Optical changes and association with axial elongation in children wearing orthokeratology lenses of different back optic zone diameter

Abstract

Purpose To compare changes in ocular aberrations in children wearing orthokeratology (ortho-k) lenses with a back optic zone diameter (BOZD) of 6 mm (6-MM group) or 5 mm (5-MM group) and their associations with axial elongation (AE) over two years. Methods Seventy Chinese children, aged 6 to < 11 years, with myopia between − 4.00 to − 0.75 D, were randomly allocated to 5-MM and 6-MM groups. Ocular aberrations were measured, rescaled to a 4-mm pupil, and fitted with a 6th order Zernike expansion. Measurements, including axial length, were taken prior to commencing ortho-k treatment and then every six months over two years. Results After two years, the 5-MM group displayed a smaller horizontal treatment zone (TZ) diameter (by 1.14 ± 0.11 mm, P < 0.001) and less AE (by 0.22 ± 0.07 mm, P = 0.002) compared with the 6-MM group. A greater increase in total root mean square (RMS) of higher-order aberrations (HOAs), primary spherical aberration (SA) ($${\mathrm{C}}_{4}^{0})$$ C 4 0 ) , and coma were also observed in the 5-MM group at all follow-up visits. The horizontal TZ diameter was significantly associated with changes in RMS HOAs, SA (RMS, primary and secondary SA), and RMS coma. After controlling for baseline parameters, RMS HOAs, RMS SA, RMS coma, and primary ($${\mathrm{C}}_{4}^{0})$$ C 4 0 ) and secondary ($${\mathrm{C}}_{6}^{0})$$ C 6 0 ) SA were significantly associated with AE. Conclusions Ortho-k lenses with a smaller BOZD created a smaller horizontal TZ diameter and a significant increase in total HOAs, total SA, total coma, and primary SA and a decrease in secondary SA. Of these ocular aberrations, total HOAs, total SA, and primary SA were negatively correlated with AE over two years. Trial registration: ClinicalTrial.gov, NCT03191942. Registered 19 June 2017, https://clinicaltrials.gov/ct2/show/NCT03191942.

Comparison of two different orthokeratology lenses and defocus incorporated soft contact (DISC) lens in controlling myopia progression

“…Recent studies have aimed to explore new optical designs for OK lenses or SCLs to enhance myopia control efficacy [ 22 , 36 , 40 ]. Decreasing the BOZD design in OK lenses has better controlled AL elongation in our previous study [ 22 ] as well as other studies [ 21 , 41 , 42 ]. For instance, Pauné et al found a 0.06 mm/year less AL growth in Caucasian children with 4.7 or 5.0 mm-BOZD DRL lenses compared with those wearing lenses with a BOZD ranging from 5.6 to 6.6 mm [ 21 ].…”

The Impact of Back Optic Zone Design in Orthokeratology on Visual Performance

“…The argument behind the effort of inducing a smaller TZD was based on the finding that HOAs induced by OrthoK treatment are protective against myopia progression, and preliminary studies have reported a potential dose-dependent response such that a smaller TZD was associated with better axial inhibiting effects. 7 , 8 , 20 In our study, the non-significant difference in induced HOAs between the two OZD designs in the larger pupil condition suggests a potential interaction between TZD and pupil size in the axial inhibiting effect of OrthoK. The reduced TZDs in patients with larger pupil size may not benefit from a stronger “myopia-controlling dosage” while suffering from reduced visual quality; therefore, pupil size is an important factor when considering the OZD design in the lens.…”

“…Regarding the optical quality comparison, HOAs significantly increased at 1 month in both groups, especially the Z 4 0 , coma-like, and spherical-like aberrations, a finding that has also been reported in previous studies. 7 – 9 The Z 4 0 and spherical-like aberrations in the 5OZ group were significantly higher than those of the 6OZ group under the 3-mm pupil condition but not the 5-mm pupil condition. A plausible explanation is a potential saturating effect due to the interactions between pupil size and the location of the paracentral corneal steepening, a major source of the induced HOAs in the OrthoK treatment.…”

“…Based on recent research on AL elongation and HOAs, smaller OZD-designed lenses may be more beneficial to children with small pupil size. 7 However, clinicians may not need to utilize the smaller OZD-designed lens for children with large pupil sizes, as similar effects of myopia control and better visual quality may be achieved with traditional OZD lenses.…”

“…Preliminary studies have reported a stronger myopia-inhibiting effect for designs incorporating a smaller back optic zone diameter (OZD), with the proposed mechanism of stronger RMPD and HOAs due to a smaller treatment zone (TZ), on the topographical changes associated with the smaller OZD designs. 6 , 7 Notably, significant individual variability exists regarding the topographical changes induced by OrthoK lenses, for which lenses with the same OZD do not necessarily induce a consistent corneal TZ. Moreover, the design changes incorporated into the back surface of the lenses may not transfer to induced corneal changes with a 1:1 ratio.…”