Frequently asked questions

...answered by us in detail.

Frequently asked questions about the Lang Stereotest I & II

What is the difference between the versions I and II of the Lang-Stereotest?

The test versions differ in the test objects, their disparity, the random dot pattern.

  • The Lang-Stereotest I has the 3 test objects CAT (1200''), STAR (600'') and CAR (400''). They are arranged in a triangle.
  • The Lang-Stereotest II has the 4 test objects ELEPHANT (600''), TRUCK (400''), MOON (200'') and STAR (200''). They are arranged in a quadrangle. STAR is also visible with only one eye thanks to a darker colouring.
What is the purpose of a Lang-Stereotest II if I already have the Lang-Stereotest I?
Since the screening is repeated every year in childhood in order to diagnose intervening visual disorders at an early stage, it cannot be ruled out that a child names the test figures solely on the basis of his or her memory of the last test, even though he or she may no longer be able to see them. Using a second test version with different test figures can reduce the risk of a false positive test result.
What is the difference between the old (I and II) and the new version of the Lang-Stereotest (I-R and II-R)?

The following differences exist between the old and new versions of the Lang-Stereotest:

  • The new revised (R) versions have a higher print quality and more uniform random dot patterns. The test objects are thus better camouflaged than in the predecessors.
  • On the reverse side, the arrangement of the test objects is shown laterally reversed. The examiner can orientate himself on this and control the subject's eye movements. An attentive change of gaze between the test objects is a strong indication that they have been recognised.
  • The reverse side contains a schematic drawing as well as brief instructions in English for correct test application.
  • The corners of the test cards are rounded.
What advantage does the Lang-Stereotest I have over the Titmus stereo test and TNO stereo test in screening as part of early detection measures in children?
Advantages for performance:
  • Free of glasses: This advantage over the other two tests, which require test glasses, is all the more significant the younger the children examined: The Lang-Stereotest II could be performed in 94.4% of all children in a sample of almost 2400 children between 6 and 72 months, significantly more than the other tests.
  • Perfect camouflage: The use of random-dot stereograms for screening is a clear advantage over contour tests such as the Titmus test,. With the latter, children occasionally mistakenly interpret reaching for the test object (fly), which can also be recognised with one eye, as a sign of stereopsis being present, although this is absent, for example in the presence of microstrabismus.
  • Few child-friendly pictures on the same handy test card: The positive test result can be confirmed if the child not only names the 3 objects correctly, but can also say which of the objects are furthest or least prominent.
  • Graded cross-disparities corresponding to the real 3D range for proximity: From 1200 to 200 arcseconds.
Advantages in results:
  • In a comparative study published in 2014 by Ancona et. al, the Lang-Stereotest I was found to have the highest sensitivity (89.8%) and specificity (95.2%), as well as the highest positive and negative predictive values, for screening strabismus and microstrabismus compared with the Titmus test, the TNO test and the Lang-Stereotest II.
(To explain: a test with 100% specificity reliably identifies all non-sufferers. A test with 100% sensitivity reliably identifies all patients with a disorder).

Frequently asked questions about the functionality

Which visual disorders can be diagnosed with the Lang-Stereotest?

The test can detect visual disorders in which binocular stereo vision (stereopsis) partially or completely impaired.

This includes amblyopia with its various forms. Amblyopia means amblyopia, i.e. a loss of vision in one or both sides. In the most important and most common form, strabismic amblyopia, a loss of vision occurs in the squinting eye because the brain suppresses the double images that arise due to the deviation of the axis. This loss then becomes noticeable with limited stereo vision.

In anisometropia, one eye has normal vision or only a little defective vision, while the second eye has astigmatism, short-sightedness or far-sightedness (myopia or hyperopia). This results in an indistinct visual impression on the respective retina, and vision is reduced. In the case of binocular anisometropia, as with strabismus, the disturbing image impression is suppressed on one side, so that binocular stereo vision is no longer possible.

Can the test also be passed with one-eyedness?

No. In order to create a spatial image impression in the viewer's brain, the slightly different image information of both eyes must be perceived.

