What does amblyopia mean?
Amblyopia signs and symptoms
What are the types of amblyopia?
Amblyopia diagnosis
Amblyopia treatment
What is the difference between strabismus and amblyopia?
Why am I suddenly getting a lazy eye?
Can amblyopia be corrected?
Is Amblyopia a genetic disease?
What does amblyopia mean?
Amblyopia, also called lazy eye, is a disorder of sight due to the eye and brain not working well together. It results in decreased vision in an eye that otherwise typically appears normal. It is the most common cause of decreased vision in a single eye among children and younger adults.
The cause of amblyopia can be any condition that interferes with focusing during early childhood. This can occur from poor alignment of the eyes, an eye being irregularly shaped such that focusing is difficult, one eye being more nearsighted or farsighted than the other, or clouding of the lens of an eye. After the underlying cause is fixed, vision is not restored right away, as the mechanism also involves the brain. Amblyopia can be difficult to detect, so vision testing is recommended for all children around the ages of four to five.
Early detection improves treatment success. Glasses may be all the treatment needed for some children. If this is not sufficient, treatments which force the child to use the weaker eye are used. This is done by either using a patch or putting atropine in the stronger eye. Without treatment, amblyopia typically persists. Treatment in adulthood is not effective.
Amblyopia begins by the age of five. In adults, the disorder is estimated to affect 1–5% of the population. While treatment improves vision, it does not typically restore it to normal in the affected eye. Amblyopia was first described in the 1600s. The condition may make people ineligible to be pilots or police officers. The word amblyopia is from Greek ἀμβλύς amblys meaning “blunt” and ὤψ ōps meaning “sight”.
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Read more about: Amblyopia treatment
Amblyopia signs and symptoms
Many people with amblyopia, especially those who only have a mild form, are not aware they have the condition until tested at older ages, since the vision in their stronger eye is normal. People typically have poor stereo vision, however, since it requires both eyes. Those with amblyopia further may have, on the affected eye, poor pattern recognition, poor visual acuity, and low sensitivity to contrast and motion.
Amblyopia is characterized by several functional abnormalities in spatial vision, including reductions in visual acuity, contrast sensitivity function, and vernier acuity, as well as spatial distortion, abnormal spatial interactions, and impaired contour detection. In addition, individuals with amblyopia suffer from binocular abnormalities such as impaired stereoacuity (stereoscopic acuity) and abnormal binocular summation. Also, a crowding phenomenon is present. These deficits are usually specific to the amblyopic eye. However, subclinical deficits of the “better” eye have also been demonstrated.
People with amblyopia also have problems of binocular vision such as limited stereoscopic depth perception and usually have difficulty seeing the three-dimensional images in hidden stereoscopic displays such as autostereograms. Perception of depth, however, from monocular cues such as size, perspective, and motion parallax remains normal.
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What are the types of amblyopia?
Amblyopia has three main causes:
- Strabismic: by strabismus (misaligned eyes)
- Refractive: by anisometropia (difference of a certain degree of nearsightedness, farsightedness, or astigmatism), or by significant amount of equal refractive error in both eyes
- Deprivational: by deprivation of vision early in life by vision-obstructing disorders such as congenital cataract
- Strabismus amblyopia
Strabismus, sometimes also incorrectly called lazy eye, is a condition in which the eyes are misaligned. Strabismus usually results in normal vision in the preferred sighting (or “fellow”) eye (the eye that the person prefers to use), but may cause abnormal vision in the deviating or strabismic eye due to the difference between the images projecting to the brain from the two eyes. Adult-onset strabismus usually causes double vision (diplopia), since the two eyes are not fixed on the same object. Children’s brains, however, are more neuroplastic, so can more easily adapt by suppressing images from one of the eyes, eliminating the double vision. This plastic response of the brain, however, interrupts the brain’s normal development, resulting in the amblyopia. Recent evidence points to a cause of infantile strabismus lying with the input to the visual cortex.
Those with strabismic amblyopia tend to show ocular motion deficits when reading, even when they use the nonamblyopic eye. In particular, they tend to make more saccades per line than persons with normal stereo vision, and to have a reduced reading speed, especially when reading a text with small font size.
Strabismic amblyopia is treated by clarifying the visual image with glasses, or encouraging use of the amblyopic eye with an eyepatch over the dominant eye or pharmacologic penalization of the better eye. Penalization usually consists of applying atropine drops to temporarily paralyze the accommodation reflex, leading to the blurring of vision in the good eye. It also dilates the pupil. This helps to prevent the bullying and teasing associated with wearing a patch, although sometimes application of the eye drops is challenging. The ocular alignment itself may be treated with surgical or nonsurgical methods, depending on the type and severity of the strabismus.
