Partially Sighted and Visual Acuity
Magnification, the use of high contrast text and alternative background colours may be important to many users with visual impairments. The way contents are laid out and reflow when zoomed also affects ease of reading. Too much clutter on a page can also also cause overlapping of content. Screen-reading may also be used as scrolling horizontally when text is very large can be very tiring. Further advice from UW-Madison with a video on Screen Magnification and the Web.
These tests contribute towards accessibility scores for this disability.