Deafblindness
Deafblindness is the combination of both hearing and vision loss. But it is more than the sum of its parts. Since neither sense fully compensates for the loss of the other, unique barriers to communication arise. People who are Deafblind need tactile communication and other accessible channels.
Example
A person who is Deafblind may use a refreshable braille display connected to a screen reader. Text is the only format that reaches them. So, alt text, captions and transcripts are all essential, not supplementary.
Key point
Most people identified as Deafblind have some residual vision or hearing. Complete absence of both senses is uncommon. Further, Deafblindness exists on two separate spectra. So, the degree of loss in each sense determines the specific access needs.