Comparing the effects of orthokeratology lenses and highly aspherical lenslets on axial length in myopic anisometropia

Abstract

Purpose

This study compares the influences of orthokeratology (OK) lenses and highly aspherical lenslets (HAL) on axial length (AL) in myopic anisometropia.

Methods

Retrospective analysis was performed on 225 individuals with myopic anisometropia who agreed to wear OK lenses, HAL or single-vision spectacles (SP). Subjects with bilateral myopic anisometropia (BMA) were divided into the following groups: SP-BMA, HAL-BMA and OK-BMA. Further, children with unilateral myopic anisometropia (UMA) were divided into the following groups: SP-UMA, UHAL-UMA (unilateral HAL), BHAL-UMA (bilateral HAL) and OK-UMA (unilateral OK lens). Analyzed the difference in the interocular AL elongation in different groups.

Results

For children with BMA, the interocular difference change in the OK-BMA group (0.15 ± 0.19 mm) was greater than that in the SP-BMA (−0.01 ± 0.20 mm) and HAL-BMA (−0.03 ± 0.17 mm) groups, all P < 0.001. For children with UMA, in the non-myopic eyes, the difference in AL elongation in the BHAL-UMA group (0.10 ± 0.14 mm) was less than that in the SP-UMA (0.28 ± 0.22 mm), UHAL-UMA (0.40 ± 0.22 mm) and OK-UMA (0.47 ± 0.24 mm) groups, all P < 0.001. The interocular change in the UHAL-UMA group (0.29 ± 0.36 mm) and OK-UMA group (0.35 ± 0.25 mm) were all higher than that in the SP-UMA (−0.02 ± 0.23 mm) and BHAL-UMA (0.01 ± 0.18 mm) groups, all P < 0.01.

Conclusions

OK lenses can effectively reduce the interocular AL difference for children with unilateral or bilateral myopic anisometropia. However, HAL only decreased the interocular AL difference for children with UMA when wearing unilateral HAL but it did slow down the AL elongation of the non-myopic eyes in children with UMA when wearing bilateral HAL.

Introduction

Anisometropia represents a unique example of ocular development, where the two eyes with an identical genetic background and seemingly subject to identical environmental influences but can involves asymmetric axial elongation (AE) and refractive errors change [1–3]. The mechanism of anisometropia is still unknown [1]. Myopic anisometropia is typically defined as a 1.00 D or greater difference in myopic spherical equivalent refraction between the two eyes [1]. The prevalence of anisometropia ranges from 0.6 to 4.3% in the general paediatric population and from 7 to 14% in myopes [3–5]. Recent research examined refraction in 1,577 highly myopic (spherical equivalent ≤−5.0 D) children aged 4–18 years and found that the prevalence of spherical equivalent anisometropia ≥ 1.00 D was 34.5% [5]. The development of myopic anisometropia is related to increased myopia, and the degree of anisometropia is enhanced with increases in the degree of myopia [5–8]. Anisometropia is regarded as an associated factor for myopia development, while myopia progression is a stimulus driving anisometropic development [5].

There are numerous methods for controlling myopia, including orthokeratology (OK) lenses, myopic control spectacles and soft multifocal lenses [9–12]. Tsai [13] and Long [14] found that the axial length (AL) of myopic eyes in unilateral myopic anisometropia (UMA) grew slower after wearing OK lenses, as compared to the AL of non-myopic eyes. In the study by Tsai [13], 31 subjects with UMA (12.32 ± 3.07 years old) were treated with unilateral OK lenses and after long-term treatment, the AL difference decreased significantly from 0.83 ± 0.45 mm at baseline to 0.59 ± 0.49 mm at 24 months. In a study by Long [14], the pattern of growth in the AL was compared between 252 children (8–14 years old) with anisometropia who wore OK lenses and those who wore single-vision spectacles (SP). The results revealed that the interocular AL change was−0.29 ± 0.29 mm in the children with UMA treated with unilateral OK lenses, and the interocular difference was found to improve. This improvement was also observed in children with bilateral myopic anisometropia (BMA) treated with bilateral OK lenses. Specifically, Long found that aniso-AL decreased 0.10 ± 0.15 mm in subjects with BMA after treatment with bilateral OK lenses for one year [14]. A meta-analysis by Tsai demonstrated that OK lenses can delay the progression of myopia and effectively decrease anisometropia [15]. Research suggests that OK lenses can decrease anisometropia in children due to the more robust myopic control in the more myopic eye as compared to the less myopic eye after wearing OK lenses, which effectively decreases the interocular AL variation [14, 16–17].

