What is the possibility of developing strabismus

Squint (strabismus)

What is strabismus?

Squinting (strabismus) describes an eye malposition in which both eyes do not look in the same direction when fixing an object. One eye can deviate from the target line of sight, but both eyes can also be involved.

This deviation can be manifest, i.e. constantly present and visible, or latent, i.e. not constantly, but only occasionally. The cause is usually a muscular imbalance in the six outer muscles of the eye. Often one of these muscles is clearly too short or too long.

If a pair of eyes fixes an object and depicts it on corresponding areas of the retina, the brain succeeds in merging the two visual impressions into a three-dimensional image. If the image is located in the Panum areas that are only a little outside of these retinal areas, the images usually also merge into a single image and then likewise make spatial vision possible.

With what is commonly called a slight "silver look", it usually works, with larger deviations that are visible at first glance, this is not the case, double images arise here which, if left untreated and uncorrected, can have very serious consequences, including amblyopia, the weak-sightedness of one eye.

Since humans cannot tolerate constant double vision, the brain does not tolerate them and does everything to prevent the double vision. Since simple vision has priority for the brain and comes before sharp vision, vision can initially be blurred. If the squint lasts for a long time, the brain then switches off one eye. The eye that is switched off no longer participates in seeing and is mostly weak-sighted as a result of the permanent non-use.

The technical term for this is "Amblyopia ex anopsia". This weak-sightedness does not disappear after the squint has been corrected and remains there. This person is therefore functionally one-eyed and without spatial vision.

Uncorrected squint has fatal consequences, especially for small children, because then spatial vision cannot develop in the first place. But even in adults with acquired strabismus, spatial vision is disturbed and, like in children, the path leads in the long term to weak eyesight.

Squint - shapes (directions of view)

Strabismus is a generic term for many manifestations and causes of an eye malposition, in which both eyes do not look in the same direction when fixing an object.

The layman will encounter a confusing variety of technical terms that we will break down for you here:

  • Inward squint: Strabismus convergent or esotropia is the most common form of strabismus, especially in children. In the case of latent strabismus, the inward deviation is also called esophoria.

  • Away squint: Strabismus divergent or exotropia in manifest strabismus. In latent strabismus, the outward deviation is called exophoria.

  • Squint: Strabismus sursoadductorius is called high strabismus and deorsoadductorius strabismus deorsoadductorius as a low level strabismus. The vertical squint is usually associated with another form of squint and occurs separately extremely rarely.
     
  • Curl squint: Rotatorial strabismus or cyclotropia is called incyclotropy or excyclotropy in manifest strabismus, depending on the direction of the deviation. The curling squint is called cyclophoria in latent squint.

Schielens - manifestations

So that you can first get an overview of the various forms of squint, here is a categorization of the different types of squint:

  1. Latent squint (heterophoria)
  2. Manifest squint (heterotropia, strabismus)
    1. Concomitant strabismus (heterotropia) concomitant strabismus
    2. Microstrabismus
    3. Normosensory late squint
    4. Accommodation squint
  3. Paralysis strabismus (paresis)
  4. Other types of squint
    1. Mechanically caused strabismus
    2. Pseudostrabism

Latent squint (heterophoria)

"Heterophoria" is a disturbance of the eye muscle balance, which the brain can mostly compensate for through fusion, a mechanism of two-eye vision. Most of those affected remain symptom-free, but headaches and other asthenopic complaints can occur, especially when they are tired, and double vision can also occur.

This heterophoria is often also referred to as a synonym for ametropia. Strictly speaking, however, the ametropia is a type of eye muscle imbalance that can only be determined with the measurement and correction method (MKH) according to Hans-Joachim Haase, and is then generally corrected with prism glasses.

This methodology and the subsequent correction are controversial as they have not been scientifically proven. Proponents, however, cite numerous examples of success.


Causes of latent squint

Latent squint affects around 70-80% of people and is viewed more as a normal variant than as an eye disease. It is usually only noticeable temporarily, namely when the eyes are unable to restore muscular equilibrium due to excessive fatigue or similar overloads, even through an increased amount of vergence movements.

