Amblyopia in children

Amblyopia is a functional decrease in visual acuity caused by disuse of the eye during visual development. Blindness may develop in the affected eye if amblyopia is not diagnosed and treated before age 8. Diagnosis is based on detecting a difference in visual acuity between the two eyes. Treatment for amblyopia in children depends on the cause.

There is no definitive definition of the essence of amblyopia. This term means a decrease in visual acuity that occurs when the normal development of the visual system is disrupted during the so-called "sensitive" period. If this pathology is detected in a timely manner, while the "sensitive" period has not yet ended, the defect is reversible. However, establishing a diagnosis at a later date reduces the effectiveness of treatment. It is generally accepted that amblyopia associated with monocular congenital cataract does not respond to treatment started after the first few months of life.

Amblyopia is usually considered a unilateral decrease in vision, but under certain circumstances the disorder may be bilateral. There are at least five distinct forms of amblyopia, which differ in the etiology of visual deprivation and the bilateral or unilateral nature of the process.

1. One-sided:
   • form of deprivation;
   • strabismus;
   • anisometropia.
2. Double-sided:
   • ametropic (including meridional);
   • form of deprivation.

It is believed that each of these forms has an individual duration of the "sensitive" period. Thus, the possibilities of treatment and its prospects directly depend on the etiology of the disease. For example, to achieve an effect in the treatment of anisometropic amblyopia and amblyopia that arose against the background of strabismus, several years of hard work are necessary, while amblyopia that arose against the background of occlusion is curable within a few months.

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Causes of amblyopia in children

Amblyopia occurs in approximately 2-3% of children and almost always develops before the age of two.

The brain must simultaneously receive a clear image from each eye. Amblyopia develops if there is persistent distortion of the visual image from one eye, while the visual image from the other eye is clear. The visual area of the cerebral cortex suppresses the visual image from the affected eye.

There are 3 known causes of amblyopia. Strabismus can cause amblyopia because the misalignment of the eyeballs causes different impulses to be sent from the retina to the visual cortex of the brain. Similarly, anisometropia (unequal refraction of the two eyes, most often with astigmatism, myopia, hyperopia) leads to different images on the retina, with the visual image from the eye with the greater refractive error being less focused. Impaired transparency of the visual axis anywhere between the surface of the eye and the retina (for example, with cataracts) impairs or completely interrupts the formation of an image on the retina of the affected eye.

Symptoms of amblyopia in children

Children rarely complain of decreased vision in one eye. Very young children either do not notice or cannot understand that their eyes do not see equally. Some older children may report impaired vision on one side or show poor depth perception. If strabismus is the cause, the deviation of the eyeball may be noticeable to others. A cataract, which obstructs the passage of light through the eye, may go unnoticed.

Diagnosis of amblyopia in children

Screening for amblyopia (and strabismus) is indicated for all children before school entry, optimally at age 3 years. Photoscreening is one method of screening very young children and children with developmental delays who are unable to pass subjective tests. Photoscreening involves using a camera to record images of pupillary reflexes during fixation on a visual target and red reflexes in response to light; the images are then compared for symmetry. Screening of older children consists of visual acuity testing using figure charts (e.g., rotating E charts, Allen charts, or HOTV charts) or Snellen charts.

Further testing is needed to identify the specific cause. Strabismus can be confirmed by cover-the-eye or cover-open tests. Anisometropia can be confirmed by performing a refraction test to assess the refractive power of each eye. Obstruction of the visual axis can be confirmed by ophthalmoscopy or slit-lamp examination.

It is advisable to diagnose amblyopia based on the results of visual acuity testing. In cases where visual acuity testing is impossible (in young children), the diagnosis is established based on the presence of causative factors. For example, monocular congenital cataract is necessarily accompanied by amblyopia. Therefore, screening for amblyopia is aimed at finding potential amblyogenic factors.

