What is the difference between Amblyopia and Strabismus?

This comprehensive side-by-side comparison provides a thorough explanation for understanding the difference between strabismus (crossed-eye) and amblyopia (lazy-eye).

Amblyopia vs Strabismus

Very simply, Strabismus, the medical term for "crossed-eye", is a problem with eye alignment, in which both eyes do not look at the same place at the same time. Amblyopia, the medical term for "lazy-eye", is a problem with visual acuity, or eyesight. Many people make the mistake of saying that a person who has a crossed or turned eye (strabismus) has a "lazy-eye," but lazy-eye (amblyopia) and strabismus are not the same condition. 

Both strabismus and amblyopia are treatable conditions by a vision therapy specialist.

Strabismus is the most common cause of amblyopia and amblyopia often occurs along with strabismus. However, amblyopia can occur without strabismus. But, there's more to it than this. Let's take a look at these vision disorders side-by-side.

Strabismus Amblyopia
Also known as Crossed-eyes, Squint, wandering eye, deviating eye, walleye Lazy-eye
Definition Strabismus is a condition in which the eyes do not point at the same place at the same time. One or both eyes turn inward (esotropia), outward (exotropia), upward (hypertropia), or downward (hypotropia) eithr some (intermittent) or all of the time. Amblyopia is the lack of development of clear vision (acuity) in one or both eyes for reasons other than an eye health problem that cannot be improved with glasses alone.
Types

Types of strabismus are determined by the following:

  • Which eye turns
  • Direction of the eye turn
  • Frequency of the eye turn
  • Amount of eye turn
  • Whether the turn is the same in all positions of gaze

The types of strabismus are:

  • Intermittent Strabismus
  • Constant Strabismus
  • Alternating Strabismus
  • Esotropia
  • Infantile Esotropia
  • Congenital Esotropia
  • Accommodative Esotropia
  • Exotropia
  • Intermittent Exotropia
  • Hypertropia
  • Duane's Syndrome

All three types of amblyopia result from suppression of vision in one or both eyes. The difference is in the root cause of the suppression.

  • Refractive amblyopia 
  • Strabismic amblyopia 
  • Deprivation amblyopia 
% of Population  4% 3% - 6%
Causes

People can be born with strabismus or it can be acquired later in life.

Strabismus can also develop as the result of an accident or other health problem. 

Genetics also may play a role: If you or your spouse has strabismus, your children have a greater risk of developing strabismus as well.

Strabismus occurs when there are neurological or anatomical problems that interfere with the control and function of the eyes. The problem may originate in the muscles themselves, or in the nerves, or in the vision centers in the brain that control binocular vision.

Most cases of strabismus are not a result of a muscle problem, but are due to miscommunication between the brain and the eyes. Because the eyes are pointing at different places, the brain has difficulty combining the images from both eyes into a single, 3D image.

Amblyopia begins during infancy and early childhood.

The most common causes of amblyopia are:

  • constant strabismus (constant turn of one eye),
  • anisometropia (different vision/prescriptions in each eye),
  • and/or blockage of an eye due to trauma, lid droop, etc.

Of these, strabismus is the most common cause of amblyopia.

Risk Factors

Risk factors include:

  • family history of strabismus 
  • prematurity or low birth weight
  • retinopathy of prematurity
  • conditions that affect vision, such as cataracts, severe ptosis and corneal scars
  • muscular abnormalities
  • neurological abnormalities
  • amblyopia (or lazy eye) 

People with parents or siblings who have strabismus are more likely to develop it.

People who have a significant amount of uncorrected farsightedness (hyperopia) may develop strabismus because of the additional eye focusing they must do to keep objects clear.

People with conditions such as Down syndrome and cerebral palsy or who have suffered a stroke or head injury are at a higher risk for developing strabismus.

Risk factors include:

Strabismus and significant refractive errors are risk factors for unilateral amblyopia.

Bilateral astigmatism and bilateral hyperopia are risk factors for bilateral amblyopia.

Symptoms

The obvious symptom of strabismus is an observable eye turn.

Patients with constant strabismus tend to be less symptomatic (but not asymptomatic) when compared to patients with intermittent strabismus. That’s because they often suppress the information from the eye that is turning, thus avoiding double vision and other symptoms. 

Patients with intermittent strabismus may experience more frequent symptoms. These include:

  • Poor depth perception
  • Eye strain and/or pain
  • Headaches
  • Blurry or double vision
  • Eye and/or general fatigue

Patients with strabismus may report:

  • difficulty driving,
  • difficulty reading,
  • difficulty with sports activities,
  • feeling clumsier than their peers. 

Unlike strabismus, which is generally easy to spot, you can’t detect amblyopia with simple observation, as there are no visible signs.

Typical symptoms include:

  • Poor depth perception
  • Difficulty catching and throwing objects
  • Clumsiness
  • Squinting or shutting an eye
  • Head turn or tilt
  • Eye strain
  • Fatigue with near work

A clue that your child may have amblyopia is if he or she cries or fusses when you cover one eye.

How is
it diagnosed?

Strabismus is diagnosed during an eye examination.

Testing for strabismus, with special emphasis on how the eyes focus and move, may include:

  • Patient history 
  • Visual Acuity 
  • Refraction
  • Alignment and focusing testing 
  • Examination of eye health 

Amblyopia is diagnosed during an eye examination.

Since amblyopia usually occurs in one eye only, many parents and children may be unaware of the condition. Far too many parents don't know they need to take their infants and toddlers in for an early comprehensive vision examination by an optometrist and many children go undiagnosed.

Misconceptions

Strabismus applies to any type of eye turn, not just “crossed eyes.”

Strabismus does not result from “weak eye muscles.”

People incorrectly apply the term "lazy eye" to both strabismus and amblyopia, which is why it is a bad phrase to use.

Patients are often told that amblyopia can only be treated until a certain age. This is outdated information. While early intervention is still ideal, it is never too late to treat amblyopia.

Another misconception is that the amblyopic eye is the "bad eye." While it doesn't have the same level of eyesight as the non-amblyopic eye, there may be other visual skills, such as localization, at which it is good.

Treatment 

Treatment for strabismus may include eyeglasses, prisms, vision therapy, or eye muscle surgery. If detected and treated early, strabismus can often be corrected with excellent results.

Vivid Vision is used in the treatment of strabismus. 

Treatment for amblyopia (lazy eye) may include a combination of prescription lenses, prisms, vision therapy and eye patching. In vision therapy, patients learn how to use the two eyes together, which helps prevent lazy eye from reoccurring. Vivid Vision is used in the treatment of amblyopia.

References:

American Optometric Association: Amblyopia
American Optometric Association: Strabismus
The Vision Therapy Center: The Difference Between Crossed Eye and Lazy Eye
Optometrist's Network: What is Lazy Eye?
All About Vision: Strabismus and Crossed Eyes
All About Vision: Amblyopia (Lazy Eye)

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