Only then does the disturbed binocular vision lead to complaints such as headaches and double vision. Then the fusion of the two images into a three-dimensional image is no longer possible because the images no longer lie on the corresponding halves of the retina or the surrounding panum areas. These heterophorias are therefore rather widespread variants of a normal state called orthophoria. It is not a disease.


Symptoms of latent strabismus

The constant attempt to compensate for the ocular muscle equilibrium disturbed by heterophoria can only be achieved through more or less additional muscular effort. This can lead to overuse symptoms, which are called asthenopic complaints. This discomfort can range from headache or eye pain to slight dizziness, difficulty concentrating or sensitivity to glare to double vision. If double vision occurs, the heterophoria decompensates and produces phenomena similar to a manifest squint.

 

 

Latent squint exposure test

Because the latent strabismus (heterophoria) is noticeable in both childhood and adulthood through asthenopic symptoms such as double vision, headache or dizziness, a heterophoria or ametropia is usually only detected when these appear.

One clue as to whether heterophoria could be the cause of the discomfort is a simple self-test that reveals the fusion. To do this, let both eyes fixate on an object, then cover one eye with a light-colored sheet and let the open eye continue to fixate on the object. After a while you uncover the eye. If there is no spontaneous single image vision, but the image first migrates more or less towards the other image and then merges with it, there may be heterophoria.

 

A revealing test can reveal the first signs of latent strabismus

 

Manifest squint (heterotropia)

Manifest strabismus or heterotropia is a pathological, permanent deviation of one eye from a common line of sight that is clearly visible. The manifest squint has different causes, characteristics and forms, and the squinting eyes can deviate from the parallel position in numerous different directions.

The greatest frequency among the squint directions are inward squint (strabismus convergens) or outward squint (strabismus divergens).


Concomitant strabismus (heterotropia; concomitant strabismus)

With accompanying strabismus (strabismus concomitans), both eyes move in all directions, but they do not fixate on the same object. Accompanying strabismus means that with all eye movements the cross-eyed eye does not follow the non-cross-eyed and leading eye completely, but adopts a different viewing angle.

The resulting squint angle is usually almost the same for all conceivable eye movements, but it changes for most people with a squint when looking at objects at different distances. The pulling force of the opposing outer eye muscles, however, is mostly the same.

However, the muscular equilibrium is disturbed with the accompanying strabismus, except for paralysis strabismus, and it is not possible to align the two eyes optimally on an object, so the eyes are squinted.

The concomitant strabismus, which is almost always congenital, should definitely be treated as early as possible in infancy. If this does not happen, the deviating, i.e. accompanying eye will develop weak vision in the deviating eye. The child would then be functionally one-eyed throughout its life.

In addition to the most common unilateral (monolateral) squint with a guide eye and a guided, cross-eyed eye, there are other types of accompanying strabismus. The alternating (alternating) squint has no leading eye. Here the two eyes alternate, whereby the image provided by the cross-eyed eye is suppressed by the brain. In this case, this has the positive effect that both eyes are involved fairly equally often and neither of the two eyes becomes weak-sighted.

The intermittent squint is, as the name suggests, a temporary squint, in which mostly even spatial vision is possible. Most often, this temporary squint occurs as intermittent external squint (exotropia). The phases of normal parallelism and cross-eyed deviations can be very different. Intermittent squint is a complex process with sensory characteristics and adaptation processes in the deviation phase.


Microstrabismus

Microstrabism (microtropia) is a squint that is barely perceptible when looking at the end of the squint. This minor, one-sided squint is mostly directed inwards and has a squint angle of no more than five degrees. This anomaly in the retinal correspondence is often resistant to therapy because it is often only recognized late, when the deviating eye is already poorly sighted.

Symptoms of microstrabismus

Microstrabismus is seldom perceived by laypeople as a manifest squint. One symptom in particular points to microstrabism: functioning binocular vision with pronounced spatial vision despite the squint angle of around five degrees.


