Worth 4 dot test

Worth 4 dot test
Worth 4 dot test
	Worth Four Light Test
Synonyms	W4LT
Purpose	assess degree of binocular vision

Last updated March 11, 2023

The Worth Four Light Test, also known as the Worth's four dot test or W4LT, is a clinical test mainly used for assessing a patient's degree of binocular vision and binocular single vision. Binocular vision involves an image being projected by each eye simultaneously into an area in space and being fused into a single image. The Worth Four Light Test is also used in detection of suppression of either the right or left eye. Suppression occurs during binocular vision when the brain does not process the information received from either of the eyes. This is a common adaptation to strabismus, amblyopia and aniseikonia.

The W4LT can be performed by the examiner at two distances, at near (at 33 cm from the patient) and at far (at 6 m from the patient). At both testing distances the patient is required to wear red-green goggles (with one red lens over one eye, usually the right, and one green lens over the left) When performing the test at far (distance) the W4LT instrument is composed of a silver box (mounted on the wall in front of the patient), which has four lights inside it. The lights are arranged in a diamond formation, with a red light at the top, two green lights at either side (left and right) and a white light at the bottom. When performing the test at near (at 33 cm ) the lights are arranged in exactly the same manner (diamond formation), with the difference being that at near, the lights are located in a hand-held instrument which is similar to a light torch.

Because the red filter blocks the green light and the green filter blocks the red light, it is possible to determine if the patient is using both eyes simultaneously and in a coordinated manner. With both eyes open, a patient with normal binocular vision will appreciate four lights. If the patient either closes or suppresses an eye they will see either two or three lights. If the patient does not fuse the images of the two eyes, they will see five lights (diplopia).

Indications for use

The Worth Four Light Test is indicated for use when assessing the binocular functions, the ability of eyes to work in coordination, of an individual. It can be used to develop a diagnosis or to support or confirm an initial diagnosis. It can be used when wanting to assess whether the individual has a normal or abnormal binocular single vision response (BSV). It can be used to establish whether a patient has the ability for the eyes to fuse the light that is received from each eye into 4 lights. The test is indicated with the use of a presence of a prism in individuals with a strabismus and fusion is considered present if 4 lights are maintained, with or without the use of a prism. The W4LT can also be indicated when aiding a person to develop and strengthen their fusional capacities.^{[ citation needed ]}

If the images are unable to be fused the W4LT is still indicated to help to determine if an individual appreciates diplopia (double vision) or are suppressing an image from one eye. In cases of manifest strabismus the test can help in determining the nature and type of the diplopia or which eye is suppressing. Therefore, is indicated in cases of a suspected central suppression scotoma as it can be used to detect where the lights may not be appreciated from the eye with the scotoma though in some cases of minimal deviation in the eye as demonstrated in a microtropic deviation a normal response of 4 lights may be reported. Though it can be used in these patients to prove the presence of peripheral fusion and that they have bi-foveal fixation.^{[ citation needed ]}

Other indications for the test include establishing an individual's dominant eye dominant eye compared to the other and when evaluating reduced monocular visual acuity which shows no improve on pinhole testing.

Whilst there are no contraindications of the W4LT there needs to be caution in interpreting the results of individuals with BSV in natural conditions as they may show a diplopic response under the dissociation of the test. Also in individuals who have abnormal retinal correspondence (ARC) they may provide an unexpected response, and those who have misaligned visual axis whom in natural conditions suppress may actually provide a diplopic response upon testing.

Method of assessment

The Worth Four Light Test is relatively simple to undertake. First you must place the red/green goggles over the patients eyes, with the red goggle traditionally placed over the right eye.

Next you must dim the room lighting. This allows the patient to see the lights better.

For a distance measurement, you should have the patient set up six metres away from the light source. For a near measurement, the test should be performed at approximately one third of a metre, or thirty three centimetres, with a handheld Worth's Four Lights torch.

Then, ask the patient what they see. They should respond with "I see … number of lights" provided they have understood what you have asked them. Ask them to describe the lights to you. You must ask about the colour of the lights. If they see five lights, ask whether the green dots are higher or lower than the red dots. Ask about the positioning of the dots, for example are the red dots to the left or the right of the green dots. Also ask if the dots are flashing on and off or switching between red and green.

