In a normal state, the pupils are situated in the center of the iris or are slightly shifted inwards and downwards. Such location is conditioned on the balanced interaction between the sympathetic and parasympathetic components of the pupil-motor system.

In cases of long-term and stable changes in the organs, and, consequently, viscero-iridal impulses that can occur, injury to neuro-muscular elements of the iris develop.

Fragmentary weakening and elimination of adrenergic mechanism functions lead to violating of the relationship between sphincter and dilator and “pulling” of a pupil. In this event, neither the pupil circle nor the collarette is deformed.

Decentration is considered to be significant for making diagnoses if the deviation of a pupil center from the iris center is more than 3%.