Amblyopia is a loss of best-corrected visual acuity in one or both eyes due to abnormal visual experience during visual development, with no organic lesions on ocular examination.
Abnormal visual experience, also known as “risk factors”, is the cause of amblyopia and is necessary for the diagnosis of amblyopia.
We can use “risk level” to indicate the magnitude of the effect of risk factors on amblyopia (incidence and severity), which is a guiding meaning for the diagnosis and prognosis of amblyopia.
I. Risk factors and risk level
1. Monocular versus binocular: The mechanism of amblyopia is mainly the inhibition of the amblyopic eye by the good eye, so the risk level of monocular refractive abnormalities (refractive aberrations) is significantly greater than that of binocular refractive abnormalities.
2. Refractive nature: The risk of hyperopic refractive abnormalities is greater than that of myopic refractive abnormalities.
3, refractive power: the number of refractive power (including astigmatism) is positively correlated with the degree of risk.
4.Axis of astigmatism: Among the astigmatism of the same nature and degree, the axis of astigmatism is related to the degree of risk, and its severity is generally: oblique astigmatism > retro-rational astigmatism > cis-rational astigmatism.
Second, the classification of risk factors
1. High-risk factors: >80% possibility of causing amblyopia, and generally severe amblyopia. Including high hyperopia (monocular).
2. Medium-risk factors: 40-70% possibility of causing amblyopia, and generally moderate amblyopia. including moderate hyperopia (monocular), moderate to high hyperopia (binocular,, hyperopic astigmatism, super high myopia.
3. Low-risk factors: <30% possibility of causing amblyopia, and generally mild amblyopia. including low hyperopia (monocular), low to moderate hyperopia (binocular), myopic astigmatism, and high myopia.
4. generally do not cause amblyopia or only cause very mild amblyopia: low hyperopic astigmatism, low to moderate myopic astigmatism, low binocular hyperopia, and high myopia of 800 degrees or less.
Examples
Monocular +7.0D can lead to severe amblyopia.
+7.0D in both eyes can lead to moderate amblyopia
+3.0D astigmatism can lead to moderate amblyopia
-2.0D astigmatism may not lead to amblyopia.
Some notes on risk factors
1. The risk factors discussed in this paper only refer to refractive abnormalities, excluding monocular strabismus and form deprivation.
2. The degree of risk and its classification are only the author’s experience and may not be accurate.
3. The risk level is a probabilistic concept, which only indicates the likelihood of occurrence and severity of amblyopia and is not reflected in any single case. For example, clinical cases of untreated monocular +6.0D without the occurrence of amblyopia may also be seen occasionally
4. The same level of risk factors do not cause the same “consequences” in different patients, and by the same token, the same “consequences” are not caused by the same level of risk factors.
Having said that, what is the use of identifying risk factors and their degree of risk?
(a) To help further clarify the diagnosis of amblyopia
If risk factors are present and the degree of risk is consistent with the severity of amblyopia, the diagnosis is clear. If the latter two are not always present, such as low to moderate myopic astigmatism (low risk factor) causing severe hypermetropia (severe consequence), other risk factors should be actively sought or the diagnosis of amblyopia should be denied.
(2) For young children with low-risk factors, if the degree of mild to moderate hypotropia is comparable in both eyes, the diagnosis of amblyopia can be withheld and observation is sufficient.
(2) Judging the prognosis of amblyopia treatment
The higher the risk level, the worse the prognosis, and vice versa.