and the ambient light conditions, the amount of sleep someone has had, color blindness (could be classified as bad eyesight), the actual size of the screen (for

and the ambient light conditions, the amount of sleep someone has had, color blindness (could be classified as bad eyesight), the actual size of the screen (for scrolling/line length), the font itself, the amount of experience the reader has with the latin script, the quality of font hinting, the quality of sub-pixel rendering, the quality of kerning.