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1、1,Amblyopia,2,Unilateral or less commonly, bilateral reduction of best corrected visual acuity that can not be attributed directly to the effect of any structural abnormality of the eye or the posterior visual pathway.,3,Resulting from one of following:,Strabismus - DEVIATION Anisometropia or high b
2、ilateral refractive error (Isoametropia) - DEFOCUS Visual deprivation - DEPRIVATION,4,Prevalence: 2%-4% Commonly unilateral Nearly all amblyopic visual loss is preventable or reversible with timely detection and appropriate intervention. Children with amblyopia or at risk for amblyopia should be ide
3、ntified at a young age when the prognosis for successful treatment is best. Role of screening is important,5,Amblyopia is primarily a defect of central vision. There is a critical period for sensitivity in developing amblyopia. The time necessary for amblyopia to occur during critical period is shor
4、ter for stimulus deprivation than for strabismus or anisometropia.,6,Neurophysiology:,Cells of the primary visual cortex can completely lose their innate ability or show significant functional deficiencies Abnormalities also occur in neurons in the lateral geniculate body Evidence concerning involve
5、ment at the retinal level remains inconclusive,7,8,9,10,Classification:,Strabismus Amblyopia :Deviation Anisometropia Amblyopia : DefocussAmblyopia Due to bilateral high refractive error (isometropic) :Defocuss Deprivation Amblyopia :Deviation,11,Strabismus Amblyopia,The most common form of amblyopi
6、a Strabismic amblyopia is thought to result from competitive or inhibitory interaction between neurons carrying the nonfusible inputs from the two eyes. Which leads to domination of cortical vision centers by the fixating eye and chronically reduced responsiveness to the nonfixating eye input.,12,An
7、isometropia Amblyopia,Second in frequency It develops when unequal refractive error in the two eyes causes the image on the one retina to be chronically defocused. This condition is thought to result: Partly from the direct effect of image blur in the development of visual acuity. Partly from intrao
8、cular competition or inhibition,13,14,Mild hyperopic or astigmatic anisometropia (1.5D) mild amblyopia Mild myopia anisometropia (less than -2.5D) usually doesnt cause amblyopiaunilateral high myopia (-6D) sever amblyopia visual loss.,15,Amblyopia Due to bilateral high refractive error (isometropia)
9、,isometropic amblyopia result from large, approximately equal, uncorrected refractive error in both eyes of a young child. Hyperopia exceeding 5D & myopia excess of 10 D risk bilateral amblyopia,16,Meridonial amblyopia: Uncorrected bilateral astigmatism in early childhood may result in loss of resol
10、ving ability limited to chronically blurred meridians.,17,Deprivation Amblyopia,It is usually caused by congenital or early acquired media opacity. This form of amblyopia is the least common but most damaging and difficult to treat. In bilateral cases acuity can be 20/200 or worse.,18,19,In children
11、 younger than 6 years, dense congenital cataract that occupy the central 3 mm. or more of the lens must be considered capable of causing sever amblyopia. Similar lens opacities acquired after 6 years are generally less harmful.,20,Small polar cataracts & lamellar cataracts may cause mild to moderate
12、 amblyopia or may have no effect on visual development.Occlusion amblyopia is a form of deprivation caused by excessive therapeutic patching.,21,Diagnosis,Characteristics of vision alone cannot be used to reliably differentiate amblyopia from other form of visual loss. The crowding phenomenon is typ
13、ical for amblyopia but not uniformly demonstrable. Afferent pupillary defect are Characteristic of optic nerve disease but occasiinally appear to be present with amblyopia,22,Multiple assessment using a variety of tests or performed on different occasions are sometime required to make a final judgme
14、nt concerning the presence and severity of amblyopia.,23,Binocular fixation pattern: It is a test for estimating the relative level of vision in the two eyes for children with strabismus who are under the age of about 3. This test is quite sensitive for detecting amblyopia but results can be falsely
15、 positive. Showing a strong preference when vision is equal or nearly equal in the two eyes, particularly with small angle strabismic deviations.,24,The modified Snellen technique directly measures acuity in children 3-6 years old. Often, however, only isolated letters can be used, which may lead to
16、 under estimated amblyopia visual loss. Croding bar may help alleviate this problem.,25,Crowding bar, or contour interaction bars, allow the examinator to test the crowing phenomenon with isolated optotype. Bar surrounding the optotype mimic the full of optotype to the amblyopia child.,26,Treatment,Treatment of amblyopia involves the following steps: Eliminating (if possible) any obstacle to vision such as a cataract Correcting refractive error Forcing use of the poorer eye by limiting use of the better eye.,
