Myopia ranks among the most prevalent eye conditions globally and presents a significant public health concern. In 2000, there were 1.41 billion people worldwide with myopia, and among them, 160 million had high myopia. This figure is expected to dramatically increase by 2050, with projections suggesting that up to 4.76 billion people will have myopia and 938 million will suffer from high myopia.[1] The progression of myopia and high myopia can lead to a range of complications, including pathological myopia, cataracts, choroidal atrophy, neovascularization, retinal detachment, posterior staphyloma, myopic macular degeneration, and glaucoma.[2–4] All of these are irreversible, blindness-causing eye diseases. Multiple studies have found that early-onset myopia in school-aged children has been linked to a notably elevated risk of developing high myopia.[5–7] One of the studies revealed that for children who have myopia beginning at age 7–8, the rate of high myopia exceeded 50%, while among those aged 9, the rate of high myopia was 30%.[5] The likelihood of developing high myopia in adulthood is significantly decreased for every year that the age at onset is delayed. Given the significant public health implications of myopia, it is imperative to implement appropriate interventions promptly to prevent the beginning of myopia or to slow myopia progression. Identifying individuals at the pre-myopia stage can more accurately pinpoint the precursor phase of myopia development, thereby facilitating targeted and timely interventions.

Pre-myopia is defined as a refractive state between >-0.50 D and ≤ + 0.75 D in children. When combined with risk factors such as baseline refraction, age, and other quantifiable measures, this profile indicates a high enough risk of future myopia to warrant preventative interventions.[8] Moreover, both refraction and AL progress more rapidly in premyopic children, with the rate of change decelerating following myopia onset.[9–10] Currently, clinical options for myopia prevention remain limited, including outdoor exposure,[11–13] low-concentration atropine eye drops,[14–16] repeated low-level red-light therapy (RLRL),[17] and auricular acupressure (AA).[18] However, each of these interventions has its own limitations and drawbacks. The adverse events of low-concentration atropine reported included photophobia, allergic conjunctivitis, and near-blurred vision.[4, 19, 20] RLRL therapy produced adverse effects on the fundus, encompassing retinal damage, a reduction in paracentral foveal cone density, and other subtle retinal abnormalities.[21–22] The potential adverse events of AA may include allergies, infections, subcutaneous hematomas, bleeding, and so forth.[18]

As an optical intervention for myopia control, HAL lenses utilize peripheral retinal defocus and are widely used in clinical practice due to their high safety, non-invasiveness, convenience, and effectiveness in controlling myopia progression. Clinical studies demonstrated that compared to those wearing single-vision spectacle lenses (SVL), myopic participants wearing HAL spectacles had a reductions in axial elongation of 51% to 64% and SER of 55% to 67%.[23] To date, there are reports in the literature on the effectiveness of HAL in children without myopia, including low-hyperopic and premyopic children. Zhang et al.[24] found that the children with low-hyperopia who wore plano HAL lenses for > 30 hours/week had significantly slower AL elongation compared with those wearing SVL. Wang et al.[25] reported that plano HAL lenses exhibit efficacy in slowing the progression of AL and SER among non-myopic 4- to 9-year-old children, but there was no control group and no cycloplegic refraction. This clinical study aims to evaluate the effects of spectacle lenses with HAL on axial elongation, refractive change, and accommodative and binocular function in pre-myopic ( ≤ + 0.75 D and > − 0.50 D) Chinese children.

Participants aged 6–16 years had initial cycloplegic SER ranging from > − 0.50 D and ≤ + 0.75 D, astigmatism ≤ 1.50 D in both eyes, uncorrected visual acuity (UCVA) of 20/20 or better, and anisometropia ≤ 1.50 D. The study included 66 children who completed the 6-month follow-up. The participants were divided into two groups based on the correction methods: the HAL group (n = 32) and the Control group (n = 34). Participants in the HAL group were provided with the plano HAL spectacle lenses (Essilor Co., Ltd, Paris, France) with a compliance of at least 5 days per week and a mean daily wear time of no less than 8 hours. Participants in the Control group received no correction (shown in Fig. 1). All study subjects were right-eye dominant. The exclusion criteria included (1) children with systemic or ocular diseases and (2) prior use of any pharmacological or optical interventions for myopia control before recruitment.

Objective refraction was performed at baseline under cycloplegia (0.5% compound tropicamide eye drops, Shenyang Xingqi Pharmaceutical Co., Ltd) using an autorefractor (ARK-1, Nidek, Japan). Subjective refraction and visual function were performed using a phoropter (RT-600, Nidek, Japan) at both baseline and the 6-month follow-up visit. The spherical refractive power plus half of the cylindrical refractive power was the definition of SER.

The axial length was assessed using the IOL Master 500 (Carl Zeiss, Germany), with at least five measurements per eye, and the average value was calculated for analysis. AL measurement was done without cycloplegia.

