It is a type of squint or misalignment of the eyes.
While some people have eyes that open inward ( crossed eyes ) or outward, hypertropia occurs when one eye turns upward.
It can be constant or occur only when you are tired or stressed.
Strabismus is usually diagnosed in children and affects about 2 percent of every 100 children. Hypertropia is the least common form of strabismus.
It is estimated that about one child in 400 has hypertropia. The condition can also appear in adulthood, often due to an eye disease or injury.
Symptoms of hypertropia
Children often do not complain about symptoms. In addition to the upward wandering of the eye, a parent may notice that a child tilts their head to one side to try to align the eyes for clearer vision.
Adults with the condition may also notice a subconscious head tilt and experience double vision. As with other types of strabismus, it can cause headaches and headaches.
It is not perceived by the patient but rather by the observer.
Suppression occurs when the deviation begins in the first years of life (before six years of age) when the neuroplasticity of the visual system is still capable of suppressing the image that comes from the deviated eye.
The amount of suppression, which can range from small suppressive scotomas in binocular fusion to large areas of suppression on the affected side and amblyopia, depends on several factors, such as the size of the strabismus and the age of onset.
It occurs when the deviation is acquired after a significant maturation of the visual system (7 to 8 years of age) when the suppressive mechanisms are no longer initiated.
Younger children may also have transient diplopia in acquired forms of strabismus before suppression begins. In the case of hypertropia, the diplopia is vertical.
Two images are perceived in the exact location due to a misalignment of the points of correspondence of the retina in the fovea. This symptom is rare compared to diplopia, and the same rules apply to affected patients’ ages.
It has been observed in glaucoma patients with acquired strabismus (see strabismus after surgery) due to tunnel vision and forced use of the fovea.
Causes of hypertropia
Hypertropia can be congenital or acquired, and the misalignment is due to an imbalance in extraocular muscle function.
The superior rectus, inferior rectus, superior oblique, and inferior oblique muscles affect the vertical movement of the eyes. These muscles can be paretic, restrictive (fibrosis), or overactive effect of the muscles.
Congenital cases may present developmental abnormalities due to abnormal muscle structure, usually muscle hypertropia or rarely, absence of muscle, and incorrect location. Specific and common causes include:
Sudden onset hypertropia in a middle-aged or elderly adult may be due to compression of the trochlear nerve and the mass effect of a tumor, requiring urgent brain imaging using magnetic resonance imaging to locate any space occupied by a lesion.
It could also be due to the infarction of the blood vessels that supply the nerve due to diabetes and atherosclerosis. In other cases, it may be due to an abnormality of neuromuscular transmission, that is, myasthenia gravis.
Causes of hypertropia in children
Several conditions can cause hypertropia in children.
Fourth cranial nerve palsy
The fourth cranial nerve palsy is the most common cause of hypertropia in children. The fourth cranial nerve travels from the brainstem to a muscle on the eye’s surface called the superior oblique muscle.
The nerve sends impulses to the muscle, which controls the downward movement of the eye. When the fourth cranial nerve is paralyzed (palsy) or weakened, it cannot control the superior oblique muscle properly. This causes the eye to tilt upward.
A child may be born with a weakened or paralyzed fourth cranial nerve or develop it after head trauma, such as a concussion.
Brown syndrome is a condition that causes a tight upper oblique tendon. That, in turn, restricts eye movement. Doctors are not sure what causes the syndrome, but it is commonly seen at birth.
It is also possible to get Brown syndrome after an injury to the eye socket, such as being struck by a hard object or from dental or sinus surgery.
This is another strabismus problem that people can be born with. One of the cranial nerves may not generally develop for reasons that are not entirely clear. This restricts the movement of the eye muscle.
Causes of hypertropia in adults
Causes in adults are different from causes when first seen in childhood.
A neurological event, such as a stroke, is the most common reason adults experience an eye roll, such as hypertropia.
A blood clot that causes a stroke can also damage the nerves that help control eye movement.
According to the National Stroke Association, two-thirds of people who experience a stroke find vision changes afterward.
Graves’ disease is an autoimmune disease that attacks the thyroid gland. An autoimmune disease is when your body’s immune system fights against healthy cells.
Damage to the thyroid gland can affect the muscles of the eyes and cause them to function incorrectly.
Lesions in the bones of the eye socket can cause strabismus, such as hypertropia. Cataract repair surgery can also cause this condition, although this is rare.
A brain tumor can pressure the nerves and muscles of the eye and cause the eyes to become misaligned.
Defects associated with hypertropia
Refractive errors such as hyperopia and anisometropia can be associated with patients with vertical strabismus. Lack of vertical coordination between the two eyes can lead to:
Strabismic amblyopia (due to deviating eye deprivation/suppression), cosmetic defect (most noted by parents of a young child and in photographs), and Face turn, depending on the presence of binocular vision in a particular gaze.
Diplopia or double vision, most seen in adults (maturity/plasticity of neural pathways) and suppression mechanisms of the brain to classify the images of the two eyes.