- Refractive or anisometropic amblyopia
Refractive amblyopia may result from anisometropia (unequal refractive error between the two eyes). Anisometropia exists when there is a difference in the power between the two eyes. The eye which provides the brain with a clearer image typically becomes the dominant eye. The image in the other eye is blurred, which results in abnormal development of one half of the visual system. Refractive amblyopia is usually less severe than strabismic amblyopia and is commonly missed by primary care physicians because of its less dramatic appearance and lack of obvious physical manifestation, such as with strabismus. Given that the refractive correction of anisometropia by means of spectacles typically leads to different image magnification for the two eyes, which may in turn prevent binocular vision, a refractive correction using contact lenses is to be considered. Also pediatric refractive surgery is a treatment option, in particular if conventional approaches have failed due to aniseikonia or lack of compliance or both.
Frequently, amblyopia is associated with a combination of anisometropia and strabismus. In some cases, the vision between the eyes can differ to the point where one eye has twice average vision while the other eye is completely blind.
- Deprivation and occlusion amblyopia
Deprivation amblyopia (amblyopia ex anopsia) results when the ocular media become opaque, such as is the case with congenital cataract or corneal haziness. These opacities prevent adequate visual input from reaching the eye, and disrupt development. If not treated in a timely fashion, amblyopia may persist even after the cause of the opacity is removed. Sometimes, drooping of the eyelid (ptosis) or some other problem causes the upper eyelid to physically occlude a child’s vision, which may cause amblyopia quickly. Occlusion amblyopia may be a complication of a hemangioma that blocks some or all of the eye. Other possible causes of deprivation and occlusion amblyopia include obstruction in the vitreous and aphakia. Deprivation amblyopia accounts for less than 3% of all individuals affected by amblyopia.
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Amblyopia diagnosis
Amblyopia is diagnosed by identifying low visual acuity in one or both eyes, out of proportion to the structural abnormality of the eye and excluding other visual disorders as causes for the lowered visual acuity. It can be defined as an interocular difference of two lines or more in acuity (e.g. on Snellen chart) when the eye optics is maximally corrected. In young children, visual acuity is difficult to measure and can be estimated by observing the reactions of the patient reacts when one eye is covered, including observing the patient’s ability to follow objects with one eye.
Stereotests like the Lang stereotest are not reliable exclusion tests for amblyopia. A person who passes the Lang stereotest test is unlikely to have strabismic amblyopia, but could nonetheless have refractive or deprivational amblyopia. It has been suggested that binocular retinal birefringence scanning may be able to identify, already in very young children, amblyopia that is associated with strabismus, microstrabismus, or reduced fixation accuracy. Diagnosis and treatment of amblyopia as early as possible is necessary to keep the vision loss to a minimum.
Screening for amblyopia is recommended in all people between three and five years of age.
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Amblyopia treatment
Treatment of strabismic or anisometropic amblyopia consists of correcting the optical deficit (wearing the necessary spectacle prescription) and often forcing use of the amblyopic eye, by patching the good eye, or instilling topical atropine in the good eye, or both.
Concerning patching versus atropine, a drawback is seen in using atropine; the drops can have a side effect of creating nodules in the eye which a correctional ointment can counteract. One should also be wary of overpatching or overpenalizing the good eye when treating amblyopia, as this can create so-called “reverse amblyopia”. Eye patching is usually done on a part-time schedule of about 4–6 hours a day. Treatment is continued as long as vision improves. It is not worthwhile continuing to patch for more than 6 months if no improvement continues. Treatment of individuals age 9 through to adulthood is possible through applied perceptual learning.
Deprivation amblyopia is treated by removing the opacity as soon as possible followed by patching or penalizing the good eye to encourage the use of the amblyopic eye. The earlier the treatment is initiated, the easier and faster the treatment is and the less psychologically damaging. Also, the chance of achieving 20/20 vision is greater if treatment is initiated early.
One of the German public health insurance providers, Barmer, has changed its policy to cover, as of 1 April 2014, the costs for an app for amblyopic children whose condition has so far not improved through patching. The app offers dedicated eye exercises which the patient performs while wearing an eyepatch.
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What is the difference between strabismus and amblyopia?
Strabismus and Amblyopia are not the same eye / vision condition or medical diagnosis. “Lazy Eye” is the common or vernacular term for the medical diagnosis named 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 (Crossed eyes)
- 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.
- 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.
- 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.
Amblyopia (Lazy eye)
- 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.
- 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.
- 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.
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Why am I suddenly getting a lazy eye?
The most common cause of lazy eye is an imbalance in the muscles that position the eyes. This imbalance can cause the eyes to cross in or turn out, and prevents them from working together. A significant difference between the prescriptions in each eye — often due to farsightedness but sometimes to nearsightedness or an uneven surface curve of the eye (astigmatism) — can result in lazy eye.
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Can amblyopia be corrected?
Lazy eye, or amblyopia, affects around 3 out of every 100 children. The condition is treatable and typically responds well to strategies such as eye patching and wearing corrective lenses.
The best results for lazy eye are typically seen when the condition is treated early, in children who are 7 years old or younger.
Is Amblyopia a genetic disease?
When one eye sees more clearly than the other, the brain ignores the blurry eye.
Genetics play a role, Amblyopia tends to run in families. It’s also more common in children born prematurely or those with developmental delays.