There are special scissors for cutting buttonholes. These scissors have a set screw that prevents the blades from closing and cutting beyond the set length. These scissors work well for buttonholes set perpendicular to the fabric edge, but are difficult to use for buttonholes that are parallel to the fabric edge.
This buttonhole chisel has a very sharp blade and comes with a small block of wood to set beneath the buttonhole when cutting. It is a fast and easy way to cut smooth and straight buttonhole openings without cutting into the buttonhole threads.