Strabismus Library

Amblyopia is a developmental form of vision impairment, principally in one eye (not correctable with lenses), caused by a failure in binocular vision during infancy or early toddlerhood either by misalignment of the eyes (strabismus), or when one eye has a greater farsightedness/nearsightedness and/or astigmatism, or blockage of light, such as infantile cataracts. For more information about this condition, visit visionhelp.com/amblyopia

Strabismus is a condition that results in both eyes not pointing in the same direction. The most common forms occur in childhood and is often a neuro-developmental condition occurring in early childhood, where both eyes do not align and point in the same direction. It can be present all the time or intermittently. Strabismus is rarely due to an eye muscle weakness, but is most commonly due to a failure of the binocular vision centers of the brain necessary for coordinating the eye muscles to work together. When this failure of binocular vision occurs, the brain in the young child learns to turn off (or suppress) the information from one eye to prevent double vision or confusion which leads to a crossed or turned eye (strabismus). This results in impaired depth perception (stereo acuity) and a cascade of other problems affecting balance, gross and fine motor coordination and reading fluency.

Disclaimer: While most strabismus is not due to a neurological cause, there are forms that are directly due to a neurological origin and requires a neurological consult. This would be determined by a comprehensive eye health and vision evaluation.

The amount of the eye turn or misalignment of the eyes.

Overview of Strabismus from the American Optometric Associations

An eye that turns out.

An eye that turns in.

An eye that turns in when focusing up close.

An eye that turns up or down.

An eye that turns as a result of cranial nerve damage, exhibiting loss of a range of motion.

An eye that turns the opposite direction after strabismus surgery, for example, an esotropia that becomes an exotropia after strabismus surgery.

Congenital/Infantile (postnatal to 6 months), Early Onset (6 months to 36 months)

Does the eye constantly turn? Does the eye turn intermittently (sometimes)? Does the eye
turn when focusing at near (accommodative)?

Does the eye turn when viewing at distance, near or both?

Does only one eye turn (Unilateral), or do the eyes take turns (Alternating)?

Which direction does the eye turn?
Esotropia/Exotropia,
Hypertropia/Hypotropia,
Incyclotropia/Excyclotropia

How large is the angle of deviation measured in prism diopters (PD)?
Microtropia (up to 4PD),
Small-angle strabismus (4 to 9PD),
Moderate-angle strabismus (10 to 30PD)
Large angle strabismus (>30PD)

(association with disease)

A neural adaptation to eye misalignment where the turned eye does not use the central
part of the retina (the part with the best vision) to spatially correspond (match up with) the
central part of the straight eye.

Is the angle of deviation the same in all gazes? If it is not, the eye turn is considered
noncomitant.

Is the eye turn associated with disease?

The two-eyed appreciation of depth to allow judgments of space as in driving and playing sports.

An office based, sequence of neurosensory and neuromuscular activities individually prescribed and monitored by a Doctor of Optometry to develop, rehabilitate, and enhance binocular vision, visual efficiency, visual processing and integration with other sensory functions such as balance, movement, listening and thinking.

Blocking sight in one eye through the use of a patch. While occlusion when applied early can serve to minimize the development of amblyopia, patching only contributes to the failed binocular system and can contribute further to the eyes misaligning.

Double vision resulting from both eyes not aligning on the same object in space.

An active adaptation response by the brain to eliminate double vision by shutting off the signal from the turned eye while both eyes are open. This maladaptation helps by preventing diplopia (double vision) but also exacerbates the failure of binocular vision by causing monocular vision.

A type of therapeutic lens that shifts the location of an image.

Cutting and moving the insertion point of eye muscles on the eyeball to change the alignment of the eyes. This usually results in an immediate cosmetic improvement of the eyes, and in some cases results in improved binocular vision. When the angle of strabismus is large, or eye muscles are paretic, surgery may be indicated. The surgery itself, however, does not teach the brain how to blend the images from the two eyes to create normal fusion. This is one reason why some patients misalign again at some point after surgery and need multiple operations. It is important to note that there has never been a well-controlled scientific study comparing the effects of strabismus surgery to alternative approaches.

A phase in development during which there is heightened sensitivity to external stimuli necessary for the development of a particular skill or function. While there is a critical period in human visual development, research in neuroplasticity has shown that there is not a “critical period” for the treatment of developmental forms of visual problems. This means that age is not a barrier to treatment for those with developmental strabismus. Adults can also effectively respond to vision therapy.

Unfortunately, this is rarely the case.

Medical treatment always starts with the least invasive treatment option first.

In very rare instances, there may be difficulty in the brain learning to use both eyes together properly, but the optometrist assesses for this prior to therapy beginning.

The goal is for the patient to be done within a specific period of time, often within a year. Some adult patients find that just like going to the gym on a regular schedule, they have a particular therapy procedure that they enjoy doing as maintenance.

When therapy is undertaken properly, the benefits of vision therapy are long lasting.

In rare cases regression can occur, as it may with strabismus surgery, particularly if a severe illness or brain injury is encountered.

The length of vision therapy varies with the type of strabismus.

Vision therapy can be successful at any age.

A developmental/rehabilitative optometrist judges success by the extent to which the patient has improved in being able to use both eyes together, in improved depth perception, and many other visual functions that had been limited the patient's performance prior to therapy.

A surgeon's definition of success is typically cosmetically straight eyes. A developmental optometrist not only wants the eyes to appear straight but they also want the patient to be able to use both eyes together as a team effectively, focus, track and process information efficiently.

The best overall estimate as provided in the American Optometric Association's Clinical Practice Guideline is 60% when considering primarily the appearance of the eyes. When evaluating visual function, the success rate can drop to as low as 30%.

No. We now know that the brain is plastic and forms new pathways at all ages.

What are the chances of success after one surgery?

What is the definition of success? Is it normal eye teaming or only cosmetic improvement?

What is the probability that my child’s eye will look worse after the surgery?

What is the probability that my child will need 2, 3 or more surgeries?

If amblyopia is present, will surgery improve the clarity of my child’s vision?

Will my child have improved depth perception after the surgery, i.e., stereopsis?

What are the complications (i.e. infection, risk of general anesthesia)?

Will my child need to wear glasses after the surgery?