Amblyopia

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Amblyopia
Other namesLazy eye [1]
Child eyepatch.jpg
A child wearing an adhesive eyepatch to correct amblyopia
Pronunciation
Specialty Ophthalmology, optometry
Symptoms Decreased vision
Usual onsetBefore age five [2]
Causes Poor alignment of the eyes, eye being irregularly shaped such that focusing is difficult, one eye being more nearsighted or farsighted, clouding of the lens [1]
Diagnostic method Vision testing [1]
Differential diagnosis Brainstem disorders, optic nerve disorder, eye diseases [3]
Treatment Glasses, eyepatch [1] [2] [4]
Frequency~2% of adults [5]

Amblyopia, also called lazy eye, is a disorder of sight in which the brain fails to fully process input from one eye and over time favors the other eye. [1] It results in decreased vision in an eye that typically appears normal in other aspects. [1] Amblyopia is the most common cause of decreased vision in a single eye among children and younger adults. [1]

Contents

The cause of amblyopia can be any condition that interferes with focusing during early childhood. [1] [6] This can occur from poor alignment of the eyes (strabismic), an eye being irregularly shaped such that focusing is difficult, one eye being more nearsighted or farsighted than the other (refractive), or clouding of the lens of an eye (deprivational). [1] After the underlying cause is addressed, vision is not restored right away, as the mechanism also involves the brain. [6] [7] Amblyopia can be difficult to detect, so vision testing is recommended for all children around the ages of four to five. [2]

Early detection improves treatment success. [2] Glasses may be all the treatment needed for some children. [2] [4] If this is not sufficient, treatments which encourage or force the child to use the weaker eye are used. [1] This is done by either using a patch or putting atropine in the stronger eye. [1] [8] Without treatment, amblyopia typically persists. [1] Treatment in adulthood is usually much less effective. [1]

Amblyopia begins by the age of five. [2] In adults, the disorder is estimated to affect 1–5% of the population. [5] While treatment improves vision, it does not typically restore it to normal in the affected eye. [2] Amblyopia was first described in the 1600s. [9] The condition may make people ineligible to be pilots or police officers. [2] The word amblyopia is from Greek ἀμβλύς amblys, meaning "blunt", and ὤψ ōps, meaning "sight". [10]

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 with amblyopia typically have poor stereo vision, since it requires both eyes. They further may have, on the affected eye, poor pattern recognition, poor visual acuity, and low sensitivity to contrast and motion. [11]

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 have binocular abnormalities such as impaired stereoacuity (stereoscopic acuity) and abnormal binocular summation. [12] Also, central vision in amblyopes is more crowded than central vision in normal observers. [13]

These deficits are usually specific to the amblyopic eye. Subclinical deficits of the "better" eye have also been demonstrated. [14]

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. [15] Perception of depth, from monocular cues such as size, perspective, and motion parallax remains normal.

Cause

Amblyopia has three main causes:

Strabismus

Strabismus, sometimes also incorrectly called lazy eye, is a condition in which the eyes are misaligned. [17] 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. [18] Adult-onset strabismus usually causes double vision (diplopia), since the two eyes are not fixed on the same object. Children's brains 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 interrupts the brain's normal development, resulting in the amblyopia.[ citation needed ] Recent evidence points to a cause of infantile strabismus lying with the input to the visual cortex. [19]

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. [20] [21] [ non-primary source needed ]

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. [22]

Refractive

Refractive amblyopia may result from anisometropia (unequal refractive error between the two eyes). [23] [24] 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. [25] 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. [26]

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

Deprivation amblyopia (amblyopia ex anopsia) results when the ocular media become opaque, such as is the case with congenital cataract or corneal haziness. [27] 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. [28] Deprivation amblyopia accounts for less than 3% of all individuals affected by amblyopia. [28]

