SUE FORD / SCIENCE PHOTO LIBRARY SUE FORD / SCIENCE PHOTO LIBRARY
Cover test for squint. A black cover is held over the left eye (right) of a young boy being tested for a squint. Cover tests are used to detect supp- ressed squints in children. The child is asked to look at an object while an observer covers one of his eyes. The cover is then quickly withdrawn and the newly uncovered eye watched for sideways movement, which occurs when a squinting eye corr- rects its focus. Squints in children are caused by a failure in the mechanism that aligns the eyes. They cause double vision and can lead to permanent loss of sight in one eye if left untreated. Treatment includes surgery, special glasses, and wearing a patch over the dominant eye.
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