gms | German Medical Science

Redilatation lag in the pupillary light reflex is characteristic of Horner's syndrome. The time course of the pupillary dilatation velocity and its typical changes in Horner's syndrome were analysed in this study.

By means of infrared video-pupillometry, changes in pupil size of both eyes were continuously recorded in darkness after standardised 0.1s or 30s LED-light stimulation, respectively, in a total of 15 patients with unilateral Horner's syndrome.

Pupil redilatation after short-time illumination was characterized by an approximately exponential course. Initially, dilatation velocity showed a fast linear decrease when it is plotted as a function of the achieved relative redilatation amplitude. Compared to the normal eye, this linear decrease, however, started with a shorter latency in the affected eye. Thereafter, a phase of further but slower decrease in dilatation velocity (normal eye) or of nearly constant low dilatation velocity (affected eye) occurred until the redilatation was accomplished. After constant illumination over 30s, an initially steep and nearly exponential course of pupil redilatation was observed. During the first seconds, this redilatation proceeded much slower in the affected pupils and showed a nearly linear course.

Pupil redilatation after short-term illumination proceeded in two consecutive phases with different time constants. The associated mechanical forces are the relaxation of iris sphincter muscle in the first phase and the tonus of the iris dilatator muscle in the second phase. The modified time course of pupil redilation in Horner's syndrome is, therefore, a consequence of the reduced elastic reset force and of the elevated time constant in the second redilatation phase. Consequently, the measurement of pupil redilatation velocity in dependence on the relative redilatation amplitude can make an important contribution to the diagnosis of Horner's syndrome.