The Role of Back Optic Zone Diameter in Myopia Control with Orthokeratology Lenses

Abstract

We compared the efficacy of controlling the annual increase in axial length (AL) in myopic Caucasian children based on two parameters: the back optic zone diameter (BOZD) of the orthokeratology (OK) lens and plus power ring diameter (PPRD) or mid-peripheral annular ring of corneal steepening. Data from 71 myopic patients (mean age, 13.34 ± 1.38 years; range, 10-15 years; 64% male) corrected with different BOZD OK lenses (DRL, Precilens) were collected retrospectively from a Spanish optometric clinic. The sample was divided into groups with BOZDs above or below 5.00 mm and the induced PPRD above or below 4.5 mm, and the relation to AL and refractive progression at 12 months was analyzed. Three subgroups were analyzed, i.e., plus power ring (PPR) inside, outside, or matching the pupil. The mean baseline myopia was -3.11 ± 1.46 D and the AL 24.65 ± 0.88 mm. Significant (p < 0.001) differences were found after 12 months of treatment in the refractive error and AL for the BOZD and PPRD. AL changes in subjects with smaller BOZDs decreased significantly regarding larger diameters (0.09 ± 0.12 and 0.15 ± 0.11 mm, respectively); in subjects with a horizontal sector of PPRD falling inside the pupil, the AL increased less (p = 0.035) than matching or outside the pupil groups by 0.04 ± 0.10 mm, 0.10 ± 0.11 mm, and 0.17 ± 0.12 mm, respectively. This means a 76% lesser AL growth or 0.13 mm/year in absolute reduction. OK corneal parameters can be modified by changing the OK lens designs, which affects myopia progression and AL elongation. Smaller BOZD induces a reduced PPRDs that slows AL elongation better than standard OK lenses. Further investigations should elucidate the effect of pupillary diameter, PPRD, and power change on myopia control.

Keywords: axial length; myopia progression; optic zone diameter; orthokeratology; pupillary diameter.

Conflict of interest statement

J.P. is the inventor of the DRL Orthokeratology lenses and has a commercial interest in it. The other authors do not have any proprietary or financial interest in any of the materials mentioned in this article.

Figures

Figure 1

A tangential topographic map shows the plus power ring (PPR) diameter analyzed in this study.

Figure 2

Distribution of subjects with more than 0.10 mm or less than 0.10 mm of AL change annually in relation to BOZDs higher or lower than 5.0 mm in diameter. A trend for more subjects with slower AL growth is seen in association with reduced BOZD. AL: axial lenght, L_BOZD: large back optic zone diameter, S_BOZD: small back optic zone diameter.

Figure 3

The correlation between the back optic zone diameter (BOZD) of the lenses and the plus power ring diameter (PPRD). The different PPRD sizes used in the study are represented by the mean values (blue squares), median values (flat lines), 1st and 3rd quartile interval boxes, and minimal and maximal values. The polynomial line shows the correlation between groups.

Figure 4

(A) The relative plus power ring diameter (PPRD)/pupillary effect for horizontal meridian to axial length (AL) at one year change. Vertical meridian PPRD and mean PPRD resulted in a very similar image. The group with a full effect (FE) had a pupillary diameter larger than the PPRD + 0.9 mm, the group with medium effect (ME) had a pupil between the PPRD ± 0.9, and the No Effect (NE) group had a pupillary diameter smaller than the PPRD − 0.9 mm. (B) The relative plus power ring diameter (PPRD)/pupillary effect for horizontal meridian related to spherical refraction (M) at 12 month increase. Vertical meridian PPRD and mean PPRD resulted in a very similar image and was not plotted. In figure A and B, a trend toward a dose-dependent PPRD is observed. The mean values are represented by small squares (blue); medians are shown by flat lines, 1st and 3rd quartile interval boxes; and the minimal and maximal values are plotted.