Bangerter filter’s role in regulating ocular axial length: a novel application of an established therapy

Abstract

Key messages

What is known

• Occlusion with Bangerter filters designed with different translucent microscopic diffusers is an effective treatment for anisometropic amblyopia.

What is new

• Bangerter filters were found to show an effect on slowing down ocular axial length (AL) growth.

• When rapid hyperopic reduction occurs in the non-amblyopic eye combined with persistently widening interocular AL differences, Bangerter filter application represents a more preferable alternative to patching for managing anisometropic amblyopia.

Purpose

Bangerter filter occlusion is an effective clinical method for amblyopia treatment. This study aimed to compare the nonamblyopic eyes elongation and refraction change of patching and Bangerter filter occlusion in treating patients with anisometropic amblyopia and to further investigate the effect of Bangerter filter on axial length growth.

Methods

This retrospective study included 54 patients with anisometropic amblyopia categorized by initial treatment: patching group (n = 24) and Bangerter filter group (n = 30). Consecutive records of both the amblyopia and nonamblyopia eyes were reviewed from baseline before treatment onset to follow-up visits during or post-treatment, including best corrected visual acuity, pneumatic intraocular pressure, spherical equivalent refraction (SER), axial length (AL), corneal curvature, binocular visual function, and accommodative function. In addition, macrostructures of three different densities of Bangerter filters and diffusion optics technology lenses were observed and compared.

Results

The nonamblyopic eyes in the Bangerter filter group had significantly lower AL increases from baseline (− 0.15 and − 0.20, respectively, P < 0.05) and significantly fewer SER reductions from baseline (0.45 and 0.57, respectively, P < 0.05) compared with the patching group at both two follow-up visits. The interocular AL difference between nonamblyopic and amblyopic eyes increased by 0.15 ± 0.27 mm in the occlusion group at the second follow-up (from baseline 0.23 ± 0.61 mm to second follow-up 0.38 ± 0.69 mm, P = 0.004), while it decreased by 0.18 ± 0.20 mm in the Bangerter filter group at the second follow-up (from baseline 0.72 ± 0.68 mm to second follow-up 0.54 ± 0.69 mm, P < 0.001).

Conclusions

Bangerter filter, as a traditional occlusion therapy, have been shown to effectively slow ocular AL growth thereby reducing interocular axial length disparity when compared to patching therapy in anisometropic amblyopia treatment. Rapid reduction of hyperopic refraction in non-amblyopic eyes combined with persistent increases in interocular AL difference may constitute a novel indication for Bangerter filter application.

Introduction

Amblyopia primarily causes monocular visual impairment in children. Anisometropic amblyopia is a subnormal best corrected visual acuity associated with refractive anisometropia and without pathological organic associated factors [1]. Several alternatives have been proposed for treating anisometropic amblyopia, such as refractive error spectacle correction, patching therapy, atropine or optical penalization, and occlusion therapy using Bangerter filters.

Bangerter filters, available since the 1960 s, were designed to modulate the degree of occlusion deprivation, by inducing a diffuse image defocus that grades and degrades the nonamblyopic eye visual acuity. Several previous studies have confirmed the efficiency of Bangerter filter treatment in moderate amblyopia [2–4]. The advantages of using Bangerter filters compared with patching include graded filter strengths, better patient compliance, less binocular function disruption, and lower treatment burden [5]. Several different animal experiments use translucent diffusers, such as Bangerter foil, to alter retinal image quality, further causing axial elongation [6]. Monkeys wearing three different strengths of Bangerter foil demonstrated different degrees of myopia change and ocular elongation [7]. Spatial frequency reductions within the visual acuity range induced excessive axial eye growth and myopia in guinea pigs [8].

