Many patients ask about depth perception and the loss of vision in one eye. To help explain the impact of monocular vision on depth perception, we need to define a few things.
Monocular Vision: a condition in which one eye is blind, seeing with only one eye
Binocular Vision: seeing with two eyes simultaneously
Depth Perception: ability to detect how far away an object is from other objects
When looking at depth perception, there are two sets of cues that contribute to what we perceive. Binocular cues and monocular cues.
Binocular Depth Cues:
Convergence: inward turning of eyes. The closer the object, the more convergence needed.
Stereopsis: three-dimensional vision
A person who lost sight in one eye would only be able to see monocular cues. They would not be able to view objects in 3D or stereopsis. It is helpful to remember that true stereopsis is most advantageous only up to 3 feet. After this distance, it becomes a weak visual cue. So, what about those with monocular vision? There are 7 monocular depth cues that help a person determine the distance between objects. These are all weak visual cues that can add up to be quite helpful in daily life.
Monocular Depth Cues:
Accommodation (or focusing): is the change in dioptric power of the interocular lens in order to see a near object more clearly. The more accommodation needed, the closer the object.
Linear Perspective: the visual phenomenon in which parallel straight lines will converge in the distance. If two parallel lines are assumed to be straight, then the further separated the lines become, the closer the object must be.
Interposition (or overlapping): is the visual phenomenon in which the view of one object may be blocked by another object. The object being blocked must be behind the first object.
Texture Gradient: the amount of detail in an object. The closer the object, the more detail visible. Far objects lose detail.
Relative Size: is the visual phenomenon in which larger retinal image sizes are associated with objects that are closer. An object that appears larger than a similar object will be closer.
Light and Shadow: these cues can provide feedback on the elevation or recession of an object.
Relative Brightness: is the visual phenomenon in which closer objects appear brighter than further objects.
Aerial Perspective: is the visual phenomenon of distant objects appearing hazier than closer objects. This only occurs in long distances, like mountains which appear hazy due to how far away they are.
Motion Parallax: is the apparent displacement of objects in space while moving that causes closer objects to move faster than distant objects. Think of looking out a car window when moving and seeing the objects in the distance move by slowly, but the objects close-up moving very quickly.
We hope this information will be helpful, there are also many practical suggestions in coping with monocular vision in an excellent book by Frank Brady, A Singular View.