I. Overview
Amblyopia has a prevalence of 2% to 4% and is a visual development-related disease, so understanding visual development is important for the diagnosis, treatment and prevention of amblyopia.
1. Amblyopia.
It is the best corrected vision loss in one or both eyes caused by abnormal visual experience (monocular strabismus, refractive aberration, high refractive error and form deprivation) during the visual development period, without organic lesions on eye examination.
2.Children’s visual development.
Children’s vision is gradually developed and matured, the critical period of children’s visual development is from 0 to 3 years old, the sensitive period is from 0 to 12 years old, and binocular visual development is matured from 6 to 8 years old. Different developmental stages not only differ in visual acuity, but also in the normal values of visual acuity detected by different examination methods (Table 17-3). From the signs of different stages of visual development, it can be seen that the age factor should be paid attention to when diagnosing amblyopia.
3. Amblyopia diagnostic criteria.
The Strabismus and Pediatric Ophthalmology Group in China had proposed 0.8 detected by the International Standard Visual Acuity Scale as the diagnostic standard for amblyopia in 1987, and suggested that the age factor should be paid attention to in the diagnosis of amblyopia. Similar criteria have been proposed in foreign countries during the same period. In recent years, many countries have proposed amblyopia diagnosis and referral criteria related to visual development based on clinical studies. In China, similar problems exist in the practice of amblyopia prevention and treatment, that is, some doctors or health care workers only use the criterion of 0.8 regardless of age and do not pay attention to the presence of risk factors causing amblyopia (monocular strabismus, refractive aberration, high refractive error and form deprivation, etc.), and diagnose and treat anyone with best corrected visual acuity below 0.8, which has a tendency to generalize the diagnosis of amblyopia.
The lower limit of normal visual acuity for children of different ages should be taken into account when diagnosing amblyopia: 0.5 for 3-year-olds, 0.6 for 4-5-year-olds, 0.7 for 6-7-year-olds, and 0.8 for 7-year-olds and above. 2 or more lines of difference between the best corrected visual acuity of the two eyes and the worse one is amblyopia. If a child’s visual acuity is not lower than the lower limit of normal visual acuity for children of the same age, and the difference in visual acuity between the two eyes is less than 2 lines, and no risk factors for amblyopia are found, it is not appropriate to make a hasty diagnosis of amblyopia, and it can be included as a subject of observation.
4. Screening and prevention of amblyopia.
A population-based randomized controlled study abroad found that the prevalence of amblyopia in the enhanced screening group (screened 5 times between birth and 37 months) was lower than that in the control group (screened 1 time at 37 months), 0.6% and 1.8%, respectively, with significant differences; the mean visual acuity of the worse eye in the enhanced group was better than that in the control group, and the proportion of amblyopia treated in the eye clinic before age 3 was higher than that in the control group (48% and 13%). data strongly support that early intensive screening can reduce the prevalence of amblyopia and mitigate the degree of amblyopia.
Classification
Strabismic amblyopia: occurs in monocular strabismus, and alternating binocular strabismus does not form strabismic amblyopia. Due to the abnormal binocular interaction caused by eye position deviation, the macular central sulcus of the strabismic eye receives different object images (confusion vision) is suppressed, resulting in a decrease in the best corrected visual acuity of the strabismic eye.
2, refractive parallax amblyopia: due to the large refractive parallax between the two eyes, the macula forms an object image of unequal size and clarity, and the refractive power of the larger eye has form deprivation, resulting in refractive parallax amblyopia. The difference between the two eyes is 1.5DS in the spherical lens and 1.0DC in the column lens, which can cause amblyopia to form in one eye with higher refractive error.
3, refractive amblyopia: mostly occurs in patients with high refractive error who have not worn refractive correction glasses. Mainly seen in high hyperopia or astigmatism, often bilateral, the best corrected visual acuity in both eyes is equal or similar. It is generally believed that hyperopia ≥ 5.00DS, astigmatism ≥ 2.00DC, and myopia ≥ 10DS increase the risk of amblyopia.
4. Form deprivation amblyopia: It occurs in children with refractive interstitial clouding (e.g., congenital cataracts, corneal clouding), complete ptosis, and medically induced eyelid suture or masking. Amblyopia develops due to inadequate form stimulation, depriving the macula of the opportunity to form a clear image of the object. Deprivation amblyopia can be unilateral or bilateral, with unilateral being more severe than bilateral. The time required for the development of form-deprived amblyopia is shorter than that required for the development of strabismic amblyopia, refractive error, and refractive amblyopia. Even brief monocular coverage in infants and young children can cause deprivation amblyopia, and some studies have shown that seven days of inappropriate monocular coverage can lead to irreversible amblyopia. Inappropriate monocular coverage should be avoided during the critical period of visual development.
