Corneal astigmatism after temporary discontinuation from long-term spherical and toric orthokeratology

To investigate changes in corneal astigmatism (curvatures and corneal sagittal height difference (C-sagDiff) at 8-mm chord) after temporary discontinuation from long-term spherical and toric orthokeratology (ortho-k) lens wear in a Chinese population.

Relevant data were retrieved from 110 patients (55 wearing spherical ortho-k lenses, 55 wearing toric ortho-k lenses) who have been undergoing ortho-k treatment for at least one year and stopped lens wear temporarily for scheduled lens replacement. The topographic and refraction data at baseline and post-discontinuation was collected for all the patients. Only data from the right eye was used for analysis. Corneal curvature changes and C-sagDiff at 8-mm chord in the two principal meridians within each group and the corneal astigmatism changes between the two groups were analyzed.

No significant differences in age, gender, baseline flat K (FK) and steep K (SK), myopia, refractive astigmatism, and duration of lens wear were noted between the two groups (P > 0.05). Baseline corneal astigmatism and C-sagDiff in toric ortho-k group was higher than spherical ortho-k group (P < 0.001). For both ortho-k groups, after treatment discontinuation of about 1-month (30-37 days), FK became flatter, SK remained unchanged, corneal astigmatism and C-sagDiff increased. Changes in corneal astigmatism for spherical and toric groups were 0.24 ± 0.33 and 0.32 ± 0.32 D, respectively. C-sagDiff increased from 22.85 ± 8.41 to 31.37 ± 12.98 μm and from 32.35 ± 12.39 to 45.40 ± 15.01 μm in the spherical and toric ortho-k groups, respectively. No significant between-group difference in corneal astigmatism change was found (P = 0.214). Corneal astigmatism change was affected by wearers' age and duration of ortho-k lens wear. The younger the subject and the longer the duration of ortho-k lens wear, the more significant the corneal astigmatism change after discontinuation of the treatment.

After 1-month discontinuation from long-term ortho-k lens wear, corneal flat K became flatter, steep K remained unchanged, the C-sagDiff and the corneal astigmatism increased, irrespective of whether spherical or toric lenses were used. The change of corneal astigmatism was about 0.25D on average, which was not clinically significant. There was no significant difference of corneal and refractive astigmatism change between spherical and toric ortho-k groups.