Disease Description
The concept of amblyopia is originally derived from the Greek word “amblyopia”, which means retarded vision. The concept of amblyopia has been interpreted and supplemented by experts from different countries in research and practice, and there is a basic consensus that amblyopia is an abnormality of vision in one or both eyes due to visual deprivation and or abnormal binocular interactions, without detectable organic pathology in the eye.
However, the definition of amblyopia is not uniform throughout the world. In China, the definition and diagnostic criteria of amblyopia were first formulated in 1985 by the Strabismic Amblyopia Prevention and Control Group of the Ophthalmology Branch of the Chinese Medical Association, which classified amblyopia as amblyopia with no obvious organic lesions in the eye and with functional factors causing distance visual acuity below 0.9 that cannot be corrected. It also emphasized that children under 6 years of age need to pay attention to the age factor in the diagnosis.
Amblyopia is further classified as mild, moderate or severe according to the level of corrected visual acuity. Visual acuity 0.8~0.6 is mild amblyopia; visual acuity 0.5~0.2 is moderate amblyopia; visual acuity ≤0.1 is severe amblyopia.
Through continuous application and summary in clinical practice for more than 20 years, and with reference to some foreign amblyopia diagnostic criteria, in 2010, the Strabismic Amblyopia Prevention and Treatment Group of the Chinese Medical Association Ophthalmology Branch supplemented the definition of amblyopia in the form of a new consensus. The definition of amblyopia is that the best corrected visual acuity of one or both eyes is lower than the corresponding age visual acuity, or the visual acuity of both eyes differs by two lines or more, due to monocular strabismus, uncorrected refractive error and high refractive error and form deprivation during the visual development period. It also gives the lower limit of visual acuity reference value for each age of developing children, i.e., not less than 0.5 for 3-5 years old; not less than 0.7 for 6 years old and above.
Morbidity
The prevalence of amblyopia in the population varies from country to country, ranging from 1-4%. This means that among the 400 million children in China, there are more than 10 million people with amblyopia.
Pathogenesis and classification
The classification of amblyopia is internationally different, but a more practical and accepted classification is to classify amblyopia into strabismic amblyopia, refractive amblyopia, refractive error amblyopia, and form deprivation amblyopia.
Strabismic amblyopia
The patient has strabismus or had strabismus. In order to eliminate or overcome the diplopia caused by strabismus, the visual cortical center of the brain suppresses the visual impulses from the strabismic eye. The long-term inhibition of macular function in the strabismic eye leads to amblyopia. This amblyopia is a consequence of strabismus and is secondary.
Refractive Amblyopia
Refractive amblyopia (anisometropic amblyuopia) is a condition in which the refraction of both eyes is unequal and is called refractive amblyopia. Due to the large difference in refractive error between the two eyes, the clarity of the image formed in the macula of the two eyes is different, or, even after wearing glasses to correct the refractive error, the size of the image formed in the macula of the two eyes is obviously unequal, resulting in the image not being fused into one image, and the visual center of the brain can only suppress the image from the eye with the larger refractive error, and amblyopia occurs in that eye over time. Amblyopia can easily occur when the difference between the two eyes is ≥1.5D for spherical lens and ≥1.0D for column lens.
Refractive amblyopia (ametroic amblyopia)
Ametropic amblyopia occurs in patients with high refractive error who have not worn corrective lenses, especially in those with high hyperopia or astigmatism. It is mostly bilateral, with similar vision in both eyes. The prognosis is good because the visual acuity can be improved gradually with appropriate glasses. Hyperopia ≥ 3.0D, myopia ≥ 6.0D and astigmatism ≥ 2.0D are prone to amblyopia.
Form deprivation amblyopia
Form deprivation amblyopia is caused by insufficient retinal macular disuse or stimulation. Amblyopia occurs in children with corneal opacities, ptosis, congenital cataracts, or long-term inappropriate coverage of one eye, where the macula cannot receive normal light stimulation to form a clear image because light does not enter the eye sufficiently. Morphological deprivation amblyopia can be unilateral or bilateral and is often combined with strabismus or nystagmus. This type of amblyopia not only has poor visual acuity, but also has a poor prognosis.
