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  1. 50 Years Supporting Paediatric Vision Testing Worldwide Since 1975

What is Stereovision, and Why Test for it?

Stereopsis (giving stereovision) is the brain’s ability to perceive depth and three-dimensional structure by combining the slightly different images seen by each eye.

Because our eyes are spaced apart, they capture the world from slightly different angles. The brain processes these disparities to create a single, unified perception of depth, allowing us to judge distances, navigate our environment, and interact with objects with precision.

This ability, known as stereopsis, is a fundamental aspect of human vision and plays a helpful role in daily tasks such as catching a ball, driving, and even simple hand-eye coordination. In short, it allows us to judge distances accurately and interact with our environment with confidence. Those lacking in stereopsis learn to compensate to some degree.

 

What Happens if You Don’t Have Stereovision?

Without stereovision, the brain cannot combine the slightly different images from each eye into a single three-dimensional perception of depth.

Instead, depth and distance must be judged using other visual cues, such as perspective, motion, and shadows. While many people lacking stereopsis adapt well, everyday tasks like catching a ball, pouring a drink, or judging steps and curbs can be more challenging.

Activities that require precise depth perception, such as driving, certain sports, or intricate manual tasks, may also be affected. Some individuals may experience eye strain or difficulty in crowded visual environments, particularly when switching focus between near and far objects.

 

 

How Does Poor Stereopsis Affect Everyday Life?

Individuals with reduced stereovision (stereopsis) may struggle with:

  • Judging distances, such as when driving or walking down stairs
  • Hand-eye coordination, making tasks like pouring liquids or catching objects more difficult
  • Reading and learning difficulties, particularly in young children
  • Performance in sports, where depth perception is essential for timing and spatial awareness, such as ball catching 


When is the Best Time to Test for Stereovision?

Stereovision can be tested from a few months of age, and early detection is key for identifying and addressing potential vision issues.

The best time to test for good stereopsis depends on the purpose of the assessment:

  • Infants and Young Children: Testing as early as 6 months to 2 years can help detect problems like strabismus (eye misalignment) or amblyopia (lazy eye) when treatment is most effective. Young children naturally develop binocular vision in the first few years of life, and early testing can check this process is occurring normally.
  • Preschool and School-Age Children (3-7 years): Routine screening during early school years helps identify vision problems that could affect learning, reading, coordination, and sports performance. Many parents and teachers find it helpful to be aware of the importance of good depth perception for academic and motor skill development.
  • Teenagers and Adults: While stereovision is often thought to develop only in early childhood, emerging research shows that vision therapy and targeted interventions can improve stereopsis even in older children, teens, and adults. This is particularly relevant for those experiencing depth perception difficulties that impact driving, careers, or sports.
  • Elderly Patients: Stereopsis can decline with age, and regular testing in older adults can help identify conditions such as cataracts or macular degeneration that may affect depth perception and increase fall risks.

The Frisby Stereotest is particularly useful across all age groups, as it provides a quick, accurate, engaging way to assess stereopsis without requiring special glasses.  It allows allows repeat testing without the patient learning to pass by guessing or memory.

 

 

What Causes Poor Stereopsis?

Poor stereopsis, or reduced depth perception, occurs when the brain struggles to merge the slightly different images from each eye into a single 3D perception of space. This can result from several factors, ranging from early childhood visual development issues to acquired conditions later in life.

Common Causes of Poor Stereopsis

Strabismus (Eye Misalignment)
When the eyes are not properly aligned—such as in esotropia (eye turns inward) or exotropia (eye turns outward)—the brain may suppress the image from one eye to avoid double vision, leading to reduced or absent stereovision.

Amblyopia (Lazy Eye)
If one eye has significantly poorer vision than the other (often due to a high prescription difference, strabismus, or deprivation from conditions like congenital cataracts), the brain may rely more on the stronger eye, reducing its ability to develop stereopsis.

Anisometropia (Unequal Refractive Error)
A large difference in prescription between the two eyes can cause unequal image clarity or size (aniseikonia), making it difficult for the brain to fuse images together for stereovision.

Monocular Vision Loss or Impairment
If one eye has significant vision loss due to conditions like cataracts, retinal disease, or optic nerve damage, stereopsis is impaired or absent.

Congenital Absence of Stereopsis
Some individuals never develop stereovision, either due to early developmental issues or unknown neurological factors. They may rely entirely on monocular depth cues to judge distances.

Brain and Neurological Conditions
Stroke, traumatic brain injury, or certain neurological disorders affecting visual processing can disrupt binocular vision and depth perception.

Age-Related Changes
Stereopsis can decline with age due to changes in vision, including presbyopia (long sightedness), cataracts, or reduced neural processing of binocular information.


Can Poor Stereopsis be Corrected or Improved?

While some causes of poor stereopsis are permanent, others can be improved with vision therapy, corrective lenses, surgery (for strabismus), or cataract removal. Emerging research on neuroplasticity also suggests that some adults may be able to improve stereovision with targeted interventions.

Testing for stereopsis with a reliable tool like the Frisby Stereotest can help detect issues early and guide appropriate management.

 

Some professions like surgeons and forklift truck drivers are assessed for stereopsis. 


Is Testing for Stereopsis Just for Children?

No, stereovision testing isn’t just for children. Adults and teenagers can also experience disruptions in depth perception due to eye injuries, neurological conditions, or vision imbalances. Recent research highlights that the brain retains a degree of neuroplasticity beyond early childhood, meaning that with targeted therapies, stereovision issues can sometimes be improved later in life.

Regular stereovision assessments can also be critical for professions requiring precise depth perception, such as pilots, surgeons, fork-lift truck drivers and professional drivers, which is why screening for stereopsis is a requirement for some  professions. Additionally, for elderly individuals, maintaining good depth perception can help prevent falls and improve mobility.

By incorporating stereovision testing into routine eye exams, eye care professionals can help detect hidden vision problems, guide treatment options, and improve the quality of life for individuals of all ages.