Abstract
PurposeTo determine if the spatial distribution of the relative corneal refractive power shift (RCRPS) explains the retardation of axial length (AL) elongation after treatment by either orthokeratology (OK) or multifocal soft contact lenses (MFCLs).MethodsChildren (8–14 years) were enrolled in the OK (n = 35) or MFCL (n = 36) groups. RCRPS maps were derived by computing the difference between baseline and 12-month corneal topography maps and then subtracting the apex values. Values at the same radius were averaged to obtain the RCRPS profile, from which four parameters were extracted: (1) Half_x and (2) Half_y, i.e., the x- and y-coordinates where each profile first reached the half peak; (3) Sum4 and (4) Sum7, i.e., the summation of powers within a corneal area of 4- and 7-mm diameters. Correlations between AL elongation and these parameters were analyzed by multiple linear regression.ResultsAL elongation in the OK group was significantly smaller than that in the MFCL group (p = 0.040). Half_x and Half_y were also smaller in the OK group than the MFCL group (p < 0.001 each). Half_x was correlated with AL elongation in the OK group (p = 0.005), but not in the MFCL group (p = 0.600). In an analysis that combined eyes of both groups, Half_x was correlated with AL elongation (β = 0.161, p < 0.001).ConclusionsThe OK-induced AL elongation and associated RCRPS Half_x were smaller than for the MFCL. Contact lenses that induce RCRPS closer to the corneal center may exert better myopia control.
Highlights
The incidence of myopia has risen over the last several decades (Williams et al, 2015; Holden et al, 2016), in East Asian countries where about 80% of the 18-year-olds are myopic (Rudnicka et al, 2016)
Thirty-seven multifocal soft contact lenses (MFCLs) subjects were enrolled in this registered clinical trial1 (Registration number: ChiCTR-OOC-17012103)
We found that axial length (AL) elongation and the new index Half_x in the OK group were significantly smaller than that in the MFCL group
Summary
The incidence of myopia has risen over the last several decades (Williams et al, 2015; Holden et al, 2016), in East Asian countries where about 80% of the 18-year-olds are myopic (Rudnicka et al, 2016). OK lenses have a reversegeometry on the back surface that flattens the central zone of the cornea and steepens the mid-peripheral zone during overnight wear (Sridharan and Swarbrick, 2003). During the day, this altered corneal front surface induces myopic defocus on the peripheral retina (Charman et al, 2006; Queiros et al, 2010, 2018), and this may be a mechanism for myopia retardation (Smith et al, 2009; Benavente-Perez et al, 2014). Daytime MFCL wear directly imposes peripheral retinal myopic defocus when the lenses are worn (Sankaridurg et al, 2011; Allinjawi et al, 2016)
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