Pathophysiology
However, in animal models of form-deprived amblyopia and in human autopsies of amblyopia, evidence of structural abnormalities has been found at the level of the cerebral visual cortex and lateral geniculate body. Research into the pathogenesis of amblyopia will continue to be a topic of exploration for vision professionals.
Clinical features
(a) Visual acuity is lower than normal, not only in the bare eye but also in corrected visual acuity and meets the diagnostic criteria for amblyopia.
(b) Visual “crowding”, i.e., the amblyopic eye’s ability to recognize individual visual letters is significantly higher than the ability to recognize rows of letters. For example, if the child is shown only a single letter of the letter E in a row of 0.3, the amblyopic eye can easily recognize it, but once the letter E is shown in a row, the amblyopic eye has difficulty in identifying the direction of the opening.
(iii) The amblyopic eye has reduced contrast sensitivity
(iv) Electrophysiological changes in the amblyopic eye, with prolonged P100 wave latency and reduced amplitude of visual evoked potentials.
(v) Abnormal gaze properties. In normal people, the object falls in the macula of both eyes and forms clear vision when looking at the target. In patients with amblyopia, some of them do not take the central concave gaze, and the projection microscopy can reveal paracentral concave gaze, macular gaze and peripheral gaze. The more the gaze point deviates from the macular sulcus, the lower the visual acuity and the more difficult it is to treat.
(f) Abnormal visual function of both eyes. Amblyopia not only causes low visual acuity, but also endangers the normal development of binocular visual function, resulting in tertiary visual function defects. For example, near stereopsis abnormalities such as Titmus or TNO, or, after visual function examination with a simultaneous vision machine, the child is found to have no Class III stereopsis, a small range of Class II fusion function or inability to fuse, or even no Class I simultaneous vision function. Binocular vision is an advanced visual function that humans possess to ensure that the two eyes work together and play their proper role in working life. Impairment or loss of this function will affect a person’s quality of learning, life and work.
Clinical Examination
Visual acuity examination
Naked and corrected visual acuity is the first information that the doctor should obtain. Once corrective eyeglasses are worn, only corrected vision is usually sufficient for follow-up examinations.
Eye position and eye movement function examination
This is used to exclude strabismus and eye muscle abnormalities.
Anterior segment of the eye and fundus examination
This is a routine ophthalmic examination to exclude organic eye disease. The fundus examination is particularly important to examine the nature of gaze.
Refractive status examination
This is mainly a dilated pupil examination. The purpose of dilated pupil examination is to understand the nature and degree of refractive error, the presence of refractive aberrations, and the corrected visual acuity of the patient, which is an essential routine examination for the diagnosis of amblyopia. At the same time, for patients with corrective refractive errors, getting the correct prescription for glasses through dilated eye examinations and fitting the right glasses is the prerequisite and primary method for amblyopia treatment.
Other eye examinations
This includes all examinations of the ophthalmology specialty. After the basic examination as above, if further exclusion of other eye problems is necessary, other ophthalmic examinations can be selected for further detailed investigation. Examples include intraocular pressure measurement, fundus photography, fundus fluorescence angiography, OCT, corneal topography, etc.
Systemic examination and imaging
Examination of the whole body.
Diagnosis and differential diagnosis
The diagnosis of amblyopia needs to be strictly in accordance with the definition and classification criteria of amblyopia in China, and attention should be paid to the identification of low vision caused by organic lesions. Before the diagnosis of amblyopia in children, special attention should be paid to differentiate it from retinitis pigmentosa, yolk-like macular degeneration, Stagard’s disease, optic cone optic rod cell dystrophy, leber’s disease, uveitis, optic nerve or macular dysplasia, etc. In clinical practice, we sometimes encounter children whose vision does not increase or even progressively decreases after long-term treatment for amblyopia in outside hospitals, but after careful examination in our hospital, they are diagnosed with Stagard’s disease, retinitis pigmentosa and other fundus pathologies.
