If an assessment requires watching and interpreting an image or video to answer a question, such as seeing bubbles in a video of baking soda react to vinegar to understand a chemical reaction is taking place, an alternate version of the assessment describes the same process in sounds or words that can be read aloud.
Test content requires sight in order answer questions, such as only offering a video of baking soda and vinegar, when the tested content standard does not require interpreting information in a video.
Students with visual impairments require text and grahics to be read aloud, so any graphic should be easily and concisely described in words.