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Abstract

BACKGROUND:

Amblyopia is a neurological deficit in binocular vision that affects 3% of the population and is the result of disruptions in early visual development.

OBJECTIVE:

In this study, we used a visual perceptual learning system for the short-term treatment of children with ametropic amblyopia and evaluated the clinical efficacy of this system in terms of visual plasticity.

METHODS:

We conducted a retrospective analysis of the clinical data of 114 children (228 eyes) with refractive amblyopia, who were aged 6.51 $\pm$ 1.51 years. Prior to the treatment, we evaluated all children with amblyopia using the visual information processing test. We determined the type of amblyopic defect according to the type of amblyopia, corrected visual acuity, and advanced visual function test results. Based on the type of defect, each child with amblyopia was given short-term visual perception training for 10 days. Finally, we compared the results of visual acuity and visual information processing tests before and after the treatment.

RESULTS:

The best-corrected visual acuity of patients was better after 10 days of visual training than that before training ( $P<$ 0.05). The perceptual eye position after training improved with statistically significant differences in horizontal and vertical perceptual eye position (both $P<$ 0.05) compared to that before training. The number of amblyopic children without suppression in both eyes was 81 cases (71.1%) after training which was higher than that (65 cases, or 57.0%) before training, with a statistically significant difference ( $P<$ 0.05). Binocular fine stereopsis and dynamic stereopsis improved after training with a statistically significant difference (both $P<$ 0.05).

CONCLUSION:

In this study, it was found that patients with amblyopia showed visual plasticity. Moreover, continuous visual perceptual learning improved the best-corrected visual acuity and recovered stereopsis in children with refractive amblyopia.

Keywords

Refractive amblyopia stereopsis visual perceptual learning visual plasticity

1. Introduction

Amblyopia is a condition in which the best-corrected visual acuity is lower than the age-appropriate normal visual acuity, or the visual acuity of both eyes differs by two lines or more due to monocular strabismus, uncorrected anisometropia, high refractive error, and form deprivation during the period of visual development [1]. Amblyopia is a neurological deficit in binocular vision that affects 3% of the population and is the result of disruptions in early visual development [2]. The main feature of amblyopia is the absence of perfect stereopsis. The development of stereopsis begins in the early postnatal period, and the establishment of binocular visual function is closely related to the visual experience during visual development [3]. Residual binocular visual function and inter-ocular suppression predict the level of monocular visual acuity for patients with amblyopia, which may also be an important pathogenesis of vision loss in such patients [4].

This condition is a common cause of vision loss and impairment of partial binocular visual functions in children. In addition, amblyopia can be attributed to a lack of normal plasticity [5].

Plasticity can be of significance in the treatment of ocular and brain diseases and in the evaluation of materials and surgical techniques including refractive surgery, cataract surgery, and presbyopia correction. Visual perceptual learning is a novel clinical treatment of amblyopia, in addition to refractive correction and occlusion therapy [6, 7]. Therefore, this study investigated the efficacy of short-term visual perception training on the recovery of visual acuity and binocular stereopsis in patients with ametropic amblyopia, to confirm the existence of visual plasticity in children with amblyopia.

2. Materials and methods

2.1 Clinical information

We selected 114 children (228 eyes) with refractive amblyopia who were treated in the outpatient clinic of Guangxi Optometry Center from January 2021 to October 2022. These children met the diagnostic criteria specified by the National Strabismus Prevention and Treatment Group (2011) of the Chinese Academy of Ophthalmology [1]. Our sample included 61 males and 53 females. These children were aged 5–12 years with a mean age of (6.51 $\pm$ 1.51) years, of which 74 cases (64.9%) were aged 5–6 years, 32 cases (28.1%) were aged 7–9 years, and 8 cases (7.0%) were aged 10–12 years.

According to refractive status, there were 103 eyes (45.18%) with compound hyperopic astigmatism, 49 eyes (21.49%) with mixed astigmatism, 34 eyes (14.91%) with simple hyperopic astigmatism, 32 eyes (14.04%) with compound myopic astigmatism, 17 eyes (7.46%) with simple hyperopia, and 4 eyes with simple myopic astigmatism (1.75%). Mild to moderate amblyopia (best-corrected visual acuity below the low limit of normal for the corresponding age and $\geqslant$ 0.2) was seen in 227 eyes (99.56%), and severe amblyopia (best-corrected visual acuity $<$ 0.2) in 1 eye (0.44%). None of the patients could achieve the same visual acuity as their peers after more than 3 months of refractive correction with glasses.