This series of questions is essential in order to ensure you correctly record exactly what the patient is seeing, so that the clinician can interpret the patient's results and then make an accurate diagnosis.

Recording and interpreting outcomes

When recording results for the W4LT it is important to ask the patient a series of questions in order to ensure you correctly record exactly what they are seeing. This is essential in order to interpret the patient's results and then make an accurate diagnosis.

The questions are:

How many lights are you seeing?
What colour are they? Where are they located?
Are all the lights in line? Or are some higher than the others?
Do all the lights show up at one time, or are they flashing on and off?

When recording results it is important to indicate the test used, a description of the lights seen and an indication of what the result means. It is also important to note the distance at which the test was conducted and whether or not the patient wore their own refractive correction.

Where communication is difficult between clinician and patient, such as in the presence of a language barrier, or when working with a child, it may be a good idea to get the patient to draw what they are seeing. The clinician can then interpret the results from the image.

Results

There are a number of possible results demonstrated by a W4LT

Normal retinal correspondence

In the absence of a deviation, the patient will see the lights exactly as they appear. When questioned they will report that:

They see 4 lights, 1 red, 2 green and one mixed colour
The two green lights will be to either side with the red light slightly above them and the mixed coloured light below the red

This is recorded as : W4LT (D): 4 lights (BSV)

Abnormal retinal correspondence

It will be demonstrated on cover test that the patient has a manifest deviation. When questioned about the lights the patient will give a normal response and will see the lights exactly as they appear. They will report that:

They see 4 lights, 1 red, 2 green and one mixed colour
The two green lights will be to either side with the red light slightly above them and the mixed coloured light below the red

This is recorded as : W4LT (D): 4 lights (ARC)

NB: ARC can only be confirmed in conjunction with additional clinical tests for retinal correspondence. The patient must demonstrate a manifest deviation on cover test. Despite their apparent deviation, when tested with the W4LT they will produce a normal BSV result, indicating the presence of Abnormal Retinal Correspondence.

Esotropia

In an Esotropic (ET) deviation, the patient will experience uncrossed diplopia. When questioned about the position of the lights, they will report that:

They see 5 lights, 2 red and 3 green
The lights are horizontally displaced, seen side by side
The 2 red lights from the right eye are seen on the right side
The 3 green lights from the left eye are seen on the left side

This is recorded as: W4LT (D): 5 lights (Uncrossed Diplopia) ET

NB: The clinician will be unable to indicate which eye is the deviating eye based on these results alone. The results should be interpreted with other clinical findings in order to produce a final diagnosis.

Exotropia

In an Exotropic (XT) deviation, the patient will experience crossed diplopia.

When questioned about the position of the lights, they will report that:

They see 5 lights, 2 Red and 3 Green
The lights are horizontally displaced, and are seen side by side
The 2 Red Lights from the Right eye are on the left side
The 3 Green lights from the Left eye are on the right side

This is recorded as: W4LT (D): 5 lights (Crossed Diplopia) XT

NB: The clinician will be unable to indicate which eye is the deviating eye based on these results alone. The results should be interpreted with other clinical findings in order to produce a final diagnosis.

Hypotropia or hypertropia

In cases of vertical deviations, patients will report that:

They see 5 lights: 2 red and 3 green
The lights are vertically displaced in relation to one another
The green lights (left eye) are on top of the red lights (right eye),

which is interpreted as : R HT or LHypoT

The red lights (right eye) are on top of the green lights (left eye),

which is interpreted as: RHypoT or L H T

This is recorded as: W4LT (D): 5 lights (vertical diplopia)

The clinician can relate the position of the lights directly back to the deviation and height of the eye (i.e.) the higher lights belong to the lower eye, and the lower lights belong to the higher eye.

NB: If the lights are not situated directly above one another, but are also separated horizontally, it is normally indicative of a mixed deviation where there is a horizontal, as well as vertical strabismus present.

Suppression

In cases of manifest strabismus, it is not always expected that the patient will experience diplopia.

Suppression is indicated when the patient reports that:

They see only the 3 Green lights from the Left eye

Which is interpreted as R Suppression

They see only the 2 Red lights from the Right eye

Which is interpreted as L Suppression

They see 2 Red lights OR 3 Green lights

All 5 lights are never present at the same time, but the patient is switching between the two responses. This result is interpreted as Alternating Suppression

This can be recorded as:

W4LT (D): 3 Lights (R Supp.)

