Amblyopia has three main causes: * Strabismic: by<unk>  (misaligned eyes) * Refractive: by anisometropia (difference of a certain degree of nearsightedness, farsightedness, or astigmatism), or by significant amount of equal refractive error in both eyes * Deprivational: by deprivation of vision early in life by vision-obstructing disorders such as congenital cataract<unk> <unk> , sometimes also incorrectly called lazy eye, is a condition in which the eyes are misaligned.<unk>  usually results in normal vision in the preferred sighting (or "fellow") eye (the eye that the person prefers to use), but may cause abnormal vision in the deviating or strabismic eye due to the difference between the images projecting to the brain from the two eyes. Adult-onset<unk>  usually causes double vision (diplopia), since the two eyes are not fixed on the same object. Children's brains are more neuroplastic, so can more easily adapt by suppressing images from one of the eyes, eliminating the double vision. This plastic response of the brain, interrupts the brain's normal development, resulting in the amblyopia. Recent evidence points to a cause of infantile<unk>  lying with the input to the visual cortex. Those with strabismic amblyopia tend to show ocular motion deficits when reading, even when they use the nonamblyopic eye. In particular, they tend to make more saccades per line than persons with normal stereo vision, and to have a reduced reading speed, especially when reading a text with small font size. Strabismic amblyopia is treated by clarifying the visual image with glasses, or encouraging use of the amblyopic eye with an eyepatch over the dominant eye or pharmacologic penalization of the better eye. Penalization usually consists of applying atropine drops to temporarily paralyze the accommodation reflex, leading to the blurring of vision in the good eye. It also dilates the pupil. This helps to prevent the bullying and teasing associated with wearing a patch, although sometimes application of the eye drops is challenging. The ocular alignment itself may be treated with surgical or nonsurgical methods, depending on the type and severity of the<unk> . Refractive Refractive amblyopia may result from anisometropia (unequal refractive error between the two eyes). Anisometropia exists when there is a difference in the power between the two eyes. The eye which provides the brain with a clearer image typically becomes the dominant eye. The image in the other eye is blurred, which results in abnormal development of one half of the visual system. Refractive amblyopia is usually less severe than strabismic amblyopia and is commonly missed by primary care physicians because of its less dramatic appearance and lack of obvious physical manifestation, such as with<unk> . Given that the refractive correction of anisometropia by means of spectacles typically leads to different image magnification for the two eyes, which may in turn prevent binocular vision, a refractive correction using contact lenses is to be considered. Also pediatric refractive surgery is a treatment option, in particular if conventional approaches have failed due to aniseikonia or lack of compliance or both. Frequently, amblyopia is associated with a combination of anisometropia and<unk> . In some cases, the vision between the eyes can differ to the point where one eye has twice average vision while the other eye is completely blind. Deprivation and occlusion Deprivation amblyopia (amblyopia ex anopsia) results when the ocular media become opaque, such as is the case with congenital cataract or corneal haziness. These opacities prevent adequate visual input from reaching the eye, and disrupt development. If not treated in a timely fashion, amblyopia may persist even after the cause of the opacity is removed. Sometimes, drooping of the eyelid (ptosis) or some other problem causes the upper eyelid to physically occlude a child's vision, which may cause amblyopia quickly. Occlusion amblyopia may be a<unk> of a hemangioma that blocks some or all of the eye. Other possible causes of deprivation and occlusion amblyopia include obstruction in the vitreous and aphakia. Deprivation amblyopia accounts for less than 3% of all individuals affected by amblyopia.
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