Recent applications of diffusion optics technology (DOT) spectacles slowed axial growth and prevented myopia progress by reducing retinal contrast [9]. The light scattering feature is integrated across the DOT lens and is achieved by applying translucent and irregularly shaped microscopic diffusers to the lens surface. Similarly, different translucent microscopic diffuser shapes are designed on the Bangerter filters to attenuate the different ranges of spatial frequencies by scattering microelements [10]. Therefore, the association of the Bangerter filter application with the AL of the human eye was investigated.

The current study analyzed the AL changes in the nonamblyopic eyes of children with anisometropic amblyopia treated with a Bangerter filter and compared them with those treated with traditional patching.

Methods

Participants

This observational retrospective study enrolled 54 children with anisometropic amblyopia who received patching therapy or Bangerter filter occlusion therapy in Sapling Ophthalmology Clinic from November 2020 to May 2024. The Clinical Research Ethics Committee approved this study which followed the tenets of the Declaration of Helsinki.

Consecutive records of patients presenting mild or moderate anisometropic amblyopia associated with refractive anisometropia (at least − 2.00 diopters [D] difference for myopia, + 1.50 D difference for hyperopia, and 2.00 D difference for astigmatism) were reviewd [11]. An ophthalmologist first diagnosed anisometropic amblyopia based on medical history, best corrected visual acuity (BCVA) is between 20/25 and 20/100 in the amblyopic eye, refractive error obtained after cycloplegia, slit-lamp biomicroscopy and fundus examination. The optometrist was responsible for checking the ophthalmologist’s treatment regimen, and overseeing the subsequent preparation of spectacles and Bangerter filters, as well as providing guidance on occlusion therapy. Children treated with spectacle correction combined with daily patching or Bangerter occlusion filter (Ryser Optik, St. Gallen, Switzerland) in the nonamblyopic eye and follow-up at least once every 6 months in the first year were included. Exclusion criteria: (1) children combined with other ophthalmic diseases, such as cataract, keratitis and glaucoma; (2) children who had a history of serious diseases, including neurological and mental disorders; (3) Children with abnormal eye movement, inability to gaze independently, or symptoms of vertical strabismus; (4) previous treatment for strabismus or amblyopia; and (5) children who did not cooperate with the treatment or discontinue follow-up.

The patients were categorized into patching group(24 patients) and Bangerter filter group(30 patients) based on the initial treatment. Patients in the patch group were assigned to patch for 2 or 4 h a day according to amblyopia severity. Bangerter filters of 0.6 or 0.8 fixed-densities were selected to place on the spectacle lens according to clinical needs, and the spectacles were to be worn full time. The prescription of the spectacles and the selective use of these two treatments were adjusted based on the follow-up examinations, such as refractive error and bilateral visual acuity. Twelve of the 24 patients in the patching group were adjusted from patching treatment to Bangerter filter occlusion treatment after at least two follow-up visits. This study identified three primary reasons for treatment discontinuation of patching therapy and subsequent transition to Bangerter filter therapy among 12 pediatric patients: (1) suboptimal treatment compliance due to psychological aversion to patch wear in social settings; (2) dermatological hypersensitivity reactions to occlusion patch adhesives; and (3) inability to maintain prescribed occlusion duration requirements secondary to athletic or artistic training commitments. In the Bangerter filter group, 11 patients still insisted on follow-up after achieving the visual acuity treatment goal and ending the occlusion treatment. AL was measured before Bangerter filter occlusion therapy onset and at four different follow-up visits: within 6 months during Bangerter filter occlusion, within 7–12 months during Bangerter filter occlusion, 1 year after removing Bangerter filter, and 2 years after removing Bangerter filter. The average follow-up time of the patching group and Bangerter filter group was 17.46 and 17.17 months, respectively.