Cyclotropia is a cyclotorsional deviation of the eyes (rotation around the visual axis), mainly when the root cause is a paresis of the oblique muscle causing the hypertropia.
Diagnosis of hypertropia
Hypertropia is best treated by an eye doctor, ophthalmologist, or optometrist. Your doctor may ask about your family’s medical history and if you have had any eye trauma. They will then perform various eye tests.
For example, you may be asked to read from an eye chart, or your doctor may shine a light on your pupils to see how they reflect light.
If your doctor suspects something like a brain tumor, they will order imaging tests, such as a CT scan or MRI, to visualize internal organs.
Ocular deviation tests to evaluate hypertropia
A light source in front of the examiner is directed at the patient’s eyes, while the patient is asked to fixate the light source directly.
The corneal light reflection is observed. The Hirschberg test is considered normal when the corneal light reflections are slightly off-center nasally (around 5º, due to the kappa angle).
In the case of hypertropia, the light reflection of the deviating eye lies below the light reflection of the fixing eye. The amount of deviation can be roughly estimated by multiplying the deviation millimeter by 15PD.
This test uses prisms to complement the Hirschberg test. The prisms are placed in front of the deviated eye, base down in the case of hypertropia, and progressively increase until a neutral Hirschberg test is obtained.
It benefits patients who do not cooperate reasonably in the previous test, especially with low vision.
Cover / discover test
When done correctly, the cover / uncover test allows the diagnosis of tropias. To accomplish this, the physician needs to briefly cover the eye that is being fixed and see if there is a refixation movement of the other eye.
In the case of hypertropia, the non-fixating eye moves downward as it requires fixation. If no refixation is seen, the other eye may be the fixation eye, which is covered, and the test is performed again.
The cover must be concise, as a prolonged cover will break the binocular fusion and cause a possible phobia that can be misinterpreted as a-tropia.
A pure euphoria will not have a positive cover/discovery test, while a trophy will also be associated with a positive alternative cover test.
A simultaneous test of the prism cover
A test can estimate the angle of deviation attributable to a tropia. The amount of pupil distance that must be added to reverse refixation movements in the deviated eye corresponds to the deviation angle.
This should not be confused with the alternate prism cover test for correcting a component of the physiognomy, in which case the binocular fusion is interrupted.
In the case of incomitant strabismus due to muscle paresis or restrictive syndromes, a prism is placed over the eye with limited ductions to measure primary deviation, and a second prism is placed in front of the good eye to measure secondary deviation.
The deviation is always more significant when the eye with limited ductions is fixed (i.e., the prism is over the normal eye).
Four Worth Light Test (Worth’s Dot W4LT abbreviation)
It allows the diagnosis of diplopia and suppression. A different light filter is placed in front of each eye, a green light filter and a red one. The patient is asked to look at four different points:
Two green dots on each side; a red dot at the top; a white point at the bottom form a cross.
The green points can only be seen with the naked eye with the green light filter, and the red point can only be seen with the red filter, while the white point can be seen with both eyes. If the patient sees five lights instead of 4, diplopia is present.
If the lights seen by one eye are below the expected position, it means that the eye is hypertrophic (the image is projected in the upper retinal quadrants, which perceive the lower visual fields). If the patient sees fewer than four lights, suppression is present.
Red filter test
The same principle as the Worth dot test, but with only a light source and a light filter (red) in front of the eye to examine.
The patient seeing a pink light is an expected test result. If two lights are perceived, diplopia is present. If the patient only sees a white light, the suppression of the eye with the red filter is present.
Maddox bar test
A Maddox bar is placed in front of each eye while the patient is asked to look at a light source. In this way, each eye will only see a linear line of light.
To test a vertical tropia, Maddox rods must be positioned to create 180 ° stripes. If one streak is perceived below the other, there is hypertropia/euphoria.
Since the Maddox rod test is highly dissociative, it does not allow a differential diagnosis between a phobia and a tropia.
Bagolini Striated Glasses Test (BSGT)
This test is very similar to the Maddox rod test, except that Bagolini’s fluted lenses allow the better vision of the peripheral visual field, giving more binocular clues.
This way, there is less dissociation, and a better distinction is possible between a small suppression scotoma with peripheral fusion and a large suppression scotoma.
A laparoscopic test is a test where different images are presented to each eye, independent of each other, and can move freely. A synoptophore is an example of a laparoscopic test.
In the case of sinoptophore, the patient is asked to look inside each arm with the corresponding eye while the arms move freely and present different images in the right and left eyes.
The subjective angle is the angle between the two arms, where the patients perceive that the images merge; that is, binocular vision is obtained.
The target angle is determined by turning the lights on and off while changing the angle until no refixing movements can be detected. It corresponds to the angle obtained through the test of the cover of the alternative prism.
Differential diagnosis between paresis and an antagonist restriction
Forced Duction Test: if there is a restriction, the forced duction test is positive, whereas a pure paresis allows complete forced ductions.
Saccades of the eye: In the case of a restriction, regular saccades can be observed until the full restrictive range is reached, where it stops abruptly. In the case of paralysis, abnormal saccadic eye movements are observed.
