title: Quantifying interactions between accommodation and vergence in a binocularly normal population.
abstract: Stimulation of the accommodation system results in a response in the vergence system via accommodative vergence cross-link interactions, and stimulation of the vergence system results in an accommodation response via vergence accommodation cross-link interactions. Cross-link interactions are necessary in order to ensure simultaneous responses in the accommodation and vergence systems. The crosslink interactions are represented most comprehensively by the response AC/A (accommodative vergence) and CA/C (vergence accommodation) ratios, although the stimulus AC/A ratio is measured clinically, and the stimulus CA/C ratio is seldom measured in clinical practice. The present study aims to quantify both stimulus and response AC/A and CA/C ratios in a binocularly normal population, and determine the relationship between them. 25 Subjects (mean ± SD age 21.0 ± 1.9 years) were recruited from the university population. A significant linear relationship was found between the stimulus and response ratios, for both AC/A (r² = 0.96, p < 0.001) and CA/C ratios (r² = 0.40, p < 0.05). Good agreement was found between the stimulus and response AC/A ratios (95% CI -0.06 to 0.24 MA/D). Stimulus and response CA/C ratios are linearly related. Stimulus CA/C ratios were higher than response ratios at low values, and lower than response ratios at high values (95% CI -0.46 to 0.42 D/MA). Agreement between stimulus and response CA/C ratios is poorer than that found for AC/A ratios due to increased variability in vergence responses when viewing the Gaussian blurred target. This study has shown that more work is needed to refine the methodology of CA/C ratio measurement.
authors.affiliation: Department of Vision Sciences, Glasgow Caledonian University, Cowcaddens Road, Glasgow, Scotland G4 0BA, United Kingdom. Laura.Sweeney@gcu.ac.uk
authors.forename: Laura E
authors.initials: LE
authors.lastname: Sweeney
authors.forename: Dirk
authors.initials: D
authors.lastname: Seidel
authors.forename: Mhairi
authors.initials: M
authors.lastname: Day
authors.forename: Lyle S
authors.initials: LS
authors.lastname: Gray
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology*; D000328:Adult; D003290:Convergence, Ocular / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D010775:Photic Stimulation / Q000379:methods; D012044:Regression Analysis; D015348:Vision, Binocular / Q000502:physiology*; D055815:Young Adult