Data were obtained from a normal clinical population regarding heterophoria, associated phoria and short‐term prism adaptation in an attempt to differentiate between those subjects with symptoms and those without. Correlation between heterophoria, associated phoria, prism adaptation and symptoms was low. A short prism‐adaptation test was found to be of little value in diagnosing decompensated heterophoria in the general population. Subjects diagnosed as having decompensated heterophoria did not have an abnormal short‐term prism‐adaptation system. The clinical implications of these findings are discussed in relation to the diagnosis of decompensated heterophoria and the prescribing of prismatic corr