The goals of this study are:

• To determine whether the visual acuity improvement obtained with part-time (6 hours) patching is equivalent to the visual acuity improvement obtained with full-time patching (all or all but one waking hour) for severe amblyopia.
• To develop more precise estimates than currently available for the visual acuity improvement that occurs during treatment of amblyopia with patching.
• To identify factors that may be associated with successful treatment of amblyopia with patching.

Amblyopia is the most common cause of monocular visual impairment in both children and young and middle-aged adults. Patching has been the mainstay of amblyopia therapy. It is generally held that the response to treatment is best when it is instituted at an early age, particularly by age two or three, and is poor when attempted after eight years of age.

For severe amblyopia, it is generally accepted that occlusion with patching is the standard of care. Other modalities of treatment, such as atropine penalization and optical penalization, are widely considered insufficient as initial treatments for severe amblyopia. However, controversy exists with regard to how many hours per day of patching should be prescribed. Advocates of full-time patching purport that such a regimen is needed to restore visual acuity more rapidly and more effectively. Advocates of part-time patching believe it to be better tolerated by the child and family, therefore producing less stress on the parent-child relationship and producing better results through better compliance. Part-time patching may also promote the development of binocularity in patients who have "straight-eyes", reduce the chance of a straight-eyed patient developing manifest strabismus or losing stereopsis, and reduce the incidence of reverse- or occlusion-amblyopia.

The study is a randomized trial comparing daily patching regimes for children with severe amblyopia. It will consist of about 160 children. Patients in the severe (20/100 to 20/400) group will patch part-time (6 hours) or full-time (all or all but one waking hour) of each day for the 4 month study period. There are at least two follow up visits during the 4-month period. Visual acuity is the major study outcome. It is assessed at the 4-month exam.

Inclusion Criteria:

• Patients must be less than 7 years of age with the original cause of amblyopia as strabismus or anisometropia (a refractive error difference of more than one diopter between the two eyes.)
• Visual acuity in the amblyopic eye must be between 20/100 and 20/400.
• Visual acuity in the sound eye of 20/40 or better.
• There must be at least 3 lines of acuity difference between the two eyes.

Exclusion Criteria:

• Patching treatment (other than spectacles) within six months prior to enrollment and other amblyopia treatment of any type used within one month prior to enrollment.