The separation of the image information is ensured by the lenticular lens. With prolonged viewing with one eye or slight sideways or tilting movement, the areas in which the test figures are located can sometimes be made out. However, spatial recognition is not possible due to the lack of image content for the second eye.

Can the test detect visual impairment, i.e. reduced visual acuity?
No. The test is not intended to assess visual acuity, even though stereo vision (stereopsis) may be impaired by uncorrected visual impairment. In case of a negative or questionable positive screening test result, the assessment of visual acuity in both eyes is therefore recommended.
Are there any diseases of the nervous system for which the test can be used?
The test basically detects intact binocular random dot stereo vision (global stereopsis) with high sensitivity and specificity. Diseases that render the eyeball, the eye muscles or parts of the visual pathway (eye - optic nerve - optic chiasm - corpus geniculatum laterale - primary visual cortex) non-functional can impair stereo vision. This can be the case, for example, with an inflammatory brain disease or after a stroke.
How can you distinguish a pseudo-squint from a real squint with the test?

In pseudo-squinting (pseudo-strabismus), the child may seem to squint inwards (strabismus convergens) due to a so-called epicanthus, especially when looking to the side. In this case, the white of the sclera (white sclera) disappears behind the nasal fold of the eyelid (epicanthus fold). These children pass the stereo test, usually to the great relief of their parents, i.e. it is only a pseudo-squint and not a real squint.

Other anatomical peculiarities also occasionally simulate strabismus in adults, such as a particularly narrow or wide distance between the pupils, with unequally sized scleral triangles on the nasal or temporal side of the eyes. Here, too, strabismus can be ruled out by demonstrating stereo vision with a positive test result.

When tilting the test card sideways, the test objects disappear, then suddenly appear behind the image plane. Is this normal?
Yes, this is due to the construction of the lenticular. For correct testing and a maximum stereo effect with the figures migrating towards the viewer, it is therefore essential to hold the test card frontoparallel or perpendicular to the viewing axis when looking straight ahead.

Frequently asked questions about use

Is the test also suitable for adults?
Yes, the Lang-Stereotest works very well for all age groups. Adults who need reading glasses should use them, because the test distance corresponds to the normal reading distance of 30-40cm.
Are only doctors allowed to use this test?

No. The test can also be used by all professionals who are well acquainted with the basics of eye physiology and the most important clinical pictures of the eyes and their treatment. This includes orthoptists, optometrists and also opticians.

Furthermore, the test can be used by medical staff or assistants (e.g. teachers) after they have received appropriate training.

The less specialised the testers are in eye diseases, the more cautiously questionable or negative results must be interpreted even when screening is done correctly.

From what age can I use the test?
Stereoscopic vision is usually fully developed between the fourth and sixth month of life. The test can be used as soon as the child can look at the test card calmly for a while. Most children can be tested without any problems in the second year of life, and some infants can even be tested at the end of the first year of life.

Frequently asked questions about the LANG-STEREOPAD

What are the differences of the LANG-STEREOPAD® compared to the LANG-STEREOTEST® I and II?
Th Lang-Stereopad® differs from the other Lang-Stereotests® in the following features:
  • 6 instead of 3 test figures with different disparity, individually arranged on a magnetic square test card of 6.4 x 6.4cm each.
  • Larger range between highest (1000'') and lowest (50'') disparity: STAR 1000'', CAR 600'', CAT 400'', MOON 200'', SUN 100'', STAR 50''. The test figures STAR, CAT and CAR, are also included in the Lang-Stereotest® I-R, but with a different disparity.
  • Red test panel 15cm x 21cm, on which the test cards stick magnetically.
  • Available separately on request: Magnetic handle for the back of the test panel.
The Lang-Stereopad® has its own trademark.
What are the advantages of the LANG-STEREOPAD compared to the LANG-STEREOTEST I/II?

The LANG-STEREOPAD® basically works according to the same proven principle of the spectacle-free Random Dot Stereotest, i.e. like the Lang-Stereotest® I and II.

