Exotropia A sign

Introduction A-exotropia: also known as exotropia A sign, exotropia Aphenomenon, A-external oblique, divergent strabismus A syndrome, ie When looking straight up, the number of external slopes becomes smaller or even disappears, while when viewed directly below, the number of external slopes increases. Look at the distance, there is no change in the number of near-outside slopes, often the upper oblique muscle function is too strong, and the eyeball is invaginated when the eye position is received. The patient may have a mandibular adduction performance, a small solid vision of both eyes, and often have a horror.

Cause

Reasons for exotropis A sign:

(1) Causes of the disease

There are many reasons for the formation of AV signs, including factors of the extraocular muscle itself, anatomical factors, innervation factors, and genetic factors.

(two) pathogenesis

There are many reasons for the formation of the AV sign, which can be summarized as follows:

1. Causes of horizontal muscles Urist believes that the formation of the AV sign is related to the difference in strength between the inner and outer rectus muscles when looking up and down. In the physiological state, when the eyes are gazing upward, there is a slight increase in the separation effect (straight vision is due to the excessive action of the lateral rectus muscle, V-eotropia is due to the action of the medial rectus muscle, and A-exotropia is due to the medial rectus Insufficient strength, A-Esotropia is caused by insufficient strength of the external rectus muscle. In short, the V sign is caused by excessive muscle level, and the A sign is caused by insufficient level of muscle strength.

2. Reasons for the oblique muscle Jampolsky believes that the strength of the superior and inferior oblique muscles is an important reason for the formation of the AV sign. Because the secondary action of the oblique muscle causes the eyeball to turn outward, when the strength of the lower oblique muscle is too strong, it can cause the V phenomenon; when the strength of the lower oblique muscle is insufficient, the phenomenon of A is caused; the strength of the superior oblique muscle is too strong and causes the phenomenon of A. Insufficient strength of the superior oblique muscle causes a V phenomenon. In short, when the horizontal inclination is increased upwards, it is caused by the reason of the inferior oblique muscle, and when the downward inclination is increased, the horizontal inclination is increased, which is caused by the upper oblique muscle. Von Noorden believes that abnormal function of the oblique muscle is a common cause of AV syndrome, and AV syndrome with abnormal anatomical function often causes rotatory strabismus. Rotational strabismus is produced by AV syndrome with abnormal anatomical function. After correction of the horizontal muscle end tilt, the squint can not be corrected. This squint was confirmed by fundus photography.

3. The reason for the upper and lower rectus muscles Brown believes that the function of the upper and lower rectus muscles is a cause of the formation of the AV sign. Because these two muscles have a secondary effect on the inner rotation of the eyeball, the upper rectus muscle force When it is too strong, it can cause the phenomenon of A; when the strength of the superior rectus muscle is weak, it will cause V phenomenon; when the strength of the lower rectus muscle is strong, it can cause V phenomenon; the strength of the lower rectus muscle is weaker and cause the phenomenon of A. In short, the difference in the horizontal slope when looking directly above is caused by the cause of the superior rectus muscle, and the difference in the horizontal slope when looking directly below is caused by the lower rectus muscle.

4. Reasons for horizontal-vertical rectus The person who holds this opinion believes that the AV sign is caused by abnormalities in both the horizontal and vertical muscles, and is not caused by the abnormality of a certain muscle alone. Some patients may be mainly caused by excessive or weak horizontal muscles, resulting in secondary changes in vertical muscles; while others may be mainly excessive or weak in vertical muscle function, leading to secondary changes in horizontal muscles. , or changes in both horizontal and vertical muscle function to form an AV sign.

5. Anatomical reasons

(1) The AV sign is related to the shape of the face: such as the Mongolian-like face (upward movement of the outer crotch) can cause A-inner and V-external; and the anti-Mongolian (Caucasian) face (no change in the outer crotch) A bit or a slight shift) can cause A-outer skew and V-inner skew.

(2) Fascia abnormalities: such as Brown's superior oblique sheath syndrome often combined with V-external oblique, which is due to the lack of elasticity of the superior oblique muscle sheath, resulting in forced abduction during the upturn. In Johnson's adhesion syndrome, mechanical distribution can also occur when rotating vertically.

(3) abnormal muscle attachment point: Some people think that some patients with V phenomenon have higher attachment points of the medial rectus tendon than normal, and the attachment position of the lateral rectus tendon is lower than normal. In addition, the advance or backward movement of the attachment point may also cause an AV sign.

6. Causes of innervation Clinically, the AV sign is rarely caused by anatomical factors, but it is more common due to paralytic factors. Because it can be seen from the definition of AV sign, it is a subtype horizontal strabismus with vertical non-common strabismus, which means that regardless of the horizontal slope or vertical slope, the muscles are too strong. Or too weak imbalance. The vertical rectus and oblique muscles are mainly inconclusive, both horizontal and vertical muscles have effects, but the two of them are most important and cannot be explained clearly. The vertical muscles have both neurological and mechanical effects, while the horizontal muscles are Muscles may be more prominent when they are too strong or too weak.

In addition, there is also a physiological V phenomenon, that is, in the case where there is no strabismus in the original eye position, when the eye is gazing upward, an external oblique can be generated (up to 17 ), and when looking downward, an A phenomenon can be generated (up to 5 ). There are many, this may be related to the innervation factor.

