Lateral phoria at distance: contributions of accommodation

Area of Science:

• Ophthalmology
• Optometry
• Vision Science

Background:

• Lateral heterophoria at distance is commonly used to assess tonic vergence.
• Recent studies indicate vergence in darkness is more convergent than typical phoria measures.
• A discrepancy exists between dark vergence and distance phoria measurements.

Purpose of the Study:

• To investigate the role of accommodation in the discrepancy between dark vergence and distance phoria.
• To determine if accommodation influences distance phoria measurements.
• To identify the most accurate model for predicting distance phoria.

Main Methods:

• Experiment I: Measured distance phoria, vergence, and accommodation in 19 young adults.
• Experiment II: Evaluated three models of accommodation's influence on distance phoria in 13 young adults.
• Utilized hierarchical regression analysis to assess relationships between variables.

Main Results:

• Dark vergence was correlated with, but significantly more convergent than, distance phoria.
• Distance phoria measures were related to negative accommodation and dark vergence.
• A model incorporating negative accommodation, accommodative vergence, and dark vergence best predicted distance phoria.

Conclusions:

• Distance phoria is significantly influenced by the accommodation response to the fixation target.
• Dark vergence serves as a more straightforward indicator of tonic vergence.
• Accommodation should be considered when interpreting distance phoria in clinical assessments.