While research suggests that highly aspherical lenslets (HAL) can effectively prevent the AL from increasing too fast [11, 18], the effects of this method on anisometropia are still unknown. Therefore, this study compared the interocular difference in AE among individuals with myopic anisometropia treated with OK lenses, HAL or SP.

Methods

Subjects

The sample comprised 225 individuals with myopic anisometropia who were equipped with OK lenses, HAL or SP for myopia control. Subjects were treated at the Eye Hospital of Wenzhou Medical University between January 2019 and December 2022. The study inclusion criteria were: (1) age 8–14 years; (2) myopia diagnosed in at least one eye; optimal corrected vision equal to or better than 0.1 (LogMAR) in each eye; spherical equivalent refraction (SER) ranging from + 1.00 D to−6.00 D; astigmatism ≤ 2.00 D; (4) optical correction with the above three methods, respectively, for about 12 months; (5) refraction of spectacles in the non-myopic eye ranging from + 0.50 to−0.50 D; (6) no history of using atropine for myopia, including during the follow-up period; and (7) no history of ocular diseases (such as strabismus, amblyopia and binocular vision anomalies), trauma or systemic diseases. In this paper, myopia was defined as a SER less than−0.50 D, while anisometropia was defined as a SER greater than or equal to 1.00 D [14]. The SER of the more myopic eye was at least 1.00 D less than the SER of the less myopic eye. SER of−0.50 D to + 0.50 D was considered non-myopic, and non-myopic eyes in UMA children with a SER of−0.50 D to + 0.50 D did not require optical correction due to clear vision. This study was performed in accordance with the Declaration of Helsinki and was approved by the Wenzhou Medical University Eye Hospital’s Ethics Committee (2023−186-K−151). As this was a retrospective study, the ethics committee agreed that children were not required to provide written informed consent.

Instrumentation

OK lenses (Euclid, USA, 4 curves, material: Boston Equallens II, lens diameter: 10.6 mm, jessen factor: 0.75D) wearers wore contact lenses for eight hours continuously during sleep and did not wear contact lenses or glasses during the day. The non-myopic eyes in the OK-UMA children were not adjusted.

The HAL used for the myopic eyes in this study were highly aspherical lenses [11, 18]. Some non-myopic eyes in the HAL-UMA children were corrected by myopic control glasses (BHAL-UMA) while the rest of the children wore single-vision glasses (UHAL-UMA). The children who wore HAL and SP wore the glasses at all times during the day. Each subject underwent a comprehensive baseline eye examination, including a slit-lamp examination, as well as tests for refraction, AL, corneal topography and intraocular pressure, among others. The AL was collected using an IOLMaster (Zeiss IOLMaster, Germany), and the values of five measurements were averaged. The signal-to-noise ratio (SNR) of the single axial measurement was greater than 2.0, and the SNR of the combined signal was greater than 32. All children were treated by doctors who had worked in the OK field at the hospital for over a decade, and the AL measurements were performed by the same doctor in the morning.

Methods

In total, 36 children with UMA (optical correction duration 11.90 ± 0.72 months) and 33 children with BMA (optical correction duration 12.03 ± 0.73 months) treated with OK were assigned to the OK-UMA and OK-BMA groups, respectively. Further, 54 children with UMA (optical correction duration 11.61 ± 1.17 months) and 33 children with BMA (optical correction duration 12.06 ± 1.20 months) treated with HAL were assigned to the HAL-UMA and HAL-BMA groups, respectively. Refraction, age and AL-matched UMA (n = 38, optical correction duration 11.89 ± 1.40 months) and BMA (n = 31, optical correction duration 12.42 ± 1.18 months) children treated with SP were assigned to the control groups (SP-UMA and SP-BMA), as shown in Fig. 1. The interocular AE difference was compared among these groups. The difference in the interocular AE was defined as the AL of the less myopic eye compared to the AL of the more myopic eye (see equation below).

Fig. 1.

Grouping of subjects

Axial elongation (AE)

Difference in the AE of the more myopic eyes = Final AL - Baseline AL

Difference in the AE of the less myopic eyes = Final AL - Baseline AL

Interocular AL difference change = Difference in the AE of the more myopic eye - Difference in the AE of the less myopic eye

For the subjects treating with HAL and SP were instructed to their wear spectacles for more than 12 h per day. For the subjects treating with OK were instructed to their wear ortho-k lenses for 8–10 h per night, they were followed up on the first day, first week, and first-month post-Orthokeratology, then at 2–3 month intervals. Residual refraction was re-tested at each 6-month interval follow-up visit. Spectacle glasses were updated when residual refraction changed by more than 0.50D.