2.2 Treatment methods

•
Before treatment, we examined the anterior segment and fundus of both eyes. Except for ocular organic lesions and systemic organic diseases, there was no intellectual disability and no psychological disturbances. Additionally, eye position was examined by the occlusion method. The ciliary muscle was paralyzed using 1% atropine eye ointment twice daily for three days. Computer optometry and retinoscopy were performed and appropriate spectacles were prescribed.
•
After the children used the spectacles for three months, we used the binocular vision perception examination and assessment system to test the binocular stereopsis function in the outpatient clinic. The children underwent short-term binocular visual plasticity training based on the results of the visual function examination, for 20 min per day (specific schedule: 10 min training, 30 min rest, and then 10 min training) for 10 days. We compared the visual function parameters before and after training.
•
Visual acuity: The best-corrected visual acuity before and after training was checked with a standard logarithmic visual acuity chart and was converted to logMAR visual acuity.
•
Visual perception was examined, and this included: (1) Perceptual eye position, (2) Binocular suppression degree, (3) Fine stereopsis: (Zero-order stereopsis), and (4) Dynamic stereopsis (First-order stereopsis).
•
According to the results of the visual information processing test, the defects during processing were initially evaluated, targeted, and then individualized training was developed based on the corresponding training model.

2.3 Statistical analysis

We used SPSS 26.0 software to analyze the data, and the change in visual acuity before and after training was evaluated with the group $t$ -test, and $<$ 0.05 was considered a statistically significant difference. Additionally, the $\chi^{2}$ test was used to compare the differences between groups, and a difference of $<$ 0.05 was considered statistically significant.

3. Results

3.1 Changes in visual acuity values before and after treatment

As shown in Table 1, we observed statistically significant differences in the best-corrected visual acuity of patients before and after training ( $P<$ 0.05). Specifically, the best-corrected visual acuity of patients after training was superior to that before training.

Table 1
Comparison of spectacle-corrected visual acuity before and after training (LogMAR)

	Right eye	Left eye
Before training	0.19 $\pm$ 0.14	0.18 $\pm$ 0.09
After training	0.16 $\pm$ 0.12	0.06 $\pm$ 0.10
$t$	13.35	17.43
$P$	0.000	0.000

Table 2

Perceived eye position before and after training

	Horizontal	Vertical
Before training	42.17 $\pm$ 54.78	8.78 $\pm$ 14.27
After training	26.53 $\pm$ 23.09	4.78 $\pm$ 3.21
$t$	3.40	2.85
$P$	0.001	0.005

As shown in Table 3, there were 81 patients (71.1%) without binocular suppression after training and this was higher than 65 patients (57.0%) without binocular suppression before training, showing an improvement in binocular suppression of patients after training but the difference was not statistically significant ( $P<$ 0.05).

There were 81 cases (71.1%) where 4 ${}^{\text{th}}$ order fine stereopsis existed after training which was higher than 65 cases (57.0%) with 4 ${}^{\text{th}}$ order fine stereopsis before training, and the differences were statistically significant ( $P<$ 0.05), as shown in Table 4.

3.2 The results of the visual information processing test

As seen in Table 2, we found that both horizontal and vertical perceptual eye positions after training were improved compared with pre-operative levels, with statistically significant differences (both $P<$ 0.05).

Table 3
Comparison of suppression degree before and after training (cases/percentage)

	No	Yes
Before training	65 (57.0%)	49 (43.0%)
After training	81 (71.1%)	29 (28.9%)
$t$	4.875
$P$	0.038

Table 4

Comparison of fine stereopsis before and after training (cases/percentage)

	Level 0	Level 1	Level 2	Level 3	Level 4
Before training	27 (23.7%)	8 (7.0%)	6 (5.3%)	8 (7.0%)	65 (57.0%)
After training	18 (15.8%)	3 (2.6%)	1 (0.9%)	11 (9.6%)	81 (71.1%)
$X^{2}$	9.87
$P$	0.043

Table 5

Comparison of dynamic stereopsis before and after training (cases/percentage)

	Non-passing at high speed	Passing at high speed	Passing at low speed
Before training	14 (12.3)	12 (10.5)	88 (77.2)
After training	6 (5.3)	5 (4.4)	103 (90.4)
$X^{2}$	7.26
$P$	0.027

Data in Table 5 shows that 103 patients (90.4%) passed with dynamic stereopsis at low speeds after training which was higher than 88 patients (77.2%) that passed with dynamic stereopsis at low speeds before training, and the difference was not statistically significant ( $P>$ 0.05).

4. Discussion

4.1 Plasticity in amblyopic children

Previous reports indicated that the sensitive period of human visual development was before the age of 12 years, beyond which visual plasticity no longer existed and it was difficult to recover visual function impairment [8]. However, recent research has revealed that the plasticity period of the human visual system may be longer [9], and that plasticity of the visual cortex can be reactivated through pharmacological treatment and environmental enrichment-based visual perceptual learning and physical exercise [10, 11].

In clinical practice, perceptual learning is the behavioral manifestation of visual plasticity, that is, repeated practice of challenging tasks is associated with marked and sustained enhancements in visual performance [12]. The plasticity of the nervous system, specific visual stimulation, and visual learning training are utilized to activate different visual signaling pathways, correcting and improving the information processing of the nervous system for treating amblyopia [13, 14].

