Simple stereopsis testing, ideal for young children
Frisby Stereotests are a simple and effective screener and assessment test of stereopsis vision. There's no need for special glasses, and they are suitable to use on young children and even babies.
"..the most useful subjective test of stereopsis for young children is the Frisby Stereotest."
Dr Margaret Woodhouse, School of Optometry & Vision Sciences, Cardiff University
For over 40 years, the Frisby Stereotest has been popular with ophthalmologists & orthoptists. For many it is their test of choice.
What is Stereovision?
Stereovision is a term used to identify the process in which the slight differences between the images of the world in the two eyes, arising from their different viewpoints, gives us a three dimensional depth perception.
What are stereovision tests used for?
Stereoscopic vision and depth perception testing can be helpful as part of a range of measures used in the identification of conditions such as:
- a squint (strabismus)
- lazy eye (known as amblyopia, which is reduced vision in one eye that cannot be resolved by optical corrections)
- reduced stereopsis (stereopsis is 3D depth perception using the sight differences between the images in the two eyes), shown by lowered stereoacuity (reduced ability to see small differences in the depth of objects)
Where are stereovision tests used?
Stereovision tests are primarily used in the vision and eye-health care of children, both as a vision screening tool for reduced or no stereopsis, severe amblyopia and other binocular vision defects, and also as a way of monitoring the progress of treatments.
They are not only used for children, however, but also for testing stereoscopic vision in adults of all ages including the elderly, where a diagnosis of reduced or absent stereovision is increasingly recognised as a possible factor trips and falls, and so contribute to care plans.
Some professions also require good stereoscopic vision and use testing, for example for fork lift truck operators and pilots.
Who administers the Frisby Stereotest?
They are used by opticians, orthoptists and by ophthalmologists in hospital departments.
They are also used by paediatricians, in Early Years medical and vision screening programmes, and as a screening instrument for certain professions.
The Frisby Stereotest is a Random Element Test using a Real Depth Object
The Frisby Stereotest uses a kind of random dot design but without the typical disadvantages (see below) of random dot stereograms which require the patient to wear red/green or polaroid spectacles.
Random dot patterns eliminate monocular cues (i.e. ways in which the patient could pick up other clues from the testing environment, such as shadows), which could lead to a patient 'guessing' a correct test response.
There are four benefits to not using stereograms with special spectacles.
1. Some young children do not want to wear spectacles, hence reducing their concentration on the test.
2. The practitioner is more easily able to watch the patient’s eyes as they take the test, which is very important, particularly when testing young children and other groups with language barriers. The Frisby Stereotest does not require a verbal response: seeing where the patient is looking can be sufficient for a judgement of Stereopsis Demonstrated, or the young patient can be trained to point at the target if they have stereopsis.
3. If the patient has fragile binocular single vision, wearing glasses can be dissociating and lead to a misleading result.
4. There is no need to share glasses amongst patients, which is better for health and safety reasons and for reducing the risk of infection transmission. This is particularly important in the era of Covid-19.