Statistical analyses

Referring to Long’s research [14], the interocular AE difference in OK-UMA was−0.29 ± 0.29 mm and in SP-UMA was 0.02 ± 0.32 mm, according to the formula, at least 16 cases are required for each group for UMA children; the interocular AE difference in OK-BMA was−0.10 ± 0.15 mm and in SP-UMA was 0.03 ± 0.20 mm, according to the formula, at least 30 cases are required for each group for BMA children.

The data were processed using SPSS 24.0 statistical software. The measurement data were expressed as X ± s. The differences in the baseline data among the three optical correction groups were analysed using ANOVA. First, the normality of the data was tested using the Shapiro-Wilk method. The interocular AE was normally distributed for the BMA and UMA groups. The differences in the interocular AE between the three optical correction groups were tested using independent samples t-tests. The differences in the interocular AE between the more and less myopic eyes under the different optical correction methods were analysed using paired t-tests, respectively. P < 0.05 indicated a statistically significant difference.

Results

Basic data for BMA children

There were no significant differences in the baseline parameters, including the baseline SER, baseline spherical refraction (SE), baseline astigmatism (As) and baseline AL, among the OK-BMA, HAL-BMA and SP-BMA groups (all P > 0.05; Table 1).

Table 1.

Comparison of the differences in the baseline parameters of BMA under three methods

		SP-BMA (n = 31)	HAL-BMA (n = 33)	OK-BMA (n = 33)	F	P
Age (years)		11.03 ± 2.20	10.64 ± 1.66	10.85 ± 1.33	0.409	0.665
Interocular difference of SER (D)		–1.96 ± 0.70	–1.70 ± 0.53	–1.77 ± 0.61	1.541	0.219
The more myopic eyes	SER (D)	–3.15 ± 1.23	–3.15 ± 1.35	–3.40 ± 0.73	0.546	0.581
	SE (D)	–2.86 ± 1.24	–2.84 ± 1.26	–3.05 ± 0.69	0.373	0.690
	As (D)	–0.56 ± 0.40	–0.62 ± 0.48	–0.67 ± 0.45	0.417	0.660
	AL (mm)	25.01 ± 0.83	24.99 ± 0.80	25.02 ± 0.82	0.013	0.987
The less myopic eyes	SER (D)	–1.19 ± 0.84	–1.46 ± 1.39	–1.64 ± 0.55	1.668	0.194
	SE (D)	–0.81 ± 0.91	–1.13 ± 1.34	–1.23 ± 0.48	1.590	0.209
	As (D)	–0.74 ± 0.54	–0.65 ± 0.43	–0.80 ± 0.49	0.804	0.450
	AL (mm)	24.20 ± 0.76	24.27 ± 0.83	24.34 ± 0.71	0.284	0.753

Note: SER: spherical equivalent refraction, SE: spherical refraction, As: astigmatism, AL: axial length

Comparison of the difference in AE among the BMA children under the three optical correction methods

In the more myopic eyes, the AE of the SP-BMA group (0.32 ± 0.19 mm) was greater than that of the OK-BMA (0.12 ± 0.15 mm, P < 0.001) and HAL-BMA (0.15 ± 0.18 mm, P < 0.001) groups, but there was no significant difference between the HAL-BMA and OK-BMA groups (P = 0.508). In the less myopic eyes, the AE of the HAL-BMA group (0.12 ± 0.15 mm) was significantly less than that of the SP-BMA (0.31 ± 0.21 mm, P < 0.001) and OK-BMA (0.27 ± 0.16 mm, P = 0.001) groups. However, there was no statistically significant difference between the SP-BMA and OK-BMA groups (P = 0.378). The interocular AE difference in the OK-BMA group (0.15 ± 0.19 mm) was greater than that of the SP-BMA (−0.01 ± 0.20 mm, P < 0.001) and HAL-BMA (−0.03 ± 0.17 mm, P < 0.001) groups. There was no significant difference between the HAL-BMA and SP-BMA groups (P = 0.704) (Fig. 2).

Fig. 2.