Treatment of the disease
Amblyopia should be treated as early as possible, and the effectiveness of treatment is related to the age of onset and the age at which treatment begins. There is a possibility of recurrence after amblyopia is cured. Early detection and early treatment should be pursued, and observation should be continued for 2-3 years after cure.
The first step in the treatment of amblyopia is to dilate the pupil and fit the patient with appropriate glasses. After that, coverings and other treatments will be chosen according to the patient’s specific situation.
Refractive correction principles
1. For patients with internal strabismus, the first prescription for farsighted eyes should be fully corrected, while myopic eyes should be given a low prescription to obtain the best visual acuity.
2.Patients with exotropia, farsightedness ≤ +2.5D generally do not need prescriptions; >+2.5D are prescribed to obtain the best visual acuity with low prescriptions, the amount of reduction generally does not exceed 1/3. myopic eyes are fully corrected according to the results of optometry.
3, not with strabismus patients, generally according to the best corrected visual acuity, according to the refractive error reduction 1/3 to 1/4 to determine the glasses prescription.
Masking therapy
Covering the healthy eye and forcing the amblyopic eye to gaze. It is the preferred method of treatment for amblyopia and is suitable for patients with central and paracentral gaze.
1.Regular masking: all-day masking, with the number of days between masking and opening determined by age and visual acuity.
2.Part-time masking: Covering the healthy eye for several hours a day.
3.Incomplete coverage: A translucent film is attached to the healthy eye lens so that the vision of the healthy eye is more than 2 lines below the vision of the amblyopic eye.
The choice of masking method will be decided by the professional doctor according to the patient’s specific situation.
In addition to masking therapy, fine training such as needle threading, tracing, plate tying, amblyopia apparatus or training CD-ROM, fine visual work in software, etc. can be used to help the amblyopic eye improve its visual acuity.
Visual stimulation therapy (CAM visual stimulator treatment)
1, usually not covered, only cover the healthy eye when treatment, or two amblyopic eyes are covered separately for non-covered eye training. Usually 7-10 minutes of training at a time.
2. Suitable for patients with macular central sulcus amblyopia, mild to moderate amblyopia, and amblyopia with myopic eyes. The best results are achieved in binocular refractive error amblyopia.
Other treatment methods
1, suppression therapy: the use of overcorrected or undercorrected lenses and daily drops of atropine eye ointment to suppress the function of the healthy eye, and the amblyopic eye wears normal corrective lenses to see far or wears overcorrected lenses to see near. The advantage of this treatment is that it can prevent masking amblyopia without covering the eye; it is also suitable for patients with occult nystagmus amblyopia, but the disadvantage is that the course of treatment is long and expensive, and it is not as effective as traditional masking.
2.Posterior image therapy: Using strong light to dazzle the peripheral part of the retina of the paracentral gaze eye, including the paracentral gaze area, so as to produce inhibition, and at the same time using black discs to shield the macula to protect it from the glare of strong light, and then training under indoor flash light to improve the macular function of the amblyopic eye, this therapy is called vision enhancement therapy. During the treatment period, the amblyopic eye should also be covered on weekdays to prevent consolidation of paracentral gaze. The healthy eye is covered during treatment. After each treatment, the paracentral gaze eye is still covered, and after the amblyopic eye is converted to central gaze, the treatment is continued with the traditional masking method. Posterior image therapy was very popular around 1950, but is rarely used today because it is labor-intensive, time-consuming, expensive, and not suitable for preschoolers. It is also very difficult to achieve results without proper operation.
3, red filter therapy: basically no longer used.
Comprehensive treatment of amblyopia
According to the type and degree of amblyopia, the nature of the gaze, the patient’s age, previous treatment, etc., a set of comprehensive treatment for patients is often better than a single treatment can achieve better results. The development and efficacy of a combination therapy depends on the professional experience of the physician, the level of care in the hospital, and the compliance of the patient and parents.
