Discovered: What causes blindness!

There are two types of AMD -- wet and dry. Drugs have only been developed to stabilise wet AMD, which is the most aggressive one. But, currently there is no effective treatment for "dry" AMD, a less serious form of the disease.

Ophthalmologist Dr Jayakrishna Ambati of University of Kentucky and colleagues have found that a toxic protein builds up and kills off retinal cells, leading to the devastating dry Age-related Macular Degeneration.

A molecular mechanism leads to a condition known as geographic atrophy or dry macular degeneration, the major cause of untreatable blindness, say the scientists, raising hopes that devastating AMD could be stopped before victims become almost completely blind, the `Daily Express` reported.

Interestingly, according to their study, an enzyme called Dicer protects against dry AMD.

When Dicer levels drop, it leads to the build-up of a toxic type of an RNA molecule, a macromolecule the same as DNA and proteins. The molecule causes retinal cells to die in patients with dry AMD.

In a healthy eye, the Dicer enzyme would degrade the RNA particles, preventing them from launching the poisonous attack on the eye`s vital cells, say the scientists.

The discovery led them to develop what they describe as two "promising" therapies to prevent the condition. In fact it showed that they`re both effective particularly when tested using laboratory models.

The findings have been published in the `Nature` journal.