Comparison of the AE difference among three methods of lens-wearing in BMA (a: the AE in the more myopic eyes under various methods, b: the AE in the less myopic eyes under various methods, c: the interocular AE difference under various methods; **P < 0.01, ***P < 0.001)

Comparison of the difference in AE between the more and less myopic eyes of BMA children under the three types of optical correction methods

In the SP-BMA (t = 0.339, P = 0.737) and HAL-BMA (t =−0.961 P = 0.34) groups, there was no significant difference in AE between the more and less myopic eyes. However, in the OK-BMA group, the AE in more myopic eyes was significantly less than that in the less myopic eyes (t =−5.752, P < 0.001) (Fig. 3).

Fig. 3.

Comparison of the AE to wearing lenses between more and less myopic eyes under three methods in BMA (***P < 0.001)

Baseline data for the UMA children

There were no significant differences in the baseline age, baseline SER, baseline SE, baseline As and baseline AL among the OK-UMA, UHAL-UMA, BHAL-UMA and SP-UMA groups (all P > 0.05; Table 2).

Table 2.

Comparison of the difference of the baseline parameters of UMA in different groups

		SP-UMA (n = 38)	UHAL-UMA (n = 26)	BHAL-UMA (n = 28)	OK-UMA (n = 36)	F	P
Age (year)		10.50 ± 1.66	10.00 ± 1.36	10.71 ± 1.65	10.64 ± 1.66	1.124	0.342
The interocular SER difference (D)		−2.09 ± 0.73	−2.36 ± 0.95	−2.00 ± 0.87	−2.29 ± 0.65	1.356	0.259
Myopic eyes	SER (D)	−2.08 ± 0.77	−2.30 ± 1.01	−2.11 ± 0.86	−2.27 ± 0.58	0.533	0.660
	SE (D)	−1.88 ± 0.72	−2.04 ± 1.01	−1.87 ± 0.83	−2.07 ± 0.57	0.590	0.623
	As (D)	−0.41 ± 0.35	−0.50 ± 0.32	−0.49 ± 0.37	−0.40 ± 0.27	0.721	0.541
	AL (mm)	24.32 ± 0.60	24.49 ± 0.80	24.58 ± 0.85	24.67 ± 0.94	1.319	0.271
Non-myopic eyes	SER (D)	0.00 ± 0.36	0.06 ± 0.28	−0.12 ± 0.27	0.02 ± 0.46	1.185	0.318
	SE (D)	0.24 ± 0.37	0.33 ± 0.23	0.15 ± 0.28	0.21 ± 0.42	1.239	0.298
	As (D)	−0.48 ± 0.44	−0.54 ± 0.42	−0.54 ± 0.40	−0.38 ± 0.36	1.048	0.374
	AL (mm)	23.42 ± 0.52	23.49 ± 0.64	23.73 ± 0.72	23.68 ± 0.84	1.547	0.206

SER: spherical equivalent refraction, SE: spherical refraction, As: astigmatism, AL: axial length

Comparison of the difference in AE among the UMA children under the three optical correction methods

In the more myopic eyes, AE in the SP-UMA group (0.30 ± 0.17 mm) was significantly greater than that of the OK-UMA (0.12 ± 0.13 mm, P < 0.001), UHAL-UMA (0.12 ± 0.13 mm, P < 0.001) and BHAL-UMA (0.09 ± 0.15 mm, P < 0.001) groups, but there were no statistically significant differences among the UHAL-UMA, BHAL-UMA and OK-UMA groups (all P > 0.05). In the non-myopic eyes, AE in the BHAL-UMA group (0.10 ± 0.14 mm) was significantly less than that in the OK-UMA (0.47 ± 0.24 mm, P < 0.001), SP-UMA (0.28 ± 0.22 mm, P = 0.001) and UHAL-UMA (0.40 ± 0.22 mm, P < 0.001) groups. The AE in the SP-UMA group was also significantly less than that in the OK-UMA (P < 0.001) and UHAL-UMA (P = 0.025) groups, but there was no significant difference between the OK-UMA and UHAL-UMA groups (P = 0.199). The interocular AE difference in the UHAL-UMA group (0.29 ± 0.36 mm) was significantly greater than in the SP-UMA (−0.02 ± 0.23 mm, P < 0.001) and BHAL-UMA (0.01 ± 0.18 mm, P < 0.001) groups, and the interocular AE difference in the OK-UMA group (0.35 ± 0.25 mm) was also significantly greater than in the SP-UMA (P < 0.001) and BHAL-UMA groups (P < 0.001). However, there was no statistically significant difference between the UHAL-UMA and OK-UMA groups (P = 0.321). See Fig. 4.

Fig. 4.