7. Causes of abnormal convergence and fusion function When looking down, if you can't keep the fusion, you can produce the A phenomenon; when you can't keep the fusion when you look up, you can produce the V phenomenon, which is common in intermittent exotropia.

8. Genetic factors There are few reports on genetic factors related to AV signs in the literature. In China, a case of 11 cases of V-exotropia in 5 generations was reported, which is autosomal dominant. Only one case of surgery was performed, and no abnormality of extraocular muscle adhesion was observed during the operation.

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

an examination

Related inspection

Vision eye examination

Examination and diagnosis of external oblique A sign:

No special laboratory tests are required.

1. General examination to check the naked eye (and correction) far and near vision, external eye condition, refractive status, refractive interstitial, gaze nature and fundus conditions.

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

(1) The prismatic visor method is used to check the strabismus when the original eye position, the top right side, and the right side are gazing.

(2) Retinal correspondence, fusion function, stereoscopic function check, and measurement of AC/A ratio.

(3) Double-eye solid vision examination to understand the scope of gaze and provide a basis for selecting surgical methods.

(4) The Hes screen checks the functional status of the extraocular muscles.

3. Precautions in AV syndrome examination

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

(2) The patient should be allowed to look at the small visual target when looking close. In order to reduce the influence of the adjustment factor on the eye position, the 3D lens can be worn after the examination.

(3) The horizontal slope and the inclination of the upper and lower gaze positions were measured at 33 cm and 6 m, respectively. It was suggested that repeated examinations should be used as a basis for diagnosis.

(4) Mostly the slope of the inspection by the prism and cover method shall prevail. Turn the angle of 25° up or down to check the inside and outside slope. Some people think that turning the angle of 15° is enough (Duke-Elder), because the gaze position is too up or too down to cause illusion.

(5) pay attention to check the oblique muscle function and squint

1 The judgment of the superior oblique muscle function is divided into 4 levels according to the Parks classification method, and the difference between the vertical inclination of the eyes and the vertical inclination of the left and right turns of 30° and the vertical inclination of the eyes are examined. Class A.1: 30°.

2 The determination of the lower oblique muscle function is divided into three levels according to the Meng Xiangcheng classification method: A.1 level (1 degree): that is, the upper oblique appears when the internal rotation; B.2 (2 degrees): the extreme internal rotation Only the upper oblique is displayed; C.3 (3 degrees): the upper oblique appears when turning inward.

3 Rotation strabismus was determined by a fundus camera. According to Kong Lingyuan's measurement method, the average value of the normal optic disc-center concave angle was 7.381°, and the range of variation was 1.429° to 13.333°. The fovea is located at 0.343 PD below the geometric center plane of the optic disc.

Differential diagnosis

Differential diagnosis of exotropia A sign:

(1) A-esotropia: also known as esotropia A sign, esotropia Aphenomenon, A-endotropy, convergent strabismus A syndrome That is, the number of internal inclinations increases when viewed from the top, and the number of internal inclinations decreases or even disappears when viewed from the front. When looking far and near, the internal inclination is almost equal. When the eye is turned inward and downward, the upper oblique muscle function is too strong, and the eyeball is invaded when the eye position is received. The patient may have a mandibular uplift.

(2) V-esotropia: also known as esotropia V sign, esotropia Vphenomenon, V-internal, convergegent strabismus V syndrome That is, the number of internal slopes increases as you look down, and the number of internal slopes becomes smaller or even disappears when viewed from the top. The internal oblique angle is much larger than the farsightedness, and the lower oblique muscle function is often too strong. The patient may have a mandibular adduction performance, and the two eyes have a small solid vision and often have a horror.

(3) A-exotropia: also known as exotropia A sign, exotropia Aphenomenon, A-external oblique, strabismus A syndrome (divergent strabismus A syndrome) ), that is, when viewed from directly above, the number of external slopes becomes smaller or even disappears, and when viewed from directly below, the number of external slopes increases. Look at the distance, there is no change in the number of near-outside slopes, often the upper oblique muscle function is too strong, and the eyeball is invaginated when the eye position is received. The patient may have a mandibular adduction performance, a small solid vision of both eyes, and often have a horror.

(4) V-exotropia: also known as exotropia V sign, exotropia Vphenomenon, V-external oblique, strabismus V syndrome (divergent strabismus V syndrome) ), that is, when the angle is upward, the number of external slopes increases, while when viewed directly below, the number of external slopes decreases or even disappears. The external slope is much larger than the near view (the separation is too strong), and the lower oblique muscles are often too strong. The patient may have a mandible lifting phenomenon.

(5) X-phenomenon: X-phenomenon: that is, in the original eye position, the orthodontic or slight exotropia, when viewed directly above or below, the external inclination increases, showing an "X" shape.

(6) XA-phenomenon (X and A phenomenon): When the original eye position is slightly exotropy, the number of external oblique angles when looking upwards is increased less than when the direct oblique angle is observed.

(7) XV-phenomenon (X and V phenomenon): When the original eye position is slightly exotropy, the number of external oblique angles when looking upwards is much larger than the number of external obliques when looking directly downward.

(8) -phenomenon: -phenomenon: When the original eye position, the number of internal inclination is small or no internal oblique, and the number of internal inclination increases when looking upward and directly below.

(9) Y-phenomenon: Y-phenomenon: When the original eye position and the direct downward gaze, the number of external inclination is small or no external oblique, and the number of external inclination is significantly increased when looking directly above. It is a variation of V-exotropia.

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