Researchers at University College Hospital in London published a study in the journal Brain about a test which will predict development of glaucoma several years before the symptoms appear. They use a fluorescent dye that sticks to the cells in the retina that are about to die. All an optician has to do is look at the back of the eye and if the retina is illuminated in white fluorescent dots then the patient has a problem.

Researchers recruited eight healthy adults without eye disease and eight adults being treated for early glaucoma at the hospital, with no other eye disease. People had an injection of the fluorescent dye (one of four different doses) then had their eye scanned by an infrared laser ophthalmoscope. The researchers assessed the images and compared those from healthy people and people with glaucoma.

Researchers also looked to see what happened to the people with glaucoma during their future clinical follow-up visits, for up to 16 months. They then looked to see if the test results predicted how their glaucoma progressed. Participants with glaucoma had on average more than twice as many white spots showing dying nerve cells as people with healthy eyes.

People with glaucoma whose disease got worse over the following months also had more white spots than those whose disease stayed the same. Among people without eye disease, older people had more white spots. No-one had major side effects linked to the injection (one person found it painful and one person had a bruise afterwards).

Glaucoma affects 60 million people around the world and most have lost a third of their vision by the time they are diagnosed. The disease is usually caused by changes to the pressure inside the eye that kills the retina’s nerve cells. As these cells become stressed and sickly, they start to change their chemistry and more fatty structures move to the outside of the cell.

In Phase I clinical trials – the earliest form of trial designed to check new treatments are safe – the technique could spot the difference between the eyes of healthy patients and those with glaucoma.

Prof Francesca Cordeiro, from the UCL Institute of Ophthalmology, told the BBC News website: “For the first time in humans we have a test that identifies [glaucoma] disease activity before the disease develops.

Current treatments to control the eye’s internal pressure can stop or slow down the progression of the disease, although they cannot reverse the damage already done.

The study involved only a small number of patients in safety trials. The UCL’s study, published in the journal Brain, says more research is “clearly needed”.

Bethan Hughes, from the Wellcome Trust, which funded the research, said: “This innovation has the potential to transform lives for those who suffer loss of sight through glaucoma, and offers hope of a breakthrough in early diagnosis of other neurodegenerative diseases.