To evaluate the changes of corneal transparency undergoing overnight orthokeratology treatment.

Prospective cohort study. Right eyes of juvenile myopic patients fitted with Ortho-K CL at Qingdao Eye Hospital were enrolled. Corneal optical density values were measured by the Pentacam Scheimpflug system before orthokeratology and at 1 day, 1 week, and 1, 3, 6, and 12 months after wearing. Four concentric radial zones centered on the apex of the cornea (≤2 mm, >2 mm and ≤6 mm, >6 mm and ≤10 mm, and>10 mm and ≤12 mm diameter) were applied. Anterior layer (anterior 120 μm), central layer, and posterior layer (posterior 60 μm) were defined according to corneal depth. The data analysis were used One-Way Repeated Measures ANOVA and LSD test.

Forty patients (40 eyes) with myopia (24 male and 16 female, age 10.76±1.74 years) were in enrolled. Corneal optical density value was 13.18±0.23 before orthokeratology, then showed a decreasing trend at the early stage, but there was no statistical difference (within 3months: t=-1.594, -1.472, 0.064, 1.971; P>0.05). The value increased significantly and reached the peak (15.31±0.23, t=7.613, P<0.01) at 6-month, and was still maintained in a high value at 1-year (15.15±0.24, t=7.227, P<0.01). Anterior, central, and posterior layer of corneal optical density values had a downward trend at early stage, and increased significantly in 6-and 12-month (anterior layer t=7.143, 6.177, central layer t=7.508, 6.563, posterior layer t=6.722, 8.533;P<0.01). Only the values decreased significantly in posterior layer at 1-week (baseline 10.21±0.14 vs. 1-week 9.91±0.14, t=-2.348, P=0.024). The corneal optical density value of ≤2 mm diameter began to increase significantly at 1-month (baseline 12.88±0.14 vs. 1-month 13.31±0.19, t=2.158, P=0.037),>2 mm and ≤6 mm diameter at 3-month (baseline 11.71±0.13vs. 3-month 12.50±0.19, t=3.213, P=0.003), and>6 mm and ≤10 mm diameter at 6-month (baseline 11.40±0.30vs. 6-month 13.70±0.33, t=7.635, P=0.000). The high values lasted for 1 year at this three areas. However, >10 mm and ≤12 mm diameter had no obvious change in optical density ( F=1.668, P>0.05). In addition, the significant reduction of optical density values at early stage were mainly concentrated in the posterior layer of the cornea and the>6 mm and ≤10 mm diameter.

Orthokeratology transiently increases corneal transparency of the posterior layer and the>6 mm and ≤10 mm diameter at early stage. However, long-term wearing can cause a decrease of transparency within a 10 mm diameter range. The corneal transparency changes first at the center of the optical zone, then gradually expanding to the periphery, and the anterior, central and posterior layers of cornea are all affected. We speculate orthokeratology affect the corneal oxygen supply and compress cornea mechanically, that leads to corneal stromal remodeling.(Chin J Ophthalmol, 2019, 55:435-441)

Myopia; Contact lenses; Corneal stroma; Densitometry