Normosensory late squint

The normosensory late squint is not congenital and usually occurs in the phase after the third year of a child's life until they start school. It manifests itself as a sudden manifest internal squint through a lost ability to fuse, which leads to double vision. The affected child often turns a blind eye or tightens it. In contrast to congenital squint forms, when normosensory late squint occurs, the development of binocular vision is usually already complete.

Symptoms of normosensory late squint

The symptoms of normosensory late squint are similar to those of decompensated heterophoria or manifest squint in early childhood. This type of squint occurs suddenly between the ages of three and seven years. It manifests itself as a lost ability to fuse, which leads to double vision. The little patients often turn a blind eye or screw a pinch. If you are already able to describe your symptoms, you will also give double images as symptoms.


Accommodation squint

The eye needs the complex functional cycle of convergence (looking downwards inwards) and accommodation (adjusting the refractive power of the eye) to fix and image nearby objects. The most common cause of accommodative squint is undiscovered or not fully corrected farsightedness. If an uncorrected or undercorrected farsighted person looks into the distance, he can increase the refractive power of the lens through accommodation so that he can see clearly. Because accommodation is coupled to convergence, there is an internal squint. There are also other purely and partially accommodative forms of strabismus.


Causes of manifest internal squint in young children

Internal squint in young children is one of the forms of manifest squint. Actually, one does not really know the cause of the internal squint in early childhood. What is known are the risk factors for this form of concomitant strabismus. These risk factors include an increased occurrence of this form of squint in the parents' families. So there is a high probability of inheritance. This mostly congenital and not acquired type of squint affects around six percent of all small children in Central Europe.

Other causes of childhood, congenital and manifest strabismus can be eye diseases. A child may have already been born with a cloudy lens or acquired eye diseases such as inflammation of the retina or optic nerve.

Further risks for internal squint in early childhood are premature birth or farsightedness that is not or not fully corrected. There is also a certain risk in small children if the two eyes differ greatly in the strength of their ametropia. These types of early childhood squint are acquired and not innate.

 

 

Causes of manifest squint that only occurs in adulthood

If it first appeared in adulthood and was not present from childhood, there can be many causes for manifest squint. Many eye diseases that affect the retina, optic nerves and eye muscles are just as much a part of it as structural anomalies such as Brown's syndrome as a tendon thickening of an eye muscle. Endocrine orbitopathy, with its inflammatory processes in the eye muscles, can also change the structure of the eye muscles.

An injury such as an orbital floor fracture (fracture of the floor of the bony eye socket) in which there are entrapment and injuries to many parts of the eye can trigger a manifest squint. In all of these cases, the resulting strabismus is called secondary strabismus.


Symptoms in a child's manifest strabismus

For the layperson, a slight misalignment of the eyes or one eye, as is the case with microstrabismus, can hardly be seen. It is therefore important, especially in children, to pay attention to these symptoms and, if suspected, to present the child to the ophthalmologist immediately:

  • Photosensitivity
  • Watery eyes
  • Chronic eyelid inflammation
  • Covering one eye
  • Squinting an eye
  • A more or less crooked head position
  • Motor insecurity and clumsiness in motion sequences
  • Disgruntlement with apparently baseless whining and irritability

Of course, children also experience double vision or blurred vision, but when this symptom occurs they are often not able to express it.


Manifest squint test

Except for the microstrabismus, there is no need for a test or self-test for manifest strabismus, as is the case with latent strabismus, because manifest strabismus cannot be overlooked even in small children. You can also use this table to compare in which direction your child is squinting:

The most common squinting direction is internal squint, as shown in the figure above. If you have the slightest suspicion that your child shows one of these patterns of eye positions, take him to the ophthalmologist as soon as possible so that no permanent damage such as the weak-sightedness of the deviating eye forms.