Pathophysiology

Amblyopia is a developmental problem in the brain, not any intrinsic, organic neurological problem in the eyeball (although organic problems can lead to amblyopia which can continue to exist after the organic problem has resolved by medical intervention). [29] The part of the brain receiving images from the affected eye is not stimulated properly and does not develop to its full visual potential. This has been confirmed by direct brain examination. David H. Hubel and Torsten Wiesel won the Nobel Prize in Physiology or Medicine in 1981 for their work in showing the extent of the damage to ocular dominance columns produced in kittens by sufficient visual deprivation during the so-called "critical period". The maximum "critical period" in humans is from birth to two years old. [30]

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 are maximally corrected. [31] In young children, visual acuity is difficult to measure and can be estimated by observing the reactions of the patient 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. [32] 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. [33]

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. [17] :130 [34] Atropine appears to result in similar outcomes to patching. [35] [36] If there is overpatching or overpenalizing the good eye when treating amblyopia, "reverse amblyopia" can result. [22] [37] 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. [38]

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. [22] 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. [39]

One of the German public health insurance providers, Barmer, has changed its policy to cover, as of 1 April 2014, the cost of software for amblyopic children whose condition did not improve through patching. The app offers dedicated eye exercises that the patient performs while wearing an eyepatch. [40]

Evidence for vision therapy is unclear as of 2011. [41]

Older age

Treatment of individuals age 9 through to adulthood is possible through applied perceptual learning. [12] [42] Tentative evidence shows that perceptual training may be beneficial in adults. [43] [44]

Epidemiology

Amblyopia occurs in 2–5% of the population in Western countries.[ which? ] [31] [45] In the UK, 90% of visual health appointments in the child concern amblyopia. [46]

Depending on the chosen criterion for diagnosis, 1–4% of the children have amblyopia. [47]

Research

A 2009 study, [48] widely reported in the popular press, [49] has suggested that repetitive transcranial magnetic stimulation may temporarily improve contrast sensitivity and spatial resolution in the affected eye of adults with amblyopia. This approach is still under development, [50] and the results await verification by other researchers. Comparable results may be achieved using different types of brain stimulation, [51] such as anodal transcranial direct current stimulation [52] and theta burst rTMS. [53]

A 2013 study concluded that converging evidence indicates decorrelated binocular experience plays a pivotal role in the genesis of amblyopia and the associated residual deficits. [54] Another study of 2013 [55] suggests that playing a version of the popular game Tetris that is modified such that each eye sees separate components of the game may also help to treat this condition in adults. [56] Furthermore, the effects of this kind of therapy may be further enhanced by noninvasive brain stimulation [51] as shown by a recent study using anodal tDCS. [57]

A 2014 Cochrane review sought to determine the effectiveness of occlusion treatment on patients with sensory deprivation amblyopia, but no trials were found eligible to be included in the review. [28] However, good outcomes from occlusion treatment for sensory deprivation amblyopia likely rely on compliance with the treatment.

See also

Related Research Articles

<span class="mw-page-title-main">Esotropia</span> Form of strabismus

Esotropia is a form of strabismus in which one or both eyes turns inward. The condition can be constantly present, or occur intermittently, and can give the affected individual a "cross-eyed" appearance. It is the opposite of exotropia and usually involves more severe axis deviation than esophoria. Esotropia is sometimes erroneously called "lazy eye", which describes the condition of amblyopia; a reduction in vision of one or both eyes that is not the result of any pathology of the eye and cannot be resolved by the use of corrective lenses. Amblyopia can, however, arise as a result of esotropia occurring in childhood: In order to relieve symptoms of diplopia or double vision, the child's brain will ignore or "suppress" the image from the esotropic eye, which when allowed to continue untreated will lead to the development of amblyopia. Treatment options for esotropia include glasses to correct refractive errors, the use of prisms, orthoptic exercises, or eye muscle surgery. The term is from Greek eso meaning "inward" and trope meaning "a turning".

