Generality
Amblyopia is a condition characterized by weakened vision in one eye. The disorder, also known as "lazy eye", is the leading cause of visual impairment among children.
Causes
Amblyopia is the medical term used to indicate reduced vision in one of the eyes, since the eye and the brain unevenly or visually process visual input. This condition occurs when the nerve pathways between the brain and the eye are not adequately stimulated.
Amblyopia can be caused by any condition that disrupts the normal visual development or use of the eyes, including strabismus (when the eyes are misaligned and do not look in the same direction) or the difference in the quality of vision between the eyes ( for example, if one eye is more myopic, presbyopic or astigmatic than the other). Sometimes amblyopia is caused by other eye diseases, such as cataracts.
How vision develops
The brain and the eye work together to analyze and process visual information. Light enters the eye, where the retina translates the image into nerve signals that are sent, thanks to optical pathways, to the brain. The latter combines visual stimuli from each eye into a three-dimensional image.
Children must learn to see, or more specifically, their brain must learn how to interpret the nerve signals that are sent from the eyes via the optical pathways. It takes about 3-5 years before children can see clearly as adults and up to 7 years before the visual system develops completely. If a deficiency affects one of the eyes during growth, the quality of the signals becomes disrupted and this, in turn, influences the interpretation of the images. This means that the child can see less clearly from one eye and tends to entrust his vision to the other. Often, the amblyopic eye structures appear healthy and functional, but they are not used correctly, as the brain is favoring the other eye (called dominant). As a result, the brain increasingly relies on the dominant part and begins to ignore the signals received from the amblyopic eye.
Causes
Common conditions that negatively affect vision development and cause amblyopia are:
- Strabismus . Strabismus is a rather common condition; it is due to a muscular imbalance that prevents the coordinated alignment of the eyeballs: one eye looks straight ahead, while the other looks to the left, to the right, up or down.
The brain of children is neuroplastic, that is it can easily adapt and eliminate any problems, such as the vision of blurred or double images, suppressing the signals coming from one eye. An effect of this visual deviation is amblyopia.
- Refraction errors . Refraction errors are caused by structural alterations of the eye, which does not focus the image correctly. The dominant eye is typically the one that provides the brain with the clearest image. When the image from the other eye is blurred, an abnormal development of one half of the visual system is determined.
This form of lazy eye is the result of a significant difference between the vision in each eye (anisometropia), due to myopia, hypermetropia or an imperfection on the surface of the eye (astigmatism).
Amblyopia is often associated with a combination of strabismus and anisometropia. Typically, these vision problems are treated with the constant use of glasses or contact lenses.
- Less common conditions . Deprivation amblyopia (or non-vision) can occur in people with eye diseases, such as congenital cataract. Like other conditions that create opacity, the disease prevents normal visual input from reaching the eye and results in a perturbed vision. If this form of amblyopia is not treated during the early stages, it may recur or persist after the cause is removed.
Sometimes, a lazy eye is the first sign of an eye tumor. Other less common conditions that can cause vision impairment include:
- Ocular disorders, such as a corneal ulcer or scar;
- Congenital cataract (opacity of the crystalline lens present from birth);
- Glaucoma ;
- Drooping eyelid (ptosis);
- Choroidal hemangioma (benign vascular tumor).
Symptoms
To learn more: Symptoms Amblyopia
The final result of all forms of amblyopia is a deficit of visual acuity in the amblyopic eye; the extent of this defect may be slight or severe.
To understand if a child has a lazy eye it is sometimes necessary to interpret certain signs; in fact, in fact, younger children do not realize that something is wrong with their vision, or they are aware of it but are unable to explain their discomfort. Older children may complain about the inability to see well with one eye and highlight problems with reading, writing and drawing. Sometimes, the only obvious symptoms of a lazy eye are related to an underlying condition, such as strabismus, congenital cataract or eyelid ptosis.
Signs and symptoms of amblyopia may include:
- Difficulty in vision in one eye;
- Involuntary movement of an eye inward or outward: in some cases it can be seen that one eye looks in a different direction than the other (this could be due to a squint);
- Low contrast sensitivity;
- Low sensitivity to movement;
- Poor depth perception: children with a lazy eye usually have trouble judging the distance between themselves and objects with precision. This can make some activities more difficult, such as catching a ball.
Amblyopia is generally unilateral, but it is not excluded that it may arise in both eyes.
