The critical period for visual development is before 2 years of age (before 3 years of age) and the sensitive period for visual development is before 8 years of age (5 years of age, 13 years of age). During this stage, the visual environment influences the development of the visual system, which shows an extraordinary sensitivity to abnormal stimuli. A poor visual environment predisposes to amblyopia, especially during the critical period of visual development, but it is also the best age to treat amblyopia.
In April 1996, the National Amblyopia and Strabismus Control Group of the Chinese Academy of Ophthalmology defined amblyopia as: any amblyopia without obvious organic lesions in the eye, caused mainly by functional factors, with distance visual acuity <0.9 and cannot be corrected is classified as amblyopia.
Classification of amblyopia
I. Classification according to the degree of amblyopia
1. Mild amblyopia: corrected visual acuity of 0.8 to 0.6.
2, moderate amblyopia: corrected visual acuity of 0.5 to 0.2.
3.Severe amblyopia: corrected visual acuity <=0.1.
Here the visual acuity refers to the corrected distance visual acuity.
Etiological classification
There are two types of amblyopia: form deprivation amblyopia, strabismic amblyopia, refractive amblyopia, refractive error amblyopia and others.
1. Form vision deprivation amblyopia
In infancy, due to refractive interstitial clouding, severe ptosis, and inappropriate masking, light stimuli cannot enter the eye normally, depriving the macula of the opportunity to receive clear image stimulation and causing serious impairment of visual function development. Three factors influence the degree of form deprivation amblyopia.
(1) The age at which the form deprivation begins.
(2) The duration of the form deprivation.
(3) The mode and degree of form deprivation (complete or partial, monocular or binocular). This type of amblyopia is mostly severe, difficult to treat, and has a poor prognosis. Early detection of possible causes and early treatment (etiology, amblyopia). For example: early surgery for congenital cataract; timely optical correction; avoidance of medically induced form deprivation; effective visual acuity monitoring after etiological treatment.
2.Strabismic amblyopia (strabismic amblyopia)
The patient has strabismus or has had strabismus. The strabismus causes double vision and visual confusion that makes the patient extremely uncomfortable. The visual cortex of the brain actively inhibits the visual impulses transmitted from the macula of the strabismic eye, and the macular function of the strabismic eye is suppressed for a long time, and amblyopia is formed. Amblyopia occurs in the strabismic eye with monocular amblyopia. The clinical characteristics of strabismic amblyopia are.
(1) Early onset (<2 years old), long duration, constancy, and monocular strabismus predispose to amblyopia with a higher degree; the size of the strabismus angle is not related to the degree of amblyopia.
(2) Internal strabismus is more frequent than external strabismus, and the degree of amblyopia is more severe.
(3) Eccentric gaze and abnormal retinal correspondence are the difficulties in the treatment of strabismic amblyopia.
3. Refractive amblyopia (anisometropic amblyopia)
Even if the refractive error is corrected, the image size caused by the refractive error is still unequal, which makes it difficult or impossible to fuse the two eyes into one, and the visual cortex inhibits the function of the heavier side of the refractive error, resulting in amblyopia. Monocular amblyopia. The clinical characteristics of refractive error amblyopia are
(1) hyperopia and astigmatism are easy to form amblyopia, the two account for about 97%; the degree of amblyopia is related to the degree of refractive parallax; moderate and low myopic refractive parallax is not easy to cause amblyopia, high myopia has pathological changes, low vision is not amblyopia.
(2) Positive eye position.
(3) Central or paracentral concave gaze.
(4) Better prognosis, more peripheral fusion and rough stereopsis.
(5) If no screening is performed, it is mostly detected late.
(6) Treatment: optical correction, suppression of the dominant eye.
4.Refractive amblyopia (ametropic amblyopia)
It occurs in patients with high refractive error who have not worn corrective glasses. It is mostly seen in hyperopic and astigmatic eyes, and the broad form of deprivation prevents the normal development of visual function and forms amblyopia. Refractive errors are mostly: hyperopia > 3.00 D, myopia > 6.00 D, astigmatism > 2.00 D. The clinical characteristics are
(1) Bilateral: visual acuity (sc, cc) is equal or close in both eyes; no significant refractive aberration.
(2) Positive eye position: there is no competition between the two eyes, so it does not cause the macular function inhibition.
(3) Treatment is based on optical correction, and the prognosis is better.