Our vision changes in the blink of an eye
Eyelids and their effect on corneal topography
Eyelids do a whole lot more than hold up our eyelashes and keep the sun out, a Queensland University of Technology PhD optometry researcher has found.
A study by Scott Read of QUT's Institute of Health and Biomedical Innovation found the upper eyelid's pressure and shape of its opening work to change the shape of our eyes throughout the day.
Dr Read found the biggest changes were amongst people who maintained a downward gaze for a long time while reading or doing close work.
"The first study found that there were highly significant changes to the contours of the cornea (the eye's front surface) throughout the day when we tested at 9am, 1pm and 5pm over three days of the week," Dr Read said.
"The study found horizontal bands of distortion appeared on the cornea where the eyelid would have been sitting and that this increased during the day but went back to normal by the next morning.
"As these changes appear to be related to forces from the eyelids themselves and were more marked in people who spent a lot of time reading in downward gaze it is certainly one reason why people's vision may be slightly worse at the end of the day or after doing a lot of close work.
"It suggests that people should take a short break from reading or close work at least every hour."
Dr Read said some changes were also found in corneal astigmatism (which can lead to distortion of vision due to irregularities of the cornea), a condition that affects up to 60% of people.
In a second study on 100 normal-sighted young subjects, Dr Read described the shape of the eyelid opening at different angles of gaze and compared this with the contours of the cornea to find out how eyelid characteristics and corneal shape affected each other.
He found significant associations between the angle, shape and size of the eyelids and the shape of the cornea.
"It appears eyelids do play a part in determining the shape of the cornea. One explanation is that pressure from the eyelids is involved in the cause of corneal astigmatism.
"As yet we have no concrete evidence on what causes astigmatism but this helps us move towards finding a cause."
His findings would provide the groundwork for new understanding about astigmatism in children and in older age.
"Children are born with a high degree of astigmatism and the cornea changes shape rapidly in the first four years of life, so the study's findings could shed light on how some people go on to develop astigmatism," he said.
"Astigmatism also changes in older age, so this may help to explain some of these changes that happen to our vision in older age."
Dr Read's research would also open our eyes to new areas of research on accurately measuring pressure from the eyelids, and how these corneal changes may affect the development of short sightedness.
Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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