Attainment of a certain standard (eg, 6/6 to 6/12)

Does not account for initial severity of amblyopia—ie, how much improvement has occurred

Fellow eye acuity not considered

A visual acuity of notional equivalence to a legal or occupational standard—eg, driving a motor vehicle

An in improvement considered to be of clinical significance in visual acuity of the amblyopic eye (often 2 or 3 lines measured with Snellen charts or 0.2 log units as measured on a log based test

Does not account for initial severity of amblyopia

Initial acuity dictates whether this achievement would benefit the child

Fellow eye acuity not considered

Assumes understanding of the acuity/function relation

Snellen chart has non-linear scale increments, therefore “n” lines improvement differs in actual acuity change dependent on the acuity level and chart used

Simple indicator of clinical significant improvements

Equal visual acuity of amblyopic and fellow eye

Does not account for initial severity of amblyopia

Accounts for individual variations in visual acuity of fellow eye and visual development during treatment

Acknowledges that normal binocular vision is optimised by identical inputs from each eye

Difference between amblyopic and fellow eye acknowledges extent of residual amblyopia

Proportional improvement (ie, log unit change in visual acuity/difference between amblyopic eye at start and fellow eye at end of treatment)

Need to define level of proportional improvement that constitutes good outcome

Accuracy compromised when occlusion amblyopia occurs