I. Basic understanding of amblyopia
Amblyopia training is a long-term systematic treatment, and among the various treatment methods for amblyopia, the masking method is the most important, cost-effective and long-standing method, and its efficacy has been confirmed by a large number of studies and clinical practice. However, for clinical practitioners, the types and methods of masking are flexible and cannot be generalized, and not all patients with amblyopia can be treated with the masking method, which can even be counterproductive if not done properly. The drawback of the masking method is the poor compliance, but sometimes the flexibility of the masking method can greatly improve the compliance of patients and their families while ensuring the efficacy of the treatment. This makes the treatment more accessible.
1. Definition of amblyopia
Amblyopia is defined as a condition in which the corrected visual acuity is less than 0 or 8 or the difference in visual acuity between the two eyes is more than two rows due to functional factors without obvious organic lesions. However, this definition is not very reasonable and overemphasizes monocular vision. Amblyopia is a developmental disorder and degeneration in which the visual system is disturbed, hindered and inhibited by the lack of visual stimulation. This includes shape, color, light, and stereoacuity.
2.The classification of amblyopia
According to the general causes of amblyopia, amblyopia will be divided into strabismic amblyopia, refractive error amblyopia, refractive parallax amblyopia and form deprivation amblyopia.
3.Treatment of amblyopia
The treatment of amblyopia should be characterized first. Refractive correction, masking therapy, suppression therapy and visual stimulation therapy are usually used for central gaze amblyopia. Paracentral gaze amblyopia is usually treated with posterior image therapy, red filter therapy, Hedinger light brush therapy, traditional masking method and medication, etc. In this paper, we only discuss masking therapy.
II. Amblyopia masking therapy
1.Overview of masking therapy
Using an opaque mask (or eye patch) to cover the healthy eye and open the amblyopic eye. Deprive the healthy eye of form stimulation and give only the amblyopic eye form stimulation. Improve and exercise the competitiveness of the amblyopic eye to remove the inhibition of the healthy eye. The key to the masking method is that it requires the cooperation of the patient and strict adherence to the method of operation and the duration of masking in order to rapidly improve visual acuity. Masking therapy can reduce the stimulation of abnormal retinal correspondence and effectively transform paracentral gaze into central gaze.
2.Applicable objects of masking therapy
Masking therapy is mainly applied to patients with strabismus, refractive parallax and amblyopia with a difference in visual acuity of more than two lines in both eyes.
3.Classification of masking therapy
a. According to the purpose of masking, there are therapeutic masking, preventive masking and inversion masking.
Therapeutic masking: mainly refers to covering the dominant eye and forcing the amblyopic eye to gaze in order to make it develop rapidly to the same visual acuity as the dominant eye in a short period of time through high-dose high-intensity visual stimulation of the amblyopic eye.
Prophylactic masking: Adjustment of visual acuity by alternate masking or gradual masking to make the visual acuity of both eyes equal.
Inverted masking method: for paracentral gaze amblyopia, try to cover the amblyopic eye first to make it change to central gaze, and then change to traditional masking method.
b. According to the covering method, there are monocular covering method, alternate covering method and intermittent covering method.
Monocular masking method; applicable to patients with refractive amblyopia and strabismic amblyopia. For patients under 3 years old, they can be continuously covered for 3 days and opened for 1 day; for patients over 3 years old, they can be continuously covered for 3~5 days and opened for 1 day, and rechecked every month.
Alternate masking method: Applicable to refractive amblyopia and monocular strabismic amblyopia or binocular visual acuity inequality. This method is based on the different corrected visual acuity of both eyes using 4:1 or 5:1 method of masking, so that the visual acuity of both eyes will rise in balance.
Intermittent masking method: For those with central gaze, masking can be performed intermittently to suit different needs. Some doctors advocate that the masking should be performed intermittently and full masking should be used for a short period of time, and the masking can be stopped if the vision of the healthy eye decreases during the review and continued after the vision returns.
c, according to the degree of coverage is divided into complete coverage method, incomplete coverage method, gradual coverage method, micro-coverage method.
