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.