Cause
Amblyopia has three main causes:

Strabismic: by strabismus (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

Strabismus
Strabismus, sometimes also incorrectly called lazy eye, is a condition in which the eyes are misaligned. Strabismus 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 strabismus usually causes double vision (diplopia), since the two eyes are not fixed on the same object. Childrens 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 brains normal development, resulting in the amblyopia. Recent evidence points to a cause of infantile strabismus 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.
Amblyopia was first described in the 1600s. The condition may make people ineligible to be pilots or police officers. The word amblyopia is from Greek ἀμβλύς amblys, meaning "blunt", and ὤψ ōps, meaning "sight". Signs and symptoms
Many people with amblyopia, especially those who only have a mild form, are not aware they have the condition until tested at older ages, since the vision in their stronger eye is normal. People with amblyopia typically have poor stereo vision, since it requires both eyes. They further may have, on the affected eye, poor pattern recognition, poor visual acuity, and low sensitivity to contrast and motion.Amblyopia is characterized by several functional abnormalities in spatial vision, including reductions in visual acuity, contrast sensitivity function, and vernier acuity, as well as spatial distortion, abnormal spatial interactions, and impaired contour detection. In addition, individuals with amblyopia have binocular abnormalities such as impaired stereoacuity (stereoscopic acuity) and abnormal binocular summation. Also, central vision in amblyopes is more crowded than central vision in normal observers.These deficits are usually specific to the amblyopic eye. Subclinical deficits of the "better" eye have also been demonstrated.People with amblyopia also have problems of binocular vision such as limited stereoscopic depth perception and usually have difficulty seeing the three-dimensional images in hidden stereoscopic displays such as autostereograms. Perception of depth, from monocular cues such as size, perspective, and motion parallax remains normal.