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Updated: Jun 17, 2026
12:03
A Method for Tracking the Time Evolution of Steady-State Evoked Potentials
Published on: May 25, 2019
Vergence position of rest: spontaneous variability.
Joanna M Otto1, Michael Bach, Guntram Kommerell
1Universitäts-Augenklinik, Freiburg, Germany.
Strabismus
|December 17, 2009
Summary
The ideal prism strength for comfortable vision varies significantly between individuals and even for the same person over time. Repeated measurements are crucial to ensure prism stability before prescribing.
Area of Science:
- Ophthalmology
- Optometry
- Vision Science
Background:
- Investigated the vergence resting position (horizontal component) in individuals with normal vision.
- Utilized Risley prisms for continuous modulation of prismatic strength.
- Assessed subjective visual comfort at different viewing distances (400 cm and 50 cm).
Purpose of the Study:
- To determine the variability in the preferred prismatic strength for comfortable viewing.
- To assess the stability of the vergence resting position over time.
- To inform clinical practice regarding prism prescription.
Main Methods:
- Twenty observers with normal vision participated in two sessions, 1-6 weeks apart.
- Each session included 8 trials where observers adjusted Risley prisms for maximal visual relaxation.
- Measurements were taken at 400 cm and 50 cm viewing distances.
Main Results:
- The standard deviation among trials was ±1.4 prism diopters.
- Significant changes in preferred prism strength were observed between sessions for many participants.
- At 400 cm, 10/20 observers changed by >1.0 prism diopter (up to 3.3 PD); at 50 cm, 11/20 changed by >1.0 PD (up to 5.1 PD).
Conclusions:
- The prismatic strength perceived as most relaxing exhibits considerable variability.
- Practitioners should verify the stability of preferred prismatic strength through multiple sessions before prescription.
- Consistency in prism adjustment is essential for effective visual correction.
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