phoria
Introduction
Introduction to hidden oblique Heterophoria (phoria) means that the eyeball can maintain binocular monocular vision in situ or in motion only with the help of corrective fusion reflexes, or that the two eyes exhibit skewness in the absence of fused reflexes. Most of the clinical symptoms caused by occultation come from the constant tension of the brain to maintain visual disturbances caused by imperfect binocular fixation. These are the main symptoms of eye-strain, which vonGraefe and Donders call. The main symptoms for muscular eye fatigue (muscularasthenopia) are: headache, photophobia, decreased near vision, and sometimes far vision loss. basic knowledge The proportion of illness: 0.001% Susceptible people: no special people Mode of infection: non-infectious Complications: headache, nausea and vomiting
Cause
Cause of occlusion
Static slant (30%):
Static heterophoria or anatomic heterophoria, the local anatomical relationship between the eyeball and its appendages is the primary in determining the position of the eye and its free movement, only when these factors are relatively normal. In the case of close symmetry, both eyes can maintain the orthodontic movement of both eyes. Since such complete symmetry is rare, it is obvious that this is the basic cause of occlusion. Common anatomical factors include: asymmetry of the eyelid An abnormality in the shape of the wall or skull, or an abnormality in the shape of the eyeball (such as high myopia) and an abnormality in the volume of the eyeball or swelling of the contents or displacement of the eyeball, so that the free movement of the eyeball is suppressed, but the most common is Muscle abnormalities, including obvious length, walking, volume and scleral attachment points, the medial rectus adhesion point is higher, the lateral rectus muscle attachment point is later, easy to produce implicit oblique; the medial rectus muscle is weak or The attachment point is lower, the external rectus muscle is stronger or the attachment point is higher, and the external oblique is easy to occur; the anatomical abnormality of the upper and lower rectus muscles or the upper and lower oblique muscles or the attachment point abnormality is caused by the oblique One reason, these and other minor changes do not cause strabismus, as age increases, the ability to coordinate decreases, and changes in organ function and muscle and ligament deficiencies lack, and the imbalance of the eyes produces and expands. The disease and function decline of the muscle itself must also be included. Finally, the abnormal Alpha angle caused by the abnormality of the macular position may cause difficulties in the joint of the binocular visual axes. The slant caused by these structural factors may be common or non-common. The imbalance of the eyes in different gaze directions can be asymmetrical.
Dynamic slant (30%):
Kinetic heterophoria, also known as accommodational hetemphoria, is caused by the inconsistency between regulation and convergence. Most of the extraocular muscle imbalance is due to regulation and convergence. Coordination function is caused by abnormality. Usually, the relationship between regulation and aggregation (AC/A ratio) is relatively fixed. If the ratio is abnormal, the set caused by each diopter adjustment is too small or too much; Breaking the balance of the AC/A ratio, because the set needs to be changed in order to see the object at a certain distance, and the set changes accordingly; sometimes the abnormal AC/A ratio and the uncorrected refractive error can exist at the same time, and the adjustment and the collection are not Coordination promotes the development of dynamic slanting. When patients cannot adequately control slanting, in order to obtain clear binocular monocular vision, motor fusion reflex will compensate for abnormal AC/A ratio, so that perceptual fusion continues to be different. The degree of difficulty, this will inevitably lead to its excessive use.
Therefore, when anatomical or innervation factors do not work, in patients with moderately hyperopic eyes without correction, too close work in the emmetropic eye, or in acquired presbyopia, due to the need to increase adjustment, there will be It develops into a tendency of intrinsic slanting. Congenital myopia is often over-collected due to closeness, and it may also develop into an implicit slant. Conversely, congenital astigmatism or acquired myopia does not require adjustment, and the developed aging eye does not need to be assembled. Mixed astigmatism or high astigmatism does not need to be adjusted or aggregated. In these cases, external oblique slanting can occur. Therefore, when doing squint examination, anyone with ametropia should wear corrective glasses to check, such as a new wearing mirror. Accurate results should be obtained after 4 weeks of wearing the mirror and then checking.
Neurogenic slant (20%):
The slant caused by the abnormal innervation of the extraocular muscles is called neurogenic heterophoria, which includes many factors: the eye muscles are paralyzed or the sputum condition affects the underlying neurons, and the abnormal or irregular stimuli are low. Coordination area, disturbing the proprioceptors that connect the eye movement organs, or the disharmony of the high-level center, all of which cause paralytic or spastic strabismus have little effect on the eye movement, and the fusion movement can be controlled in order to keep the eyes gaze The skew becomes potential.
