ispell-skip-tib

ispell-skip-tib is a variable defined in `ispell.el'.
Its value is

nil

Documentation:
Does not spell check `tib' bibliography references when non-nil.
Skips any text between strings matching regular expressions
`ispell-tib-ref-beginning' and `ispell-tib-ref-end'.

TeX users beware: Any text between [. and .] will be skipped -- even if
that's your whole buffer -- unless you set `ispell-skip-tib' to nil.
That includes the [.5mm] type of number...

You can customize this variable.