Young children who have a squint are significantly less likely to be invited to birthday parties compared to their peers with normally aligned eyes, the results of a new study indicate.

Swiss researchers digitally altered photographs of six children from six identical twin pairs to create inward and outward types of visible squint - known as strabismus - to compare against normally aligned eyes.

They then asked 118 children aged between three and 12 to select which of the identical twins they would be prepared to invite to their birthday party. All of the children were either patients at an eye clinic themselves, or were the the siblings of patients, but all had normally aligned eyes.

They were asked to make a choice four times, giving them the chance to select the faces of up to four children with a squint. If squints were to make no difference to selection, an average selection of two children with a squint would be expected, the researchers explained.

The study found that factors such as the clothes being worn, gender or the type of squint made no difference to the likelihood of selection. Furthermore, children under the age of six did not make any distinction between the twins with a squint or normally aligned eyes.

However the researchers found that from the age of six, the participants were significantly less likely to select the picture of children with a visible squint.

Among the 48 children aged between six and eight, 18 did not select any child with a squint, 17 selected this type of child once, 11 did so twice, two did so three times, while none did so four times.

This compares with 31 children aged between four and six, one of whom did not select any child with a squint. However 21 selected a child with a squint once or twice, while nine children in this age group made this selection three or four times.

When asked if they had noticed anything particular about the twins, 19% of the four to six year olds commented on eye alignment, a figure that rose to 39% after being asked to pay attention to the eyes in the pictures.

Among six to eight year olds, 48% noticed the squint, which rose to 77% after being asked to pay attention to the eyes.

The researchers pointed out that a childhood squint can have a lasting psychological impact on the individual concerned and that ‘visible differences in general have a negative impact on how children are perceived by peers'.

"Our results show that schoolchildren with strabismus seem less likely to be accepted by their peers, so corrective surgery for strabismus should be performed before the age of six years, when negative social implications may arise," they concluded.

Details of these findings are published in the British Journal of Ophthalmology.