Clinically, this kind of slanting is divided into two categories.
(1) Sub-nuclear slant:
Because the subordinate neurons are involved in the occlusion caused by a single extraocular muscle dysfunction, often non-common occult, this slant is mostly temporary, if the extraocular muscle function is fully restored, the slant can disappear, but The recovery of function is often incomplete or undergoing some changes, including the contraction or extension of muscles and ligaments, and leading to permanent skewness, and most of the transition to common slanting, it is worth noting that the movement of the eye requires only any muscle. A little strength, the deviation is not due to the weakening of the function of a single muscle, but the imbalance of the distribution of neuromuscular coordination functions. In addition, the complete common slant is rare, and even if there is, it gradually changes.
(2) Nuclear slanting:
Due to the slanting of the superior neuronal lesions, most of them are common slanting, which may involve the same direction movement or the anisotropic movement. If the degree is slight, the slant is oblique.
In addition, the cause of occlusion is closely related to the strength of fusion function: both kinetic fusion and perceptual fusion are related to slanting. If the fusion function is well developed, the fusion range is large, and even if there is skew, it can be fused. Conversely, if the fusion function is not well developed, a mild balance disorder will cause difficulty in fusion, and both eyes will be unstable and visual fatigue symptoms will occur; when the fusion function is seriously lacking, any tendency to skew will Immediately becomes strabismus, when there is a lack of fusion due to blindness of one eye, there will be different skew at different ages. Of course, there are certain individual differences. Usually, exotropia will appear blindly at birth or shortly after birth; In the case of infants or early childhood, esotropia occurs in a blind eye; if there is an internal or external strabismus between the child and the middle-aged blind, the eye is often maintained in a positive position within a few years and eventually is exotropia; The vast majority of blindness in the year will inevitably lead to exotropia. This difference is largely due to the difference in fusion reflection. In the absence of fusion at birth, the eye is in a physiological rest (abduction). After blindness in childhood, the blind fusion is determined by the rich fusion reflection. This is because the instinct needs to be in the process of gathering. The eyes affect each other regardless of the blind eye, and the gradual decrease of the fusion reflection with age, especially the reduction of the use of the collection after the presbyopia makes the eye position favorable for abduction.
The etiology and pathogenesis of occult is complicated. A kind of slanting can be caused by many factors. Static and dynamic factors can exist at the same time. Neurological factors sometimes exist. Therefore, slanting is often horizontal and vertical slanting exists at the same time. There are also rotational slanting at the same time, but the clinical symptoms are mostly similar, so it should be examined in detail to confirm the diagnosis and appropriate treatment.
Prevention
Concealed prevention
Pay attention to the diet and supplement the vitamins and nutrients that are lacking in the body.
Prevention methods are different for children of different ages, but the key is to prevent children from seeing things that are close together.
1. Baby: Parents must not hang their favorite toys too close.
2, young children: because they can get toys, parents should always pay attention to avoid him watching toys at close range.
3, preschool children: should take them outdoor activities, and intentionally guide them to see things in the distance.
It is not conducive to prevent children from strabismus by installing lights in the cradle or turning the lights on at night.
Complication
Oblique complication Complications, headache, nausea and vomiting
Concealed slant is very common in normal people, and there are usually few complications. Some of them often have abnormal refractive errors, unclear vision, and decreased vision. It is mainly easy to cause eye fatigue, because eye fatigue causes headache, eye pain, heavy eyelids, blurred vision, and even temporary diplopia and dizziness, nausea and other symptoms, but after a little rest, the symptoms can disappear.
Symptom
Concealed symptoms common symptoms visual impairment strabismus double vision
Most of the clinical symptoms caused by occultation come from the constant tension of the brain to maintain visual disturbances caused by imperfect binocular fixation. These are the main symptoms of eye-strain, which von Graefe and Donders put. Known as muscular asthenopia, the main symptoms are: headache, photophobia, decreased near vision, and sometimes distant vision. Occasionally, when the fusion function declines, the deviation becomes dominant, and diplopia It will occur with obvious intermittent strabismus. Most of the symptoms are relieved after one eye is closed. The test of periodically closing one eye or the other is a good test method. It can be used to confirm whether the symptoms are caused by the oblique. However, the visual fatigue caused by other causes, such as the object image, can be lifted by closing it.
