Binocular vision provides redundancy, improves object visibility, and allows for depth perception. Stereopsis is important for predators to judge distance. Vision abnormalities can impair binocular vision, requiring corrective lenses or surgery.
A creature with two eyes used together to view a single image is said to have binocular vision. Creatures with binocular vision have many advantages over one-eyed creatures or creatures that are unable to use their multiple eyes together. At a very basic level, a second eye provides a safe level of redundancy; if one eye is lost, another is still there, allowing the creature to see. Using two eyes together also improves a creature’s ability to see objects that are, for whatever reason, difficult to see. In general, due to the distance between two eyes, a creature with binocular vision will have a wider field of vision than a creature without.
Another important aspect of binocular vision is stereopsis, which allows creatures to perceive depth. Stereopsis occurs when two eyes perceive an object and its surroundings from two slightly different angles, which naturally occurs due to the slightly different positions of the eyes. Due to the different angles, the eyes are able to perceive depth and distance. This is especially important for predatory animals, which need to judge the distance between themselves and their prey. It is a little less important to prey on animals; their eyes tend to be set far apart, which gives them a much wider field of vision.
Having two different eyes seeing two slightly different images can have some interesting effects. In some cases, often involving some kind of damage or disturbance, one eye sees an image that is very different from the other eye. In some cases, the different images seen by the eye are merged. Sometimes a creature experiences double vision, in which it sees two often overlapping images of the object.
There can be many different vision abnormalities and disorders that tend to impair vision in different ways. In some people, differences in the muscles in each eye cause one eye or the other to drift, misaligning proper binocular vision. Eye tests looking for binocular vision abnormalities usually test that an individual’s eyes are both able to work together to track an object, stay focused on an object, and work together to see only one object at a close or long distance. If the eyes fail to perform these tasks, corrective lenses or surgery may be needed to repair the eyes and bring them back to full working order.
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