  • While the latter are primarily used for initial stereopsis screening, the Lang-Stereopad® is particularly ideal when the test needs to be repeated, i.e. when the screening result is uncertain or questionable, as well as for patients treated for visual impairment.
  • Since the test figures can be presented individually or in combination (but not more than three at a time), guessing is made impossible by positioning alone.
  • By rotating the test cards by 90 degrees, individual test cards can be blinded, i.e. made unrecognizable, so that the examination is made possible with the so-called "preferential looking method": the test person must prove that he or she can distinguish between blinded and stereoscopic test cards. This makes the test result more unambiguous and independent of the examiner's interpretation, especially for people who can recognize the test figures but cannot name them verbally (babies and people with speech impediments, for example after a stroke).
  • The stereo threshold can be determined by gradually presenting test cards with less disparity and spatial migration of the test figures: for example, if a person no longer recognizes the test figure SUN 100'' but the test figure MOON'' 200'', the stereo threshold is 200''.
  • In addition to the early detection and prevention of amblyopia, the LANG STEREOPAD® thus opens up very important new fields of application for the testing of binocular stereo vision, both in the clinical field (neurology, i.e. all diseases of the central nervous system) and in the clinical field, as well as in the field of occupational medicine: testing and assessment in occupational groups and activities where intact stereo vision is required (medical personnel, especially in surgery, pilots, truck drivers, professional divers, occupations involving work on rapidly rotating machines with a risk of injury, welders, high-voltage current technicians, grinders and precision mechanics, painters, architects and graphic designers).
What does Preferential Looking Method mean? How is it implemented in the Lang Stereopad? What are the advantages of this examination method?
The Preferential Looking Method is a method used in the study of vision in young children. This method is based on the observation that children naturally tend to focus on images or objects that catch their eye first, for example, by providing a special depth perception.

In stereo vision tests based on the principle of preferential looking, children are placed in front of a board or screen on which two or more pictures or objects are shown, one of which offers a particular depth perception. The child is then asked to focus on a particular picture or object. The child's behaviour during the test, particularly the length of time his or her gaze lingers on each of the images, is then recorded and evaluated to draw conclusions about his or her stereo vision abilities.

With the Lang-Stereopad, one of two or three test images providing depth perception is shown simultaneously with one (or two) test cards rotated 90 degrees and thus blinded. The child has passed the test if he/she has been interested in the test card with depth perception for a longer period of time and has turned away from the others.

An advantage of the preferential looking method is that it is easy to perform and evaluate and does not require language skills. It is also a natural and child-friendly approach, as children usually focus on the pictures or objects that are most interesting to them.
However, there are also limitations to using the preferential looking method. Children aged 1-2 years do not yet have the same complex visual processing skills as older children or adults and may therefore have difficulty understanding or performing the tasks of the test. It may also be difficult to interpret the child's behaviour during the test as they are not yet able to verbally express their thoughts and feelings. It is important that the test is administered under optimal conditions and by experienced testers.

Translated with DeepL
Are the test cards of the LANG-STEREOPAD also available individually?
No, the product is only offered as a complete set, consisting of six different test cards, the test plate, the test instructions and the storage box. If you lose individual test cards, please contact us directly.
Is it mandatory to use the red test plate when testing with the Lang stereo pad?

Yes, this is recommended in any case, for the following reasons: 1. so that the test card(s) is (are) seen quietly, upright and at the correct reading distance. 2. to prevent false positives, for example, when the test cards are picked up by the subject and moved in such a way that the figure, although not actually spatial, is recognised by its outline.

It should be noted that the clinical testing and standardisation of the Lang Stereopad has been carried out using the test card. For this reason, the manufacturer declines responsibility for incorrect test results obtained by testing that deviates from the instructions for use.

Are the magnets on the test cards dangerous? Does the red test card contain a magnet?
There are two rather weak neodymium magnets in each test card, which normally do not pose any health problems. The red test card does not contain a magnet.

Other questions

How can one determine by the simplest of means whether a person has binocular stereo vision?

If no stereo test is available, the Lang two-pencil test can be used to distinguish true binocular stereo vision from monocular spatial vision.

The test person is given a pencil and a second pencil of the same type is held out with the tip pointing upwards. The subject is now asked to cover his left eye with the palm of his left hand and to hit the tip of the examiner's pencil from vertically above with the tip of his own pencil. Typically, this is difficult, i.e. the points usually do not hit each other at first go but after several repetitions.