In addition to visual insufficiency, the oblique oblique is also related to many other activities. Obviously, when the oblique tilt is obvious in the near view, the close reading of the patient reading, fine work, etc. becomes very difficult; It will affect activities that require rapid response, such as ball sports. Under normal circumstances, the effect of implicit inclination is close, and the effect of external oblique is far away, but this is not always the case. When the implicit inclination is caused by insufficient separation, Vision will be particularly affected, as the near-invisible slant is weakened, which is often related to the low AC/A ratio. When the implicit slant is due to over-collection and high AC/A ratio, the near-sight will be affected; Similarly, when the oblique skew is caused by the weak set and the low AC/A ratio, the influence is close. When the external oblique is caused by the excessive separation and the high AC/A ratio, the influence is far, and the near-outer is weakened. .
The main features of the slanting symptoms are: First, although most people have slanting, there are few people with clinical symptoms. Usually, the horizontal slanting is less painful, although sometimes it is painful; the vertical slant is large. Partially causing pain; rotatory slanting causes all pain, different individuals have different reactions, some can compensate, while others may cause difficulty in gaze at 1 or less, but in the latter In the case, it is necessary to pay attention to distinguishing visual fatigue caused by other factors, such as refractive error, object image, etc. In addition to these factors, if the inconspicuous occlusion causes strong functional symptoms, its cause is usually physical weakness or psychology. Factor, not eye, the second characteristic of slant is the diversity of symptoms. The symptoms are not only the imbalance of the extraocular muscles, but also the fusion force needed to overcome the imbalance, not only the different symptoms between different individuals, but also the same Individuals have different symptoms at different times, work fatigue, learning tension, physical weakness, mental disorders, etc. can cause and aggravate the slant, causing symptoms.
Normally, the presence or exacerbation of slanting symptoms is less dependent on the degree of skewness and depends on the following four conditions:
1 skewed force, if the fusion transposition is suitable and stable, the symptoms will not appear;
2 patients' occupations, individuals engaged in fine work are prone to symptoms;
3 the physical condition of the patient;
4 The patient's psychological quality, in the physical and mental adjustment of the individual, he lives within the scope of physical and psychological adaptation, he will not appear the symptoms of slanting, of course, this is not to say that ophthalmic treatment is not important.
Examine
Obscure inspection
Concealed inspection
(1) Cover-to-cover test: The cover-uncover test can check the skew controlled by the fusion mechanism when the eyes are open, but if there is a slant, the cover breaks the fusion at a glance. When the eye is covered, the deflection occurs. After fully covering the eye, the cover piece is quickly removed. The examiner can determine whether the cover eye has deflected after the cover piece and form a fusion motion when the cover is removed. Sometimes, no matter what cover The occultation of the eye becomes oblique, so the occlusion test should be repeated after the occlusion-de-covering test. After covering one eye, the slanting is easy to change into slanting. It is a feature of weak fusion force and often insufficient fusion force. This inspection is important. The clinical significance (Figure 1), premise: the patient must have the ability to look at the target during the examination. Advantages: simple operation, objective and reliable results. Disadvantages: small hidden slant may be ignored, but can be measured by Maddox rod method, covering method It is rough and only used for screening. It is necessary to cover the eyes - to cover the test. The 6m and 33cm gaze should be checked at the same time. In order to completely break the contact of the eyes, the cover-to-cover must be covered. Repeat several times, on the other hand, it must be covered for a long time, at least 2s, in order to completely block the binocular reflex, otherwise it is not easy to check accurately.
(2) Triple prism plus cover method: This method is an objective quantitative test method. Firstly, the direction of the eye position deflection is detected by the alternating cover method. If the angle is implicit, the bottom is placed at the bottom of the covered eye. If the prism is oblique, the bottom of the prism is inward, and the upper bottom is placed obliquely downward. When the cover is removed, if the covered eye still rotates, increase the prism degree until the eye stops rotating. The prism power is the number of hidden degrees, and there are vertical or horizontal skews. The horizontal position is corrected first, and the vertical position is corrected.
