Test procedure and areas of use

Early detection, screening, stereopsis assessment

Use of Lang-Stereotests® explained in a nutshell

Our products offer a proven spectacle-free method for testing the spatial vision of babies from 6 months, toddlers, school children and adults.

The Lang-Stereotests® I and II and the Lang-Stereopad® are primarily suitable for detecting the presence of stereopsis, i.e. binocular stereo vision in a person.

Persons with a positive test result have intact stereopsis. It may be inferred from this that both eyes and the visual cortex work together effectively and in a coordinated manner.

A negative test result basically signals a one-sided visual impairment without providing the exact cause. An ophthalmological examination is necessary. In children, microstrabismus or amblyopia is suspected.  Early treatment in childhood can help improve amblyopia.

Application areas of our stereo eye tests

Lang-Stereotests® are often used for

Lang-Stereotests® are also suitable for:

Stereo vision testing should be done by professionals or trained personnel.

Advantages of spectacle-free Lang-Stereotests® compared to other stereo tests

  • Spectacle-free stereopsis testing: no red-green glasses, polarising glasses or apparatus are necessary
    • Increased testability of younger children and babies
    • problem-free testing of spectacle wearers
    • strongly reduced time for the test procedure
  • Assessment of eye movements possible without spectacles
    • Suitable for children of preverbal age
    • Suitable for patients with speech and language disorders.
  • Higher test sensitivity and specificity for strabismus, strabismic amblyopia and microstrabismus
  • Special advantages of the Lang-Stereopad®:
    • can be used successfully with children of preverbal age, individuals with speech and language disorders and deafness, by use of the Preferential-Looking Method.
    • Reliable results with test repetitions, as guessing the test figures is not possible. Therefore, also suitable for adults in the context of appraisals and aptitude tests.
  • More reliable results than all contour stereo tests

Problems with glasses in many other stereo tests

Problems with stereo tests that require glasses

Many other stereotests use additional glasses or lenses. These include, for example, polarised glasses or red-green glasses, which have to be put on the test person.

The children are often more interested in the glasses or lenses than in the test and are highly distracted. Young children strip off the glasses after a short time and feel uncomfortable with them.

It is not possible for the examiner to observe eye movements. Examining babies is impossible.

Small spectacle wearers have a particularly difficult time, as they have to wear a second pair of glasses. This makes the examination more difficult and the test result is often inconclusive.

Lang-Stereotests® are, however, performed without glasses.

Screening babies and young children

Regular stereopsis screening in babies and toddlers is essential to detect stereo vision disorders, especially amblyopia, at an early stage. It also helps to detect small-angle strabismus (microstrabismus), which is hardly noticeable in everyday life. Early treatment helps to improve amblyopia.

Who is tested and when? Babies and toddlers from the first or second year of life, depending on the screening programme, every one to two years.

What is tested? It is checked whether stereo vision has developed normally after birth and remains intact over time.

Why is testing already done in babies and young children? Visual disorders with stereopsis limitation can develop at any time from birth. Since stereopsis is fully developed in babies from the 4th month of life, it makes sense to subject children to stereopsis screening as early as possible. In this way, newly occurring disorders of stereo vision can be detected early and treated in a targeted manner. Hence, damage caused by disturbed developmental processes in the interaction between the eye and the brain can be prevented during this sensitive phase.

A one-sided vision loss (amblyopia) is usually not noticed by the affected child itself or its caregivers, just as little as small-angle strabismus (microstrabismus), which can also lead to amblyopia. This can lead to permanent impairment of spatial vision and increases the risk of blindness if the healthy eye is lost.

Lang-Stereotests® also help to distinguish pseudostrabismus from true strabismus. In a positive case, an intact stereopsis can be concluded, and the child is spared a possible misdiagnosis and further examinations.

How are babies and young children tested? The stereopsis examination is done on babies and toddlers when they are sitting comfortably in the lap of a familiar person. The examiner is at the same sitting height opposite the child.

To attract attention for the examination, babies and toddlers are first shown the Lang Fixation Cubes or Lang Fixation Sticks, which have child-friendly colourful pictures on them. In this way, the child is introduced to the figures that are also included in the Lang stereotest.

As soon as the child is calm and interested, the test card of the Lang-Stereotest® I is presented to him at a distance of 30 to 40 cm. Children of preverbal age can point to the recognized test figures, and the examiner can observe eye movements at the same time. Children of speaking age should point to the test figures and name them correctly.

Many users prefer the Lang-Stereopad® for initial screening from 6 months of age, which allows examination using preferential looking procedure. With this method, it is not necessary for a child to be able to name the test figures to detect stereopsis, as it is based solely on observation of interest and gaze behaviour for the 3D object.

