Table 2.

Inclusion criteria and rationale for patient selection

Criteria	Comment
Children aged 3–7 years	Accurate measurements of letter based visual acuity are unattainable in 50% of children under the age of 3 years but attainable in 75% of children 3.25 years of age.28 It is important that measurements are consistent and accurate, thus children under the age of 3 years are excluded from the study. Children over 7 years of age are not included as they fall outside the accepted sensitive period for visual development
Visual acuity of 0.1 log units or lower in worst eye and/or interocular difference of at least 0.1 log units	Visual acuity of 0.1 log units or worse is considered to be abnormal in this age group
Presence of anisometropia and/or strabismus	This group forms the majority of the population of children with amblyopia29
No other ocular pathology	Form deprivation amblyopia is excluded because this forms a clinical entity distinct from the general population with amblyopia
No previous occlusion treatment	Dose-response functions in previously treated children may differ from those in whom treatment has already been undertaken
Knowledge of previous spectacle history	All subjects undergo full adaptation to their spectacles before entering the occlusion phase of the study. If children enter the study having already been prescribed spectacles it is important to establish that full spectacle adaptation has occurred
No learning difficulties	To obtain accurate and consistent measurements of visual function from every subject it is necessary to exclude patients with learning difficulties
Parental/guardian consent	In accordance with local ethics committee requirements