Glaucoma is "a disease of the eye marked by increased pressure within the eyeball that can result in damage to the optic disc and gradual loss of vision" (Merriam-Webster definition). The eyes of people suffering from glaucoma tend to have a bluish-grey and white appearance. The word glaucoma comes from the Greek word glaukos, and glaucous is another word incorporating a similar form, meaning "of a light bluish-grey or bluish-white colour", or having a "frosty appearance" (Merriam-Webster dictionary definitions). It would thus appear that these terms of similar form may reflect conceptual associations, as a consequence of a linguistic process known as semantic shift.

Greek mythological literature refers to Glaucus as a fisherman who was transformed into a sea-god/fish. The term Glaucus can also refer to the bluish colour of the sea. The colour of the transformed god/fish was blue. It would seem possible that the dual meanings of Glaucus are associated with semantic drift.

Glaucus (as a fisherman) was transformed after consuming a "marvellous herb", also referred to as a "weed". According to Greek myth, when Glaucus was transformed into a fish-like creature, he became extremely thirsty. Having been a land-dwelling human, he became a marine sea god-fish, and his thirst was quenched by living in the sea. It may not be coincidental that one of the effects of Cannabis is to induce thirstiness. This serves as a basis for suggesting that the "weed" or "marvellous herb" in the Glaucus myth refers to Cannabis. (The term "weed" in Shakespearean literature has also been linked to the use of Cannabis).

It may be entirely coincidental that Cannabis is one means of alleviating the symptoms of glaucoma.


ACKNOWLEDGEMENTS

I would like to thank Paula Richards (Glaucoma Foundation) and Prof Beverley Kramer (Department of Anatomical Sciences, University of the Witwatersrand) for assistance with this article.