Examinations

The baseline binocular data before initiating patching therapy or Bangerter filter occlusion therapy were recorded, including BCVA using the Snellen decimal scale, IOP, refractive status recorded as spherical equivalent refraction (SER), AL, and corneal curvature (Mean-K) measured by IOL master (Zeiss, Germany). IOP was also compared between the two groups to eliminate potential interference of IOP on the evaluation of AL elongation [12–14]. Examination data were collected within 6 months and between 7 and 12 months after treatment for the first and second follow-up visits, respectively. Binocular visual function examination with synoptophore, Titmus near stereoscopic vision, positive relative accommodation (PRA), and negative relative accommodation (NRA) was recorded at baseline and the second follow-up visit in the Bangerter group. The interocular difference included in the analysis was obtained from the data difference between nonamblyopic and amblyopic eyes in the same participant.

A set of three new unused Bangerter filters (Ryser Optik, St. Gallen, Switzerland) graded 0.8, 0.6, and 0.3 as labeled was also tested. Macrophotographs of these filters and DOT lenses (NIKON-ESSILORCO., LTD, Japan) were acquired under a bright field using an Axio Imager 2 microscope (Zeiss, Germany).

Statistical analysis

Baseline characteristics, including age, gender, visual acuity of the amblyopic eye, intraocular pressure of the amblyopic eye, and SER of the amblyopic eye, were collected and compared between the two groups using independent t tests. Data are presented as the mean and standard deviation for each group. Normality was tested using the Shapiro–Wilk test. The non-parametric Wilcoxon test was used for non-normally distributed data. In addition, within the Bangerter group, paired t tests were conducted to evaluate the differences in visual function adaptation between the baseline and the second follow-up with data analysis based on the nonamblyopic eye.

R version 4.3.2 was used for all statistical analyses. A linear mixed-effects model was used to investigate the associations of the Bangerter and Patching groups with ocular AL and SER error. The model incorporated a times and group interaction term to investigate the difference in the treatment effects over time. Participant ID was included as a random variable to develop a random intercept model. The model was adjusted for age, gender, intraocular pressure, and visual acuity as covariates. A P value of < 0.05 indicated statistical significance. Finally, GraphPad Prism 9.0 was used to plot the changes in ocular AL or the interocular difference of AL at baseline and follow-up visits.

Results

Characteristics of the participants

This study enrolled 30 and 24 patients in the Bangerter filter and patching groups, respectively, based on the inclusion and exclusion criteria. The data of the patching group was obtained from 24 amblyopic eyes and 24 nonamblyopic eyes receiving patching treatment. The mean age of the patching group was 5.87 (standard deviation [SD]: 1.83) years. The data of the Bangerter filter group was obtained from 30 amblyopic eyes and 30 nonamblyopic eyes receiving Bangerter filter occlusion treatment. The mean age of the Bangerter filter group was 6.33 (SD: 1.75) years. The baseline SER of the patching and Bangerter filter groups were 2.87 (SD: 2.68) and 2.92 (SD: 2.30), respectively. Table 1 lists the characteristics of patients in both groups. No significant differences in age, gender, SER, IOP, AL, ACD, and mean-K were described at baseline between the patching eyes and Bangerter filter-treated eyes (P > 0.05).

Table 1.

Baseline characteristics of the treatment groups

Parameter	Patching group (N = 24)	Bangerter filter group (N = 30)	P
Age, years	5.87 ± 1.83	6.33 ± 1.75	0.355
Gender,%(number)
Male	37.5% (9)	46.7% (14)	0.689
Female	62.5% (15)	53.3% (16)
Amblyopia eye, R/L	8/16	11/19	1.000
SER,D	2.21 ± 2.30	1.95 ± 1.92	0.588
IOP, mmHg	15.88 ± 2.98	16.17 ± 3.01	0.724
AL, mm	21.92 ± 0.89	22.11 ± 1.06	0.484
ACD, mm	3.27 ± 0.27	3.26 ± 0.39	0.946
Mean-K, D	43.12 ± 1.52	43.65 ± 1.89	0.267

Data are present as the mean ± standard deviation or proportions

VA visual acuity, SER spherical equivalent refraction, D diopters, IOP intraocular pressure, AL axial length, ACD anterior chamber depth, Mean-K mean keratometry