• In early childhood: a bright red reflex from the fundus in both eyes excludes the presence of deprivation amblyopia, which accompanies defects such as cataracts and corneal opacity.
• At the age of 1 to 2 years: assessment of the symmetry of the brightness of reflexes from the fundus, a test with alternate closure of the right and left eyes, a refraction test to exclude strabismus and refractive disorders.
• At the age of 3 to 6 years: determination of visual acuity, screening for anisometropic amblyopia, as well as amblyopia due to strabismus.

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Treatment of amblyopia in children

The main obstacle to achieving high visual acuity in children with congenital monocular and binocular cataracts is deprivation amblyopia. To achieve a good functional effect, surgical intervention should be performed in the first months of the child's life, and the optical center should be kept clean throughout the postoperative period. Periodic examinations are mandatory to detect refractive errors and select the appropriate contact lens.

However, a significant number of patients with monocular congenital cataracts treated with this method fail to achieve high visual acuity. Results are significantly better in cases of binocular cataracts, but many patients never achieve normal visual acuity.

Successful treatment of amblyopia requires the elimination of the visual organ pathology. In most cases, it is necessary to occlude the better (fixing) eye. Accordingly, the following goals are pursued when treating any form of amblyopia:

1. deprivation form of amblyopia - release of the optical axis by surgical methods;
2. amblyopia against the background of strabismus - restoration of the correct position of the eye;
3. anisometropic amblyopia - correction of refractive errors.

The occlusion regime is usually established after checking the visual acuity of both the fixating and amblyopic eyes. Excessive occlusion of the fixating eye can provoke the development of obscuration amblyopia. An alternative to occlusion is penalization of the fixing eye: in this case, cycloplegia of the fixing eye is used. To increase the effectiveness of pleoptic treatment, a hypermetropic refraction is created on the fixing eye. In some cases, this method is preferable, especially in the treatment of amblyopia that has developed against the background of strabismus and nystagmus. Occlusion as an attempt to improve functions is recommended even if amblyopia is combined with anatomical disorders of the affected eye.

Application of occlusion

The more significant the vision loss in amblyopia, the more difficult it is to treat with occlusion. Failure of occlusion therapy is the main reason for the low effectiveness of amblyopia treatment, occurring with a frequency of 30-40%. And although there is no reliable technique for occlusion treatment, when treating children for whom occlusion has not yielded results, the following rules must be followed.

1. Make sure that the parents fully understand the purpose and importance of the occlusion prescription. Without their sincere participation, the treatment is doomed to failure.
2. If the child is old enough, explain to him the necessity of the prescribed treatment.
3. Wipe the skin before applying the occluder. Colloidal preparations can be used to protect the skin.
4. It is better to apply the occluder while the child is sleeping.
5. It is better to strengthen the outer surface of the occluder with an additional layer of adhesive tape.
6. Use soft cotton gloves with wrist straps to prevent your child from removing the occluder.
7. Use soft elbow braces for your child. They can be made of cardboard or other non-traumatic materials.
8. Praise and reward your child in other ways whenever positive results from the occlusion are seen.
9. Remember to emphasize the need for occlusion at each subsequent examination of the child.

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Monocular form of deprivation

Most researchers recommend performing surgical intervention in the first 2-3 months of life to achieve high visual acuity. In the postoperative period, optical correction and occlusions should be prescribed without delay. Partial occlusions (50-70% of the entire waking time) are prescribed to avoid the risk of developing obstructive amblyopia of the fixating eye and, more importantly, inducing nystagmus in the fixating eye.

Binocular form of deprivation

If surgical intervention and rehabilitation measures are carried out in a patient with bilateral congenital cataracts in the absence of nystagmus, the risk of developing bilateral deprivation amblyopia is practically absent. However, when nystagmus appears, visual acuity is significantly reduced, even with intensive treatment. In many cases of binocular deprivation, there is also a monocular form and, to equalize visual acuity, it is necessary to perform occlusion of the leading fixing eye. Complications in cataract surgery in children are very important and are often incomparable with complications that occur in adult patients. These complications include the following.

