Lazy eye generally refers to amblyopia (weak eye). 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. Some of the confusion may be due to the fact that an eye turn can cause lazy eye. In other words, amblyopia can result from a constant unilateral strabismus (i.e., an eye that turns or deviates all of the time).
You can read more about the difference between amblyopia and strabismus here.
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: refractive, strabismic, and deprivational. Read more about amblyopia here.
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 is also known as anisometropic amblyopia. This occurs when there is a high degree of nearsightedness or farsightedness in one or both eyes.
Strabismic Amblyopia is caused by a misalignment of the eyes. The weak eye is often suppressed to prevent double vision, or diplopia.
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.
Strabismus is a misalignment of one or both of the eyes. This misalignment can cause stereo blindness, suppression, amblyopia, and/or diplopia. There are several classifications of strabismus depending on how the eyes are misaligned. Read more about strabismus here.
Convergence Insufficiency is a fairly common visual condition which is also (1) confused with lazy eye; (2) not easily discernible to the observer and (3) not detected by the standard 20/20 eye test.
Based on 2010 census data, there were about 18 million people with strabismus and 9.2 million with amblyopia in the United States. About 19.2 million have been diagnosed with lazy eye in the US alone. There are about 2.5 million children under age of 10 with lazy eye, and 250,000 more born every year in the United States. Binocular Vision Dysfunction Pandemic, Dominick M. Maino">
If you think that those are big numbers consider that, "A clinical trial to determine the prevalence of binocular vision dysfunction amblyopia."> within the general population suggested the possibility of up to 56% or 60 million men, women, and young adults with symptoms associated with a binocular vision dysfunction."
First, what is lazy eye? Lazy eye is a common term for a group of disorders called amblyopia and strabismus. Lazy Eye typically begins during infancy and early childhood.
The most common causes of amblyopia are:
Of these, strabismus is the most common cause of amblyopia.
Typical symptoms of Lazy Eye can include:
A clue that your child may have amblyopia is if he or she cries or fusses when you cover one eye.
Amblyopia is the medical term for lazy eye. Typically, the first line of treatment for patients with amblyopia is prescription eyeglasses or contact lenses. Treatment of amblyopia can also include vision therapy, eye patching, eye drops, prism glasses, refractive surgery, or a combination of those options. In vision therapy, patients learn how to use the two eyes together, which helps prevent lazy eye from reoccurring. Vivid Vision is used successfully in the treatment of lazy eye.
Unfortunately there is a lot of misinformation surrounding lazy eye and it has lead to people not seeking or receiving care.
We regularly hear from people who have been told they simply have to live with their lazy eye and that nothing can be done to treat it. As with many conditions, diseases, and treatments in the medical world, research has furthered our knowledge and understanding of amblyopia and strabismus over time with an extensive amount of progress happening over the last decade or two. Much of this is based on new understanding of the pathophysiology that has come in part thanks to advancements in new brain-imaging methods such as functional MRI. Neuroplasticity is the term used to describe the ability of the nervous system to change and adapt. It was once thought that the neuroplasticity of the visual system was lost after adolescence, but recent clinical trials have led to a massive shift in thinking about adult neuroplasticity.
We now know that there is not a “critical period” in which amblyopia must be treated. The “recovery period” for these conditions continues through life—albeit easier to treat if diagnosed and treated earlier. It is now known and supported widely by research from vision science, optometry, ophthalmology, and neuroscience, that patients of any age can successfully be treated for amblyopia (including strabismic amblyopia). Again, despite these advancements, it is still best if these conditions are diagnosed and treated early on.
Recent research (Ziak et al has shown visual acuity as well as stereo acuity can improve at statistically-significant levels in amblyopic patients outside of the “critical period” using virtual reality vision therapy technology. Another recent study (Ho et al, 2019) also showed improved visual acuity and stereo acuity in amblyopic and strabismic patients aged 3-69 using virtual reality vision therapy technology who were previously unsuccessful in traditional patching or occlusion therapy.
Sometimes, a lazy eye is caused by unequal acuity in the two eyes, despite perfect eye alignment. For example, one eye may have significant nearsightedness or farsightedness, while the other eye does not. Or one eye may have significant astigmatism and the other eye does not. In such cases, the brain relies on the eye that has less uncorrected refractive error and "tunes out" the blurred vision from the other eye, causing amblyopia in that eye from disuse. This type of lazy eye is called refractive amblyopia (or anisometropic amblyopia). These patients will not show an eye turn, their eye alignment is just fine. You can read more about refractive amblyopia here.
In other cases, lazy eye is caused by something that obstructs light entering and being focused on the light-sensitive cells of the retina. This can happen even in a baby's eye, such as a baby with a congenital cataract. This is called deprivational amblyopia and these patients also do not often exhibit an eye turn.
Unfortunately, despite all good intentions, school vision screenings can give a false sense of security when it comes to vision problems beyond general distance acuity. These screenings are designed to alert parents and teachers to the possibility of a visual problem, but should not take the place of a visit to an eye care practitioner. It may seem hard to believe, but lazy eye is just one of the vision problems commonly missed during school screenings and during early childhood wellness checks at the pediatrician’s office. In school, pediatricians are provided a very limited amount of training and education regarding eyes and vision. They perform very basic screenings, not comprehensive assessments. Lazy eye can only be diagnosed by an eye care professional. Because early intervention improves treatment outcomes, it is important to have your child seen within the first year of life. The InfantSEE® program from the American Optometric Association provides a cost-free comprehensive evaluation during the first year of life with optometrists trained to evaluate pediatric and infant patients.
You may enjoy this blog post about more of the myths and misconceptions about lazy eye- "Lazy Eye: 12 Things You Didn't Know"