(3) Maddox rod method: This method is a qualitative inspection method, which makes the shape of the two eyes different to eliminate the fusion. The Maddox rod is a one with several side-by-side cylindrical lenses (glass rods) installed in one lens frame. A special inspection lens can be placed on the trial frame. According to the refractive principle of the cylinder, a light can be refracted into a strip of light by the Maddox rod. The direction of the light is perpendicular to the arrangement of the glass rod by the column of the Maddox rod. The lens is placed vertically in the axial position or horizontally placed in front of the patient's eye. The patient's eyes are always looking at the light spot at 5m or 33cm to judge the slanting property. When measuring the horizontal slant, the Maddox rod level is measured. Put it in front of the right eye, let the patient's eyes look at the light bulb at the same time. If the vertical light is coincident with the light spot, it means there is no hidden slant. If it is biased to one side, there is slanting. If the right eye sees the vertical light, it is in the left eye. The left side of the spot is seen to form a cross-over double vision, which is an external oblique. Otherwise, the vertical light is located on the right side of the light spot, forming an ipsilateral double vision, which is an implicit oblique. If, the Maddox rod is placed vertically. In front of the right eye You can measure the presence or absence of vertical slanting. Through the eyes of the vertical Maddox rod, the bulb is horizontally crossed. If the horizontal line is just across the center of the bulb, there is no vertical slanting. If the right eye sees the horizontal light at the left eye. Under the light spot, it is hidden on the right eye or under the left eye; otherwise, if the horizontal light seen by the right eye is above the light spot seen by the left eye, it is the lower right eye or the left eye. .
(4) Maddox rod plus prism method: Maddox rod and prism test is a subjective quantitative test method, which is a front-mounted Maddox rod and the other front pre-triangular prism, such as an implicit oblique. The bottom of the prism is outward. If the edge is oblique, the bottom of the prism is inward. If it is oblique, the other side should be placed at the bottom, such as the lower oblique, and the other should be bottom-down when wearing the prism; If the prism is worn with the same eye (that is, the Maddox rod and the prism are placed in front of one eye), the direction of the bottom of the prism should be reversed. At the same time, look at the light source at 5m or 33cm, and increase the prism power in turn until the strip light coincides with the light spot. The prism power used at this time is the degree of hidden slope.
(5) Markov fixation difference meter: Maddox fixation disparity meter is the compensation for the existence of recessive slanting if the prism is corrected after applying the Markov method. The possibility is quite high, and the Markov fixation difference meter should be used to further evaluate the compensatory recessive slant. The Markov fixation difference meter can be divided into two types: far vision and near vision. They all have a central view (Fig. 5), which uses OXO for common vision of both eyes, and a vertical line on the upper and lower sides of X is seen by one-sided vision, which is generated by polarized light separation method. The patient feels up and down due to the difference of fixation. The vertical line is slightly offset from the position of X. The Markov design is to calculate the degree of visual axis offset by the position where the two perpendicular lines are offset on the OXO. The prism is used to return the two single-sided lines to the central position of the OXO. The degree of the prism is the value of the fixation difference. If the difference value of the fixation is high: if the implicit inclination is above 8~10, the external oblique angle of 15 or more is regarded as compensation for the recessive slant, so the horse Good fixation difference is useful when checking for compensatory recessive slant At that time, you should be aware of the visual fatigue of the patient. The visual disturbance symptoms are not caused by refractive errors alone. When the symptoms appear, such as covering one eye, the patient is forced to make a single eye, and the symptoms will be greatly reduced. at this point.
(6) Red glass or Maddox rod plus tangent rule method: Red glass or Maddox rod plus tangent scale test is also a subjective quantitative test method. The tangent ruler is made of a ten wooden frame. There are two rows of numbers on the top, and there is a light in the center. The large characters on the ruled ruler are used for inspection of 5m distance. The small characters can be used for inspection of 1m distance. When checking, the patient stands at a distance of 1m or 5m in front of the ruler, and the front red glass is placed at a glance. Lens or Maddox rod, letting both eyes look at the light in the center of the tangential ruler at the same time. The distance between the red light or the bright line of the red lens or the Maddox rod is off the light (the number on the tangential ruler) is hidden. The degree of inclination, according to the position of the red spot or the strip light, directly detects the degree of concealment in the horizontal or vertical part of the tangent.
(7) red-green lens method: red-green lens method (red-green test) is to use two eyes to wear red and green lenses and look at the general bulb, it is to use two eyes to different colors to eliminate fusion, the method is one Wearing red lenses in front of the eyes, wearing green lenses in front of the eyes, looking at the light source 5m away from the front of the eye, such as two red and green eyes, indicating the separation of the eyes, there is a hidden oblique existence.
