Lateral canthotomy (and cantholysis) is an incision to the lateral canthal ligament of the eye which decompresses the orbit when a retro-orbital haematoma is compressing the optic nerve and threatening to permanently damage vision.
It is therefore a sight-saving procedure aimed at treating orbital compartment syndrome.
Indications are discussed here:
McInnes G, Howes DW.
Lateral canthotomy and cantholysis: a simple, vision-saving procedure.
These videos demonstrate the procedure on human cadavers:
This paper describes a case done by a prehospital critical care team in New South Wales:
Hill C, Reid C, Tzannes A, Burns B, Bartlett M.
Prehospital lateral canthotomy.