An eye drop that treats glaucoma while you sleep has been developed by scientists.
It is based on a chemical found in cannabis and could end the misery of twice daily drops that are often ineffective.
The condition is triggered by a build-up of pressure that damages cells in the optic nerve. It is the second biggest cause of blindness.
The breakthrough could lead to better therapies for other serious eye disorders - including macular degeneration which also destroys sight.
Professor Vikramaditya Yadav, a biomedical engineer at British Columbia University in Canada, said: "Medicated eye drops are commonly used to treat glaucoma - but they're often poorly absorbed."
"Less than five per cent of the drug stays in the eye because most of the drops just roll off the eye.
"Even when the drug is absorbed it may fail to reach the back of the eye where it can start repairing damaged neurons and relieving the pressure that characterises glaucoma."
To solve these problems his team created a watery gel - or hydrogel.
This was then filled with thousands of nanoparticles containing a chemical called CBGA (cannabigerolic acid).
It is found in the marijuana plant has already shown promise in relieving symptoms of glaucoma.
The disorder blights the lives of more than 500,000 people in England and Wales. Many more may not know they have the condition.
Current eye drops taken daily or twice daily can lower internal eye pressure to help prevent damage to the optic nerve.
When the researchers applied their drops on donated pig corneas - which are similar to human corneas - they were absorbed quickly and reached the back of the eye.
Prof Yadav said: "You would apply the eye drops just before bedtime - and they would form a lens upon contact with the eye.
"The nanoparticles slowly dissolve during the night and penetrate the cornea. By morning the lens will have completely dissolved."
Previous research shows cannabinoids like CBGA are effective in relieving glaucoma symptoms.
But this is the first cannabis-based eye drop to be developed because cannabinoids don't easily dissolve in water, said the researchers.
Co-author Syed Haider Kamal, a research associate in Prof Yadav's lab, said: "By suspending CBGA in a nanoparticle-hydrogel composite we have developed what we believe is the first cannabinoid-based eye drops that effectively penetrate through the eye to treat glaucoma.
"This composite could also potentially be used for other drugs designed to treat eye disorders like infections or macular degeneration."
The team whose gel is described in the journal Drug Delivery & Translational Research is now working to scale up production and develop more anti-glaucoma cannabinoid molecules using genetically engineered microbes.
Glaucoma is caused by the death of cells in the retina at the back of the eye.
It affects 60 million people globally - a tenth of whom are completely blind. It often affects both eyes.
The eyeball contains a fluid called aqueous humour which is constantly produced by the eye, with any excess drained though tubes.
Glaucoma develops when the fluid cannot drain properly and pressure builds up - known as intraocular pressure.
This can damage the optic nerve - which connects the eye to the brain - and the nerve fibres from the retina, the light-sensitive nerve tissue that lines the back of the eye.
Symptoms include intense eye pain, nausea, headaches, seeing rings around lights and blurred vision.
Worldwide, it is the second leading cause of blindness, according to the World Health Organisation.
Early diagnosis is important because any damage to the eyes cannot be reversed. Treatment aims to control the condition and minimise future damage.
If left untreated, glaucoma can cause visual impairment. But if it's diagnosed and treated early enough, further damage to vision can be prevented.
Some studies show half of patients stop taking their prescription glaucoma eye drops after a year - leaving them vulnerable to vision loss.
A once a night routine - before going to bed - could improve adherence.