diplopia Flashcards
TAO
When associated with vision loss, thyroid associated orbitopathy requires immediate action (2/2 enlarged EOM compressing ON at orbital apex).
Medical management: steroids to decrease extraocular muscle swelling.
Surgical management: orbital decompression surgery to remove one, two, or three walls of the orbit thereby expanding the orbital space. Often times steroids are a temporizing measure to prevent further optic nerve decline while surgical decompression is planned.
TFT’s would be obtained before starting steroids as this would help guide future management. These values, to include TSI need to be known, and eventually knowing their value (even if pending) is important. Steroids may alter TSI values.
Myasthenia
Myasthenia gravis can cause “pseudo eyelid retraction” which is actually a consequence of Herring’s law of equal innervation. In a patient with pseudo eyelid retraction, the apparently normal superior eyelid is actually ptotic. In an effort to elevate a weak, ptotic eyelid, both eyelids provide additional innervational input. The increased effort raises the ptotic eyelid to a normal level while raising the normal eyelid to a retracted position. If this patient had pseudo retraction of the left eye then manually elevating the right eye would cause the left eye to drop down to a normal or ptotic position (“eye lid curtaining” sign).
INO
All of the answer choices are findings of internuclear ophthalmoplegia (INO) but the only finding that MUST be present for the diagnosis is a slow adduction on the affected side as compared to abduction velocity of the contralateral eye. This may be the only finding in subtle or partially-resolved INO. By convention, laterality of INO is based on the eye with slowed adduction (i.e. a right INO results in lag of adduction in the right eye). A right INO may result in left beating nystagmus in the left eye when looking to the left (aka “abducting nystagmus”).
one and a half
One-and-a-half syndrome combines the features of internuclear ophthalmoplegia (INO) with an ipsilateral horizontal gaze palsy.
In this case, a RIGHT one-and-a-half syndrome would result in impaired adduction OD (due to the right INO) as well as impaired abduction OD and impaired adduction OS (due to the right gaze palsy). The only horizontal eye movement left (“the half”) is abduction of the LEFT (contralateral) eye. This contralateral eye would classically display an abduction nystagmus as typically occurs in an INO.
This syndrome is classically caused by a stroke or other lesion of the PONS region which contains the medial longitudinal fasciculus (MLF) and paramedian pontine reticular formation (and CN VI nucleus). Vertical gaze is unaffected in this syndrome.
This contralateral eye would classically display an abduction nystagmus as typically occurs in an INO.
MLF lesion
Most people know that a lesion of the MLF causes an ipsilateral INO. You must also know, however, that a lesion of the MLF often causes a skew deviation in addition to an INO.
Vestibular and cerebellar input (through the vestibular nuclei) project to the 3rd and 4th nerve nuclei to coordinate vertical gaze. This vestibular / cerebellar input also travels through the MLF (along with the interneurons connecting CN III and 6).
A lesion of the MLF, therefore, often causes both INO and a skew deviation. In case you are unclear on the topic, a skew deviation is a vertical strabismus that can be comitant or incomitant. There are many different presentations of skew deviations but when caused by a MLF lesion, the hypertropic eye is located on the side of the lesion.
Gaze palsy
A gaze palsy to one side means that BOTH eyes have limited motility to that side. For instance, a complete left gaze palsy means that the right eye is unable to adduct past midline and the left eye is unable to abduct past midline. A lesion of the CN6 nucleus or PPRF would be expected to cause an ipsilateral gaze palsy. A severe INO often causes an inability to adduct the eye on the same side as the lesion; the lack of adduction in one eye is NOT the same as a gaze palsy.
GCA
Giant cell arteritis (GCA) is a source of anxiety for ophthalmologists because it has a wide assortment of presentations and is often visually devastating if not diagnosed and treated early. The majority of GCA cases present with arteritic anterior ischemic optic neuropathy although less common presentations include posterior ischemic optic neuropathy, central retinal artery occlusion, branch retinal artery occlusion, choroidal infarction, and diplopia from ischemia of the extraocular muscles and/or ocular motor nerves.
GCA is a high yield topic for standardized tests and should always be on your radar when test taking (or seeing patients in clinic for that matter). Any elderly patient with new onset headaches and transient vision loss episodes should be evaluated carefully for GCA. In such a patient, findings of profound choroidal filling abnormalities (shown in FA above) are HIGHLY suggestive of GCA.
