Eye Zen
眼静
Strabismus (Squint)
Eye Misalignment
Understanding Strabismus, Binocular Vision & Spectacle Solutions
What Is Strabismus?
Strabismus, commonly known as a squint or eye turn, is a condition in which the two eyes are not properly aligned and do not consistently point in the same direction.
One eye may be directed towards the object being viewed while the other eye turns:
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Inward
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Outward
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Upward
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Downward
The eye misalignment may be constant or intermittent, and the same eye may turn consistently or the deviation may alternate between the two eyes.
A manifest eye deviation is also known as a tropia.
Because our two eyes normally work together as a coordinated visual system, strabismus can affect binocular vision differently from person to person.
Some individuals may experience double vision, while others may have reduced stereopsis or few obvious visual symptoms.
At Eye Zen Optical in Singapore, we focus on personalised optical solutions for customers with complex spectacle requirements, including visual difficulties associated with strabismus, binocular vision and double vision.
What Is the Difference Between Strabismus and Tropia?
The terms are closely related.
Strabismus is the general term used to describe an eye-alignment condition.
Tropia refers to a manifest eye deviation — an eye is actually misaligned under the viewing conditions in which the deviation occurs.
Different names are used according to the direction of the eye turn.
Types of Strabismus
Esotropia — Inward Eye Turn
Esotropia occurs when one eye turns inward towards the nose.
It can be constant or intermittent and may occur at distance, near or both.
In some children, certain forms of esotropia can be associated with significant hyperopia (long-sightedness).
Exotropia — Outward Eye Turn
Exotropia occurs when one eye turns outward, away from the nose.
An intermittent exotropia may be more noticeable at certain times, such as when a person is tired, unwell, looking into the distance or not concentrating on a visual target.
Hypertropia — Upward Eye Turn
Hypertropia occurs when one eye is positioned higher than the other.
Vertical eye misalignment can sometimes be associated with double vision, depending on its cause and the individual's visual adaptation.
Hypotropia — Downward Eye Turn
Hypotropia occurs when one eye is positioned lower than the other.
As with other forms of strabismus, the visual effect depends on the degree, cause and duration of the misalignment.
Constant and Intermittent Strabismus
Strabismus does not always occur continuously.
Constant Strabismus
The eye deviation is consistently present.
Intermittent Strabismus
The eyes may appear aligned at some times but become misaligned under particular conditions.
An intermittent eye turn may become more noticeable when someone is:
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Tired
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Unwell
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Daydreaming
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Not concentrating
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Looking at particular distances
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Performing prolonged visual tasks
The circumstances in which the eye turns can provide useful information during professional assessment.
Strabismus and Binocular Vision
Binocular vision describes how our two eyes work together as a coordinated visual system.
Normally, both eyes are directed towards the same visual target.
Each eye receives a slightly different image, and the brain combines the information from both eyes into a single visual perception.
When the eyes are misaligned, the visual information presented by the two eyes may no longer correspond normally.
How the brain responds depends on several factors, including:
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Age when the strabismus developed
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Type of strabismus
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Size of the deviation
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Whether it is constant or intermittent
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Vision in each eye
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How the visual system has adapted
This is why two people with apparently similar eye turns may have very different visual experiences.
Strabismus and Double Vision
Strabismus can sometimes cause binocular double vision, also known as diplopia.
When the eyes are directed towards different locations, the brain may receive images that do not align normally.
In some individuals, this results in seeing two images instead of one.
However, not everyone with strabismus experiences double vision.
Someone who developed strabismus during childhood may have adapted differently from an adult who suddenly develops an eye turn.
This distinction is important.
New or sudden double vision or eye misalignment should receive prompt medical assessment rather than being assumed to be a spectacle problem.
Strabismus and Stereopsis
Stereopsis is the ability to use the slightly different images from our two eyes to obtain binocular depth information.
When eye alignment is disrupted, stereopsis may also be reduced.
This is sometimes described as reduced stereoscopic or 3D vision.
However, reduced stereopsis does not mean that a person sees the world as completely flat.
The brain also uses other visual cues such as perspective, relative size, movement, shadows and overlapping objects to judge depth.
The effect of strabismus on stereopsis varies considerably between individuals.
Strabismus and Amblyopia
Strabismus and amblyopia are different conditions, although they can occur together.
Strabismus
Strabismus refers to eye misalignment.
Amblyopia
Amblyopia, commonly called lazy eye, refers to reduced vision resulting from abnormal visual development during childhood.
If one eye is consistently misaligned during visual development, the brain may favour visual information from the other eye in some cases.
This can be associated with amblyopia.
However:
Strabismus does not automatically mean amblyopia, and amblyopia does not automatically mean strabismus.
Children with suspected eye misalignment or reduced vision should receive appropriate professional eye assessment.
What Is the Difference Between Strabismus and Phoria?
Strabismus/tropia and phoria both relate to eye alignment, but they are not the same.
Tropia
A tropia is a manifest eye deviation.
The eye is actually misaligned under the viewing conditions in which the tropia occurs.
Phoria
A phoria is generally a latent tendency for the eyes to deviate.
When both eyes are working together effectively, the visual system may maintain alignment.
The deviation becomes more apparent when binocular fusion is disrupted, such as when one eye is covered.
Both can be relevant to binocular vision, but their visual effects and management can differ.
What Symptoms Can Occur With Strabismus?
Strabismus affects people differently.
Possible symptoms or signs may include:
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Visible eye misalignment
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Double vision
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Intermittent double vision
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Eye strain
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Visual fatigue
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Difficulty maintaining comfortable single vision
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Reduced stereopsis
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Difficulty with precise depth judgement
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Closing or covering one eye
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Tilting or turning the head
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Difficulty adapting to spectacles
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Visual discomfort during particular tasks
Some people may have an obvious eye turn without experiencing significant visual discomfort.
