## 1 Introduction  
Myopia, also known as near-sightedness, is one of the most common types of refractive errors and can lead to blindness. It is a worldwide public health issue. Myopia (spherical equivalent \(>-\)0.5 D) and high myopia (spherical equivalent \(>-\)5.0 D) were estimated to affect 22.9% (1406 million) and 2.7% (163 million) of the world's population, respectively, in 2000, and these values are projected to increase to 50% (4758 million) and 9.8% (938 trillion), respectively, by 2050 [1]. In Taiwan, early-onset myopia (\(\leq\)7 years of age) may increase the risk of high myopia among schoolchildren [2, 3]. High myopia is associated with complications such as cataracts, glaucoma, retinal detachment, myopic macular degeneration, visual impairment, and blindness [1, 4, 5, 6]. The World Health Organization (WHO) has reported that uncorrected refractive errors are the main reason for 42% of visual impairments and 3% of blindness [7]. However, 80% of visual impairments are avoidable, and even a 50% reduction in the rate of developing myopia can decrease the prevalence of high myopia by as much as 90% [7; 8]. Eliminating the main causes of all preventable and treatable blindness and improving vision health are paramount [9].  
The proposed mechanisms underlying myopia development include excessive accommodation and uncoordinated eye growth due to the response of retinal signals to sustained extended near work [10]. The current common therapeutic approaches to myopia include the use of glasses or contact lenses, laser eye surgery, and atropine eyedrops [11]. Alternative approaches to prevent and delay the progression of myopia include avoiding using eyes at close distances for a long period, increasing outdoor time [12; 13], acupressure or electroacupuncture [14; 15; 16], and eye exercise training [17; 18; 19].  
Eye exercises are often used in physiotherapeutic optometric vision therapy, which establishes effective ways of using the eyes as well as muscle relaxation techniques, biofeedback, eye patches, or eye massages, alone or in combination, to improve visual clarity [18; 19]. However, few studies have comprehensively evaluated a 3D-based vision training (VT) program to improve visual clarity. Auditory frequency following responses (FFRs), generated by periodic or nearly periodic auditory stimuli at low frequencies, is a powerful neural processing tool of the visual cortex and affects the optic and visual nerves [20]. Electrical stimulation (ES) or electrical acupuncture/acupoint stimulation is a safe and effective technique that may have therapeutic applications in controlling myopia [16; 21; 22; 23; 24].  
Binaural differences in the alpha-band (8-14 Hz) stimulus recognize the visual target and causes the visual stimulation of resonance rhythms [25]. However, the effect of 3D-based VT plus FFR generated by auditory binaural frequency entrainment remains unknown.  
ES is commonly used in physical therapy to relax hypertonic muscles, reduce muscle spasms, and improve muscle discomfort symptoms [26]. This response is effected through the excitation-contraction-relaxation cycle in muscles by mediating Ca\({}^{2+}\) levels [27]. ES was reported to reduce tetanic tension in an animal model [28]. ES is often applied directly to acupoints or motor points in the muscle. Bilateral orbital Taiyang (EX-HN5) acupoints have been reported to prevent myopia in animal studies [16], but no human trials have been conducted.  
In the present study, we applied 3D-based VT, FFR generated by visual cortex-activated auditory binaural frequency entrainment, and ES to evaluate the best observed outcome intervention and examine the effectiveness of multimodal interventions in preventing the progression of myopia among Taiwanese schoolchildren. Our findings may provide useful information for the promotion of visual health and prevention of deterioration for schoolchildren and their parents.