W4LT (D): 2 Lights (L Supp.)

W4LT (D): 2 or 3 Lights (Alt. Supp.)

Advantages and disadvantages

Advantages

Can be quick and simple to perform in the clinic as the test is easy to orientate and the red green goggles are simply put over the eyes. There is no turning of lenses, as in Bagolini Striated Glasses Test which is another test measuring binocular functions, making the interpretation of the results less complicated
There are no large glasses frames such as in the Bagolini striated glasses test so the goggles are minimally obstructive to the patient's vision^[1]
Refractive correction can be worn under the goggles ^[2]
Good starting point when investigating the nature of diplopia i.e. to find manifest, intermittent, crossed or uncrossed diplopia
It is less dissociative than a cover test ^[1]
Can be used to determine if a patient will demonstrate binocular single vision with corrective prism or head posture^[1]
Relatively easy to record and interpret the results

Disadvantages

Subjective in nature and relies on patient responses
The patient must have fusion and stereopsis to get accurate results
It is a highly dissociative test resulting in responses being less relevant to what the patient sees in their normal daily environment, as the environment would normally be different ^[3]

A. Lights need to be off or dimmed in order to see the dots / lights

B. There is no common colour to fuse

C. Dark filters in the goggles are used and are less like natural conditions and therefore less relevant to what the patient sees in their normal daily environment

People with Red/green colour blindness cannot accurately perform the test as the colours used on the test are red and green
The test results are only useful in combination with other testing and results and not on their own
If performing the test twice, for example at near and at distance, the patient (especially children) may remember their previous answer and simply give the same answer from the last test, providing inaccurate results^[1]

Related Research Articles

Esotropia is a form of strabismus in which one or both eyes turns inward. The condition can be constantly present, or occur intermittently, and can give the affected individual a "cross-eyed" appearance. It is the opposite of exotropia and usually involves more severe axis deviation than esophoria. Esotropia is sometimes erroneously called "lazy eye", which describes the condition of amblyopia; a reduction in vision of one or both eyes that is not the result of any pathology of the eye and cannot be resolved by the use of corrective lenses. Amblyopia can, however, arise as a result of esotropia occurring in childhood: In order to relieve symptoms of diplopia or double vision, the child's brain will ignore or "suppress" the image from the esotropic eye, which when allowed to continue untreated will lead to the development of amblyopia. Treatment options for esotropia include glasses to correct refractive errors, the use of prisms and/or orthoptic exercises and/or eye muscle surgery. The term is from Greek eso meaning "inward" and trope meaning "a turning".

In biology, binocular vision is a type of vision in which an animal has two eyes capable of facing the same direction to perceive a single three-dimensional image of its surroundings. Binocular vision does not typically refer to vision where an animal has eyes on opposite sides of its head and shares no field of view between them, like in some animals.

<span class="mw-page-title-main">Strabismus</span> Eyes not aligning when looking at something

Strabismus is a vision disorder in which the eyes do not properly align with each other when looking at an object. The eye that is focused on an object can alternate. The condition may be present occasionally or constantly. If present during a large part of childhood, it may result in amblyopia, or lazy eyes, and loss of depth perception. If onset is during adulthood, it is more likely to result in double vision.

<span class="mw-page-title-main">Diplopia</span> Double vision

Diplopia is the simultaneous perception of two images of a single object that may be displaced horizontally or vertically in relation to each other. Also called double vision, it is a loss of visual focus under regular conditions, and is often voluntary. However, when occurring involuntarily, it results in impaired function of the extraocular muscles, where both eyes are still functional, but they cannot turn to target the desired object. Problems with these muscles may be due to mechanical problems, disorders of the neuromuscular junction, disorders of the cranial nerves that innervate the muscles, and occasionally disorders involving the supranuclear oculomotor pathways or ingestion of toxins.

An eye examination is a series of tests performed to assess vision and ability to focus on and discern objects. It also includes other tests and examinations pertaining to the eyes. Eye examinations are primarily performed by an optometrist, ophthalmologist, or an orthoptist. Health care professionals often recommend that all people should have periodic and thorough eye examinations as part of routine primary care, especially since many eye diseases are asymptomatic.

