These periods of stress on the nervous and vision system are part of normal development, but can adversely affect some children, even those whose vision has been fine. Eyes that are crossed do not function properly. The messages each sends to the brain are so different that the brain cannot fuse them into one image, as occurs with normal two-eyed vision. This can result in double vision or in difficulty doing tasks that require two-eye coordination. It also can interfere with the development of other vision skills.
Lazy eye is another side effect or complication stemming from crossed-eyes.
It also can be a side effect of a vision condition in which one eye is much more nearsighted or farsighted than the other. With both situations, the brain receives different messages from each eye and is unable to fuse them into one image. Therefore, the brain disregards the message from the one eye. Since the ability to see sharply and clearly is a learned skill, the visual acuity never develops properly in the disregarded eye. The resulting one-eyed vision can affect other vision skills, such as the ability to judge distances, but people with lazy eye often will not notice this.