Asthenopia, Associated Phoria, and Self-Selected Prism.

Area of Science:

• Ophthalmology and Vision Science
• Human Physiology
• Visual Optics

Background:

• The vergence position of rest, or phoria, is known to fluctuate over time.
• Understanding factors influencing visual comfort during reading is crucial for managing eye strain.

Purpose of the Study:

• To investigate the correlation between the vergence position of rest (phoria) and subjective discomfort experienced during reading.
• To determine if heterophoria measurements predict reading-related discomfort in individuals with and without eye strain.

Main Methods:

• Examined 40 subjects (20 asthenopes, 20 non-asthenopes) with normal ocular health.
• Measured associated phoria (AP) and self-selected prism (SSP) at near, assessing visual comfort via a visual analogue scale after 30 minutes of reading.
• Repeated measurements across 6 sessions to evaluate intra-individual variability and correlations.

Main Results:

• Significant correlations were found between AP and SSP in both asthenopic (r=0.81) and non-asthenopic (r=0.73) groups.
• Neither AP nor SSP were significantly different between asthenopes and non-asthenopes.
• No significant intra-individual correlation was observed between the magnitude of discomfort and AP or SSP in either group.

Conclusions:

• The study does not support a causal relationship between horizontal heterophoria (measured by AP or SSP) and reading discomfort.
• Subjective visual discomfort during reading appears to be independent of the measured vergence position of rest.