WASHINGTON, Oct. 9 (Xinhua)-- A study published on Tuesday in the journal PLOS Biology showed that near-sightedness and far-sightedness develop through different molecular pathways.

The findings provides a new understanding of myopia, which is expected to affect nearly half the world's population in the next three decades, and opens the way for development of drugs to prevent it.

Myopia occurs when the eye grows too long, increasing the distance between lens and retina such that the image produced by the lens comes into focus at a point in front of, rather than on, the retina.

In hyperopia, the opposite occurs. The eye is too short, and the focal point is behind the retina.

Researchers from Columbia University induced either myopia or hyperopia in marmosets, by placing lenses in front of their eyes.

When marmosets were exposed to defocus of either type in one eye for up to five weeks, the activity of genes in the exposed retina changed compared to the non-exposed retina.

But they found that the molecular pathways affected were for the most part different between the two types of defocus.

While both types of defocus induced changes in important cellular signaling pathways, with the scores of genes affected in each case, only a small handful were affected by both types of defocus, according to the study.

There were also gene activity differences over time in each type, with little overlap between those affected within the first 10 days and those affected after five weeks.

They found that 29 of the genes whose activity changed in response to defocus were localized within chromosomal regions (called quantitative trait loci) previously associated with human myopia in large-scale genetic studies.

The findings suggested that variations in the expression of genes involved in the normal regulation of eye shape in response to defocus contribute to nearsightedness, according to the researchers.

"The results of this study show that the retina can distinguish between myopic and hyperopic defocus and responds to defocus of opposite signs by activating largely distinct pathways," said Andrei Tkatchenko with Columbia University.

"Identification of these pathways provides a framework for the identification of new drug targets and for the development of more effective treatment options for myopia," said Tkatchenko, the paper's corresponding author.