[The use of prisms in postural equilibrium]

The syndrome of postural deficiency represents an alteration of tonic and postural equilibrium, related to the affectation of the reception, transmission and integration of proprioceptive and visual information. The physiological, semiological and therapeutical basis of the syndrome of postural deficiency are discussed. In order to prescribe a postural therapeutical prism, the ophthalmologist may choose among two methods with common physiological base. The former, proposed by the Paris School, tries to use the prism treatment in order to obtain a re-equilibrating hypertonia: the latter, used by the Lisbon School, tries to create initially an equilibrating relaxation and, since it is much easier to use during the ophthalmological consultation and faster is preferred by most authors.