Binocularity, or binocular vision, refers to the use of the two eyes together as a team. A misalignment between the two eyes, even when it is temporary, can contribute to visual discomfort and a decline in visual performance. Sometimes, it can also result in double vision or blurred vision.
A failure of accurate binocular vision can manifest itself in many forms -- for example ‘convergence insufficiency’, ‘binocular instability’ and ‘unstable or decompensated heterophoria’. This can sometimes lead to academic challenges and behavioural compensation in children and also eyestrain in both children and adults. For example, the eyes need to point in the same direction. When a child is reading, the eyes will need to be turning inwards to maintain focus on the object.
There is evidence that binocular instability contributes to the reading difficulties and spelling errors that some children make. Such problems can be remediated through vision therapy. The treatment allow the child (and/or adult) to gain control of their binocular vision by encouraging the two eyes to point accurately towards the same direction and for the visual system to work efficiently.