Others may experience symptoms even when the misalignment appears relatively subtle.
Symptoms alone cannot determine the cause, so appropriate professional assessment is important.
Can Glasses Help With Strabismus?
Spectacles can play an important role in the visual management of some forms of strabismus, but glasses are not a complete solution for every type of eye misalignment.
The appropriate approach depends on factors including:
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Type of strabismus
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Refractive prescription
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Age
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Direction and degree of deviation
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Whether the strabismus is constant or intermittent
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Whether double vision is present
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Binocular vision
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Underlying cause
For some people, accurately correcting myopia, hyperopia or astigmatism may be important.
Other cases may require assessment or management by an optometrist, ophthalmologist, orthoptist or another appropriate eye-care professional.
Hyperopia and Esotropia
Certain forms of inward eye turn in children can be associated with significant hyperopia (long-sightedness).
A person with hyperopia may use additional accommodation — the eye's focusing mechanism — to maintain clear vision.
Accommodation and convergence are linked.
In some children, the additional focusing effort associated with hyperopia can therefore be accompanied by excessive inward movement of the eyes.
Appropriate spectacle correction can be important in these cases.
However, not every esotropia is caused by hyperopia, and an eye turn should be professionally assessed.
Why Can Spectacles for Strabismus Be Complex?
When strabismus is associated with double vision or other binocular visual difficulties, comfortable spectacles may involve more than obtaining the correct refractive prescription.
Factors that can influence the finished spectacle include:
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Prescription
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Differences between the two eyes
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Lens design
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Optical centration
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Pupillary measurements
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Frame size
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Frame positioning
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Vertex distance
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Previous spectacle prescription
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Distance and near requirements
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Individual adaptation
This is why someone can occasionally have a prescription that appears correct but still experience visual discomfort through the finished spectacles.
For complex visual requirements, how the prescription is translated into the finished spectacles matters.
How Eye Zen Optical Approaches Complex Strabismus-Related Spectacle Problems
At Eye Zen Optical, we do not assume that every strabismus problem can be solved simply by changing a spectacle prescription.
Our optical approach is to understand the relationship between:
your symptoms + prescription + both eyes + binocular vision + lenses + frame + everyday visual requirements
Depending on your situation, we may consider:
Your Symptoms
When does the problem occur?
Is the eye turn constant or intermittent?
Do you experience double vision?
Is it worse when tired?
Does it occur mainly at distance or near?
Do you feel more comfortable closing one eye?
Understanding the visual experience provides important context.
Your Current and Previous Prescriptions
Changes in prescription can influence visual comfort.
Previous spectacles and how well you adapted to them can therefore provide useful information.
Differences Between Your Eyes
Differences in prescription or visual function between the two eyes may be relevant to binocular comfort.
Binocular Visual Requirements
Where appropriate, the relationship between the two eyes needs to be considered rather than looking at each eye completely independently.
Lens Design and Optical Positioning
Lens design, optical centration and frame positioning can influence how the finished spectacles perform.
Your Everyday Visual Needs
Reading, computer work, driving and general daily activities place different demands on vision.
An appropriate spectacle solution should take these requirements into consideration.
Referral When Necessary
Some strabismus-related problems require assessment beyond spectacle dispensing.
Where appropriate, further assessment by an optometrist, ophthalmologist or other qualified healthcare professional may be recommended.
Allen — Founder & Optician at Eye Zen Optical
Allen has worked in opticianry since 2005 and founded Eye Zen Optical in Singapore in 2022. His work focuses on personalised spectacle solutions, including complex spectacle requirements, prism-related prescriptions and progressive-lens difficulties.
Frequently Asked Questions
Is strabismus the same as a squint?
Yes.
“Squint” and “eye turn” are commonly used terms for strabismus.
Is tropia the same as strabismus?
A tropia is a manifest eye deviation and is a form of strabismus.
Strabismus is the broader term for eye misalignment.
What is the difference between tropia and phoria?
A tropia is a manifest eye deviation.
A phoria is generally a latent tendency for the eyes to deviate that may remain controlled while both eyes are working together.
Can strabismus cause double vision?
Yes.
Strabismus can cause binocular double vision in some individuals because the eyes are not directed towards corresponding visual targets.
However, not everyone with strabismus experiences double vision.
Does strabismus affect 3D vision?
It can.
Eye misalignment may reduce stereopsis in some individuals.
The effect depends on the type and duration of the strabismus and how the visual system has developed or adapted.
Is strabismus the same as lazy eye?
No.
Strabismus refers to eye misalignment.
Lazy eye, or amblyopia, refers to reduced vision resulting from abnormal visual development during childhood.
They can occur together but are not the same condition.
Can glasses correct strabismus?
Spectacles can play an important role in certain forms of strabismus, particularly when refractive error contributes to the problem.
However, spectacles do not correct every type of strabismus.
Should an adult with a new eye turn have it checked?
Yes.
New eye misalignment or sudden double vision in an adult should receive appropriate professional or medical assessment because there are many possible causes.
Personalised Optical Solutions for Strabismus in Singapore
If you have strabismus, an eye turn, double vision or difficulty achieving comfortable vision with your current spectacles, the appropriate solution may require more than simply changing your prescription.
At Eye Zen Optical, we consider:
your prescription + both eyes + binocular vision + lens design + optical positioning + frame + visual requirements
as part of the complete spectacle solution.
Our aim is to determine whether an appropriate optical solution can provide clearer and more comfortable vision while recognising when further professional or medical assessment is required.
Eye Zen Optical
71 Kallang Bahru #01-529D
Singapore 330071
WhatsApp / Call: +65 8048 8379
Book a consultation with Eye Zen Optical to discuss your visual concerns.