Using the Lang-Stereopad®, the Preferential Looking method is also suitable for children with speech or language disorders, language barriers or limitations in direct communication.

Who tests babies and toddlers?   Performers of stereopsis screening in babies and toddlers mainly include paediatricians, public health nurses, midwives, orthoptists and paediatric ophthalmologists.

Routine screening of (pre)school children

Performing stereopsis screenings as part of screening and school entry examinations is a precaution to fully check stereo vision in a whole age group of children. Early treatment in childhood can prevent irreversible one-eyedness.

Who is tested and when? Small children and preschoolers are tested once or several times from the age of 3, depending on the screening programme, and school children are often tested before the start of school at the initial examination and the subsequent serial examinations.

What is examined? It is checked whether stereo vision has developed normally in infancy and remains intact. Often, visual acuity (visual acuity) at distance and near is also tested on this occasion.

Why are children tested as part of routine examinations? Through early and repeated testing, disorders of stereo vision can be detected, specifically treated and thus permanent damage prevented. Unilateral amblyopia is just as rarely noticed by those affected as small-angle strabismus (microstrabismus), which can also lead to amblyopia. Unilateral amblyopia leads to a permanent impairment of spatial vision and increases the risk of blindness in case of loss of the healthy eye.

How are preschool and school-age children tested?

The test is done when the child is standing or sitting. The examiner is opposite the child so that he or she is at the same eye level and can easily observe the child's eye movements. Stereopsis screening is done from the age of 3 with the Lang-Stereotest® I and II or the Lang-Stereopad®.

The examiner holds the Lang-Stereotest® I or II with both hands calmly in front of the child at a reading distance of 30 to 40 cm, so that the child can look at the test card vertically from the front without disturbing light reflections. The child is asked to say what he/she sees without the examiner mentioning or pointing to the test figures.

Once the child has discovered the test figures, he or she may be asked to name or tap on the test figures that stand out the most and least from the picture plane.

If the child already knows the test, it is possible to switch between the two versions of the  Lang-Stereotest®, I and II. If only one test is available, the test card can be shown so that the test images are upside down to ensure that the test images are not simply recited from memory.

The Lang-Stereopad® offers an alternative, as all six test pictures can be presented individually or in alternating combinations to ensure that the test figures cannot be guessed.

For children with language disabilities or a language barrier, examiners prefer the Lang-Stereopad®, which allows testing by use of the Preferential Looking Method. With this method, it is not necessary for a child to be able to name the test figures to detect stereopsis, as it is based solely on observation of interest and gaze behaviour for the 3D object.

Who tests children in the context of routine examinations? Typical users in the context of routine examinations are mainly public health officers, paediatricians, school doctors, ophthalmologists, orthoptists and public health nurses.

Here you can find an overview of all countries with and without stereopsis screening and information on the worldwide use of the Lang-Stereotest®.

Ophthalmological examinations in case of known visual disorders

Stereopsis screening in younger and older patients with known visual disorders or diseases of the nervous system.

Stereopsis tests are used regularly in most ophthalmic institutions as well as by eye doctors, orthoptists, optometrists and opticians to check binocular stereo vision in all age groups. Not all stereotests are equally suitable for all disorders. Lang-Stereotests®, especially the Lang Stereopad®, are among the most demanding tests because of their high specificity for stereopsis.

Joseph Lang, as the simultaneous discoverer of microstrabismus and inventor of the Lang-Stereotest®, has shed light on the importance of strabismus in the development of strabismic amblyopia. In this form of strabismus, stereopsis is no longer achieved even with therapy, which means that it is futile or frustrating to continue to examine these patients with the Lang-Stereotests®.

There are, however, a number of disorders of binocular vision that can be improved, or reversed, by therapy, which include several forms of strabismus without amblyopia and anisometropia. The success of this treatment can be well checked and documented with the Lang-Stereotests®, primarily with the Lang Stereopad®.

Since strabismus and amblyopia often run in families, the next of kin of patients with the described disorders, i.e. the siblings of children with strabismus, must be mentioned here as an important additional target group.

The novel Lang-Stereopad® was also developed, among other things, for the examination of patients with a speech disorder (aphasia) using the Preferential Looking procedure.

© Adobe Stock - Lena May

Users of Lang-Stereotests® for Stereopsis Exams

  • For known visual disorders: Ophthalmologists, orthoptists, optometrists, and opticians.
  • For general diseases or diseases of the nervous system: Lang-Stereotests® are regularly used by specialists in other fields, especially by internists and neurologists in with the neurological examination.

