Myopia causes blurred vision. The most common problem for those who are shortsighted is difficulty seeing distant objects clearly. Some myopic children have never had clear distance vision and so are not aware of what they are missing. School vision screening will often detect myopia. Frowning and screwing up the eyes in an effort to see better is common and this may cause headaches. Shortsighted children will sometimes hold reading material quite close. In their mid to late forties most people with perfect distance vision need reading spectacles, however many people with myopia can see close work clearly without them.