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Strabismus vs Amblyopia: The Difference Between Crossed Eye and Lazy Eye

Posted by The Vision Therapy Center

The Difference Between Strabismus and Amblyopia

Understanding the difference between strabismus and amblyopia can be confusing, as the two functional vision problems share some similar characteristics.  We produced a side-by-side comparison, including what to do if you think you’re suffering from either issue (or both)!

What is the Difference Between Strabismus and Amblyopia?

Strabismus is a problem with eye alignment, in which both eyes do not look at the same place at the same time. Amblyopia is a problem with visual acuity, or eyesight. Even with prescription glasses, a person with amblyopia cannot see an image clearly in one or both eyes. Both conditions are functional vision problems which result from poor development of eye teaming. As is the case with all functional vision problems, they can be treated at any age.

Strabismus and amblyopia can be treated at any age.

What do we mean by “functional” vision? Functional vision is how your entire visual system -- the eyes, the brain, the visual pathways -- work together to help you interact with the environment.  They include the visual skill areas of eye teaming, eye focusing and eye movement.

You can learn more about functional vision problems and how they are detected here.

The Breakdown: Amblyopia vs. Strabismus

We’ve produced an “at-a-glance” chart to help you understand the main differences between amblyopia and strabismus.

 

Strabismus

Amblyopia

Slang Term

Crossed eyes

Lazy eye

Definition

Strabismus is a condition in which both eyes do not look at the same place at the same time. It occurs when one or both eyes turn in, out, up or down some or all of the time.

Amblyopia is the lack of development of clear vision in one or both eyes for reasons other than an eye health problem that cannot be improved with glasses alone.

Cause

Strabismus is a severe problem with eye teaming, one of the three visual skill areas that make up functional vision.

Because the eyes are pointing at different places, the brain has difficulty combining the images from both eyes into a single, 3D image.

In cases where the image of one eye is affected, the brain cannot effectively combine the two images and it suppresses, or “turns off,” one of them.  The constant suppression of an image from one eye can lead to the development of amblyopia in that eye.

In cases where the images of both eyes are affected, the brain never develops the ability to see clearly with both of the eyes.

Correcting Misconceptions

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

Strabismus does not result from “weak eye muscles.”

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

Some people think amblyopia can lead to blindness, which it cannot.

A third 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.

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



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: Results from an uncorrected high prescription in one or both eyes.

Strabismic amblyopia: Results from a constant eye turn in one eye.

Deprivation amblyopia: Results from impaired vision in one eye due to physical problems in the eye.

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 non-strabismic functional vision problems. That’s because they often suppress the information from the eye that is turning, thus avoiding double vision and some of the accompanying symptoms of poor eye teaming.

Patients with intermittent strabismus may experience more frequent symptoms of a functional vision problem.  These include:

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

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

However, because this is a functional vision problem, typical symptoms involve:

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

Treatment

Many people consider surgery as a means of treating strabismus. While this can reduce the amount of the eye turn, it doesn’t address the underlying functional vision problem of poor eye teaming. This is why several surgeries are often required.

Vision therapy addresses the root cause by enabling the person to develop their eye teaming skills.

In some cases, the best approach may be a combination of vision therapy and surgery. Even in these cases, the non-invasive treatment option of vision therapy should be done first.

Traditional treatment includes prescribing glasses and then patching the non-amblyopic eye with an eye patch. Alternatively, prescription eye drops can be used to ‘patch’ the non-amblyopic eye by blurring the vision in that eye.

However, as is the case with strabismus, patching alone  does not address the root cause of the condition, which is poor development of eye teaming skills.

In conjunction with patching and/or prescribing glasses, vision therapy should be considered to develop eye teaming skills and improve functional vision to prevent regression.


A Functional Vision Exam Will Determine if You Have Strabismus or Amblyopia

If you or your child has any of the symptoms mentioned in the chart, the next step is to undergo a Functional Vision Exam.  

While a primary care optometrist is able to detect a condition like strabismus or amblyopia, a developmental optometrist conducts a Functional Vision Exam that includes additional testing to assess the visual skill areas of eye teaming, eye focusing and eye movements. This additional testing allows the doctor and patient to fully understand the vision problem. Because the developmental optometrist has experience in treating these conditions with vision therapy, they are best suited to discuss treatment options and prognosis for improvement.

What happens if strabismus or amblyopia is detected during an exam?

If strabismus and/or amblyopia are detected in the exam, additional tests specific to those conditions are performed in order to fully characterize the condition. This information will aid the developmental optometrist in determining the prognosis for improvement with vision therapy.

After the functional vision exam is complete, the developmental optometrist will likely recommend perceptual testing, which uses standardized tests to assess how the functional vision problem affects visual information processing.

For more in-depth information on each condition, visit our strabismus or our amblyopia pages.  If you would like to take The Vision Quiz to see if you have symptoms associated with either issue, click below.

Take The Vision Quiz Now

Topics: Amblyopia (Lazy Eye), Strabismus (Crossed Eyes)