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Purpose: The aim of this study was to investigate the changes in refractive, biometric and topographic ocular parameters among university students in Portugal during a 3-year period. Methods: A 3-year longitudinal study comprised 118 Portuguese university students from the School of Science (34 males and 84 females; mean age 20.6 ± 2.3 years). Ocular refraction, corneal curvature (CR) and eccentricity, and A-scan biometry were conducted under cycloplegia. The sphero-cylindrical refractive results were converted into vector representations ( M, J0 and J45) for statistical analysis. Myopia was defined as M ≤ −0.50 D, emmetropia as M > −0.50 D and < +0.50 D and hyperopia as M ≥ +0.50 D. Results: At the beginning of the study sphero-cylindrical refraction ( M) ranged from −6.75 to +3.00 D, with a mean value of 0.23 ± 1.46 D [mean ± standard deviation (S.D.)]. Eighty-three students presented astigmatism with a mean value (±S.D.) of −0.52 ± 0.41 D, and a maximum of −2.25 D. After 3 years the mean refractive change for the M component was −0.29 ± 0.38 D ( p < 0.001) and non-significant changes of 0.02 ± 0.16 D ( p = 0.281) for the J0 component and 0.01 ± 0.09 D ( p = 0.784) for the J45 component. Prevalence of myopia increased by 5.1%, while the prevalence of hyperopia decreased by 9.4%. Myopia progression ≥0.5 D was observed in 22% of the population. Axial length, vitreous chamber depth and lens thickness increased significantly while anterior chamber depth and central CR did not change significantly. Conclusions: This study shows a change in refraction towards myopia accompanied by a vitreous chamber elongation in a Portuguese population comprising science students during the first three years of their university course. Younger students were more likely to show clinically significant myopia progression. [ABSTRACT FROM AUTHOR]