The mechanism of plasticity is of great importance in the diagnosis and treatment of children with amblyopia. Specifically, the theoretical basis for the existence of visual plasticity in children with amblyopia might provide a novel approach for the treatment of amblyopia, and visual plasticity can be a practical tool to correct clinical problems in ophthalmology.

In this study, with 10 days of visual perception training, the spectacle-corrected visual acuity, binocular suppression, and binocular stereopsis of patients improved with statistically significant differences, thus clinically confirming visual plasticity in children with amblyopia. This result provides a novel idea for the clinical treatment of older children or children with refractory or other types of amblyopia such as strabismic amblyopia and anisometropic amblyopia.

4.2 The treatment of amblyopia

Children with amblyopia often develop one or more types of neurological deficits, such as reduced visual acuity, decreased spatial contrast sensitivity, reduced vernier acuity, spatial distortions, abnormal spatial interactions, and contour discrimination deficits. Traditional methods of treating amblyopia in children that have been effective are occlusion therapy, depression therapy, correction with use of spectacles, and fine visual acuity training.

Nevertheless, the human visual system is complex. Furthermore, amblyopia in children is a highly common example of neurological component deficit in the processing of visual perception, which cannot be corrected by glasses or remedied by surgery. Accordingly, individualized treatment systems based on virtual technology, which focus on the use of different techniques to mitigate or correct defects, have been developed for the treatment of amblyopia and their efficacy has been confirmed in numerous clinical studies [15, 16].

In this study, we clinically evaluated binocular interactions and stereoscopic perception of multi-dimensional space of patients with visual information processing deficits using the brain imaging binocular vision training system and binocular visual training method. We designed a suitable treatment plan for each child after finding the corresponding deficits using reasonable prescription principles to gradually improve visual deficits and elevate visual acuity and binocular visual function, thus reconstructing and restoring binocular visual function and increasing visual acuity [17].

In the present study, we found that the spectacle-corrected visual acuity of children with amblyopia improved significantly after visual perception training, and this result is consistent with the findings of Yang et al. [5, 6, 18]. Horizontal perceptual eye position and binocular suppression in children with amblyopia were better after the treatment than before the treatment. This may be because horizontal eye position deficits in children with amblyopia usually manifest as confused relationships between binocular perceptual eye positions accompanied by gaze instability, visual acuity decrease and deficits, monocular suppression, and physiological eye position deficits.

The binocular perceptual eye position and the suppression of the eyes with poor vision in children with amblyopia improved after repeated visual perception training, while the visual acuity and visual performance of the eyes with poor vision substantially increased. These findings suggest that the binocular visual functions such as stereopsis, binocular integration, and binocular interaction could be repaired to the level of perceptual eye position, and the visual acuity of the eyes with poor vision in children with amblyopia was markedly enhanced after the biological model stimulation of binocular visual balance and modular binocular visual training.

Furthermore, in this study, we found that the visual acuity and visual function of children improved after only 10 sessions of visual perception training, and some patients with amblyopia did not have yet have visual functions close to that of their normal peers. Therefore, visual perception training still requires repeated stimulation for acquiring more durable and stable visual acuity and visual function.

5. Conclusion

In this study it was found that visual plasticity existed in children with ametropic amblyopia. Therefore, we used the knowledge of neuroplasticity and short-term visual perception training treatment to regulate the factors in the critical period which effectively improved binocular visual acuity and visual function in children with amblyopia. Nonetheless, in clinical practice we still require different examination models for developing the neurological deficit model of amblyopia to define specific training programs [19]. This training program also has potential to be replicated in other types of patients with amblyopia, such as with older or adult patients with amblyopia.

Ethics approval and consent to participate

The study approved by the Ethics Committee of The People’s Hospital of Guangxi Zhuang Autonomous Region and conducted in accordance with the Declaration of Helsinki. Written informed consent was obtained from all participants.

Competing interests

The authors declare that they have no competing interests.

Funding

None to report.

Data availability statement

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

Footnotes

Acknowledgments

We would like to acknowledge the hard and dedicated work of all staff that implemented the intervention and evaluation components of the study.

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Evaluation of visual plasticity in patients with refractive amblyopia treated using a visual perceptual learning system

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSION:

Keywords

1. Introduction

2. Materials and methods

2.1 Clinical information

2.2 Treatment methods

3. Results

3.1 Changes in visual acuity values before and after treatment

Table 1 Comparison of spectacle-corrected visual acuity before and after training (LogMAR)

Table 3 Comparison of suppression degree before and after training (cases/percentage)

4.1 Plasticity in amblyopic children

4.2 The treatment of amblyopia

5. Conclusion

Ethics approval and consent to participate

Competing interests

Funding

Data availability statement

Footnotes

Acknowledgments

References

Table 1
Comparison of spectacle-corrected visual acuity before and after training (LogMAR)

Table 3
Comparison of suppression degree before and after training (cases/percentage)