Varicella zoster virus
Varicella zoster virus is a great mimicker and can cause ocular motor palsies, choroidopathy with choroidal filling abnormalities, and anterior ischemic optic neuropathy. The vast majority of VZV-related ocular and orbital sequelae occur in concert with or following an ipsilateral, painful vesicular facial rash, however. Case reports of VZV vasculitis without rash mimicking GCA exist in the literature but are exceedingly rare and would be unlikely to show up on a standardized test.
TAO
Thyroid usually causes HyPOtropia and Esotropia on affected side.
Ocular neuromyotonia
- rare cause of episodic diplopia lasting typically 30-60 seconds
- prior brain radiation (usually skull-base for meningioma)
- occurs months to years later s/p initial insult
- spasms of some or all muscles supplied by cranial nerves 3, 4, or 6, It is thought that this is due to tonic discharges of the offending cranial nerve related to some sort of prior insult (radiation, surgery, etc)
- Rx: carbamazepine
oculomotor apraxia (may not have diplopia)
- def: inability to initiate voluntary saccades
- congenital oculomotor apraxia - these pts use horizontal head thrusts past the points of interest
- acquired: bilateral lesions of the supranuclear gaze pathways of the frontal and parietal lobes, such as from bilateral strokes
- pts may blink to break fixation, then turn their head to fixate on something else
- pursuits: relatively unaffected
PSP
downward gaze affected (smaller and slower)
saccades affected more than pursuits
slow volitional saccades, but reflexive saccades (saccades directed towards an unanticipated target) are often initially normal
skew deviation
-def: vertical misalignment of gaze that cannot be assigned to a single nerve or muscle weakness
-with INO: hypertrophic eye often on SAME SIDE as adduction deficit (MR dysfxn),
Skew deviation (SD) is admittedly confusing, but a few simple concepts will help clarify the entity. SD is a supranuclear disorder caused by a disruption of vestibular input (from the utricle and semicircular canals) to the brainstem nuclei responsible for vertical eye movement (CN III and IV). SD arises from either cerebellar or brainstem pathology but is difficult to more accurately localize.
SD can result in comitant or incomitant vertical deviations which can complicate diagnosis. For unclear reasons, SD often manifests as weakness of the inferior rectus muscle(s). Skew deviation presenting with bilateral inferior rectus weakness presents with alternating hypertropia as detailed in the question, often localizes to the cervicomedullary junction, and can be associated with downbeat nystagmus.
Alternating hypertropia can occur in bilateral CN IV palsies but in that case there would be hypertropia of the adducting eye (not abducting eye) so that there is a right hypertropia in left gaze and a left hypertropia in right gaze. This occurs because superior oblique weakness is most evident in the adducted position while inferior rectus weakness is most evident in the abducted position.
CN III palsy (especially a partial CN III palsy with superior and inferior rectus weakness) can result in a hypertropia that alternates with up-gaze and down-gaze. With a partial right CN III palsy, for instance, there may be a left hypertropia on up-gaze and a right hypertropia on down-gaze.
Bilateral inferior rectus restriction can occur with thyroid associated ophthalmopathy and would cause a left hypertropia on right gaze and a right hypertropia on left gaze.
Isolated ischemic cranial neuropathy
The classic teaching (what you should use on the test) is that neuro-imaging is not necessary in these patients assuming the aforementioned features are present because the yield is very low. There is now, however, controversy on the issue because some clinicians will immediately perform neuro-imaging on patients with isolated 3rd, 4th, or 6th nerve palsies that are clinically consistent with microvascular palsy. The MRI is expected to be normal in all patients with 3rd, 4th, or 6th microvascular palsies but some argue that observing clinically apparent microvascular palsies will result in missed diagnoses in 10-14% of cases.
In general, 6th nerve palsies cause horizontal binocular diplopia that is worse at distance. This makes sense considering the eyes converge at near so less abduction is necessary to maintain alignment.
Restriction strabismus (vs paretic strabismus)
Restriction strabismus is difficult to distinguish from paretic strabismus based on extraocular motility alone. Techniques to confirm restriction include forced duction testing with cotton swabs or forceps and the aforementioned comparison of IOP in primary gaze and gaze away from the restricted muscle.