Possible Stereopsis Screening Test Results:

The test result can be positive, negative or uncertain .

  • Negative is equivalent to "stereo-negative": the child did not recognise any of the test figures. A negative test result is a strong indication for the presence of strabismus, strabismic amblyopia or amblyopia due to pronounced anisometropia. Children with microstrabismus do not pass the test in the vast majority of cases. If the test result is negative, the child's gaze typically wanders aimlessly over the test card and away from it.
  • We speak of an uncertain or questionably positive test result if the child was only able to recognise and name part of the test figures correctly. Or if in the Lang stereotest® I / II he or she was able to locate the figures in the correct place, but was unable to identify them.
  • Positive means "stereo-positive": A positive test result means intact stereo vision is present. All test figures shown were perceived spatially by the child.
  • Positive also means exclusion of pseudo-strabismus: A supposed strabismus (pseudo squint) can be easily distinguished from a real strabismus with the help of the Lang-Stereotest®. The reason for the deception may be an unusual width or narrowness of the bridge of the child's nose, giving a false impression of strabismus. This can cause the whites of the eyes to appear smaller or larger on the nose than on the outside. Fortunately, this impression normalises as the facial skull develops.
    In adults, too, anatomical peculiarities such as a particularly narrow or wide distance between the pupils and unequally sized scleral triangles on the nasal or temporal side of the eyes can feign strabismus and can be clarified with the help of the Lang- Stereotest®.
Genuine strabismus or pseudostrabismus?

Possible diagnoses in case of a negative test result:

Stereo vision screening does not provide a diagnosis of disease, but helps to establish the indication for an ophthalmological examination. The Lang-Stereotests® were created by Joseph Lang primarily for the purpose of early detection of bilateral stereo vision disorders in young children.

A negative test result basically signals a one-sided visual impairment due to which part of the image information is lost, but without providing the exact cause.

Negative stereopsis due to beginning amblyopia or micro-strabismus
A negative test in young children raises suspicion of strabismus with a squint angle of less than 5 degrees (micro-strabismus), which is very difficult to detect even for experts. This is not a problem of the eye or eye muscle, but a central control problem in the brain.

Strabismic amblyopia: In healthy individuals, both eyes fixate on the same object, resulting in a three-dimensional image in the brain. If one eye squints, different images are created on the retinas, which the brain cannot process properly. It fades out the squinting eye and uses only the healthy eye for image processing. In children, this can lead to the brain not being able to develop spatial vision properly and the squinting eye permanently losing vision.

Early diagnosis and treatment are crucial to fully develop the squinting eye and prevent the development of amblyopia. Temporarily covering the healthy eye reactivates image formation in the squinting eye. However, covering therapy is only possible up to an age of about seven years, and up to a maximum of ten years, as full performance of the visual system is developed throughout this period.

Negative stereopsis in children and adolescents due to pre-existing visual disorders and strabismus.

Disorders of binocular stereopsis can be caused by strabismus, unilateral blindness (amaurosis) or various forms of amblyopia. Severe unilateral or bilateral refractive anomalies (anisometropia) can also lead to these disorders.

Strabismus in childhood can often only be corrected by surgery on one of the eye muscles to change the position of the eyeball muscle and restore the parallel position of the two eyes. The central control system in the brain, which is responsible for the eyes and their muscles, must then adjust to the new situation, which unfortunately cannot always be guaranteed. Ideally, stereopsis is also recovered with the surgical treatment.

Negative stereopsis in adults:

In adults, all disorders of the entire visual organ, from the eyes to the nerve tracts to the cerebral cortex, should be considered in the case of a negative test result. In addition to the forms of strabismus and amblyopia already mentioned, these include inflammatory diseases, circulatory disorders, excess pressure in the brain and tumours. In the case of such causes, many other symptoms are usually present.

Cover therapy for the treatment of strabismus
© Adobe Stock - galitsin
© Adobe Stock - sasha1806
© Adobe Stock - sasha1806

Driving aptitude, occupational aptitude, career choice and sports career

Further areas of application of stereopsis screening with the Lang-Stereotest I & II and the Lang Stereopad.

Authority reports on fitness to drive

In many countries, an ophthalmological certificate is required by the authorities to check the fitness to drive for the professional driving of certain vehicles, in which a stereo test is prescribed.

These include licences for commercial passenger transport, road and rail freight transport, shipping, aviation, driving emergency vehicles, transport of dangerous goods and the military.

© Adobe Stock - Erik

This is because good binocular stereo vision checked by stereo tests, is essential for driving these vehicles safely. Poor spatial vision can affect reaction time and spatial awareness skills, increasing the risk of accidents.