<span class="mw-page-title-main">Eyepatch</span> Small patch that is worn in front of an eye

An eyepatch is a small patch that is worn in front of one eye. It may be a cloth patch attached around the head by an elastic band or by a string, an adhesive bandage, or a plastic device which is clipped to a pair of glasses. It is often worn by people to cover a lost, infected, or injured eye, but it also has a therapeutic use in children for the treatment of amblyopia. Eyepatches used to block light while sleeping are referred to as a sleep mask.

Orthoptics is a profession allied to the eye care profession. Orthoptists are the experts in diagnosing and treating defects in eye movements and problems with how the eyes work together, called binocular vision. These can be caused by issues with the muscles around the eyes or defects in the nerves enabling the brain to communicate with the eyes. Orthoptists are responsible for the diagnosis and non-surgical management of strabismus (cross-eyed), amblyopia and eye movement disorders. The word orthoptics comes from the Greek words ὀρθός orthos, "straight" and ὀπτικός optikοs, "relating to sight" and much of the practice of orthoptists concerns disorders of binocular vision and defects of eye movement. Orthoptists are trained professionals who specialize in orthoptic treatment, such as eye patches, eye exercises, prisms or glasses. They commonly work with paediatric patients and also adult patients with neurological conditions such as stroke, brain tumours or multiple sclerosis. With specific training, in some countries orthoptists may be involved in monitoring of some forms of eye disease, such as glaucoma, cataract screening and diabetic retinopathy.

<span class="mw-page-title-main">Strabismus</span> Eyes not aligning when looking at something

Strabismus is a vision disorder in which the eyes do not properly align with each other when looking at an object. The eye that is pointed at an object can alternate. The condition may be present occasionally or constantly. If present during a large part of childhood, it may result in amblyopia, or lazy eyes, and loss of depth perception. If onset is during adulthood, it is more likely to result in double vision.

Anisometropia is a condition in which a person's eyes have substantially differing refractive power. Generally, a difference in power of one diopter (1D) is the threshold for diagnosis of the condition. Patients may have up to 3D of anisometropia before the condition becomes clinically significant due to headache, eye strain, double vision or photophobia.

<span class="mw-page-title-main">Diplopia</span> Double vision

Diplopia is the simultaneous perception of two images of a single object that may be displaced horizontally or vertically in relation to each other. Also called double vision, it is a loss of visual focus under regular conditions, and is often voluntary. However, when occurring involuntarily, it results in impaired function of the extraocular muscles, where both eyes are still functional, but they cannot turn to target the desired object. Problems with these muscles may be due to mechanical problems, disorders of the neuromuscular junction, disorders of the cranial nerves that innervate the muscles, and occasionally disorders involving the supranuclear oculomotor pathways or ingestion of toxins.

Pediatric ophthalmology is a sub-speciality of ophthalmology concerned with eye diseases, visual development, and vision care in children.

Ocular dominance, sometimes called eye preference or eyedness, is the tendency to prefer visual input from one eye to the other. It is somewhat analogous to the laterality of right- or left-handedness; however, the side of the dominant eye and the dominant hand do not always match. This is because both hemispheres control both eyes, but each one takes charge of a different half of the field of vision, and therefore a different half of both retinas. There is thus no direct analogy between "handedness" and "eyedness" as lateral phenomena.

Stereopsis is the component of depth perception retrieved through binocular vision. Stereopsis is not the only contributor to depth perception, but it is a major one. Binocular vision happens because each eye receives a different image because they are in slightly different positions on one's head. These positional differences are referred to as "horizontal disparities" or, more generally, "binocular disparities". Disparities are processed in the visual cortex of the brain to yield depth perception. While binocular disparities are naturally present when viewing a real three-dimensional scene with two eyes, they can also be simulated by artificially presenting two different images separately to each eye using a method called stereoscopy. The perception of depth in such cases is also referred to as "stereoscopic depth".

