Superior Oblique Paresis;
Inferior Oblique Overaction;
Fourth Nerve Palsy;
Wray, Shirley H.
Shirley H. Wray, MD, PhD, FRCP, Professor of Neurology, Harvard Medical School; Director, Unit for Neurovisual Disorders, Massachusetts General Hospital
Superior Oblique Paresis;
Inferior Oblique Overaction;
Fourth Nerve Palsy;
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The patient is a 64 year old engineer who noted whilst driving around Thanksgiving time double vision with one image on top of the other.
Vertical double vision persisted and he was referred to the Massachusetts General Hospital for evaluation.
1991 Hyperthyroidism with Graves’ Disease treated with radio active iodine.
1989-1990 Writer’s cramp treated with botulinium toxin injection
1989 Cancer of the colon, status colonectomy.
No previous episodes of diplopia
No strabismus as a child or need to wear prism glasses
No history of head or eye trauma
Synthroid 600 mg
Positive for diabetes
Mother died cancer of the ovary
Visual acuity 20/20 OU corrected
Visual fields, color vision, pupils and fundus examination normal.
Tests for diplopia showed:
Left (contralateral) head tilt
Good stereopsis in primary gaze 6/9 circles.
Hypertropia OD primary gaze
Hypertropia most marked with right head tilt
Hypertropia diminished, almost absent, left head tilt
Hypertropia almost fully corrected with prism glasses at distance.
Exophthalmometry 23 OU base 97 normal orbital resilience.
Ocular Motility OD:
Hypertropia and excyclotorsion
Superior oblique (SO) paretic
Inferior oblique (IO) overaction with elevation of the globe looking left.
Cranial nerves 3 and 6 normal
Ocular Motility OS:
Full eye movements
Hypotropia on cover/uncover test
CT of the Orbits 1/17/92:
Study showed enlargement of the inferior rectus muscle bilaterally and the right medial rectus muscle attributed to earlier Graves’ disease in the past associated with hyperthyroidism.
Brain MRI showed:
Calcification of the wall of the carotid siphon and changes consistent with small vessel microangiopathy.
The patient was tested with two Maddox rods and found to have an 8 diopter right hyper with the right eye extorted approximately 5 diopters in primary position. Diagnosis fourth nerve palsy, presenting in a somewhat unusual manner, possibly modified by his early Graves’ disease and persistent enlargement of the inferior recti OU and the medial rectus muscle OD.
Right fourth nerve palsy
Mild thyroid associated orbitopathy
Strabismus surgery was not recommended.
He returned in June 1992 and annually until July 1996 with no change in ocular motility.
This tape records the “diplopia” history. The patient answers a list of specific questions with regard to his vertical double vision from a right fourth (trochlear) nerve palsy. He had no diplopia with one eye covered confirming binocular diplopia.
With a history of vertical diplopia, attention is paid to the ocular muscles controlling vertical gaze.
• SO: Paresis SO resulted in impaired downgaze in the adducted position with absent incyclotorsion of the eye
• IO: Overaction of IO with elevation of the eyeball on gaze left, in the adducted position
Alternate cover test:
OD moved down to take up fixation (hypertropia)
OS moved up to take up fixation (hypotropia)
Review of old photographs showed that he had a longstanding left head tilt which helped establish the chronicity of the fourth nerve palsy.
The Three-Step Test aids in establishing the diagnosis.
Step 1 – Identify which eye is hypertropic e.g. hypertropia OD.
Step 2 – Determine whether the hypertropia increases on right or left gaze
Step 3 – Bielchowsky’s head tilt test: Tilt the head to the right and to the left. Hypertropia is maximized as the head is tilted toward the side of the lesion and minimized on contralateral head tilt, as in this case.
The most reliable clinical test to diagnose fourth nerve palsy is the Bielchowsky’s head tilt test. During right head tilt, the right eye incyclotorts (SO and SR), and the left eye excyclotorts (IO and IR) During left head tilt, the right eye excyclotorts (IO and IR) and the left eye incyclotorts (SO and SR).