AL growth of nonamblyopic eyes in the patching and Bangerter filter groups

Table 2 shows the slowing effect of the Bangerter filter on ocular axial growth and SER reduction. The mean follow-up period at the first and second visits is 5.29 months and 10.88 months for the patching group and 4.83 months and 10.03 months for the Bangerter filter group, respectively. The intercept values of models for AL and SER are 21.36 and 1.69, respectively. The Bangerter filter group had less AL growth (− 0.15 and − 0.20, respectively, P < 0.05) and more preserved hyperopia in SER (0.45 and 0.57, respectively, P < 0.05) at two follow-up visits compared with the Patching group after controlling for fixed and random effects.

Table 2.

Axial length and spherical equivalent refraction at Baseline and two follow-up visits in the Bangerter filter group and patching group and their comparison

	Variables		$\mathrm{\beta }$	95% CI	P
AL	Times	BF baseline (reference)	0.000	–	–
		BF first follow-up visit	0.160	[0.100, 0.219]	< 0.001
		BF second follow-up visit	0.289	[0.229, 0.348]	< 0.001
	Times*group	Baseline* patching (reference)	0.000	–
		First follow-up visit*BF	− 0.148	[− 0.227, − 0.068]	< 0.001
		Second follow-up visit* BF	− 0.201	[− 0.280, − 0.121]	< 0.001
SER	Times	BF baseline(reference)	0.000	–
		BF first follow-up visit	− 0.390	[− 0.591, − 0.190]	< 0.001
		BF second follow-up visit	− 0.510	[− 0.711, − 0.309]	< 0.001
	Times*group	Baseline* patching (reference)	0.000	–
		First follow-up visit* BF	0.448	[0.179, 0.718]	0.001
		Second follow-up visit* BF	0.573	[0.304, 0.842]	< 0.001

Values indicated the linear mixed model results with the fixed effect estimates(β) and 95% confidence intervals (CI). The p values indicate the statistical significance of the corresponding effects, with values P < 0.05 considered statistically significant.

AL axial length, SER spherical equivalent refraction, BF Bangerter filter, group*times represent the interaction term between time and group

Different trends of axial growth in Bangerter filter-treated eyes and contralateral eyes

The mean baseline AL of amblyopia eyes was shorter than that of nonamblyopia eyes in both the patching and Bangerter filter groups (Fig. 1). The AL increase at the second follow-up visit in patched nonamblyopic eyes (22.21 ± 0.89 mm vs. 21.92 ± 0.89 mm) was slightly longer than in amblyopic eyes (21.76 ± 1.20 mm vs. 21.54 ± 1.19 mm) (Fig. 1A). Figure 1B shows that AL of Bangerter filter occlude nonamblyopic eyes (22.20 ± 1.05 mm vs. 22.11 ± 1.06 mm) increased significantly less than that in amblyopic eyes (21.76 ± 0.86 mm vs. 21.54 ± 0.84 mm) at the second follow-up visit. The interocular AL difference between nonamblyopic and amblyopic eyes increased by 0.15 ± 0.27 mm in the occlusion group at the second follow-up (from baseline 0.23 ± 0.61 mm to second follow-up 0.38 ± 0.69 mm, P = 0.004), while it decreased by 0.18 ± 0.20 mm in the Bangerter filter group at the second follow-up (from baseline 0.72 ± 0.68 mm to second follow-up 0.54 ± 0.69 mm, P < 0.001). The trend of AL changes in amblyopic eyes and nonamblyopic eyes revealed that Bangerter filter occlusion treatment slowed down the AL in nonamblyopic eyes, thereby reducing interocular AL differences.

Fig. 1.

