Binocular vision changes in university students: a 3-year longitudinal study.

PURPOSE The aim of this study was to investigate the changes in accommodation and binocular vision parameters during a period of 3 years and to evaluate their potential influence on the refractive changes observed over the same period of time in a population of university students in Portugal. METHODS A 3-year longitudinal study was conducted comprising 118 young adults (34 males and 84 females; mean age: 20.6 +/- 2.3 years). Examinations consisted of subjective refraction, dissociated phoria and vergences at distance and near vision, accommodative convergence/accommodative ratio, lag of accommodation, and the negative and positive relative accommodation. RESULTS There were statistically significant differences between the first (2002) and the second examination (2005) relative to distance and near phoria, and break and recovery points for the base-in and base-out at distance vision. Statistically significant differences were also obtained for the blur and break points for the base-out, and for break and recovery points for the base-in at near vision. As regards accommodation parameters, we verified a statistically significant difference for all parameters measured. Comparing the baseline values of patients who suffered a myopic shift > or =0.50 D with those from patients who did not experience such a shift, we observed a statistically significant difference for the break value of the base-in at distance vision (equal to 12.2 +/- 3.6 for the group without refractive error alteration and 15.8 +/- 6.8 for the other group) and for the break value of the base-in at near vision (equal to 22.4 +/- 5.2 and 24.8 +/- 5.5 for the group without refractive error alteration and for the other group, respectively). CONCLUSIONS We observed significant changes in near heterophoria, fusional vergences, and positive relative accommodation. The break values of the base-in fusional vergence account as significant predictors of myopic shift in young adults.