Medication
In recent years, there have been medical attempts to treat amblyopia with medications, and some results have been reported, especially in older amblyopic patients, who are willing to try some oral medications as an adjunct to amblyopia treatment. The exact efficacy and mechanism of treatment remain to be further studied.
Treatment considerations
1. Covering the eye: This is a very specific and practical issue, which is related to the effectiveness of masking therapy. First of all, covering the healthy eye must be strict and thorough, and the eye shield must be impervious to light. It is best to use non-irritating eye patches to tighten the skin around the eyes without leaving gaps to prevent peeking of the affected child’s healthy eyes. When using eye shields, the gap around the eye should also be narrowed as much as possible.
2. Be alert to the occurrence of masked amblyopia: Follow-up examinations should be reinforced during the masking period. It is important to check the visual acuity of the healthy eye at each follow-up visit to be on the alert for the occurrence of masked amblyopia. In infancy and early childhood, a brief masking of one eye may also cause similar form deprivation amblyopia, so special attention should be paid.
3.Strabismus: If there is no strabismus or only intermittent strabismus before treatment, constant strabismus (acute strabismus) may occur after masking therapy. After opening both eyes for a period of time, the internal strabismus can disappear on its own. After transient masking of the healthy eye, both eyes can be maintained in an orthotropic position, and the visual acuity is improved.
4. Amblyopia recurrence: The biggest problem of amblyopia treatment is how to consolidate the effect and prevent recurrence. Before the development of vision, every cured amblyopia patient may have a relapse. All cured amblyopes should be followed up until visual maturity. We believe that a 3-year follow-up period is appropriate for the cure of amblyopia.
The main reason for recurrence is that the patient does not follow the doctor’s orders for regular follow-up, or opens the healthy eye on his own before the normal vision obtained has been consolidated.
In order to maintain the effect of treatment, the eye can be opened gradually after the amblyopia is cured; or the eye can be covered with a translucent film for a period of time so that the vision of the eye is more than 2 lines lower than that of the amblyopic eye, in order to maintain the vision obtained in the amblyopic eye.
If the visual acuity of the amblyopic eye does decrease again, the eye can be covered again, and the visual acuity of the amblyopic eye can be gradually improved to the original level. At the same time, the monocular function training should be strengthened to consolidate the treatment effect.
Parents’ cooperation: Parents’ concern and active cooperation are related to the success or failure of amblyopia treatment. Parents should be informed of the hazards of amblyopia, its reversibility, treatment methods and possible situations during the initial consultation, so that they can get twice the result with half the effort. Adherence to medical prescriptions, regular attendance, supervision of the child’s homework, and timely reporting of problems are all beneficial and necessary measures to promote successful treatment.
Prognosis of the disease
Amblyopia occurs early in visual development as a result of an imbalance in the input of visual stimuli from both eyes, with the dominant eye becoming the healthy eye and the inferior eye becoming the amblyopic eye. The outcome of amblyopia treatment is closely related to age, and the younger the age, the better the outcome and the greater the likelihood of functional cure. In addition, the effectiveness of amblyopia treatment is also closely related to the nature, degree and nature of amblyopia gaze. Early onset, late treatment, heavy degree, and paracentral gaze have a long course and poor prognosis. Poor compliance with treatment is also a common reason for poor outcomes. Amblyopia treatment emphasizes early detection, timely and reasonable treatment, and cure in adulthood is basically hopeless. The best results should be achieved by actively treating amblyopia in preschool, a period of high plasticity in visual development.
Disease prevention
Early detection, early diagnosis, and early treatment are the only ways to achieve the best results in amblyopia treatment and to create a chance for complete cure. Therefore, popularizing knowledge about visual development, conducting early and regular vision screening in maternal and child health institutions and early childhood education systems, and establishing a reasonable and standardized referral mechanism so that children with low vision can be examined and treated in a timely manner are important measures and effective means of amblyopia prevention and treatment.