Vergence position of rest:
spontaneous variability.
(Position de repos : variabilité spontanée)
Otto JM, Bach M, Kommerell G.
Universitäts-Augenklinik, Freiburg, Germany.
BACKGROUND: We
determined the vergence position of rest (horizontal component) in two sessions,
1 to 6 weeks apart. Each session contained 8 trials. Twenty observers with
normal eyes looked through Risley prisms that allowed a continuous modulation of
their strength. We asked the observers to look at a fully fusionable picture,
and to adjust the prisms such that viewing appeared most relaxing. The viewing
distances were 400 cm and 50 cm.
RESULTS: The standard deviation among the 8 trials of each session,
averaged over the two sessions, the viewing distances of 400 cm and 50 cm, and
the 20 observers, was + or -1.4 prism dioptres (cm/m). From the first session to
the second, many observers changed the preferred prism significantly. At a
viewing distance of 400 cm, 10 of 20 observers changed their preferred prism by
more than 1.0 prism diopter, up to 3.3 prism diopters. At a viewing distance of
50 cm, 11 of 20 observers changed their preferred prism by more than 1.0 prism
diopter, up to 5.1 prism diopters.
CONCLUSIONS: The prismatic strength estimated as being most relaxing can
be very variable. Before considering a prescription, the practitioner should
determine whether the preferred prismatic strength remains reasonably stable. To
ascertain this consistency, more than one session seems to be necessary.
Retour à la bibliographie d'Octobre 2009
(Dernière mise à jour de cette page le 27/08/10)