The A And V Syndromes

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The A And V Syndromes
Body Parts: Head
Medical Subjects: Eye
Overview

What Is The A And V Syndromes

The A-V syndromes is a sub-type horizontal strabismus accompanied by vertical incoherence strabismus, that is, when looking up and down, the horizontal inclination changes obviously, and it is named after the letters "A" and "V".

Cause

What's The Cause Of A And V Syndromes

Aetiological Agent

There are many reasons for the formation of A-V syndrome, including extraocular muscles, anatomical factors, innervation factors and genetic factors.

Pathogenesis

There are many reasons for the formation of A-V syndrome, which can be summarized as follows:

1. The cause of horizontal muscles. Urist believes that the formation of A-V syndrome is related to the difference in strength between the inner and outer rectus muscles when they look up and down. In physiological state, when eyes look upward, the separation effect increases slightly (< 15△), and when eyes look downward, the aggregation effect increases slightly (< 10△), but they do not exceed the normal limit. The above physiological differences are due to the different effects of the external rectus muscle and the internal rectus muscle. It is generally believed that the V phenomenon is caused by too much physiological difference, while the A phenomenon is caused by too little physiological difference. That is to say, V- exotropia is caused by excessive action of external rectus muscle, V- esotropia is caused by insufficient strength of internal rectus muscle, and A- esotropia is caused by insufficient strength of external rectus muscle. In a word, V sign is caused by excessive horizontal muscle strength, while A sign is caused by insufficient horizontal muscle strength.

2. Causes of oblique muscles. Jampolsky believes that the strength of superior and inferior oblique muscles is an important reason for the formation of A-V syndrome. Because the secondary action of the oblique muscle makes the eyeball turn outwards, the V phenomenon can be caused when the strength of the lower oblique muscle is too strong. However, when the strength of inferior oblique muscle is insufficient, A phenomenon will be caused. Excessive strength of superior oblique muscle leads to A phenomenon. V phenomenon is caused by insufficient strength of superior oblique muscle. In a word, the increase of horizontal slope when looking directly upward is caused by the inferior oblique muscle, while the increase of horizontal slope when looking downward is caused by the superior oblique muscle. Von Noorden thinks that the abnormal function of oblique muscle is the common cause of A-V syndrome, and A-V syndrome with abnormal function of oblique muscle often causes rotational strabismus. Rotational strabismus is caused by A-V syndrome with abnormal oblique muscle function, which can not be corrected after being corrected by the inclination of the horizontal muscle end. This rotational strabismus was confirmed by fundus photography.

3. Causes of upper and lower rectus muscles. Brown believes that the functional strength of the upper and lower rectus muscles is one of the reasons for the formation of A-V sign. Because these two muscles have the secondary function of turning the eyeball inward, when the strength of the upper rectus muscle is too strong, it can cause A phenomenon. When the strength of the superior rectus muscle is weak, it will cause V phenomenon. When the strength of lower rectus muscle is strong, it can cause V phenomenon. Weak strength of lower rectus muscle leads to A phenomenon. In a word, the difference of horizontal inclination when looking directly upward is caused by the superior rectus muscle, while the difference of horizontal inclination when looking directly downward is caused by the inferior rectus muscle.

4. The cause of horizontal-vertical rectus muscle. Those who hold this view think that the A-V sign is caused by the abnormality of both horizontal and vertical muscles, not by the abnormality of one muscle alone. Some patients may be mainly caused by excessive strength or weakness of horizontal muscles, resulting in secondary changes of vertical muscles. Other patients may be mainly because the vertical muscle function is too strong or too weak, resulting in secondary changes in horizontal muscles, or both horizontal and vertical muscle functions have changed to form A-V syndrome.

5. Anatomical reasons:

  • A-V syndrome is related to facial shape: for example, Mongolian face can cause A- introversion and V- exoversion. The Caucasian faces can cause A- extraversion and V- introversion.
  • Fascia abnormality: For example, Brown's superior oblique sheath syndrome is often complicated with V- exotropia, which is due to the lack of elasticity of the superior oblique sheath, resulting in forced abduction during upward rotation. In Johnson adhesion syndrome, it can also produce the mechanical distribution phenomenon when rotating vertically.
  • Abnormal muscle attachment point: Some people think that the attachment position of the inner rectus tendon of some patients with V phenomenon is higher than that of normal people, while the attachment position of the outer rectus tendon is lower than that of normal people. In addition, the forward or backward movement of the attachment point can also cause A-V sign.

