Further evidence for the fusional nature of the compensation (or 'eating up') of prisms in concomitant strabismus.

The fusional nature of the phenomenon of prism compensation in strabismus was studied. At first a general survey was performed on the characteristics of anomalous fusional movements (a.f.m.). The influence of different kinds of stimuli (foveal and peripheral fusionable targets, non-fusionable targets) on a.f.m. was considered, and finally the effect of a sensorial obstacle to fusion was investiaged. It is concluded that 'eating up' the prisms is definitely a phenomenon of fusional nature, although it has special features which are interpreted as a consequence of the initial pathological condition. In this way the puzzling prism compensation also in subjects with normal retinal correspondence may be explained.