Exams and Diagnosis
A lazy eye should ideally be diagnosed and treated as early as possible. However, amblyopia is not always obvious. Many cases of lazy eye are diagnosed during routine eye exams, before the parents realize the presence of a disorder.
Doctors monitor vision during routine child check-ups, especially if there is a family history of strabismus, infantile cataract or other eye conditions. This means that if a child has a lazy eye, it is possible to diagnose and treat the condition before it is too late to correct it. Children between the ages of 3 and 5 should undergo a full eye exam before starting school and further checks at least every two years. Amblyopia is usually diagnosed around the age of four. Depending on the circumstances, the doctor may refer you to a specialist (ophthalmologist or optometrist).
Treatment
In children, the treatment of amblyopia is aimed at correcting the eye with reduced vision (amblyopic eye). Generally, early management of the disorder is sufficient to avoid problems later in life.
Most cases can be treated (as usual) in two phases. First of all, the underlying problem is corrected, for example with the constant use of glasses and / or contact lenses to correct a visual defect. The child is then encouraged to use the weaker eye again so that the vision can develop properly. This result can be obtained by covering the dominant eye with a bandage or by giving a few drops of atropine, to temporarily compromise the sight of the same. Treatment is effective, but vision recovery is a gradual process that takes several months.
Depending on the cause and extent of the disorder, treatment options may include:
Corrective lenses
In the event of myopia, hypermetropia or astigmatism, the ophthalmologist may prescribe corrective glasses. These must usually be worn constantly and the patient must undergo regular checkups. Glasses can also help treat a strabismus and, in some cases, they can resolve amblyopia without having to resort to further treatment. An alternative to glasses is contact lenses, although these may only be suitable for older children.
Surgery
For children with congenital cataracts, surgery may be necessary, followed by vision correction with glasses or contact lenses. The procedure can be performed under local or general anesthetic and can take a minimum of 20 minutes. Cataract surgery can resolve blurred and distorted vision. The child can be hospitalized overnight to monitor the recovery process. Subsequently, the application of an eye patch or eye drops may be necessary. Surgery can also be applied to correct strabismus. The operation allows to strengthen or weaken the eye muscles responsible for the misalignment of the eye. By itself, however, surgery does not completely solve amblyopia: vision does not improve, but the lazy eye will be aligned with the healthy one, to work better together. Children with cross-eyed amblyopia will still need careful monitoring and appropriate therapy. This treatment is usually considered before the surgical correction of strabismus is performed.
Encourage the use of the amblyopic eye
A number of different treatment options can be used to encourage the child to use the non-dominant eye:
- Occlusion with a patch (patching). This therapy involves placing an opaque plaster, with an adhesive edge, directly on the skin above the dominant eye, forcing the child to use the other. The recovery process can take some time, depending on how serious the problem is and how much the child cooperates with the use of the patch. Most children will have to wear the patch for a few hours a day (about 3-6 hours), for several weeks or months. Some ophthalmologists believe that the performance of particular activities (reading, coloring, watching a television program etc.) during the time in which the patient maintains the patch can be more stimulating for the brain and facilitate a faster recovery. An ophthalmologist should regularly check how the dominant eye occlusion is affecting the child's vision. The application of the adhesive plaster can be very effective in improving the sight of the lazy eye, especially if adopted before the patient reaches 7-8 years of age.
- Collirio (atropine). A drop of atropine a day or twice a week can temporarily blur the sight in the strongest eye. Atropine treatment indirectly stimulates vision in the weaker eye and helps the part of the brain that manages vision to develop more completely. Side effects that can occur after using eye drops include eye irritation, redness of the skin and headache. However, these manifestations are infrequent and rarely exceed the benefits of treatment. This therapy can be as effective as the occlusion of the dominant eye with a plaster. Often, the choice of treatment is a matter of patient preference. Therapy may not be effective when the dominant eye is nearsighted.
See also: Remedies for Ambliopia "
Prognosis
Children who are treated before the age of 5 usually recover almost completely. In some cases, patients may continue to have problems with depth perception. If it is not managed in a timely manner, amblyopia results in permanent visual impairment or muscle problems that may require several surgical procedures. If the condition is correctly diagnosed and treated at an early age (ideally around two years), the outlook for children with a lazy eye is good. During the first six to nine years of life, the visual system develops very quickly. In this growing period, complex connections are created between the eye and the brain. Amblyopia is more difficult to treat if the development is complete, but it is still possible to intervene to improve vision in the weaker eye.