Paralysis strabismus (paresis)

Paralysis strabismus occurs both as partial paralysis (paresis) and as full paralysis (paralysis) and can occur on one or both sides due to neurological diseases, as a consequence of a stroke, as a result of an accident or as a result of an ocular muscle disease and particularly often affects the II., IV. And VI. Cranial nerve., But also the peripheral eye muscle nerves and the points where the nerves meet the eye muscles.

The squint angle depends on the direction of view, because the squinting eye is restricted in movement, or movement is completely impossible for one or more eye muscles. This restriction of movement means that the cross-eyed eye cannot follow the healthy eye in all directions.


Causes of paralysis strabismus

However, it is not only diseases that directly affect the eye, processes of change or injuries that can lead to this secondary strabismus, as in paralysis strabismus, which usually occurs very suddenly.

There are many different causes for paralysis squint. This is often a nerve paralysis that causes one or more eye muscles to fail or, in the case of partial paralysis, are at least so impaired that the eye in question begins to squint. Such paralysis can trigger inflammation or eye muscle disorders.

But the paralysis squint can also have a completely different cause. An eye or brain tumor, multiple sclerosis, an aneurysm of a blood vessel, or circulatory disorders affecting the eye muscle nerves can be responsible. These circulatory disorders are not so rare in diabetics and hypertensive patients (people with high blood pressure).

Some cases of secondary strabismus also start as neurological impairments, such as those that can arise in strokes.However, in up to 30% of patients with strabismus, the cause cannot be found beyond doubt.


Symptoms of paralysis squint

Strabismus rarely remains hidden from the observing layperson, because the eye with paresis (partial paralysis) or paralysis (total paralysis) does not participate in the eye movements, or only to a very limited extent.

The size of the squint angle is therefore sometimes larger and sometimes smaller, depending on the viewing direction. Especially at the beginning of the sudden paralysis strabismus, the patient tries to fixate with the paretic or paralyzed eye. This leads to a secondary angle when fixing that is larger than the angle of the healthy eye.

This sometimes leads to disorientation in the patient. Compulsive head postures result from the attempt to compensate for the lack of mobility of the eye by moving the head and to eliminate double images within the usual field of vision as far as possible and, in the best case, to enable single binocular vision.

Other types of squint

There are other types of squint that are less common. The mechanically conditioned strabisms lead to structural changes and movement disorders. This form of strabismus includes Brown's syndrome as a thickening of the tendons of an eye muscle, endocrine orbitopathy, in which inflammatory processes structurally change the eye muscles. Also an orbital floor fracture (fracture of the floor of the bony eye socket) which can lead to entrapment. The pseudostrabismus is a "faked" squint that does not represent an actual strabismus. The most common example is the epicanthus medialis, called slit eyes in the Volskmund. Facial asymmetries can also be the cause of pseudostrabism.

Strabismus - finding

If a child is presented to the ophthalmologist with the suspicion of latent or manifest strabismus, a very comprehensive examination program begins, because even the obvious manifest strabismus can have very different causes and, as a result, serious consequences. A similarly complex test program is also completed in adults with suspected heterotropia (manifest strabismus) or decompensated heterophoria.

Before the examinations begin, a detailed discussion with the patient or the parents is carried out to determine which symptoms and complaints were present, whether there were familial accumulations of strabismus, illnesses or accidents.

In any case, the ophthalmologist will check for secondary strabismus to rule out an underlying serious eye or general disease that may not yet have been recognized. The whole eye is subjected to an intensive examination.

 

Refraction determination to determine ametropia

 

This comprehensive program initially includes the completely normal refraction determination in order to rule out ametropia or to optimally correct any existing ametropia. Hyperopia (farsightedness) that is not or not fully corrected can lead to strabismus and, in the end, weak vision in one eye.

If the ametropia has been corrected, a Schober test or a similar test is usually carried out first, with which the binocular vision is tested. This test already shows whether there is a latent squint in these eyes and how strong it is.

 

Schober test for binocular vision

 

The cover / reveal test, which enables a reliable statement to be made as to whether the subject is squinting, is particularly helpful for small children for whom such test arrangements cannot yet be carried out. Your ophthalmologist will then also recognize a possible forced posture of the head and test the mobility of the eyes.