Axial length changes of amblyopia and nonamblyopic eyes. A Axial length changes in the patching and B Bangerter filter groups. Data are shown as the mean ± standard deviation (SD)

Longitudinal change of the AL before and after Bangerter filter occlusion treatment

The medical records of 12 patients who were treated with patching and then changed to Bangerter filter occlusion were reviewed, and it was revealed that the AL of the nonamblyopic eyes treated with Bangerter filter increased less than that of the lateral eyes (Fig. 2). Figure 2A shows a more slowly increased AL in nonamblyopic eyes at the third (mean AL: 22.10 mm) and fourth follow-up visits (mean AL: 22.21 mm) during Bangerter filter occlusion treatment than at the first (mean: AL 22.00 mm) and second follow-up visits (mean AL: 22.14 mm) during patching treatment. In addition, three patients demonstrated slightly shortened AL during Bangerter filter occlusion therapy (Fig. 2A).

Fig. 2.

Axial length changes in 12 participants undergoing patching therapy followed by Bangerter Filter occlusion therapy. A Axial length changes of the nonamblyopic eye in follow-up visits from treatment onset. B Interocular difference of axial length changes in follow-up visits from treatment onset. Single participant data are represented by different symbols and colors; the solid line connects the AL measurements acquired before occlusion therapy onset and at four continuous follow-up visits during therapy. Gray bars represent the average mean AL or interocular difference of AL

Further analysis of the ocular AL of 11 patients treated with Bangerter filter occlusion and followed up for > 1 year after occlusion removal revealed that the interocular differences in the AL demonstrated an increasing trend compared with that during Bangerter filter occlusion (Fig. 3). Mild axial shortening of the nonamblyopic eye occurred in 2 patients during Bangerter filter occlusion treatment (Fig. 3A). The interocular difference of AL during Bangerter filter occlusion treatment (0.79 and 0.70 mm) was significantly reduced compared with that before treatment (0.99 mm). The interocular difference of the AL in follow-up visits (0.77 and 0.76 mm) was slightly larger than that during the Bangerter filter occlusion and then remained relatively stable during the long-term follow-up visits after the Bangerter filter removal (Fig. 3B).

Fig. 3.

Axial length changes during and after Bangerter Filter occlusion therapy in 11 participants. A Axial length changes of the nonamblyopic eye in follow-up visits. B Interocular difference of axial length changes in follow-up visits during and after Bangerter Filter occlusion therapy. Single participant data are represented by different symbols and colors; the solid line connects the AL measurements acquired before occlusion therapy onset and at four continuous follow-up visits during therapy. Gray bars represent the average mean AL or interocular difference of AL

Effect of Bangerter filter on binocular visional function and accommodative function

The parameters, such as divergence and convergence fusion, stereoacuity, NRA, PRA, and the accommodative response, revealed no significant differences in the second follow-up visit compared to the baseline (Table 3).

Table 3.

Changes in binocular visual function and accommodative function in Bangerter filter group

	Baseline	Second follow-up visit	P
Fusion function (circular degree)
Fusional divergence	− 7.90 ± 3.96	− 6.83 ± 2.57	0.222
Fusional convergence	13.37 ± 8.07	13.83 ± 8.20	0.825
Stereoacuity (arc sec)	317.33 ± 470.50	226.00 ± 311.58	0.380
NRA(D)	2.13 ± 0.44	2.22 ± 0.39	0.441
PRA(D)	− 2.02 ± 0.99	− 2.10 ± 0.99	0.770
Accommodative response (D)	0.36 ± 0.23	0.32 ± 0.38	0.609

Data are present as the mean ± standard deviation

NRA negative relative accommodation, PRA positive relative accommodation

Structural characteristics of Bangerter filter and DOT lens

The densities of bubbles (bubbles/mm²) in the selected field were 3.40, 3.41, and 3.44 in the 0.8, 0.6, and 0.3 filters, respectively, and approximately 7 in the DOT lens. The microbubble diameter of the DOT lens was 0.20 mm, which is almost the same as the average microbubble diameter of a 0.8-strength Bangerter filter (Fig. 4).

Fig. 4.

