Lazy eye usually does not cause any symptoms. Sometimes parents suspect vision problems because a child squints, looks cross-eyed, or holds his or her head in awkward positions to see things. In many cases, the problem is detected by a routine vision screening exam, either before or after a child starts school.
The procedures included in definitions should be repeatable by anyone or at least by peers. An example of operational definition of the term weight of an object, operationalized to a degree, would be the following: weight is the numbers that appear when that object is placed on a weighing scale.
[citation needed] An operational definition is generally designed to model a theoretical definition. The most operational definition is a process for identification of an object by distinguishing it from its background of empirical experience.