The purpose of this paper is to examine the degree of precision obtained with the various methods of measuring phoria and squint. It is not its purpose to suggest what degree of precision should be sought; rather, it attempts to show how far present methods may be relied on. Incorrect diagnoses of anomalies of the extraocular muscles can result from lack of attention to certain facts of geometry which profoundly influence such measurements. It is our belief that a higher degree of precision in the measurement of squint and phoria will reveal information not precisely obtainable with present methods.
Three factors comprise the errors in precision in any measurement:
Inherent error in means or method.
Human error in observation and manipulation.
Error in degree of reproducibility, as in high precision determinations of weight or size of an object in which an average of varying results is necessary.
The properties of