Complete masking method: refers to full-day masking, but attention should be paid to prevent the emergence of masking amblyopia. 3~4 years old children need to open the mask for 4~5 days; 4~6 years old children need to open the mask for 5~6 days; 6 years old and above can be relaxed appropriately.
Incomplete masking method: Covering for several hours in a day, or covering the dominant eye with different transparent coverings, so that the visual acuity of the dominant eye is lower than that of the amblyopic eye, so that the masking is beneficial to the establishment of binocular vision, but the incomplete masking method is applicable to those with corrected visual acuity of 0, 7 or above.
Gradual masking method: It is to cover the dominant eye with different transparency of the mask, which can be adjusted to achieve the purpose of controlling different degrees of corrected visual acuity.
Micro-covering method: It is applicable to those whose corrected visual acuity is basically restored to normal but lower than normal, for example, after the visual acuity has reached 1 or 0, the covering dose should be reduced instead of stopping covering immediately, so as to help consolidate the therapeutic effect and prevent recurrence.
Third, the choice of masking time
1.The time of covering every day
So far, there is no clear rule on how long the daily coverage should be, there is support for full-day coverage and there are reports that partial coverage can be used. At present, there are three aspects to consider clinically: a. From the assessment of efficacy, it has been reported that there is no significant difference between the efficacy of full-day coverage and partial coverage, and there is no significant difference in the effect on the visual acuity of the healthy eye within the same time, but the main issue to consider is compliance, therefore, if there is no problem with compliance, it is better to choose full-day coverage, and the so-called full-day coverage is not easy for children. C. From the stage of masking treatment, when the visual acuity is poor at the beginning, in order to restore the visual acuity of the amblyopic eye in a short time and make the visual acuity of both eyes comparable, full day masking is recommended. The full-day masking is advocated. When the corrected visual acuity is better close to normal or has reached normal, the amount of daily coverage can be reduced appropriately, which does not affect the treatment effect and the patient is happy to accept.
2.Total covering time
There is no exact rule on how much total masking time should be. Usually, as long as the diagnosis is accurate, the prescription luminosity is reasonable, and the effect is most obvious within 6 months with the masking treatment, it is usually believed that the ideal total masking time is 400 hours, no matter it is full day masking or short time masking.
3.Termination of covering time
For when to stop the masking, it is generally believed that there are four situations: a. Both eyes can alternately gaze; b. After the masking to improve the visual acuity of the amblyopic eye to equal vision in both eyes; c. After strict masking, the visual acuity of the dominant eye decreases should stop the masking or reduce the masking time and adjust the masking scheme; d. Strictly masking the healthy eye for 3 months, but the visual acuity of the amblyopic eye does not see any improvement, should stop the masking.
IV. Covering precautions
For general patients, the purpose of masking is to eliminate the inhibition of the amblyopic eye by the dominant eye, so that the amblyopic eye can recover to the same visual acuity as the dominant eye in a short time. Therefore, in most cases, the masking of the dominant eye should be strictly and thoroughly performed.
In children of different ages, considering that the visual acuity of the dominant eye is also in the developmental stage despite the amblyopia, masking will inevitably cause a decrease in the visual acuity of the dominant eye. Therefore, while covering the dominant eye, it is important to develop different masking plans for children of different ages. Regular review should be done to prevent the loss of visual acuity in the dominant eye. If there is a decrease, the masking should be stopped or the masking scheme should be adjusted.
Masking should not be used for patients with occult nystagmus, as masking will only increase the magnitude of the nystagmus. Consideration should be given to the use of suppression therapy.
V. Evaluation of masking therapy
The main characteristics of masking therapy are: good efficacy, low cost, affects appearance, poor compliance, and can cause masking amblyopia. The masking depends on different refractive conditions, different corrected visual acuity, and different nature of gaze.
Conclusion: Amblyopia is a common eye disease during childhood development, and its prevention and treatment are very important. It is characterized by the plastic stage of human visual development, and as long as it is detected early and a reasonable treatment plan is used in a timely manner, most patients can achieve satisfactory results. Among them, the efficacy of the masking method is certain, for different patients according to different circumstances using different masking programs, which include different masking time, different masking length, different courses of treatment, different ways, depending on the patient’s compliance, the nature and type of amblyopia to be treated.