The pathogenesis of amblyopia
The pathogenesis of amblyopia is extremely complex, and von Noorden summarized the results of his own and other laboratories’ research to explain the pathogenesis of amblyopia clinically by two theories: abnormal binocular interactions and form deprivation (Table 17-5).
IV. Clinical examination of amblyopia
1.Visual acuity examination.
2.Refractive status examination: ciliary muscle paralysis followed by photometry to obtain an accurate refraction number.
3.Nature of gaze examination: the central sulcus reflex under the direct examination lens is located in the 0~1 ring for central gaze, 2~3 rings for paracentral sulcus gaze, 4~5 rings for macular gaze, and 5 rings for peripheral gaze.
4, electrophysiological examination: visual evoked potential (VEP) includes pattern reversal visual evoked potentioals (P-VEP) and flash visual evoked potential (F-VEP). potential (F-VEP), which is mainly used to determine disorders of the optic nerve and visual conduction pathway, and is manifested by prolonged latency and decreased amplitude of P100 waves in amblyopic eyes. The F-VEP test is available for infants and children.
V. Treatment of amblyopia
Once amblyopia is diagnosed, it should be treated immediately, otherwise it will become very difficult to treat amblyopia when the age exceeds the sensitive period of visual development. The efficacy of amblyopia treatment is related to the timing of treatment, the earlier the onset, the later the treatment, the worse the efficacy. The basic strategy for treating amblyopia is precise prescription and masking of the dominant eye.
1.Elimination of the cause: correction of refractive error, early treatment of congenital cataract or congenital complete ptosis, etc.
2. Covering treatment: Conventional covering treatment, i.e., covering the dominant eye, has been used for more than 200 years to force amblyopic eyes and is still the most effective treatment for monocular amblyopia. When using the masking method, the change in visual acuity of the masked eye must be closely observed to avoid the occurrence of masking amblyopia in the masked eye. The follow-up time is determined by the age of the child, and the younger the child, the shorter the follow-up interval: 1 week for 1-year-old children, 2 weeks for 2-year-old children, and only 1 month for 4-year-old children. Because amblyopia treatment is easy to repeat, after the vision balance of both eyes, we should gradually reduce the masking time and slowly stop the masking treatment in order to consolidate the therapeutic effect.
3, optical drug therapy (suppression therapy): research found that patients with low to moderate refractive aberration, using one eye to see far, the other eye to see near, not formed amblyopia. Based on this finding, artificially causing one eye to see far and one eye to see near is the basis of repression therapy for amblyopia. It is suitable for children with moderate or low monocular amblyopia and poor compliance with masking therapy.
(1) Brachytherapy. For children with best corrected visual acuity ≤ 0.3. The dominant eye is dilated with 1% atropine daily and corrective glasses are worn so that the dominant eye can only see at a distance. The amblyopic eye adds +3.00D to the corrective spectacles so that it can see at near distances without adjustment.
②Distance suppression method. For children with best corrected visual acuity >0.3. The dominant eye is overcorrected by +3.00D so that it can see only at close distances. The amblyopic eye wears only best-corrected glasses to promote it to see far away. A multicenter randomized controlled clinical trial conducted by the American Pediatric Eye Disease Study Group showed that masking therapy and atropine suppression therapy produced similar results for children aged 3 to 7 years with moderate amblyopia (visual acuity between 0.2 and 0.5 in the amblyopic eye), and both could be used as initial treatment for amblyopia in such children.
Other treatments: posterior image therapy, red filter (wavelength 640 nm) method, Hedinger brush are also effective methods of amblyopia treatment, mainly suitable for paracentral gaze. Visual stimulation therapy (CAM) is more effective for central concave gaze and refractive amblyopia, and can be used as an adjunct to masking therapy to shorten the course of treatment.
5, comprehensive therapy: for central gaze amblyopia, conventional masking therapy, or suppression therapy, combined with visual stimulation therapy (CAM), auxiliary fine training; for paracentral gaze amblyopia, can be taken after the image, red filter or Hedinger brush stimulation to change the nature of gaze, to be converted to central gaze, and then treated according to the central gaze amblyopia. Direct conventional masking is also possible.