In a second step, the subject is asked to repeat the hit attempt with both eyes open, which normally succeeds immediately. However, if this second attempt turns out to be as difficult as the first, then there is a suspicion of limited binocular stereo vision in amblopia.

Why is a random dot stereo test like the Lang-Stereotest generally preferable to a contour stereo test when the latter are much easier to pass?

The problem with contour stereotests is that they give too many false positives, especially when used by non-expert lay people.

"False positive" means that based on the object recognition, a binocular stereopsis is falsely postulated, although the object was not seen spatially at all.

This is because the decisive criterion for proving binocular stereopsis is that a presented stereo visual stimulus actually leads to a spatial sensation by stimulating the neurons responsible for it. In random dot stereopsis tests, the recognition of figures is made possible solely by this stereo stimulus, and not by the natural outlines, colour or surface structures, as is the case, for example, with the "fly" of the Titmus test.

Random dot stereotests are therefore not generally "more difficult" than contour stereotests, but they provide significantly more reliable results, i.e. the detection of stereopsis is thus much more reliable.

Why is the price range at which the LANG-STEREOTEST are offered on the market so high?

Answer: For years, the manufacturing company Lang-Stereotest AG has pursued a uniform and stable pricing policy towards its distribution partners and end customers based on the price in Swiss francs, basically without price fixing or price agreements. Currency fluctuations, intermediate trade, warehousing, as well as variable transport and import fees are the main reasons for the price differences.

In e-commerce, however, there are isolated offers where it is unclear whether it is just one of the two test versions or a set of two consisting of both versions. Lang-Stereotest AG cannot be held responsible for this, but would be grateful for any information. We will contact the respective dealer with the request to make his offer clearer.

Questions from test subjects or the parents of tested children

My one and a half year old daughter was diagnosed with strabismus...

Question: My one and a half year old daughter was diagnosed with strabismus. She did not pass the Lang stereo test. Should I get such a test to train stereo vision with her?

Answer: No. The treatment of strabismus, or strabismic amblyopia, follows clear treatment guidelines with the aim of stimulating the weak eye more than the healthy eye. Random dot stereograms such as the Lang stereotest, however, are not suitable for this purpose; instead, visual stimuli that can be recognised by one eye are required. Such a training treatment would therefore not only be pointless but extremely frustrating for parents and child.

Our paediatrician did the test with our 4-year-old son and said everything was fine, although...

Question: Our paediatrician did the test with our 4-year-old son and said everything was fine, although he did not name the car as such, but said he saw a fish at that spot. Our older daughter and I cannot see the figures at all because of microstrabismus. What should I do?

Answer: In the case of a questionable positive test result, as in this case, it is advisable to have a detailed examination by an ophthalmologist. The ophthalmologist has further examination methods with which a suspected diagnosis can be confirmed.

Question about apparative photoscreening (PlusOptix)
Question: Our 4-year-old son has already been tested twice by the paediatrician as normal by means of apparative photoscreening. However, there are people in our family with vision problems, including strabismus. Is it true that for small squint angles below 8 degrees, the Lang-Stereotest is the more reliable method to detect early strabismus due to microstrabismus in children?

