According to the BGI/GUV-I 850-0 (§ 7.2) following checks have to be performed.
This check is in fact also a maintainance operation because the eye-shower has to be set into operation and is in this situation flushed with fresh water. This is important since otherwise the water will become contaminated which is bad for eyes.
It is a good idea to do an extended check at least once a year.
This quick instruction may be put close to the eye shower. It is a WORD-document and may and should be adjusted to your local needs. If you print it out 1:2 scaled down only one sheet of paper is needed.