The Lang Stereopad® provides a quick guide to whether or not stereopsis is present in vehicle drivers. Since the Lang Stereopad® randomly presents all 6 test images individually or in alternating combinations, it ensures that the test figures cannot be guessed.

Competitive sports: stereo vision and career planning

Most ball sports require intact binocular stereo vision to determine distances and speeds of objects quickly and accurately. In addition to football, handball, volleyball and basketball, these include golf, baseball, tennis and hockey.

Good stereo vision can also be an advantage in sports such as fencing, slalom, high jump and in some martial arts such as boxing and karate or juggling.

If a young sports enthusiast is looking to start a professional sports career and become successful, the presence of good stereopsis should be checked. The Lang-Stereotests® are very suitable for this purpose.

In case of abnormalities, an ophthalmologist should be consulted and the stereo threshold determined, for example with the Lang-Stereopad®. Especially for children and adolescents who are already in youth sports squads and may not have received stereo-screening yet, this examination can be crucial before entering their career.

Appraisal of professional aptitude

For some professions, good stereo vision is essential

Internationally, only some professions require a medical certificate of good stereo vision for employment. These include, but are not limited to, pilots, surgeons, firefighters, weapons-carrying government employees and various military occupations where accurate spatial perception is of great importance.

An employer may also require a certificate of good stereo vision for employment. In certain circumstances, an employer may also require a positive stereopsis as a condition of employment or may be required to obtain an opinion by the authorities.

In many other professions and certain occupations, it is valuable or even essential to have a good stereopsis in order to avoid accidents and harm, or to be able to practice that profession effectively and successfully.

The following list is incomplete and provides a rough overview of professions where good stereopsis is important: Turners, roofers, welders, blacksmiths, heavy current technicians, surgeons, crane operators, pilots, drone pilots, bus and tram drivers, locomotive drivers, shunters, forklift drivers, bowsers, excavator operators, professional divers, chimney sweeps, painters, grinders, dentists and dental technicians, precision mechanics, goldsmiths, gemstone cutters, restorers and art appraisers, forestry workers, loggers, arborists hunters, police officers, firefighters, hunters, mountain and ski guides, professional soldiers, lifeguards and many more.

Applicants of the Stereopsis tests to professional groups

Labour and education authorities as well as employers attach great importance to health and prevention of occupational diseases. Therefore, occupational candidates who meet the minimum health requirements for their respective occupations are usually promoted and trained. For standardised examinations of occupational groups, medical professionals, company doctors, school doctors, as well as ophthalmologists are called in.

A part of occupational eye examinations is nowadays performed by computer-assisted devices. However, these devices often do not provide reliable random-dot stereopsis testing. 

The use of the Lang Stereopad® can help to determine the stereopic threshold or reliably detect non-existent or loss of stereopsis. The randomly presented figures of the Lang Stereopad® cannot be guessed by the subject.

Early career: stereo vision and aptitude

The importance of early detection of binocular vision disorders cannot be overemphasised to help young adults make the best career choices.

In many countries, a high proportion of young people still do not undergo stereopsis screening, resulting in them not being confronted with possible limitations due to their monocular vision until during their school career or when choosing a career.

Despite advances in the development of technical aids, many occupations even today do not allow access for people with impaired vision, especially stereopsis impairment. In such occupations, people with stereopsis impairments may reach their performance limits and have difficulty performing their jobs effectively and safely.

Voluntarily taking a stereopsis exam can be very helpful for optimal and successful career planning.

The Lang® Stereopsis Test I and II are ideally suited for this purpose. In the event of abnormalities, clarification should be obtained from an ophthalmologist and the stereopsis threshold determined, for example, with the Lang Stereopad®

Our product range


The Lang-Stereotest® I-R is a 2021 revised version of the Lang-Stereotest® I, which was developed by J. Lang for binocular diagnostics, especially... Product details


The Lang-Stereotest® II-R is a 2023 revised version of the Lang-Stereotest® II, which was developed by J. Lang for binocular diagnostics,... Product details


With the LANG-STEREOPAD® - analogous to the proven LANG-STEREOTEST® I-R and II - random dots are combined with a cylindrical grid surface. However,... Product details

LANG fixation cube white/red

The LANG FIXATION CUBE were developed by J. Lang for the assessment of eye fixation, motility, accommodation, convergence, for the cover test and for... Product details

LANG fixation sticks

The LANG FIXATION STICK was developed by J. Lang for the assessment of eye fixation, motility, accommodation, convergence, for the cover test and to... Product details

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