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Natural selection influences the frequencies of particular alleles and phenotypes within populations in several different ways. Primarily, natural selection can be directional, stabilizing, or disruptive. Directional selection favors one extreme trait and shifts the population towards that phenotype while selecting against individuals displaying alternate traits. Stabilizing selection favors an intermediate trait with a narrow range of variation. Deviation from the optimal phenotype towards an...
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Virtual Prism Adaptation Therapy: Protocol for Validation in Healthy Adults
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Asthenopia, Associated Phoria, and Self-Selected Prism.

Guntram Kommerell1, Miriam Kromeier, Felix Scharff

  • 1University Eye Center , Freiburg , Germany.

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|July 10, 2015
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Summary

Reading discomfort is not directly linked to the vergence position of rest (phoria). This study found no significant correlation between heterophoria measurements and reported discomfort in individuals experiencing eye strain.

Keywords:
Aligning prismassociated phoriaasthenopiacircadian rhythmheterophoriaself-selected prismvergence position of rest

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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.