الفهرس 
Anterior Segment AnatomyOnly 14 pages are availabe for public view
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Abstract
At the time of birth, the visual system is immature and visual acuity is less than in a normal adult. It is developed by the individual on the basis of experience. Development of the visual pathway in the central nervous system requires that the brain receive equally clear, focused images from both eyes. Any ocular process that interferes with or inhibits the normal development of the visual pathways in the brain may result in poor vision, that is, amblyopia.
According to the National Eye Institute (NEI); Amblyopia, or lazy eye, is the most common cause of visual impairment in children and often persists in adulthood. It is reported to be the leading cause of unilateral vision loss in the 20-70 year old age group, with a prevalence of 1-4 % in various studies. Amblyopia is primarily a cortical phenomenon, caused by unequal competitive inputs from the two eyes into primary visual cortex area 17.
Anisometropia is the leading cause of amblyopia and occurs because of unequal refractive error between the 2 eyes. In general, anisomyopia of more than 2 D, anisohyperopia of more than 1 D, and anisoastigmatism of more than 1.5 D may result in amblyopia. It has been shown that the level of the anisometropia plays a direct role in the final outcome of amblyopia therapy.
Classic teaching is that amblyopia must be detected early and the pathology (strabismus, media opacity, or asymmetric refractive error) must be addressed prior to beginning treatment for amblyopia. Children with anisometropia are treated conventionally with spectacles and/or contact lenses. However, in some children spectacle correction may lead to aniseikonia, and children may become contact lens intolerant, which leads some ophthalmologists to suggest refractive surgery in these cases. By reducing anisometropia, refractive surgery has been reported to improve spectacle tolerance, facilitate amblyopia therapy, and enhance binocular vision. Each case should be fully assessed to select the appropriate operative procedure. Each technique has its own advantages and drawbacks which should be weighted before taking decision
Some studies recommended Photorefractive keratectomy (PRK) to play a role in the management of anisometropia in selected pediatric patients. Their conclusion was that; the refractive error response in children appears to be similar to that of adults with comparable refractive errors. Visual acuity and stereopsis improved despite several children being outside the standard age of visual plasticity. The major drawback to surface ablation correction in children is the high prevalence of myopic regression and the development of corneal haze likely because of the ablation of the Bowman layer in addition to long recovery period.
Laser in situ keratomeliosis (LASIK) was recommended by other studies for its rapid recovery and maintenance of an intact Bowman’s membrane. It has been reported that visual acuity and binocular vision outcomes were significantly better in children who received LASIK treatment. On the other hand Children are more likely to rub their eyes than adults, with a theoretically increased risk of flap dislocation or loss and keratectasia.