Answer: Yes. Eye screening with a photoscreener is possible for children as early as 6 months of age and is being carried out increasingly. Unfortunately, this screening does not detect small-angle strabismus. The stereopsis examination with the Lang-Stereopad which is carried out parallel to the photoscreening, is therefore absolutely recommended from the 6th month of life.
The few studies dealing with the early detection of strabismus by photoscreening, i.e. the automated photographic recording and evaluation of the eyes, suggest that so far none of the devices has sufficient sensitivity for the diagnosis of small-angle strabismus. Several authors recommend the routine use of the Lang stereotest in combination with photoscreening to avoid missing cases of microstrabismus. J. Lang was the first to emphasise the importance of microstrabismus in strabismic amblyopia, and the Lang-Stereotest he invented is therefore generally considered the gold standard method for early diagnosis of this form of amblyopia, whereas simple tests such as the Brückner test (fluoroscopy test) and the Hirschberg test (corneal imaging) require a great deal of experience for comparable results. However, there are still, albeit very rarely, isolated cases of microstrabismus that pass the Lang-Stereotest.
At what age should my child have a stereo vision examination with a stereo test for the first time in Germany?
The early detection measures for children in Germany comprise ten examinations U1 to U9, which must be carried out in specified periods. In U1 to U7 (2 years), the so-called Brückner test is recommended, but not yet a stereo test. Unfortunately, there are still isolated cases in which amblyopia has developed, which is only diagnosed at U7a, i.e. when the child is just under three years old, with failure of a stereo test. It is therefore recommended that children be examined with the Lang-Stereotest as early as the second year of life, especially if there are already cases of strabismus or amblyopia in the family. Early testing can also be attempted with other stereo tests, but the results are usually less reliable, also because very young children do not tolerate the respective necessary test glasses.
It is repeatedly said that the Lang-Stereotest is the best test for stereo vision screening in young children. Why is stereo vision screening not carried out systematically in children as early as the second year of life in Germany?
In fact, Lang-Stereotests I and II, and even more so the Lang-Stereopad, are able to provide reliable results even in children younger than 2 years. The Lang-Stereotest is one of the stereotests that has been shown in larger studies to be the easiest and most reliable stereo vision test to perform compared to other tests. In an Australian study of 2189 children aged 6 to 72 months, the Lang-Stereotest II could be used in children as young as 6 months of age and was found to be feasible in 94.4% of the whole collective, overall more frequently than any other test compared. https://pubmed.ncbi.nlm.nih. gov/22525178/

Although not provided for in the guidelines of the Joint Federal Committee on the Early Diagnosis of Diseases in Children (Children's Guideline), given the fact that amblyopia can develop in children as early as the first and second year of life, and the availability of suitable test procedures, in particular the Lang-Stereopad with the Preferential Looking Method, routine stereoscopic screening could be justified before U7a, ideally from the beginning of the second year of life, and in children with a family history of strabismus even from the 6th month of life. This is all the more true This is all the more so as in recent years the examination of infants and toddlers with photo scanners has become established in many places. Although these give good results on refractive anomalies and other disorders, they do not provide reliable information on stereopsis and fail in the case of small-angle strabismus (microstrabismus).

In Germany, there are no prevalence data on amblyopia up to the age of 7. However, according to a study by Elblein (2015), it was 5.6 % in adults between 34 and 44 years of age. According to a parent survey, 2.6% of children had strabismus in the first year of life, 2.2% in the second, 3.3% in the third and 4.1% in the fourth. These figures suggest that despite stereoscopy at the U7a screening, there are still too many cases of amblyopia which could have been diagnosed and treated earlier.

The reasons for abandoning stereoscreening would therefore have to be found in the decision-makers and the availability of the corresponding tests, especially as long as outdated convictions persist, such as this one that early detection is only worthwhile for children from the time they start school because it cannot be reliably carried out before that...

In other countries, too, stereoscreenings are often scheduled too late, due to lack of resources, but also when paediatricians or family doctors are absent or not involved in the screening, or when even ophthalmologists stick to the conventional tests that require glasses due to lack of knowledge of the Lang-Stereotests (e. g. e.g. Titmus fly or TNO) and therefore completely refrain from early testing.
Can amblyopia be reliably ruled out with the Lang-Stereotest?

No. Passing the Lang-Stereotest does not rule out all cases of amblyopia, especially not all cases of anisometropic amblyopia, or incipient strabismic amblyopia, such as a recent onset of microstrabismus. Sometimes patients with incipient or mild amblyopia do not show a true positive test result on the Lang-Stereotests, but a questionable positive test result on the Lang-Stereotests: they are able to locate the test figures correctly and compare their sizes, but their spatial perception ability is already reduced, so that they cannot identify or name the test figures correctly.

Because amblyopia or strabismus can develop slowly and often unnoticed, stereopsis screening must be performed on all children not just once during the critical phase (up to the time they start reading), but they must be examined at recurring, usually annual, intervals, and even more frequently if the test result is questionably positive.
If amblyopia is suspected, further tests by specialised experts (ophthalmologists, orthoptists) are necessary to either confirm or exclude the diagnosis.

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