HOA increased dramatically after ortho-k treatment in our subjects, consistent with previous studies,
11,13,14,18,29–31 although the magnitude of change varied substantially with the pupil size analyzed,
32 age of subjects,
33 lens design,
34 and duration of follow-up.
14 For example, Gifford et al.
11 found an approximately doubling in total HOA, spherical, and comatic aberrations (over a 4-mm pupil) in young adults (mean age 21.1 ± 1.8 years) wearing ortho-k for 1 week, whereas Hiraoka et al.
13 reported a tripling in the RMS values for total HOA, spherical, and comatic aberrations (over a 5-mm pupil, up to the fourth order) in their cohort (mean age 10.3 ± 1.4 years) undergoing ortho-k treatment for 1 year. In the participants of this study (mean age 9.1 ± 1.3 years) analyzed over a 6-mm pupil, the total HOA, spherical, and comatic aberrations RMS increased by 3, 9, and 2 times, respectively, after ortho-k treatment. Similar to the findings of Joslin et al.
31 and Chen et al.,
15 primary spherical aberration (
\({\rm{Z}}_4^0\)) and horizontal coma (
\({\rm{Z}}_3^1\)) were the most affected individual Zernike coefficients. The increase in positive spherical aberration has been previously attributed to the nature of corneal asphericity, as the reverse geometry ortho-k lens flattens the central cornea and changes its shape from prolate to oblate, whereas the increase in comatic aberrations is associated with lens decentration, similar to the change in HOA observed with a decentered LASIK treatment zone.
35 In addition, other researchers have shown that larger increases in spherical and comatic aberration RMS values were associated with more myopic correction
11 (resulting in a greater change in the corneal profile across the treatment zone) and greater lens decentration,
36,37 respectively, during ortho-k treatment.