6. Causes of innervation. Clinically, A-V sign is seldom caused by anatomical factors, but it is more often caused by paralysis factors. From the definition of A-V sign, it can be seen that it is a subtype horizontal strabismus accompanied by vertical non-concomitant strabismus, that is to say, no matter whether horizontal inclination or vertical inclination is dominant, it is combined with the imbalance phenomenon of too strong or too weak muscles. There is no definite conclusion as to which of the vertical rectus muscle and oblique muscle is the main one. Both the horizontal muscle and the vertical muscle have functions, but it is impossible to explain clearly which one is the most important. The vertical muscle has functions of nerve impulse and machinery, while the horizontal muscle may be more prominent when the muscle is too strong or too weak.

In addition, there is physiological V phenomenon, that is, in the case of no strabismus in the original eye position, when looking up, it can produce exotropia (up to 17△), and when looking down, it can produce A phenomenon (up to 5△), which may be related to the innervation factors.

7. Causes of abnormal convergence and fusion function. When you look down and can't keep fusion, you can produce a phenomenon; When looking upward can't keep fusion, V phenomenon can occur, which is common in intermittent exotropia.

8. Genetic factors. There are few reports on genetic factors of A-V syndrome in the literature. Eleven cases of V- exotropia in 5 generations of a family were reported in China, which were autosomal dominant inheritance. There was no abnormal attachment of extraocular muscles during operation in only one proband.

In a word, among the above factors, the pathogenesis of all cases cannot be explained by a simple etiology, but it is mainly caused by extraocular muscles.

Symptom

What Are The Symptoms Of A-V Syndrome

Clinical Types and Manifestations

1. A-esotropia: Also known as esotropia A sign, esotropia Aphenomenon, A- esotropia, convergent strabismus A syndrome, that is, when looking straight up, the number of internal inclinations increases, while when looking straight down, the number of internal inclinations decreases or even disappears. When looking far and near, the inclination is almost equal. When looking inward and downward, the function of superior oblique muscle is over-strong, and when the eye position is adducted, the eyeball invaginates. Patients may have mandibular uplift.

2. V-esotropia: Also known as esotropia V sign, esotropia Vphenomenon, V- esotropia, convergent strabismus V syndrome, that is, when looking straight down, the number of internal inclinations increases, while when looking straight up, the number of internal inclinations decreases or even disappears. The internal inclination is greater near than far, and the function of inferior oblique muscle is often too strong. Patients may have mandibular adduction, with small fixed visual field and frequent horror.

3. A-exotropia: Also known as exotropia A sign, exotropia Aphenomenon, A-exotropia and divergent strabismus A syndrome, that is, the number of exotropia decreases or even disappears when looking directly upward, but increases when looking directly downward. There is no change in the number of near-external inclinations from a distance, and often the superior oblique muscle is over-functional, and the eyeball invaginates when the eye position is adducted. Patients may have mandibular adduction, small fixation field of eyes, and often have horror.

4. V-exotropia: Also known as exotropia V sign, exotropia Vphenomenon, V-exotropia and divergent strabismus V syndrome, that is, the number of external inclinations increases when looking directly upward, but decreases or even disappears when looking directly downward, and the external inclinations are much larger than those near.

5. X-phenomenon: That is, in the original eye position, it is positive or slightly oblique, and when looking directly above or below, the external inclination increases, showing an "X" shape.

6. X and A phenomenon: That is, in the original eye position, it is slightly oblique, and the number of external inclinations increases when looking directly upward than when looking directly downward.

7. X and V phenomenon: That is to say, in the original eye position, it is slightly oblique, and the number of external inclinations increases much more when looking directly upward than when looking directly downward.

8. ◇-phenomenon: That is, in the original eye position, the number of internal inclinations is small or no, and the number of internal inclinations increases when looking directly up and down.

9. Y-phenomenon: That is to say, the number of external inclinations is small or no external inclinations in the original eye position and when looking directly downward, while the number of external inclinations increases obviously when looking directly upward. It is a variation of V- exotropia.

10.  -phenomenon: That is to say, the number of external inclinations is small or no when looking at the original eye position and directly above, but increases when looking at directly below. It is also the variation of V- exotropia or the reverse type of Y- phenomenon.