(8) Worth four-point test method: This method is also an inspection method that uses the difference in color of the two eyes to eliminate the fusion (see binocular visual function test).
(9) Maddox wing examination method: Maddox wing test method (maddox wing test) for measuring close-range slanting, if there is ametropia should be corrected with corrective glasses, the patient holds the Maddox wing fixed in front of the eye, through the Maddox wing joint Part of the crack and the wing separate the visuals of the two eyes. When measuring the horizontal slanting, the upper wing divides the field of view into two halves. The right eye sees a finger (or a cutting head) with its tip pointing directly above, left. The eye sees a horizontal scale, and the hidden slope can be directly read by the degree indicated by the arrow. When the vertical oblique tilt is measured, the two vertical partitions separate the two eyes, the right eye only sees a red arrow, and the left eye sees a red scale, the arrow The scale indicated is the degree of vertical slanting, and the red arrow can also move on the board to detect the rotation slant. When the arrow moves to the line that the examinee thinks is parallel to the line on the lower level of the horizontal scale, then The angle at which the arrow turns is the degree of rotation.
(10) Inclinometer test: The inclinometer is also known as the Stevens phorometer. It is a more practical eye muscle function test instrument that can measure the degree of occlusion and the muscle strength of each extraocular muscle. It is necessary to carry out in the dark room. After the patient sits on the inclinometer, adjust the instrument to a suitable position, and let the patient look at the light source 5m away in front and gaze at the distance of 33cm, and the eye without the Maddox rod is the fixation eye. The result of the examination is the degree of muscle strength imbalance between the two eyes. If it is suspected that one of the muscles of one eye has muscle strength or mild paralysis, it is feasible to check the single eye muscle strength. The examiner can check every 1~2s. Shake the hand 1 time in front of the patient's eye wearing a Mars rod to intermittently see vertical or horizontal light to prevent fusion and affect the inspection results.
1 Check the horizontal muscle strength of both eyes during the process. When the oblique oblique inspection is performed, place the Markov rod horizontally before the eye, so that the pointer of the left prism of the hidden inclinometer is aligned to the 0 position, and the examiner twists the small handle on the left side. Or the spiral below, so that the vertical light passes through the light. At this time, the scale can be observed. If it is still 0, it is the positive eye, indicating that the horizontal muscle strength of the two eyes is in equilibrium, such as the pointer is above the 0 position. The implicit oblique is below the oblique oblique, and the number pointed by the pointer is the degree of the oblique oblique.
2 Check the vertical muscle strength of both eyes to check the slanting angle, place the Markov rod vertically in front of one eye, and place the pointer of the right triangular prism sheet of the inclinometer on the 0 position. As before, as seen, the horizontal line is as seen. Through the light spot and the pointer is in the O position, there is no vertical oblique tilt, which is the vertical muscle balance of the two eyes. If the pointer is above the 0 position, it is oblique on the right eye; if the pointer is below the O position , the left eye is hidden obliquely, and its hidden slope is the scale indicated.
3 Monocular horizontal muscle strength test: When checking, rotate the prism to be placed in front of the two eyes, rotate the left eye to 90°, and then move the triangular prism base in front of the right eye upwards by 68, at this time, the two eyes are merged, right The light seen by the eye is below, the light seen by the left eye is above, when the muscles of the two eyes are normal, the two lights are on the same vertical line, and the light below is on the right side of the upper light, then the right eye is hidden. On the left side of the upper light is a hidden oblique, the triangular prism in front of the left eye is rotated to the upper side, and the lower two lights are perpendicular to each other, and the triangular prism degree at this time is the degree of the oblique degree of the right eye.
4 monocular oblique muscle strength test method: a vertical position of the Markov rod in front of the two eyes, the right eye front rotating prism, so that the base up 6 ~ 8, then the right eye sees the strip light in the left eye Below, you can see two parallel strips of light, the lower one is seen by the right eye. If the light above is horizontal, the bottom of the strip light is tilted upward, and the right inner slant can be diagnosed. The right-handed Markov rod can be adjusted until the horizontal strip light is parallel to the upper ray, and the Markov rod refers to the degree of rotation concealment. In addition, the cone can be used to check the fusion range (see both eyes). Visual function check).