Macrophotographs of the characteristic patterns of microbubbles in the Bangerter filters (BF: 0.8, 0.6, and 0.3) and the diffusion optics technology lenses (central, paracentral, and outside central regions). Each photograph corresponds to an area of 2 × 2 mm

Discussion

The study revealed a significantly slower AL growth in the nonamblyopic eye of anisometropic amblyopia children in the Bangerter group than in the patching group, as well as less growth during Bangerter filter treatment than in the fellow eye. This result contradicts the orthodox view derived from animal studies that the form deprivation achieved by diffuse or defocus foils can induce excessive ocular growth and myopia. However, this inconsistency is explained by analyzing the experimental content in more detail from the following two aspects. First, the Bangerter foils with weaker strength have less regulation on visual quality and may have a different effect on ocular axial growth unlike visual deprivation caused by the high intensity of Bangerter foil. The study using four different strengths of occlusion foils to induce myopia in chicks revealed that only < 0.1 and LP filter induced significant form deprivation myopia, the 0.6 filters demonstrated slight changes in ocular length and myopia shifts [15]. The defocus threshold for form-deprivation myopia is relatively high and substantial levels of optical defocus under this threshold typically produce axial hyperopia [16]. Rhodopsin expressed in the retina may involve form-deprived myopia formation, but has less influence on defocus myopia [17]. Second, the effects of different intensities on the ocular AL were also different in the Bangerter filter with mild and moderate visual acuity reduction. Monkeys wearing three different strengths of Bangerter foil demonstrated myopia change and axial eye growth; however, the degree of axial myopia varied directly with the degree of image degradation [7]. Bangerter filters with not < 0.4 strength caused minimal degradation of distance and near optotype acuity and did not induce a significant reduction of contrast sensitivity [18]. The guinea pig experiments revealed that spatial frequency reductions within the visual acuity range induced excessive axial eye growth and myopia. However, further detailed comparison of experimental data revealed that Bangerter foil with strength of 0.6 and 0.8 cause no significant increase in the ocular length, and the eyes with Bangerter foil with strength of 0.8 even maintained hyperopia, similar to that of the fellow eye [8]. Therefore, the 0.6 or 0.8 density Bangerter filter predominantly used in this study may have the effect of slowing the ocular axial growth.

Moreover, the inhibition effect of different intensities on chick ocular elongation was recorded with a + 7 D lens used alone, or in combination with either a 0.4, 0.2, or 0.1 Bangerter occlusion foils. In contrast, the addition of a < 0.1 Bangerter filter produced the opposite response—increased ocular elongation and myopia [19]. Moreover, diffusers of moderate density (strength: 0.4) exhibited a surprising effect on lens compensation; it resulted in more choroidal thickening and a more pronounced inhibitory effect of ocular elongation than with positive lenses alone. The effects of the other two density filters (strength: 0.2 and 0.1) on choroidal thickening and axial growth inhibition were weaker than those of wearing positive lenses alone. Therefore, it is hypothesized that the weaker diffuser improved the inhibition of AL growth induced by hyperopic defocus.

A study theorized that ocular growth regulation depends primarily on spatial frequency or contrast [15]. DOT lenses are designed based on this theory to reduce the high contrast signals that have been proven to have a slowing effect on ocular AL growth in clinical applications [9, 20, 21]. The modulation of contrast sensitivity by the Bangerter filter is related to different spatial frequencies. Bangerter foil attenuates the medium and high-range spatial frequencies more than low spatial frequencies [10]. Bangerter filters improved the contrast sensitivity at low frequencies but deteriorated it at intermediate and high spatial frequencies when external noise was present [22]. The study indicates that the translucent microscopic diffusers are very similar in diameter between the 0.8 Bangerter filter and the DOT lens of the treatment zone. It is speculated that the microscopic diffusers in weaker strength filters may reduce the contrast sensitivity of specific spatial frequencies which is involved in the mechanism that slows down the ocular axial growth.

