This chapter highlights the work by Sharif et al. [1] that presents empirical studies the authors conducted to understand and assess the challenges screen-reader users experience with online data visualizations. These studies include: (1) A qualitative study with nine screen-reader users, and (2) a quantitative study with 36 screen-reader and 36 non-screen-reader users. Through these studies, the authors shed light on the experiences of screen-reader users with online data visualizations compared to non-screen-reader users, the information they commonly seek, and the techniques and strategies that could improve their interaction experiences with online data visualizations. Additionally, the authors provide empirical evidence of the inequalities screen-reader users experience in their interaction with online data visualizations compared to non-screen-reader users. Furthermore, this chapter discusses the design recommendations put forward by the authors to make online data visualizations accessible to screen-reader users.