According to the definition proposed in 2017, amblyopia is a developmental disorder. But in the definition, the description is too disordered and illogical. So we proposed a more distinct notion to explain what amblyopia is:
During the period of visual development, due to the visual signal afferent disorder, insufficient effective stimulation in fovea macula, or macular dysplasia, the development of binocular visual function is lower than that of normal children of the same age or the difference of binocular vision is more than 2 lines, which is called amblyopia.
In this notion, there are there core elements:
The important period of visual development. It can be divided into critical period (from born to 3 years old) and sensitive period (from 3 to 12 years old). In the two periods, visual development is not mature and has strong plasticity. The younger the child is, the stronger the plasticity is, the easier to form amblyopia, and the better the therapeutic effect is. That’s why success rates of amblyopia treatment decline with increasing age.[3, 4] Which can be also provided by the data in our study.
Visual signal: Light, shape, and color.
Effective (intense, sustained, and stable) stimulation in fovea macula. That is, sustained and stable clear imaging focusing on the central fovea of macula in retina.
In this notion, we concentrate on the development of visual centre, also called “Brain Vision”. It can be explained that visual acuity depends on optical imaging of the retina, which has positive correlation with diopter, conduction of the optic nerve, which can lead different visual acuity with same diopter, and analysis of the cerebral cortex, which make difference in diopter with same visual acuity, and problems at any point can affect vision development. This is also a guide to many emerging treatments, such as perceptual learning, transcranial magnetic stimulation (TMS), and so on.[1, 5–7] And the amblyopic training program in our study is designed according to this principle.
Based on the new notion, we can divide amblyopia into 3 classes:
(1) Afferent disorder of visual signal: At the critical stage of infant visual development, because of afferent disorder of visual signal, stimulation of macula is insufficient, which will lead poor development of visual centre, and then cause amblyopia. This kind of amblyopia mainly caused by congenital cataract, opacitas corneae, infectious or non-infectious endophthalmitis, vitreous hemorrhage and ptosis.
(2) Abnormal focus site of visual signal: At the critical and sensitive stage of visual development, because visual signal focus deviates from macular area, the weak intensity of visual signals in the central fovea will affect the development of visual centre, and then cause amblyopia, like strabismus and nystagmus.
(3) Poor macular focusing of visual signal: At the critical and sensitive stage of visual development, because of failure to match corrective glasses in time, the image of the retina remains blurred, and stimulation of macula is insufficient, which then lead poor development of visual centre, and cause amblyopia. This kind of amblyopia is mainly caused by anisometropia and ametropia. In anisometropia patients, because the size of binocular retinal imaging is different, it’s difficult for visual centre to fuse the different images, so that it will actively inhibit the image in the eye with high diopter causing insufficient stimulation of macula in the eye, and then forming amblyopia. The degree of anisometropia is positively correlated with the probability and severity of amblyopia. In patients with ametropia, hyperopia will make the light focus behind the retina, and astigmatism can lead a zonal focusing on the retina, both of which can cause low intensity of visual signals in the fovea and increase risk of amblyopia. While myopia often has a good focus when looking near, and make the stimulation of macular visual signal close to normal, which decrease the risk of amblyopia.
So, based on the new classification, the basic treatment of amblyopia can be directed:
Afferent disorder of visual signal: Etiological treatment. The first stage is to remove afferent disorders through early surgery or other treatment. Only after removing afferent disorders, the visual signal can reach the central fovea, and then stimulate the development of cerebral optic cortex, avoiding amblyopia.
Abnormal focus site of visual signal: In this condition, the focus site of visual signal should be corrected to the central fovea firstly. After which, the visual signal can stimulate central fovea effectively, and then promote visual development. For example, when a patient is diagnosed with strabismus, the first thing to do is to correct the eye position by wearing glasses or surgery.
Poor macular focusing of visual signal: In order to make the light focus on the retina, refractive correction must be performed. According this principle, we consider to get the maximum plus to maximum visual acuity (MPMVA), in which condition, the image can be clearly presented on the retina.
And after the primary principle, the following steps are similar which can be divided into daily life training and professional amblyopia training. Daily life training, which means to promote use of the amblyopic eye by occluding or blurring the fellow eye in daily life, mainly contains patching and pharmacological treatment.[1, 7–9] Professional amblyopia training mainly contains perceptual learning, video gaming, dichoptic training, transcranial magnetic stimulation, acupuncture, et al.[1, 9], meaning to promote cerebral development, elevate visual acuity, and improve visual function by special training. And only after a combination of the above steps, amblyopia can be better improved.
So, according to the treatment principle of amblyopia with poor macular focusing of visual signal, we designed this study. According to the result, we can see that the treatment following the principle is effective. But we have to say it was a pity that there was no contrast group. And the studies that therapy the refractive amblyopia by full correction and under correction were short of the amblyopic training in our study, which made there is no comparability between these studies.