Falkenberg, H. K., T. R. Johansen, and H.-M. S. Thorud. “Headache, Eyestrain, and Musculoskeletal Symptoms in Relation to Smartphone and Tablet Use in Healthy Adolescents”. Scandinavian Journal of Optometry and Visual Science, vol. 13, no. 2, Dec. 2020, pp. 8-14, doi:10.5384/sjovs.vol13i2p8-14.