A team of scientists from Italy found that eye drops containing nerve growth factor appeared to protect the optic nerve and retinal nerve cells from the damage caused by glaucoma and even restored some sight loss.

The study was the work of Dr Stefano Bonini of the Department of Ophthalmology, University of Rome Campus Bio-Medico and Alberto Sordi Foundation, and colleagues. Their findings were published online before print on 3 August in the Proceedings of the National Academy of Sciences, PNAS. Bonini is professor and chairman of the Department of Ophthalmology at the University.

About 70 million people around the world suffer from glaucoma, according to figures from the International Glaucoma Association. While usually found in about 2 per cent of people over the age of 40, it can also affect children and young adults. Glaucoma is the second most common cause of blindness.

Elevated pressure inside the eye (interocular pressure, or IOP), a feature of glaucoma, damages the optic nerve and causes loss of retinal ganglion cells (RGCs) that send visual signals to the brain.

Although IOP can be controlled with drugs, there is currently no treatment that is capable of restoring retinal and optic nerve function, wrote Bonini and colleagues, who noticed that other researchers had successfully used nerve growth factor (NGF) to restore brain tissue in Parkinson's and Alzheimer's patients (glaucoma is sometimes called the "ocular Alzheimer's disease").

For this study, the researchers tested the effect of NGF in rats whose eyes had been injected with saline to induce the effect of glaucoma. They also treated three patients whose visual field was deteriorating despite receiving treatment to control IOP.

First they tested 24 rats with two doses of NGF (100 and 200 micrograms per millilitre), and found the higher dose was more effective.

Then the researchers induced glaucoma in another 36 rats and treated half of them with the 200 microgramme/L dose four times a day for 7 weeks and left the other half untreated.

They evaulated the rate of death (apoptosis) and survival of RGCs in the two groups of rats using histological, biochemical, and molecular analyses.

The results showed that the untreated rats lost 40 per cent of their RGCs through cell death resulting from 7 weeks of IOP.

However, the rats treated with NGF over the same period lost significantly fewer RGCs (measured as number of cells in a square millimeter of retina, the first group lost an average of 2,530 ± 121 while the second group lost only 1,850 ± 156 RGCs per mm2).

After initial baseline tests, three patients with advanced glaucoma were then treated with NGF eye drops for three months, after which they stopped the eye drops but were still kept under observation for another three months.

The results showed that the patients experienced improvements in visual field, optic nerve fuction, contrast sensitivity and visual acuity.

Bonini and colleagues concluded that:

"NGF exerted neuroprotective effects, inhibiting apoptosis of RGCs in animals with glaucoma. In 3 patients with advanced glaucoma, treatment with topical NGF improved all parameters of visual function."

They suggested that these findings open the door to new treatments for glaucoma and perhaps other neurodegenerative diseases as well.

Bonini told the media that this was the first time that NGF eye drops have shown potential as a treatment for glaucoma.

However, he cautioned that although these results are impressive, NGF eye drops are unlikely to be available for a while, because the compound is not yet approved for clinical use. Also, these pilot findings need to be replicated on a larger scale with clinical trials.

"Experimental and clinical evidence of neuroprotection by nerve growth factor eye drops: Implications for glaucoma."
Alessandro Lambiase, Luigi Aloe, Marco Centofanti, Vincenzo Parisi, Flavio Mantelli, Valeria Colafrancesco, Gian Luca Manni, Massimo Gilberto Bucci, Stefano Bonini, and Rita Levi-Montalcini.
PNAS published online before print August 3, 2009.
doi:10.1073/pnas.0906678106

Additional sources: International Glaucoma Association.

Written by: Catharine Paddock, PhD