Monocular Vision Impairment | Living Without Depth Perception

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monocular vision impairment

Monocular Vision is defined as vision wherein both eyes see different images. For instance, there are many birds that have monocular vision where each eye's vision is independent of the other. Although this type of vision can provide a larger field of vision, it also promotes increased difficulty with depth perception.

In humans, monocular vision impairment is usually due to one eye being blind or unable to register similar images as the other eye. This vision impairment makes it increasingly difficult for people to determine depth perception of objects in close proximity, therefore forcing them to rely on other factors to estimate visual depth.

What Causes Monocular Vision

There are a variety of circumstances that can result in monocular vision impairment. For instance, any scenario that leads to vision loss or limits the ability of both eyes to record similar images can cause monocular vision. Some of these causes may include:

  • Trauma to the eye
  • Eye injury
  • Eye surgery
  • Strabismus or Crossed Eyes
  • Amblyopia or Lazy Eye
  • Eye disorders impacting one eye such as cataracts, glaucoma and macular degeneration

Monocular Vision Test

According to the FAA's aviation criteria, a person is considered to suffer from monocular vision if they meet the following specifications.

  • Complete blindness in one eye
  • Legally blind in one eye (visual acuity and/or field of vision)
  • Suffers from Amblyopia or another eye disorder that impacts vision in one eye

Monocular View

When it comes to monocular vision, the vision in one eye is usually limited, reducing the overall field of vision by as much as 60 degrees and limiting depth perception. Below is an example of limited field of vision.

monocular vision impairment

Monocular Depth Cues: Adjusting to Monocular Vision

Depth perception is taken for granted by many, but how do people adjust and adapt to having limited or no depth perception? Well, for those who suffer from monocular vision it can be quite a frustrating adjustment period. Nevertheless, there are cues available that can help in the evaluation and determination of depth perception. Some of these cues according to may include the following:

  • Linear Perspective: By logically evaluating the parallel lines that converge onto distant objects a person can gain some perspective and approximate the object's distance.
  • Interposition or overlapping: Using other objects to determine distances, for instance if one object is partially blocked by another you know it is behind it.
  • Texture Gradient: Being aware that closer objects will provide more detail than further objects.
  • Relative Size: Awareness of external factors such as shadows can help determine an object's size relative to other objects surrounding it.
  • Motion Parallax: This cue uses the notion of speed of objects to approximate distance, where closer objects move faster than distant ones.

monocular vision cues

Although all of these cues may, on an individual basis, still provide an inaccurate depth perception by utilizing all or some of them, a person may be able to closely approximate depth approximations.

Monocular vision impairment impacts millions of people every day, and although it might limit the ability to pursue certain careers, using some of the techniques mentioned in this article can help adjust, ultimately reducing the negative impact on quality of life.

Guide for Aviation Medical Examiners | FAA
Living With Monocular Vision |


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