Comparison the AE under different groups (a: the AE in myopic eyes under different groups, b: the AE in no-myopic eyes under different groups, c: the interocular AE difference under different groups (***:P < 0.001)

Comparison of the difference in AE between the myopic and non-myopic eyes of UMA children under the three types of optical correction methods

There were no statistically significant differences in AE between the myopic and non-myopic eyes in the SP-UMA (t =−0.510, P = 0.613) and BHAL-UMA (t =−0.305, P = 0.763) groups. However, in the UHAL-UMA (t =−3.985, P = 0.001) and OK-UMA (t =−8.526, P < 0.001) groups, there was significantly less AE in the more myopic eyes than in the non-myopic eyes, as shown in Fig. 5.

Fig. 5.

Comparison the AE between myopic eyes and no-myopic eyes in different groups (**: P < 0.01, ***: P < 0.001)

Comparison of the interocular AE difference between the BMA and UMA children under the three different optical correction methods

For SP, there was no significant difference in the interocular AE difference between the BMA and UMA children (t =−0.049, P = 0.961). The interocular AE difference in the UHAL-UMA group was significantly greater than that in the BHAL-UMA (P = 0.004) and BMA (P = 0.001) groups. For OK, the interocular AE difference in UMA children was significantly greater than that in BMA children (t =−4.122, P < 0.001), as shown in Fig. 6.

Fig. 6.

Comparison of the interocular AE difference between BMA and UMA under three different methods of lens-wearing (a: comparison of the interocular AE difference between BMA and UMA under SP, b: comparison of the interocular AE difference between BMA and UMA under HAL, c: comparison of the interocular AE difference between BMA and UMA under OK; **P < 0.01, ***P < 0.001 )

Discussion

In this retrospective study, children who used OK lenses and HAL exhibited less AE than those who wore SP. The interocular AL difference in children with anisometropia was significantly reduced under OK lens treatment, for both UMA and BMA children. These results are consistent with previous studies [13–16]. In this study, after wearing HAL, slower AL growth was observed as compared to the SP group, in both the myopic eyes and non-myopic eyes. However, only the UHAL-UMA group children, which were treated with unilateral HAL, exhibited a decrease in the interocular AL difference after wearing HAL.

After wearing OK lenses for one year, AE in the OK-BMA group was found to be 0.12 ± 0.15 mm for the more myopic eyes and 0.27 ± 0.16 mm for the less myopic eyes, and the interocular AL difference decreased about 0.15 ± 0.19 mm, which is consistent with Tasi’s report [15]. In Tasi’s study, AE in the more myopic eyes changed from 0.03 ± 0.25 mm to 0.14 ± 0.12 mm and in the less myopic eyes, it changed from 0.13 ± 0.16 mm to 0.21 ± 0.19 mm. Further, the mean interocular AL difference changed from 0.01 mm to 0.10 mm [15]. In the HAL-BMA group in this study, AE was 0.15 ± 0.18 mm in the more myopic eyes after wearing HAL for one year, which was similar to that in the OK-BMA group after wearing OK lenses for one year. However, AE in the less myopic eyes in the HAL-BMA group was less than that in the OK-BMA and SP-BMA groups. This indicates that after wearing bilateral HAL for one year, bilateral AL elongation was slow in children with BMA but the interocular AL difference exhibited little reduction. However, after wearing bilateral OK lenses for one year, the interocular AL difference was reduced in children with BMA.

In this study, after wearing OK lenses for one year, AE in the OK-UMA group was 0.12 ± 0.13 mm for the myopic eyes and 0.47 ± 0.24 mm for the non-myopic eyes. The interocular AL difference decreased by about 0.35 ± 0.25 mm. After comprehensive analysis of four relevant studies of children with UMA treated with OK lenses for one year, Tasi [15] reported that the mean AE in the myopic eyes changed between 0.05 ± 0.19 mm to 0.14 ± 0.35 mm, and 0.26 ± 0.30 mm to 0.36 ± 0.23 mm in the non-myopic eyes. The mean interocular AL difference was reduced between 0.12 mm and 0.29 mm. Chen reported that after wearing OK lenses for one year, AE in children with UMA was 0.08 ± 0.15 mm in the myopic eyes and 0.39 ± 0.32 mm in the non-myopic eyes. The interocular AL difference reduced from 1.09 ± 0.48 mm to 0.67 ± 0.52 mm [19]. Zhang [20] also reported that the AE ratio of myopic eyes in UMA was 0.008 ± 0.022 mm/mo and 0.038 ± 0.018 mm/mo in non-myopic eyes with OK lenses. These results are similar to the current study. Overall, research indicates that for children with UMA or BMA, after wearing OK lenses, the interocular AL difference is reduced [14–16, 20].

