Normally the two eyes move parallel to each other in all the directions of gaze.

Squint is a misalignment of the two eyes so that both eyes are not looking in the same direction. In other words the two eyes don't look straight in the primary gaze. It is a common condition among children. It may also occur in adults.

At birth the eyes don't move together. One eye moves differently from the other till the first few months. After that the baby starts fixing the eyes on the light which is called light fixation and the eyes start moving together.

Under normal circumstances, when both the eyes have good vision and they are aligned properly, they focus on the same object. Each of the eyes sends picture ! of the same object, viewed from a slightly different angle. These two images reach the brain, where they are fused to form a single three-dimensional picture with depth perception. This is known as binocular single vision.

Six muscles control the movement of each eye. Each of these muscle acts along with its counterpart in the other eye to keep both eyes aligned properly. A loss of coordination between the muscles of the two eyes leads to misalignment. This misalignment may be the same in all directions of gaze, or in some conditions the misalignment may be more in one direction of gaze.