Table 1.

Methods of defining treatment outcome. (Proposed optimum expressions of outcome appear in lower shaded portion of the table)

Definition of treatment outcome	Disadvantage	Advantage
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	Accounts for initial severity of amblyopia Accounts for visual acuity of fellow eye Accounts for development of both eyes during treatment