However, some differences were observed in the UMA children treated with HAL in the current study. Although HAL has been shown to slow down the AE speed in previous research [11, 18], the effect of HAL on myopic anisometropia appears to be different to OK lenses. In this study, for UMA children who wore bilateral HAL, AE in the myopic eyes was similar to that in the non-myopic eyes, and this was similar to the AE of myopic eyes observed in the UMA children treated with OK lenses Thus, after wearing bilateral HAL, there was a good myopia control effect on both the myopic eyes and non-myopic eyes, which might slow down the speed of myopia progression in the non-myopic eyes. However, the interocular AL difference was not reduced. For UMA children who wore unilateral HAL for one year, AE was 0.12 ± 0.13 mm in the myopic eyes but 0.40 ± 0.22 mm in the non-myopic eyes, which is a similar result to the OK-UMA group (0.12 ± 0.13 mm in the myopic eyes and 0.47 ± 0.24 mm in the non-myopic eyes). Furthermore, AE of the non-myopic eyes in both the UHAL-UMA and OK-UMA groups was greater than that in the SP-UMA group. These results are similar to those of Tasi [15]. The mechanism underlying the faster progression of myopia in the non-myopic eyes with unilateral HAL or OK lenses is unclear. Although the interocular AL difference in the UHAL-UMA group and OK-UMA groups decreased, the progression of myopia in the non-myopic eyes must be considered.

It is generally accepted that the peripheral retinal defocus effect of OK lenses and HAL can affect myopia control [18–23]. The effect of HAL on myopia control might also apply to the non-myopic eyes; wearing bilateral HAL can slow the speed of AL elongation in the non-myopic eyes of children with UMA. However, after wearing unilateral HAL or unilateral OK lenses, the AL of the non-myopic eyes of children with UMA grew faster than that of the SP-UMA group, although the non-myopic eyes in the UHAL-UMA group only wore SP and the non-myopic eyes in the OK-UMA group did not receive any intervention. Taylo [24] reported that myopes might have reduced sensitivity to low spatial frequency S-cone stimuli, with S-cone cells being distributed around the central fovea. Previous studies have suggested that the blurry peripheral images that occur in peripheral retinal defocus and contrast signalling in the retina could slow myopia progression [22–25]. It is possible that the peripheral retinal defocus, which is formed by OK lenses and HAL, could affect the S-cone cells, thus slowing myopia progression. These blurred signals might provide good myopic control in the myopic eyes, but without any intervention, the image in the fellow non-myopic eyes is normal. On the other hand it might cause by the absence of peripheral defocus. Moreover, the value of peripheral defocus is related to the amount of myopia corrected: the more myopia correction, the more control might have in orthokeratology. It is a dose response. With the HAL, it is the same dose for each myopia power. However, more research is needed to investigate this phenomenon.

Based on clinical records, there were no severe complications in the OK-treated and spectacle-treated subjects. However, there are several limitations of this research that should be noted. First, only AL was measured, and the thickness of the choroid was not measured. OK lenses and HAL may affect the choroidal thickness to prevent growth in the AL [11, 26]. Examining changes in the AL and choroidal thickness might offer a better description of myopia progression. Further, this study only measured the AL but not the vitreous chamber depth. The corneal thickness and anterior chamber depth may be affected by OK lenses. Queiros [27] reported that both the anterior chamber depth and central corneal thickness were changed after wearing OK lenses for 12 months. Thus, future studies should measure the change in the posterior chamber depth instead of the whole axial length.

In conclusion, OK lenses effectively reduced the interocular AL difference for children with UMA and BMA. HAL only decreased the interocular AL difference for children with UMA when wearing unilateral HAL but it did slow down the AL elongation of the non-myopic eyes in children with UMA when wearing bilateral HAL. For children with UMA, there is a need to pay attention to the myopic progress of the non-myopic eyes when undergoing unilateral HAL or unilateral OK lens treatment.

Author contributions

M.C. wrote the main manuscript text and prepared figures. X.Y. X.Y. H.L.and X.W. helped collect data. X.M. guided the article.

Funding

Not applicable.

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

This study was performed in accordance with the tenets of the Declaration of Helsinki and was approved by the Wenzhou Medical University Eye Hospital ethics committee (2023−186-K−151).

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.