Diagnostic Criteria

  • V sign of external inclination: the inclination of upward fixation is larger than that of downward fixation (≥15△, 8°~9°).
  • V sign of internal inclination: the inclination of upward fixation is smaller than that of downward fixation (≥15△, 8°~9°).
  • Oblique A sign: The inclination of upward fixation is smaller than that of downward fixation (≥10△, 5°~6°).
  • A sign of internal inclination: the inclination of upward fixation is larger than that of downward fixation (≥10△, 5°~6°).
Detect

How To Check For A-V Syndrome

No special laboratory examination is required.

1. General condition examination: check the naked eye far and near vision, external eye condition, refractive state, refractive stroma, fixation property and fundus condition, etc.

2. Eye muscle examination: In addition to routine eye muscle examinations such as corneal reflection method, covering method and various diagnostic eye positions, the following examinations should also be made:

  • The strabismus of the original eye position, right above and right below was examined by prism and covering method.
  • Examination of retinal correspondence, fusion function, stereopsis function and measurement of AC/A ratio.
  • Binocular fixed visual field examination, to understand the gaze range, and to provide the basis for selecting surgical methods.
  • The functional state of extraocular muscles was examined by 4)Hess screen.

3. Matters needing attention in the examination of A-V syndrome

① If there is ametropia, corrective glasses should be worn during examination.

② When looking close, the patient should look at the small visual target. In order to reduce the influence of adjustment factors on the eye position, the patient can wear 3D lenses for examination.

③ The horizontal inclination of 33cm and 6m fixation and the inclination of the upper and lower fixation positions were measured respectively. Some people claimed that repeated examination for 3 times could be used as the basis for diagnosis.

④ The slope checked by prism plus covering method shall prevail. Turn up or down at an angle of 25 to check the internal and external inclinations. Some people think that turning up at an angle of 15 is enough, because the fixation position is too upward or too downward, it is easy to cause illusion.

⑤ Pay attention to check the oblique muscle function and rotational strabismus:

  • The judgment of superior oblique muscle function is divided into four grades according to Parks classification method. Check the vertical inclination of eyes when they turn down 30 and turn left and right 30, and the difference between vertical inclination of eyes. A. Grade 1: < 10°. B. Grade 2: 10°~ 19°. C. Grade 3: 20°~ 30°. D. Grade 4: > 30°.
  • According to Meng Xiangcheng's classification, the judgment of inferior oblique muscle over-function can be divided into three grades: Grade A.1 (1 degree): that is, those with upward inclination during internal rotation. B. Grade 2 (2 degrees): those who show upward inclination only when they turn inward extremely. C. Grade 3 (3 degrees): the upward inclination occurs when turning inward and upward.
  • The determination of rotational strabismus was performed by fundus camera. According to Kong Lingyuan's measurement method, the average value of normal disc-center concave angle was 7.381°, ranging from 1.429°to 13.333°. The fovea is located 0.343PD below the geometric center plane of optic disc.
Treatment

How To Treat A-V Syndrome

Treatment: The treatment of A-V syndrome mainly adopts surgical correction. For A- esotropia and V- esotropia, if combined with regulatory factors, glasses should be worn for correction. For patients with excessive oblique muscle function and regulatory factors, besides glasses, oblique muscle weakening should be performed as early as possible to eliminate the interference of rotational strabismus, which is beneficial to the establishment of binocular vision. Patients with amblyopia should be treated first, so that their eyes can be operated only when their eyesight is balanced or similar.

There are several surgical methods for correcting A-V syndrome.

1. Horizontal Muscle Strengthening or Weakening

Patients caused by pure horizontal muscles can only do the operation of the medial and lateral rectus muscles to solve the oblique position. The principle is the phenomenon of medial oblique A, and the lateral rectus muscles of both eyes should be strengthened. The rectus muscles in both eyes should be strengthened for the phenomenon of exotropia A. In the case of V-inclination, the rectus muscles in both eyes should be weakened. The lateral rectus muscles of both eyes should be weakened in the case of V-deviation. In a word, sign A underwent horizontal muscle strengthening operation, while sign V underwent horizontal muscle weakening operation.