Stereopsis is the component of depth perception retrieved through binocular vision. Stereopsis is not the only contributor to depth perception, but it is a major one. Binocular vision happens because each eye receives a different image because they are in slightly different positions on one's head. These positional differences are referred to as "horizontal disparities" or, more generally, "binocular disparities". Disparities are processed in the visual cortex of the brain to yield depth perception. While binocular disparities are naturally present when viewing a real three-dimensional scene with two eyes, they can also be simulated by artificially presenting two different images separately to each eye using a method called stereoscopy. The perception of depth in such cases is also referred to as "stereoscopic depth".

<span class="mw-page-title-main">Sixth nerve palsy</span> Medical condition

Sixth nerve palsy, or abducens nerve palsy, is a disorder associated with dysfunction of cranial nerve VI, which is responsible for causing contraction of the lateral rectus muscle to abduct the eye. The inability of an eye to turn outward, results in a convergent strabismus or esotropia of which the primary symptom is diplopia in which the two images appear side-by-side. Thus, the diplopia is horizontal and worse in the distance. Diplopia is also increased on looking to the affected side and is partly caused by overaction of the medial rectus on the unaffected side as it tries to provide the extra innervation to the affected lateral rectus. These two muscles are synergists or "yoke muscles" as both attempt to move the eye over to the left or right. The condition is commonly unilateral but can also occur bilaterally.

Suppression of an eye is a subconscious adaptation by a person's brain to eliminate the symptoms of disorders of binocular vision such as strabismus, convergence insufficiency and aniseikonia. The brain can eliminate double vision by ignoring all or part of the image of one of the eyes. The area of a person's visual field that is suppressed is called the suppression scotoma. Suppression can lead to amblyopia.

<span class="mw-page-title-main">Hypertropia</span> Condition of misalignment of the eyes

Hypertropia is a condition of misalignment of the eyes (strabismus), whereby the visual axis of one eye is higher than the fellow fixating eye. Hypotropia is the similar condition, focus being on the eye with the visual axis lower than the fellow fixating eye. Dissociated vertical deviation is a special type of hypertropia leading to slow upward drift of one or rarely both eyes, usually when the patient is inattentive.

A cover test or cover-uncover test is an objective determination of the presence and amount of ocular deviation. It is typically performed by orthoptists, ophthalmologists and optometrists during eye examinations.

Strabismus surgery is surgery on the extraocular muscles to correct strabismus, the misalignment of the eyes. Strabismus surgery is a one-day procedure that is usually performed under general anesthesia most commonly by either a neuro- or pediatric ophthalmologist. The patient spends only a few hours in the hospital with minimal preoperative preparation. After surgery, the patient should expect soreness and redness but is generally free to return home.

Stereopsis recovery, also recovery from stereoblindness, is the phenomenon of a stereoblind person gaining partial or full ability of stereo vision (stereopsis).

In the fields of optometry and ophthalmology, the Lancaster red-green test is a binocular, dissociative, subjective cover test that measures strabismus in the nine diagnostic positions of gaze.

The Parks–Bielschowsky three-step test, also known as Park's three-step test or Bielschowsky head tilt test, is a method used to isolate the paretic extraocular muscle, particularly superior oblique muscle and trochlear nerve, in acquired vertical double vision. It was originally described by Marshall M. Parks.

In ophthalmology, horror fusionis is a condition in which the eyes have an unsteady deviation, with the extraocular muscles performing spasm-like movements that continuously shift the eyes away from the position in which they would be directed to the same point in space, giving rise to diplopia. Even when the double vision images are made to nearly overlap using optical means such as prisms, the irregular movements prevent binocular fusion. The name horror fusionis arises from the notion that the brain is, or at least appears to be, actively preventing binocular fusion.

The Maddox rod test can be used to subjectively detect and measure a latent, manifest, horizontal or vertical strabismus for near and distance. The test is based on the principle of diplopic projection. Dissociation of the deviation is brought about by presenting a red line image to one eye and a white light to the other, while prisms are used to superimpose these and effectively measure the angle of deviation. The strength of the prism is increased until the streak of the light passes through the centre of the prism, as the strength of the prism indicates the amount of deviation present. The Maddox rod is a handheld instrument composed of red parallel plano convex cylinder lens, which refracts light rays so that a point source of light is seen as a line or streak of light. Due to the optical properties, the streak of light is seen perpendicular to the axis of the cylinder.