The study revealed significantly slowed down or even slightly shortened AL growth at the beginning of Bangerter filter treatment, and this axial growth inhibition was not so obvious at follow-up visits after 6 months. The possible explanation is that the amount of degradation with the filters decreased over time; hence, new filters should be periodically applied in amblyopia treatment [23]. Conversely, the axial ocular elongation became more pronounced than when the filter was worn when the Bangerter filter was removed from the refractive lens. The reason may be the removal of effective inhibition of the AL growth or the neural compensation for the defocus condition, which also explains the phenomenon that the ability to detect and recognize letters exhibited a marked improvement following prolonged optical defocus exposure [24]. The interocular differences in AL before, during, and after Bangerter filter treatment were consistent with the above results, which further excluded the influence of different environmental factors and individual growth stages on the longitudinal changes of ocular axial growth.

The degree of progression changes of SER and AL is not exactly synchronized. It is acknowledged that mechanisms of AL growth in progressing myopes may vary from those involved in emmetropes or amblyopia. The refractive error is dependent on many components and their interactions [24]. Thus, we selected AL as the main study parameter rather than the refractive error. Other parameters, such as binocular fusion ability, stereoacuity, and accommodative function, were not significantly different before and after the Bangerter filter treatment, which was similar to the conclusions of previous studies [25–27].

As far as is known, this is the first study in which longitudinal and intergroup analyses of the AL were performed to assess the effect of the Bangerter filter on axial growth in nonamblyopic eyes. However, the present study is primarily limited by its retrospective and cross-sectional nature. Ocular biological parameters were not acquired simultaneously for all cases, but analysis time intervals were set to provide a more representative measurement of the time course of AL changes. The retrospective design may also increase the risk of selection bias, therefore, randomized controlled prospective studies are required for a complete assessment of the effect of the Bangerter filter on AL changes. Another limitation is the relatively small sample based solely on the amblyopia treatment group. A larger sample size based on myopia and emmetropia is required, which also facilitates more detailed subgroup studies. Moreover, the current study only revealed a close association between Bangerter filter application and ocular elongation, but could not account for it. Therefore, the mechanisms underlying these associations warrant further investigation and explanation from basic research.

In summary, during the treatment of anisometropic amblyopia, attention should be paid not only to the improvement of visual acuity in the amblyopic eye but also to the changes in AL and refractive status of the non-amblyopic eye. This vigilance helps prevent monocular myopic shifts and permanent refractive structural disparities arising from progressive interocular AL differences. The findings demonstrate that Bangerter filters primarily confer protection by decelerating AL growth in the non-amblyopic eye, thereby preserving hyperopic reserve and limiting interocular AL discrepancy. Consequently, Bangerter filter application represents a superior alternative to patching when rapid hyperopic reduction occurs in the non-amblyopic eye and when interocular AL differences exhibit persistent progression.

Authors contribution

JJwrote the main manuscript text and made leading contributions to the analysis. TZ prepared all figures and assisted with writing the manuscript. YYmade supporting contributions to the analysis and interpretation of data.,and made supporting contributions to the analysis and interpretation of data. MH arranged the medical record and clinical data. XW made leading contribution to performing the ophthalmic examination and overseeing the project. YC made leading contribution to the design of the study and revision of manuscript. All authors have participated sufficiently in the work and agreed to be accountable for all aspects of the work.

Funding

This work was supported by the National High Level Hospital Clinical Research Funding (2023-NHLHCRF-YYPPLC-TJ-29) and Beijing University of Chemical Technology–China–Japan Friendship Hospital Biomedical Translational Engineering Research Center Joint Fund (XK2002-06).

Data availability

The data used to support the findings of this study are available from the corresponding author upon request.

Declarations

Ethics approval

This study was approved by the Ethics Committee of China–Japan Friendship Hospital (2023-KY-266-1) and conformed to the tenets of the Declaration of Helsinke. Informed consent was obtained from all participants.

Informed consent

Informed consent was obtained from all individual participants included in the study.

Competing interest

The authors declare no competing interests.