Thursday, June 14, 2007

Eye flickers key for fine detail .

Tiny, involuntary movements made by our eyes when we focus on something could be more useful than we might think, scientists have found. We may not be aware that our eyes are making these movements, but without them our vision fades. And scientists have now found that they could also be important in helping us to see very fine details. The research, carried out by scientists at Boston University, was published in the journal Nature.
Our eyes are never in a position of absolute rest - they are always moving slightly, much as we find it difficult to hold our hands completely steady. These tiny flickers made as we focus on something are known as fixational eye movements. They keep the image on the retina of our eyes moving, and scientists have known for about 50 years that removing this motion for a long time, by stabilising the image on the retina, causes vision to fade. This observation gave rise to the idea that the movements are necessary to refresh the responses of neurons in the visual system to prevent images we are focused on from fading.
New technique
But there has been debate over whether the movements have any other functions. Professor Michele Rucci and colleagues used a new technique for counteracting the visual effects of the eye movements to test their effects on vision. They were able to stop the effects of the movements for short periods of time, so that vision did not start to fade. They found that, without the motion, people in the study were less able to perceive fine details in images. Participants looked at a grating and had to say whether it was being oriented to the right or to the left. When the grates were very close together, people were less successful in the task if their retinas were stabilised to remove the effects of the eye movements - they got it wrong 16% more of the time.
However, when the grates were further apart there was no effect when the retinal image was stabilised. Professor Rucci said it seems that when we fixate on something we get more small eye movements which could help us focus on these details.
He said such a mechanism could be crucial to help us focus in on fine details when we need to.
And he said the findings could have clinical implications for people with conditions that result in abnormal fixational eye movements.
He said: "By showing that fixational eye movements participate in the perception of fine detail, our results may help explain the reasons behind part of these visual deficits and may contribute to the development of treatments."
Tim Hunter, a councillor for the College of Optometrists, said the research was interesting and seemed to give a "sound result" but that he would like to see the effects duplicated in other studies to confirm the finding.
He added that understanding more about how the eye works and can go wrong could give us opportunities to correct problems and improve vision in the future.

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