First, the leading, fixing eye is covered. When covering, an adjustment movement of the cross-eyed eye then takes place. Conversely, if the cross-eyed eye is covered, there is no adjustment movement.

Now it is time to determine the squint angle. The squint angle is then often measured in adults using the Maddox cross or a similar test arrangement.

Such test arrangements cannot be used for small children. Here, the squint angle is determined with the prism cover / uncover test. The child is put on test glasses in which stronger prism lenses are placed in front of the cross-eyed eye until no more deviating movement can be detected when uncovering / covering.

Further test procedures for the quality of spatial vision can now follow. Only after this careful examination will the ophthalmologist discuss the next steps and recommended therapeutic approaches with the patient or the parents.

Strabismus treatment

When the examinations have been completed, a therapy plan can be drawn up that primarily includes these options:

  1. Eyeglass correction
  2. Occlusion treatment
  3. Penalization
  4. Pleoptics
  5. Orthoptics
  6. Squint operation


1. Eyeglass correction

Correction of ametropia as a prerequisite for further therapy

It all starts with the ophthalmologist diagnosing the type of squint and ruling out possible organic causes due to eye or general diseases that may not have been discovered before.

Even with paralysis strabismus, the underlying cause must be determined. Under certain circumstances, further specialist examinations or special examinations such as magnetic resonance tomography must be carried out. A complete correction of any ametropia must also have been carried out, for example, through glasses. Only then can the actual squint therapy begin, which in turn depends on the type of squint.

A squint operation is often performed, which also solves the cosmetic problem from which children particularly suffer due to frequent teasing.


Correction of glasses with prism glasses

Prism glasses or a prism foil can be prescribed to correct a manifest squint. Often, the compatibility is first tested with prism foils, which are attached to the back of the lenses that fully correct the ametropia. With prismatic spectacle lenses, the imaging light beam is deflected in such a way that the pair of eyes again delivers a three-dimensional, sharp single image with both eyes.

 

Strabismus can be corrected with prism glasses

 

Even with paralyzed squint, double images can be temporarily or permanently eliminated with small squint angles with the help of prism glasses.

Prism glasses are also used in the care of heterophoria. These disorders of the muscular equilibrium of the eye muscles occur in 70-80% of all ametropia people and are therefore more of a normal variant than a disease. According to the opinion also expressed by many ophthalmologists, prismatic treatment comes into question when the heterophoria has decompensated, i.e. double vision occurs. Then the lowest possible prism strength at which the complaints no longer occur should be used.

Controversial and not scientifically recognized, however, is the measurement and correction method according to Hans-Joachim Haase for the determination and full correction of the ametropia with prism lenses.


2. Occlusion

The most common type of strabismus is the accompanying strabismus in early childhood. With this type of manifest squint, the therapy primarily focuses on measures to strengthen the eyesight of the cross-eyed eye and to increase the quality of the two-eyed vision.

After fitting glasses that fully correct ametropia, the main option here is occlusion therapy (exclusion therapy), which attempts to strengthen or at least maintain the vision of the cross-eyed eye by covering the leading, healthy eye. The cross-eyed eye is forced to fixate and thus participate in seeing. For this purpose, the non-squinting eye is covered with an adhesive plaster in a rhythm determined by the doctor.

In the case of small children, reliable cooperation from the parents is a prerequisite, because this is the only way the method can show success. The duration of this treatment depends on the degree of squint, the ability of the cross-eyed eye that is still intact and the age of the child at the start of treatment. It can last well into puberty.

In addition to the occlusion carried out with adhesive plasters, spectacle occlusion is also possible with a small spectacle wearer, in which a film is placed on the back surface of the eye in question. Your optician will be happy to provide you with an occlusal foil that has been appropriately cut by him and previously prescribed by an ophthalmologist and will explain to you as parents how easy it is to use.

