What Is Amblyopia?

Very simply, 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.

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. It is a problem with how the brain perceives and interprets the information coming from the amblyopic eye. It often leads to a suppression of the information coming from the amblyopic eye. There are three major types of amblyopia.

Amblyopia is a change in the nerve pathways from the retina to the brain. When this connection weakens, the eye may wander and receive fewer overall visual signals.

If left untreated, the brain may begin to disregard all visual signals sent from the weak eye. Amblyopia can result in blurred vision and lack of depth perception.

There are three main types of amblyopia. The type of amblyopia a child exhibit depends almost exclusively on the cause of the visual disruption.

Types of Amblyopia

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

Refractive Amblyopia is also known as anisometropic amblyopia. This occurs when there is a high degree of nearsightedness or farsightedness in one or both eyes.

This form of amblyopia may occur when there is a focusing difference between the two eyes. This may be caused by conditions such as astigmatism, hyperopia, or myopia. The brain only sees with the stronger eye, and as a consequence, the vision in the weaker eye does not develop.

Strabismic Amblyopia

Strabismic Amblyopia is caused by a misalignment of the eyes. The weak eye is often suppressed to prevent double vision, or diplopia. In strabismic amblyopia, the cortical ocular dominance columns remain structured, even in cases of moderate amblyopia. Only in cases of deep amblyopia are there reports of alteration of dominance columns.

Although the cortical cellular apparatus is relatively preserved, many functional changes occur in the visual system. There is active and deep suppression of the dominant eye over the deviating eye, retinal correspondence is completely lost, and cellular interactions are altered.

Deprivational Amblyopia

The least common type of Amblyopia is deprivational amblyopia, which is caused by a deprivation of vision in early childhood. This is often caused by congenital cataracts.

Deprivation amblyopia is the most severe form of this condition and can result in permanent vision loss if left untreated. This form of amblyopia occurs when one eye is deprived of clear visual signals, usually due to another eye health problem such as a cataract.

What Causes Amblyopia?

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.

What are the Signs and Symptoms of Amblyopia

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

lazy eye

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.

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 about Amblyopia

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 for Amblyopia

Treatment for Amblyopia, the medical term for 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. Modern treatment also includes the use of virtual reality software such as Vivid Vision.

Improvements are possible at any age, but early detection and treatment offer the best outcome. Even if no signs or symptoms are noticed, it is important that children are taken to an optometrist for a comprehensive visual assessment during the first year of life to help catch problems like refractive amblyopia at an early stage.

Treatment of refractive amblyopia can include vision therapy, eye patching, eye drops, refractive surgery, or a combination of those options. Vision therapy may include the use of virtual reality technology in treatment of lazy eye. It is also common for patients with refractive amblyopia to wear prescription lenses or contact lenses as a form of or as part of their treatment.

Why is it important, as a primary care optometrist, to know how to diagnose and treat amblyopia? First, it is not an uncommon condition; the prevalence has been reported to be between 1% and 5% of the population, and it is the most common cause of vision impairment in children and young adults. Second, it is critical not only to the ocular health but also to the overall well-being of our patients that we correctly diagnose and treat this condition.

It is often difficult to convince patients and parents to invest time and money into treating an amblyopic eye if the patient has good vision in the fellow eye. It is important to educate all parties about what happens if the child loses vision from injury or ocular disease in the non-amblyopic eye. Patients with amblyopia have almost twice the incidence of bilateral visual impairment as those without amblyopia, and their lifetime risk of serious vision loss in both eyes is estimated to be between 1.2% and 3.3%. A bilateral loss of visual acuity can impact a patient’s ability to drive, maintain employment and function in the world. It is our job, therefore, to not only diagnose and manage this condition, but to also educate our patients on the importance of treating amblyopia.

References

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