The question always asked is why does the hypertropia increase on right head tilt in right fourth nerve palsy.
The explanation is as follows:
During right head tilt, the otolith-ocular reflex (ocular counter roll) is activated, such that the right eye incyclotorts (SO and SR) and the left eye excyclotorts (IO and IR).
The primary action of SO is incyclotorsion, and its secondary action depression, whereas the primary action of SR is elevation and its secondary action is incyclotorsion. Thus, normally, during the right head tilt, the net movement of the right eye is incyclotorsion with minimal vertical movement because the vertical action of the SO and SR cancels each other out.
In right fourth nerve palsy, the elevating action of SR is unopposed by the palsied SO; thus, the hypertropia increases during right head tilt.
1. Skew deviation
2. Thyroid-related ophthalmopathy
3. Brown’s Syndrome
4. Primary inferior oblique overaction
No imaging studies are available in this patient.
In patients who lack a history of head trauma, Brain MRI may show relevant brainstem lesions and gadolinium enhancement usually demonstrates infiltrative or inflammatory processes involving the long course of the fourth nerve.
Often the cause of the fourth nerve cannot be ascertained and these patients require long term follow-up.
The nucleus of the fourth (trochlear) nerve lies at the ventral border of the periaqueductal gray matter at the level of the inferior colliculus in the brainstem. It lies at the dorsal margin of the medial longitudinal fasciculus.
The fascicle of the fourth nerve crosses the midline at the anterior medullary vellum (anterior floor of the fourth ventricle, before exiting the brainstem) thus, the right fourth nerve fascicle becomes the left fourth nerve which innervates the left superior oblique muscle.
The fourth nerve is the only cranial nerve that exits the brainstem on the dorsal surface and it has the longest intracranial course (approximately 75mm).
In the subarachnoid space the nerve curves around the lateral surface of the upper pons, passing between the superior cerebellar and posterior cerebral arteries to reach the prepontine cistern. It then runs forward on the free edge of the tentorium for 1 to 2 cm before penetrating the dura of the tentorial attachment and entering the cavernous sinus.
Within the lateral wall of the cavernous sinus, the nerve lies below the third cranial nerve and above the ophthalmic division (V1) of the fifth (trigeminal) nerve. It then crosses over the third nerve and receives filaments from the carotid sympathetic plexus.
To reach the orbit the nerve enters through the superior orbital fissure above the annulus of Zinn. In company with the frontal and lacrimal branches of the ophthalmic division of the trigeminal nerve. It divides into several small fascicles that innervate the superior oblique muscle.
Trauma is the commonest cause of a fourth nerve palsy. Head trauma can result in a contusion or hemorrhage of the tegmentum at the junction of the midbrain and pons. Because of the short course of the fourth nerve fascicle in the brainstem, distinguishing a nuclear from a fascicular fourth nerve palsy is virtually impossible.
Damage to the descending sympathetic fibers from the hyperthalamus in the dorsal brainstem, causes a Horner’s syndrome, and lesions of the trochlear nucleus or fascicle may be accompanied by a Horner’s syndrome. For example, a right sided midbrain lesion causes damage to the right trochlear nucleus (resulting in a left fourth nerve palsy) and damage to descending sympathetic fibers results in a right Horner’s syndrome.
If the lesion affects the fascicle of the fourth nerve as it crosses the midline, then the Horner’s syndrome is on the same side as the fourth nerve palsy.
Fourth Nerve Palsy; Graves Orbitopathy
2. Prism glasses
3. Strabismus surgery only after the palsy has been stable for at least six months using one or a combination of the following procedures:
a) Weakening of the ipsilateral inferior oblique (the antagonist of the affected superior oblique)
b) Weakening of the contralateral inferior rectus (the yoke muscle of the affected superior oblique)
c) Strengthening the affected superior oblique