Bagolini striated glasses test, or BSGT, is a subjective clinical test to detect the presence or extent of binocular functions and is generally performed by an optometrist or orthoptist or ophthalmologist. It is mainly used in strabismus clinics. Through this test, suppression, microtropia, diplopia and manifest deviations can be noted. However this test should always be used in conjunction with other clinical tests, such as Worth 4 dot test, Cover test, Prism cover test and Maddox rod to come to a diagnosis.

The prism fusion range (PFR) or fusional vergence amplitude is a clinical eye test performed by orthoptists, optometrists, and ophthalmologists to assess motor fusion, specifically the extent to which a patient can maintain binocular single vision (BSV) in the presence of increasing vergence demands. Motor fusion is largely accounted to amplitudes of fusional vergences and relative fusional vergences. Fusional vergence is the maximum vergence movement enabling BSV and the limit is at the point of diplopia. Relative fusional vergence is the maximum vergence movement enabling a patient to see a comfortable clear image and the limit is represented by the first point of blur. These motor fusion functions should fall within average values so that BSV can be comfortably achieved. Excessive stress on the vergence system or inability to converge or diverge adequately can lead to asthenopic symptoms, which generally result from decompensation of latent deviations (heterophoria) or loss of control of ocular misalignments. Motor anomalies can be managed in various ways, however, in order to commence treatment, motor fusion testing such as the PFR is required.

The Maddox Wing is an instrument utilized by ophthalmologists, orthoptists and optometrists in the measurement of strabismus. It is a quantitative and subjective method of measuring the size of a strabismic deviation by dissociation of the eyes brought about by two septa which are placed in such a way as to present fields to either eye separated by a diaphragm at the centre. The right eye sees a red and white arrow, each of which point to a scale with numbers seen by the left eye; the red arrow points to the vertical red scale and the white arrow points to the horizontal white scale. A third arrow located to the right and below the horizontal white scale is used to measure torsion

The FourPrism Dioptre Reflex Test is an objective, non-dissociative test used to prove the alignment of both eyes by assessing motor fusion. Through the use of a 4 dioptre base out prism, diplopia is induced which is the driving force for the eyes to change fixation and therefore re-gain bifoveal fixation meaning, they overcome that amount of power.

References

1 2 3 4 Roper-Hall, Gill (2004). "The 'Worth' of the Worth Four Dot Test". American Orthoptic Journal. 54 (1): 112–119. doi:10.3368/aoj.54.1.112. PMID 21149094. S2CID 38083713.
↑ Volume 1, Chapter 9. Sensory Tests and Treatment of Binocular Vision. (n.d.). Duane's Ophthalmology on CD-ROM, 2006 edition. Retrieved October 23, 2014, from http://www.eyecalcs.com/DWAN/pages/v1/v1c009.html
↑ Arthur, B. W.; Marshall, A.; McGillivray, D. (1993). "Worth vs Polarise Four-Dot Test". Journal of Paediatric Ophthalmology and Strabismus. 30 (1): 53–55. doi:10.3928/0191-3913-19930101-13. PMID 8455128.

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[RG2004-1] 1 2 3 4 Roper-Hall, Gill (2004). "The 'Worth' of the Worth Four Dot Test". American Orthoptic Journal. 54 (1): 112–119. doi:10.3368/aoj.54.1.112. PMID 21149094. S2CID 38083713.

[2] Volume 1, Chapter 9. Sensory Tests and Treatment of Binocular Vision. (n.d.). Duane's Ophthalmology on CD-ROM, 2006 edition. Retrieved October 23, 2014, from http://www.eyecalcs.com/DWAN/pages/v1/v1c009.html

[3] Arthur, B. W.; Marshall, A.; McGillivray, D. (1993). "Worth vs Polarise Four-Dot Test". Journal of Paediatric Ophthalmology and Strabismus. 30 (1): 53–55. doi:10.3928/0191-3913-19930101-13. PMID 8455128.

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