Distance heterophoria and tonic vergence

Area of Science:

• Ophthalmology
• Vision Science
• Neuroscience

Background:

• The discrepancy between tonic vergence (TV) and distance heterophoria has been attributed to accommodative divergence or proximally induced vergence.
• Understanding these components is crucial for diagnosing and managing vergence disorders.

Purpose of the Study:

• To differentiate the contributions of accommodative divergence and proximally induced vergence to the difference between TV and distance heterophoria.
• To investigate the role of open-loop accommodation in assessing distance heterophoria.

Main Methods:

• Compared tonic vergence (TV) and distance heterophoria in 20 subjects.
• Assessed distance heterophoria with open-loop accommodation to isolate its effects.
• Analyzed a subgroup exhibiting significant differences between TV and heterophoria measures.

Main Results:

• No significant difference was found between TV and distance heterophoria when accommodation was in open-loop.
• This indicates accommodative divergence likely explains previous variations observed with closed-loop accommodation.
• A subgroup (7 subjects) showed greater convergence in TV than distance heterophoria, suggesting proximally induced vergence played a role.

Conclusions:

• Accommodative divergence is the primary factor explaining the difference between tonic vergence and distance heterophoria under normal viewing conditions.
• Proximally induced vergence may contribute to variations in specific individuals, particularly when TV is more convergent than distance heterophoria.
• Assessing distance heterophoria with open-loop accommodation provides a clearer understanding of vergence system components.