With regard to the operation amount of strengthening or retreating horizontal rectus: Villaseea stipulates that the operation amount of each rectus is 5mm for inner rectus, 8mm for outer rectus, 9mm for outer rectus and 10mm for inner rectus. It is emphasized that all control ligaments should be cut back as far as possible, and the intermuscular membrane should be loosened, so that the whole muscle can be retracted into the orbit and completely relaxed. If the difference between the inclinations when looking up and down is ≥20°(35 △), three muscle operations may be considered. EOPHCT has detailed regulations:

  • Internal oblique A phenomenon: the oblique angle of view is 5°-10°when looking far and up, and if the eye position is normal when looking down, only one external rectus muscle is amputated for 10mm. If the oblique angle of view is 5°-10°when looking down, two rectus exteriors should be amputated for 10-12mm, or the rectus exteriors should be retracted by 5mm and amputated by 8mm in one eye.
  • Oblique A phenomenon: For intermittent or alternating patients, two medial rectus muscles can be amputated by 8mm. For the patients with constancy, the original eye inclination is 25°-30°, and when the difference of strabismus is greater than 10°-20°(20△-25△), the monocular rectus muscle can be amputated for 8-10 mm, and the external rectus muscle can be retracted for 8 mm.
  • Oblique V phenomenon: When the oblique angle reaches 20°when looking far, 25°-35°when looking up and 15°-20°when looking down, the internal rectus muscle will be amputated for 6mm and the external rectus muscle will retreat for 6mm on the same eye. When looking at the distance with an oblique angle of 35°, looking up at 40°and looking down at 25°, the lateral rectus muscle of both eyes was retreated, and the medial rectus muscle was amputated for 8mm in the non-main eye. Surgery should be performed at the age of 4-6 years, and orthographic training should be performed after operation.
  • The phenomenon of V-inclination: the rectus muscles of both eyes recede by 5mm, and in case of monocular strabismus with amblyopia, only the amblyopia eyes should be operated. The amount of operation should be controlled flexibly according to the patient's vision, refractive status and strabismus. Generally, the inner rectus muscle retracts 4-5 mm, the outer rectus muscle retracts 7-8 mm, the inner rectus muscle retracts less than 4-5mm and the outer rectus muscle retracts less than 6mm. A-exotropia is used to cut the internal rectus muscles of both eyes by 6mm, and A-internal oblique is used to cut the external rectus muscles of both eyes by 8mm.

2. Vertical Transposition of Horizontal Muscles

Knapp advocates this kind of operation, and thinks that the relationship between contact arc of muscle on sclera and eyeball rotation center is changed after vertical displacement of horizontal muscle. Therefore, in one vertical fixation direction, the contact arc between displaced muscle and eyeball increases, while in the other opposite vertical fixation direction, the contact arc decreases, so that the internal and external rotation force of horizontal muscle decreases correspondingly with vertical displacement of muscle, thus correcting A-V phenomenon. This operation method is suitable for cases without too strong or too weak vertical and without inclination. Moving the attachment point of horizontal rectus upward or downward can greatly enhance the effect of retraction or amputation on A-V phenomenon. There are three surgical methods:

  • A- phenomenon should move down the attachment points of two external rectus muscles (A-esotropia), or move up the attachment points of two internal rectus muscles (A-exotropia). In V- phenomenon, the attachment points of two external rectus muscles should be moved up (V-esotropia), or the attachment points of two internal rectus muscles should be moved down (V-exotropia).
  • The medial and lateral rectus muscles of one eye are displaced upward and downward at the same time to correct A-V phenomenon. This method is mostly used for the second operation or cases with severe amblyopia in one eye.
  • The horizontal rectus muscle retreats or amputates and shifts upward and downward. For V-exotropia, the lateral rectus muscle retreats and moves upward. If the original eye position has a large inclination, it moves up and down while doing retreat and truncation. In a word, the external rectus muscle moves to the open end of the "A-V" shape, while the internal rectus muscle moves to the closed end. The displacement is generally 5-10mm, that is, half to one tendon width. The difference between the upper and lower 15△-20△ can be corrected when the muscle attachment points are shifted up and down by half the tendon width.