The following tests were administered at both baseline and the 6-month follow-up visit. The distance and near ocular alignment was assessed using the Von Graefe technique on a phoropter. The accommodative convergence/accommodation (AC/A) ratio was determined through the gradient method by assessing ocular alignment through a phoropter with a + 1.00 D lens at a distance of 40 cm with a phoropter. The distance Worth-4-dot was measured with a phoropter. Negative/positive relative accommodation (NRA and PRA) was measured with a phoropter, and the lenses were adjusted in + 0.25 D/-0.25 D steps gradually until the children reported the first slight sustained blur. The accommodative response test was measured using binocular cross cylinder (BCC) with a phoropter, and the lenses were adjusted in + 0.25 D/-0.25 D steps gradually until the children reported that the vertical and horizontal lines appeared equally clear.

HAL spectacle lenses incorporate Highly Aspherical Lenslet Target technology, which utilizes concentric rings of aspheric microlenses containing a higher level of positive power to focus a subset of incident light rays anterior to the retina to minimize peripheral hyperopic defocus. Clinical studies have demonstrated that the participants with myopia wearing HAL spectacle lenses experienced a 51%-64% reduction in axial elongation and a 55%-67% reduction in SER progression compared with those wearing SVL.[23, 31]

Preliminary research is now exploring the application of HAL spectacles in children with low hyperopia. Zhang et al.[24] reported that the intervention's efficacy of HAL lenses exhibits a dose-dependent relationship in pre-myopic children. 108 Chinese children (aged 6.0-9.9 years) with SER ranging from 0.00 D and + 2.00 D were randomized into HAL and SVL groups. After one year, the changes in SER were − 0.19 D and − 0.23 D, while AL elongation was 0.24 mm and 0.19 mm in the SVL and HAL group, respectively. None of these differences were statistically significant, a finding that appears inconsistent with the outcomes of the present study. However, AL and SER changes in the HAL group were significantly associated with the wear time of the spectacles. Low hyperopic children wearing HAL lenses for > 30 hours/week had significantly slower axial elongation (0.11 mm vs. 0.27 mm), which corresponds to a 59% reduction compared to the SVL group. Our findings are basically consistent with these results (6-month AL elongation: 0.04 mm vs 0.14 mm, respectively), and the participants in our study were required to wear HAL spectacles for at least 5 days per week and a mean daily wear time of no less than 8 hours.

Additionally, a recent study found that plano HAL lenses effectively slow AL and SER progression in children without myopia (aged 4–9 years; non-cycloplegic SER: -0.50 to + 0.75 D). The annual rate of AL elongation was reduced by 0.31 mm (from 0.44 mm pre-treatment to 0.13 mm post-treatment), while SER progression was slowed by 0.42 D (from − 0.28 D/year to + 0.14 D/year).[25] However, this study did not perform cycloplegia, which led to SER measurements being inaccurate and hindered accurate assessment of the children's refractive status (pre-myopic, emmetropic, or hyperopic). Furthermore, non-cycloplegic SER measurements may introduce inaccuracies in assessing SER progression. More importantly, the absence of a control group and reliance on before-after treatment comparisons could compromise result validity.[25] Our study utilized cycloplegic refraction for baseline measurements in pre-myopic children and included a control group.

There are several studies that have examined the impacts of HAL spectacles on visual function, including visual acuity, contrast sensitivity, accommodation, and binocular vision. The study by Huang et al.[32] revealed that HAL had no significant effects on accommodative function and near phoria, with the exception of larger microfluctuations than SVL. Although short-term HAL use initially reduced VA (including scotopic and low-contrast VA), these values normalized to the level of the SVL group after 12 months. Gao et al.[33] revealed low contrast VA and reading were slightly decreased, but high contrast VA was unaffected when fixating through the periphery of HAL designs in adults. The new lens designs had no effect on any of the peripheral measurements of vision. Fengchao et al.[34] found HAL lenses had no significant influence on binocular visual or accommodative function in children with myopia who may or may not have intermittent exotropia, except the short-term accommodative microfluctuation. The current study demonstrates that after 6 months, HAL lenses have no significant effect on accommodation and binocular function, including distance and near phoria, AC/A ratio, BCC, Worth 4-dot, and PRA. This outcome is in alignment with prior research, with the exception of the NRA. Our study revealed a statistically significant (P = 0.032) but clinically slight reduction (-0.13 D) in NRA in the HAL group, potentially attributable to the optical characteristics of aspherical lenslets affecting accommodative microfluctuations or behavioral adaptation, because the subjects naturally adjust their visual behavior to reduce blur effects caused by the lenslets during near-vision tasks. However, the relatively short follow-up period in our study limits the ability to determine whether these effects represent transient adaptations or persistent changes, which need long-term further investigation.

In conclusion, our study showed that HAL spectacles have a significant control effect on the AL elongation in pre-myopic children (aged 6–16 years) with minimal impact on accommodative and binocular function (distance and near phoria, AC/A ratio, BCC, distance worth-4 dot, and PRA), except for a measured change in NRA, over a 6-month period. HAL spectacles could be a viable strategy and effective method for preventing myopia onset in clinical practice.