corneal curvature data from a historical longitudinal study were used as control. RESULTS: Compared to pre-ortho-k values, the corneal curvature became significantly flatter in the flatter meridian (-0.22 ± 0.27 D, P < 0.001) and steeper in the steeper meridian (0.06 ± 0.34 D, P=0.032) after cessation of ortho-k lens wear, resulting in a significant increase in corneal toricity (0.28 ± 0.43 D, P < 0.001), which is associated with an increase in refractive astigmatism (0.57 ± 0.57 D, r=0.465, P < 0.001). The amount of residual corneal flattening in the flatter meridian is significantly affected by the length of ortho-k treatment (t=-2.965, P=0.004) and the baseline age of subject (t=-2.841, P=0.005), but not by the baseline spherical or cylindrical refractive error (both P > 0.05). In the historical control group, there is no significant change in the corneal curvature over two years in children wearing spectacle lenses (both meridians, P > 0.05). Change of corneal toricity was more significant in the ortho-k group than in the spectacle control group (P=0.001). CONCLUSIONS: Long-term ortho-k lens wear increases corneal toricity after discontinuation of the treatment, which is associated with an increase in refractive astigmatism. A more pronounced change in corneal toricity was found in subjects who were younger to start ortho-k and have been in a longer period of treatment. This trial is registered with http://www.chictr.org.cn (ChiCTR-TNRC-11001210).