• Amblyopia. As already mentioned, amblyopia is the main obstacle to achieving high visual acuity in monocular and binocular congenital cataracts. The cause is the occlusion of the optical axis caused by the cataract. In addition, additional factors that provoke the development of amblyopia may be anisometropia and strabismus.
• Capsular Opacification. Posterior capsule opacification occurs in almost 100% of cases in young children and occurs within the first few weeks or months after surgery. This is why the lensvitrectomy technique was introduced to avoid the need for a postoperative posterior capsulectomy.

When using the aspiration technique in the postoperative period, there is often a need for YAG laser posterior capsulectomy.

• Corneal edema. Mild corneal edema may occur immediately after cataract surgery in children, especially when an intrastromal infusion cannula is used. In most cases, the edema does not persist for long and resolves spontaneously.
• Cystoid macular edema. Reports of its occurrence in children are rare.
• Endophthalmitis. Although rare, endophthalmitis occurs in pediatric cataract surgery. Surgery in the setting of nasolacrimal duct obstruction, upper respiratory tract infection, or periorbital skin pathology predisposes to the development of the complication. The functional outcome in these patients is usually poor. Glaucoma. The main complication in pediatric patients with aphakia. Its prevalence in congenital cataracts can reach 20-30%. The risk of developing the complication increases with combined microphthalmos, PGPS, and nuclear cataract. It may not manifest itself for several years after surgery. Regular measurements of intraocular pressure, examinations of the optic disc, and studies of refractive errors are recommended for early detection of glaucoma. A rapid decrease in hyperopic refraction in an aphakic eye suggests the possibility of glaucoma. The results of treatment of aphakic glaucoma in children remain unsatisfactory.
• Irregular pupil shape. Irregular pupil shape is a common consequence of cataract surgery in children, but it is of little importance for the functional outcome of the surgery. In some cases, when performing surgery for PGPS, damage to the iris may occur at the time of removal of the rigid membranous tissue and the associated traction of the ciliary processes.
• Nystagmus. Bilateral nystagmus is observed in a significant number of children with bilateral congenital cataracts. It suggests the presence of binocular deprivation amblyopia. Nystagmus also occurs in patients with monocular congenital cataracts. It can be either unilateral or bilateral, but in both cases the presence of nystagmus worsens the prognosis.
• Retinal detachment. The incidence of retinal detachment in children with aphakia has decreased since the introduction of the lensvitrectomy technique two decades ago. However, it is important to recall the results of previous studies with other types of surgical techniques for removing the lens, which emphasize that retinal detachment may not manifest itself for three or even four decades. Thus, a conclusion about the low risk of retinal detachment when performing lensvitrectomy in patients with congenital cataracts can only be made after long-term observation.
• Strabismus (usually convergent) is often present in children with monocular congenital cataract. It may occur after lens removal. Although strabismus is rare before surgery for bilateral congenital cataract, it may appear in the postoperative period. Strabismus is an additional amblyogenic factor in the problem of visual rehabilitation of these patients.

Functional results

Over the last two decades, the functional results of congenital and progressive cataracts have improved significantly. This is due to a combination of factors - an emphasis on early detection of cataracts, improvements in surgical techniques, improved quality and greater availability of contact lenses, and, in some cases, implantation of intraocular lenses. In congenital cataracts, the most important factor determining the visual outcome of surgery is early detection, which emphasizes the need for special examination of all newborns with a direct ophthalmoscope or retinoscope to exclude opacities in the lens. Despite the fact that good visual outcomes have now been achieved in bilateral congenital cataracts, and blindness and serious visual impairment as a result of surgery are rare, bilateral congenital cataracts still remain a significant problem.

The results of treatment of patients with monocular congenital cataract are worse, but they also give hope. The most important postoperative complication leading to a decrease in the initially high visual acuity is glaucoma.

Amblyopia in children can become irreversible if it is not detected and treated before the child reaches age 8, the time when the visual system is fully mature. Most children with amblyopia experience some improvement in vision if it is detected and treated before age 5. Early treatment increases the likelihood of full vision recovery. Relapse is possible in certain cases before the visual system matures.