Way back in my Moorfields days, I remember stories of little old ladies being stopped at airports while carrying large lumps of cannabis resin. After confirming the drug was for treating their glaucoma, they were invariably released. I always thought these tales were as apocryphal as the perennial favourite about the rigid contact lens wearer who continued to suffer significant lens deposition despite drinking one protein removal tablet in a glass of water each day.
Interest in the subject first took hold in the early 1970s after one study, designed to look at the impact of smoking cannabis upon the visual system of healthy volunteers, found that just 2g of cannabis lowered intraocular pressure. In some, the drop was as much as 45%. Subsequent studies confirmed that around 65% of glaucomatous eyes will experience a 30% pressure reduction after cannabis inhalation.
The ingredient with the greatest psychoactive impact, ∆-9 tetrahydrocannabinol or THC, is also thought to contribute the most to IOP lowering. It is thought that THC binding to CB1 receptors in the anterior eye both slows aqueous production and increases its outflow.
Alas, it soon became apparent that the IOP-lowering effect lasts just three to four hours and was dose-dependent, usually requiring ever greater inhaled amounts of THC to maintain the same effect. So, for many years, eye care professionals have tended to view the need for constantly being stoned, along with concerns about drug delivery by smoking, in no way justified the ocular benefits.
Until now. A report in the latest Journal of Glaucoma highlights how the legalisation of medical marijuana (MMJ) in the US is changing perceptions, with ophthalmologists reporting around a third of their glaucoma patients already using MMJ. Seventy-six percent of doctors want additional education on the topic, while 27% feel that there is still a role for MMJ in the management of glaucoma.
Mellow Goldmann.