3. The Upper and Lower Rectus Muscle Strengthening or Weakening Surgery

This is the use of upper and lower rectus adduction to correct A-V strabismus. This method is only used to correct the A-V phenomenon, but it cannot correct the horizontal inclination of the original eye position. The surgery of horizontal muscle needs to be performed simultaneously. The method is to perform reinforcement surgery for A-V exotropia, namely, A- exotropia strengthens the lower rectus, and V- exotropia strengthens the upper rectus. A-V esotropia is weakened by surgery, in which A-esotropia weakens the upper rectus and V- esotropia weakens the lower rectus. The amount of surgery for enhancement or reduction is generally 4 mm. Parks advocates that the operations of upper and lower rectus muscles should be performed in two times, using two kinds of operations, for example, the first operation of bilateral upper rectus recession (A- esotropia) or bilateral lower rectus recession (V- esotropia) in A-V esotropia, and the second operation of bilateral lower rectus resection (A- esotropia) or bilateral upper rectus resection (V- esotropia) if the correction is insufficient. A-V exotropia also points 2 operations.

4. Horizontal Displacement of Superior and Inferior Rectus Muscles

This is a surgery to correct A-V strabismus based on the principle that the nasal displacement of the attachment points of the upper and lower rectus muscles can strengthen the internal rotation force, and the temporal displacement can weaken the internal rotation force. This kind of surgery can only correct the difference of eye deviation when the eyeball is staring upward and downward, but cannot correct horizontal strabismus. Therefore, horizontal muscle surgery needs to be performed simultaneously. The method is A-V esotropia, and the upper and lower rectus muscles should be shifted to the temporal side. However, the upper and lower rectus muscles of A-V exotropia should be shifted to the nasal side. The amount of displacement is usually 5 to 7 mm, which can be combined with recession or amputation of the superior and inferior rectus muscles.

5. Strengthening or Weakening of Superior and Inferior Oblique Muscles

This is to use the external rotation of the superior and inferior oblique muscles to perform surgery to strengthen or weaken the oblique muscles to correct the A-V phenomenon. This surgery can only be performed when the superior and inferior oblique muscles are indeed too strong or too weak, otherwise secondary superior oblique or inferior oblique or rotatory strabismus of non-surgical eyes will occur after surgery, and the eye position can be corrected by cooperation with horizontal muscle surgery. The method is to perform surgery on the inferior oblique muscle for those with large changes in inclination when looking directly above. For V- exotropia, the inferior oblique muscle should be weakened, and for A- esotropia, the inferior oblique muscle should be strengthened. If the inclination is changed greatly when looking downward, the operation of superior oblique muscle will be performed. For example, V- esotropia, the superior oblique muscle should be strengthened, and A- exotropia, the superior oblique muscle should be weakened. However, for the superior oblique muscle with normal function, it should not be weakened, otherwise, rotational strabismus will occur when looking downward. When the function of the inferior oblique muscle of the ipsilateral eye is normal or excessive, the operation of weakening the superior oblique muscle is contraindicated, because in some patients, the function of the inferior oblique muscle will be further increased after the operation, resulting in secondary V-type strabismus. In conclusion, A-V exotropia requires weakening of the superior and inferior oblique muscles, while A-V esotropia requires strengthening of the superior and inferior oblique muscles. The operation of oblique muscle is non-quantitative and the operations of lower oblique muscle weakening are generally amputation, partial resection and recession. The strengthening operations include preposing and folding. The weakening of the superior oblique muscle is mainly performed by intrathecal tendon rupture, while the strengthening is mainly performed by folding and anterior transposition.

6. Rectus Junction

In this method, V- exotropia underwent interconnectivity between the medial and lower rectus muscles. V-exotropia underwent interconnectivity between the lateral and upper rectus muscles. A-exotropia underwent interconnectivity between the lateral and lower rectus muscles. A-exotropia underwent interconnectivity between the medial and upper rectus muscles. In this operation, the simple connection of the inner 1/3 and the superior (lower) rectus 1/3 could correct the deviation of 15Δ–20Δ. The simple connection of the outer 2/3 and the inferior (upper) rectus 1/2 could correct the deviation of 20Δ–25Δ. The connection of the inner (outer) 2/3 and the inferior (upper) rectus 1/2 plus the weakening of the direct antagonist (external or internal rectus) by 4–6 mm could correct the deviation of 30Δ–55Δ.

In the surgical treatment of A-V syndrome, the inclinations (including vertical and rotational inclinations) of the 9 fixation positions of the homograph and Hess screen should be carefully analyzed before operation, the postoperative changes should be correctly estimated, and the muscles (horizontal, vertical or oblique) that need to be operated on should be selected. Postoperative binocular vision and slight exotropia should also be considered in order to avoid correcting this anomaly and introducing another anomaly that would cause undue suffering to the patient.

Prognosis: Surgical treatment has a good prognosis.

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