Vision therapy (VT), or behavioral optometry, is an umbrella term for alternative medicine treatments using eye exercises, based around the pseudoscientific claim that vision problems are the true underlying cause of learning difficulties, particularly in children. Vision therapy has not been shown to be effective using scientific studies, except for helping with convergence insufficiency. Most claims—for example that the therapy can address neurological, educational, and spatial difficulties—lack supporting evidence. Neither the American Academy of Pediatrics nor the American Academy of Ophthalmology support the use of vision therapy.

<span class="mw-page-title-main">Exotropia</span> Visual disorder where eyes work independently

Exotropia is a form of strabismus where the eyes are deviated outward. It is the opposite of esotropia and usually involves more severe axis deviation than exophoria. People with exotropia often experience crossed diplopia. Intermittent exotropia is a fairly common condition. "Sensory exotropia" occurs in the presence of poor vision in one eye. Infantile exotropia is seen during the first year of life, and is less common than "essential exotropia" which usually becomes apparent several years later.

<span class="mw-page-title-main">Sixth nerve palsy</span> Medical condition

Sixth nerve palsy, or abducens nerve palsy, is a disorder associated with dysfunction of cranial nerve VI, which is responsible for causing contraction of the lateral rectus muscle to abduct the eye. The inability of an eye to turn outward, results in a convergent strabismus or esotropia of which the primary symptom is diplopia in which the two images appear side-by-side. Thus, the diplopia is horizontal and worse in the distance. Diplopia is also increased on looking to the affected side and is partly caused by overaction of the medial rectus on the unaffected side as it tries to provide the extra innervation to the affected lateral rectus. These two muscles are synergists or "yoke muscles" as both attempt to move the eye over to the left or right. The condition is commonly unilateral but can also occur bilaterally.

<span class="mw-page-title-main">Hypertropia</span> Condition of misalignment of the eyes

Hypertropia is a condition of misalignment of the eyes (strabismus), whereby the visual axis of one eye is higher than the fellow fixating eye. Hypotropia is the similar condition, focus being on the eye with the visual axis lower than the fellow fixating eye. Dissociated vertical deviation is a special type of hypertropia leading to slow upward drift of one or rarely both eyes, usually when the patient is inattentive.

Infantile esotropia is an ocular condition of early onset in which one or either eye turns inward. It is a specific sub-type of esotropia and has been a subject of much debate amongst ophthalmologists with regard to its naming, diagnostic features, and treatment.

Dichoptic is viewing a separate and independent field by each eye. In dichoptic presentation, stimulus A is presented to the left eye and a different stimulus B is presented to the right eye.

Cyclotropia is a form of strabismus in which, compared to the correct positioning of the eyes, there is a torsion of one eye about the eye's visual axis. Consequently, the visual fields of the two eyes appear tilted relative to each other. The corresponding latent condition – a condition in which torsion occurs only in the absence of appropriate visual stimuli – is called cyclophoria.

<span class="mw-page-title-main">Stereopsis recovery</span>

Stereopsis recovery, also recovery from stereoblindness, is the phenomenon of a stereoblind person gaining partial or full ability of stereo vision (stereopsis).

Alternating occlusion training, also referred to as electronic rapid alternate occlusion, is an approach to amblyopia and to intermittent central suppression in vision therapy, in which electronic devices such as programmable shutter glasses or goggles are used to block the field of view of one eye in rapid alternation.

<span class="mw-page-title-main">Ametropic amblyopia</span> Medical condition

Ametropic amblyopia is a medical condition in which the retina cannot focus on the image of a distant object, a condition often described as reduced visual acuity. This is due to large uncorrected refractive errors in the patient's optic system of the eyes. Astigmatism is one of the most frequent causes of ametropic amblyopia.

The management of strabismus may include the use of drugs or surgery to correct the strabismus. Agents used include paralytic agents such as botox used on extraocular muscles, topical autonomic nervous system agents to alter the refractive index in the eyes, and agents that act in the central nervous system to correct amblyopia.

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Further reading