Intraocular pressure: Restrictions can increase intraocular pressure when the eye moves against the restriction.
Cap Fissure: Restrictions can cause the cap fissure to narrow, while a paresis causes the cap fissure to widen.
Bielschowsky head tilt test
It allows differentiating if a vertical deviation is due to a paresis of the vertical rectus muscle or paresis of the oblique muscle. When the head is bowed, extortion and intortion movements are executed.
The superior rectus and oblique muscles are intortors, and the inferior oblique and inferior rectus muscles are extortionists.
When there is a rise in a head tilt, there is an imbalance between the vertical forces, and one of the four twisting muscles is not working correctly.
When there is one side and the side of the head tilt, either the ipsilateral superior oblique or the contralateral inferior oblique is paretic; when there is a result on the contralateral side of the head tilt, the ipsilateral incidence rate or the contralateral sarcoplasmic reticulum is paretic.
Oblique muscle over-actions are associated with an unfavorable head tilt test.
Parks-Bielschowsky three-step test
Which muscle is the culprit? The Parks-three-step test allows for determining which muscle is at the origin of a vertical deviation in cases of individual muscle paresis.
Four different muscles can cause a hypertropia; for example, a right hypertropia can be caused by paresis of a right eye depressor (proper upper rectum, right lower rectum) or a left eye elevator (left lower oblique, sarcoplasmic reticulum, left).
First, the primary gaze position is inspected, determining which eye is hypertrophic.
Second, the doctor has to determine on which side of the gaze the hypertropia increases; for example, if a right hypertropia increases in the gaze on the left side, the right superior oblique or the left superior rectus is affected.
This second step reduces the chances of 2 muscles; either an oblique or a rectus muscle. The third and final test allows the examiner to determine if the rectum or oblique muscle is affected: the bielschowsky head tilt test described above.
The tree-level test is not diagnostic when more than one muscle is affected, or there is a restrictive clause; There are some situations in which a false-positive result can lead to a misdiagnosis:
A paresis of more than one vertical muscle, vertical rectus contracture, previous vertical muscle surgery, skewed deviation, myasthenia gravis, dissociated vertical deviation, and minor vertical deviations associated with horizontal strabismus.
Differential diagnosis between Brown syndrome, superior oblique overcoming, and inferior oblique paresis
Patients with Brown syndrome will have a positive forced duction test, especially in the exaggerated Guyton hardness induction test.
There is a Y pattern in Brown syndrome, while a lambda pattern is present in the superior oblique overhang and an A in the inferior oblique paresis.
To distinguish between inferior oblique paresis and superior oblique hyperactivity, refer to the anterior head tilt test.
To make things a bit more confusing, a Y pattern can also be present when there is aberrant innervation of the lateral rectus in an ascending position or the case of bilateral inferior oblique hyperactivity.
Differential Diagnosis Between Dissociated Vertical Deviation and Inferior Oblique Overcoming
In inferior oblique hyperactivity, there is increased ipsilateral hypertropia in adduction to the contralateral side with a contralateral hypotropia.
When binocular fusion is interrupted, there is hypertropia in adduction and abduction in dissociated vertical deviation without true contralateral hypotropia.
To assess this, the doctor must check for a vertical deviation of the occluded eye while the patient looks both ways. Spielman’s translucent occluders are particularly useful.
One of the main complications of hypertropia in children is amblyopia or lazy eye. When the eyes are misaligned, the brain gets two different visual signals. A signal comes from the straight eye, and a signal comes from the eye upward.
The brain will tend to shut down the signal from the misaligned eye and focus on messages sent from the “straight” or “good” eye.
As such, the weaker eye becomes even weaker, and the stronger eye becomes stronger. The result is an unbalanced vision.
Unbalanced vision can also affect depth perception, or what is known as three-dimensional vision.
The earlier a lazy eye is detected and treated, the better. If temporary vision is not corrected, usually around age 8, lazy eyes can be much more challenging to improve.
Treatment for hypertropia
Your child will not outgrow hypertropia, and the condition will not improve on its own. There are three main treatments for hypertropia. Your doctor may suggest one or all:
Lenses that correct any nearsightedness or farsightedness can help improve the misalignment of the eyes. Also, a prism can be added to glasses to help with eye alignment.
Muscles, including eye muscles, get stronger when they are worked regularly.
Placing a patch over the strong eye for a prescribed number of hours per day will encourage the wearer to use the weaker eye, strengthening it and possibly improving vision.
A trained surgeon can strengthen weak eye muscles and loosen tighter ones to align the eyes. Sometimes there may be an overcorrection, and the surgeries may need to be repeated.
Surgical correction of hypertropia is desired to achieve binocularity, control diplopia, and correct the cosmetic defect.
The steps to achieve the same depends on the hypertropia mechanism and identifying the offending muscles causing the misalignment.
Several surgical procedures have been described that should be offered after a careful examination of the eyes, including a detailed orthoptic examination focusing on disturbances in ocular motility and visual status.
Trained pediatric ophthalmologists from the specialty fellowship and strabismus surgeons are best equipped to handle these complex procedures.