There are many different forms of communication. The best thing to do is to ask the client, if necessary through a communicator. Speech Someone who has serious sight problems and develops a hearing impairment during working life, may well have some useful hearing. In a quiet room with the correct hearing aids and possibly using a 'loop' system, you may be able to communicate through normal speech. It is important to speak slowly and clearly and not to shout.
Good lighting is also essential to help anyone who lip reads.
The deafblind manual For a person with serious sight problems who does not have any useful hearing but uses speech, the deafblind manual will be the most useful method of communication. You may need an interpreter initially. BSL is a visual rather than spoken language and like any language, has its own word order. The grammar of BSL is different from the grammar of English. Some people fluent in BSL may not have the same command of English.