This therapy step can be dispensed with in the case of alternating squint if the visual acuity of both eyes is almost equally good. The occlusion cannot eliminate the strabismus, it should lead to an approximately equal visual acuity and lead from one-sided strabismus to alternating strabismus and keep the visual acuity of both eyes stable.

Similar forms of therapy, which also have a similar effect as occlusion, are penalization and pleoptics.


3. Penalization

There are two subtypes of penalization, near penalization and distant penalization. With near penalization, the better eye is restricted by accommodation-paralyzing eye drops (such as atropine) in near vision, while the cross-eyed eye receives an overcorrection of + 1 to + 3 diopters. As a result, the cross-eyed eye only fixes in the vicinity, the healthy eye only fixes in the distance. In this way, a far-near alternation of the cross-eyed and the healthy eye can be achieved.

In the case of distant penalization, the healthy eye receives atropine and glasses with an overcorrection of + 3 D, while the cross-eyed eye receives a full correction. The lens reduces the visual acuity of the guide eye in the distance, the depth of field is also reduced. This procedure is more effective than near penalization.

Complete penalization leads to atropine in the healthy eye and omits the correction in the case of severe farsightedness. In the case of only weak hyperopia and all other cases, a strong minus lens is used. This means that objects are no longer shown in focus at any distance. This is the most effective form of penalty.


4. Pleoptics

Pleoptics describes a whole series of procedures that are used in the treatment of amblyoply caused by strabismus. New, inexpensive methods such as the further development of the occlusion method, which does not require the use of apparatus, have reduced the importance of pleotide therapy approaches.


5. Orthoptics

Orthoptics (straight vision) is a sub-area of ​​strabology (strabology) within ophthalmology (ophthalmology). Orthoptics deals with all aspects of binocular vision, including pathology and physiology with their motor and sensory components. This happens in prevention, diagnosis and therapy.

Orthoptics has produced its own job description. In visual schools, orthoptists are concerned with therapeutic measures such as exercise treatments that serve to improve binocular vision. Orthoptists have completed the Orthoptics course at universities of applied sciences with a Bachelor of Science in Health Studies and are highly specialized professionals.


6. Squint operation

While the therapeutic approaches listed above serve to minimize the consequences of a manifest secondary squint and to prevent amblyopia, the squint operation serves to reduce the size and ideally to eliminate the squint angle and to improve the appearance. Especially in early childhood internal strabismus, the successful operation leaves the eyes at least approximately parallel again and takes place between the ages of two and six.

The operation thus largely restores the equilibrium of the eye muscles. Normal three-dimensional spatial vision, however, is only rarely achieved, since the development of spatial vision was often not successful when strabismus was discovered later.

Squinting in Children and Babies?

With the exception of microstrabismus, latent strabismus can hardly be overlooked by attentive parents, even in toddlers and infants. However, if you have a family history of strabismus, ametropia or eye diseases, you should not wait for the check-up appointments, but rather present the child to the ophthalmologist as early as possible if there is even the slightest suspicion.

Your child's binocular vision in particular develops in the first three years of life. If a strabismus is only detected afterwards, it is often too late and the eye, which has been switched off from seeing to avoid double vision, is already weak.

This blindness caused by not using the eyes is irreversible and will stay with your child for a lifetime. In addition, not only a congenital muscular imbalance of the eye muscles can be the cause of the squint. Serious diseases could also be the basis, ranging from multiple sclerosis to tumors.

A manifest squint can usually hardly be overlooked even by laypeople even in toddlerhood, but this happens at the latest with the free early childhood examinations (child screening examinations for early detection).

The sooner a toddler is subjected to a thorough ophthalmological examination if strabismus is suspected, the lower the consequential damage, such as in the worst case amblyopia (weak vision) of an eye. Squint is not just a blemish. Therefore, if a child is suspected of having a strabismus, they should be examined by an ophthalmologist from 6 to 12 months at the latest.

A whole range of therapy options are available to your child, especially with an ophthalmologist specializing in strabology.

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