(11) Maddox double prism inspection method: Maddox double prism is composed of two 4 triangular prisms intersecting at the center. When checking, first cover one eye and place double prisms horizontally in front of the other eye so that the bottom of the two can just be the pupil. Divided into upper and lower halves, and the examinee looks at a horizontal line on the front of the eye chart, and sees the horizontal line as two parallel lines through the double prism. At this time, the eye will be opened and the eyes will appear at the same time. 3 parallel lines, the upper two of the three lines are observed by the double prism, and the middle one is seen by the other eye. If the three lines seen by the subject are not parallel, it indicates that there is a rotation tilt. If the double prism is worn in front of the right eye, it is found that the right end of one line is shifted to the lower line, and the left end is close to the upper line, indicating that the left eye has an outward rotation tilt, and the knob on the trial frame on the side of the triangular prism is rotated. Make the three lines parallel, and the scale indicated by the bottom edge of the double prism is the rotation hidden degree.
(12) Double Maddox rod test to measure rotatory deflection:
Insert a red and a white Maddox rod into the frame, and place the red rod in front of the eye that is considered to have a squint squint. Pay special attention to the direction of the glass rod and the 90° mark of the frame, on the Maddox rod frame. A small nick makes it easy to adjust, carefully adjust the frame so that it is completely at the correct level, the patient's head should be kept straight and conducive to gaze, such as no vertical deflection, can be a bottom down The prism is placed in front of the eye so that the patient can see two separate horizontal lines for judgment. Advantages: Quantitative diagnosis of rotational deflection can be made. Disadvantages: The rotation cannot be distinguished from the oblique and oblique, and the room must be dark.
2. Precautions
(1) The abnormal AC/A ratio is a common and important factor causing skew. If the AC/A ratio is too high, the height set at the near end will produce implicit or internal skew; if the AC/A ratio is too low, then Seeing the external oblique or exotropia when looking at the near, understanding the AC / A ratio is clinically reasonable choice of lenses, drugs and surgery to guide the skew.
(2) Those with refractive errors should be inspected and measured after wearing corrective glasses. If new glasses are worn, they should be worn for 4 weeks and then checked for oblique inclination. Because the AC/A ratio has not changed to normal after correction, it must be After a period of time, adapting it and gradually turning it into normal, it is better to check the hidden slope.
(3) In the case of regulating paralysis (for example, when dilating optometry), the slanting measurement should not be performed, because the blur of the retinal image caused by this time will induce more convergence, thus making the implicit oblique increase The tendency to reduce the slope.
(4) The first and second oblique angles of the far, close and gaze directions should be measured. Because some of the slanting angles are non-common, even in the commonality, the degree of slanting at the far and close distances is also It can be different.
(5) Since there are different degrees of convergence when looking at any finite distance, when there is a small amount of implicit oblique at a long distance, it is often physiological, such as an oblique oblique, even if the degree is small, it has clinical significance, and When looking at close range, it is the opposite.
(6) The adaptability of children's indexing is large, which will affect the evaluation of their binocular vision, especially the measurement of slanting. The time to separate the eyes should be long enough when measuring the degree of concealment.
Diagnosis
Concealed diagnosis
diagnosis
The diagnosis can be determined based on the patient's clinical presentation and clinical examination.
Differential diagnosis
It should be differentiated from paralytic strabismus, common strabismus, and congenital sternocleidomastoid muscle fibrosis.
Paralytic strabismus: a type of non-common strabismus. The strabismus caused by extraocular muscle paralysis is called paralytic strabismus. The oblique with eye movement disorder is regarded as non-common strabismus. Non-common strabismus is divided into two types: spastic strabismus and paralytic strabismus. Strabismus caused by primary muscle (nerve) spasm is extremely rare, and is only seen by chance in tetanus, neurosis, and the like. Therefore, most of the extraocular tendons encountered in clinical practice are recurrent, so non-common strabismus generally refers to paralytic strabismus.
Common strabismus: the oblique direction of the common strabismus is more common with horizontal deflection, simple vertical deviation is rare, and some can be combined with vertical deflection. If some patients with internal obliqueity have an upward slant when the eyeball is turned inside, this vertical deflection is not entirely due to extraocular muscle paralysis, but often because the inferior oblique muscle is thicker than the upper oblique muscle and the strength is too strong. During internal rotation, the strength of the inferior oblique muscle is stronger than that of the superior oblique muscle, resulting in the eyeball turning up.
