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Elderly man complains of double vision
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A 78-year-old white male presented to our clinic complaining of double vision. He stated that he awoke 6 days earlier feeling dizzy and experiencing horizontal diplopia, but that the symptoms resolved throughout the day. The diplopia had since redeveloped and become constant, and he felt that his left eye was now turning out. He also reported experiencing memory loss after taking a short nap approximately 1 month prior. He denied any transient vision loss.
The patient’s only reported medical history was a pacemaker placed in 2011, though he was taking aspirin, fosinopril sodium, Norvasc (amlodipine besylate, Pfizer), Synthroid (levothyroxine, Abbott) and ursodiol daily, which indicated that he was also being treated for hypertension, thyroid problems and gallstones. The patient was not a smoker, denied drug or alcohol use and had no known drug allergies. His ocular history was remarkable for bilateral cataract surgery.
Corrected visual acuity was 20/30-1 OD, 20/20-3 OS and 20/20-2 OD with pinhole. IOP was 14 mm Hg OD and 19 mm Hg OS measured with Tono-Pen (Reichert). Pupils were round and equal with no afferent pupillary defect. Anterior segment exam was remarkable for multiple transillumination defects and well-positioned posterior chamber intraocular lenses in both eyes. Dilated fundus exam revealed cup-to-disc ratios of 0.3/0.3 and 0.35/0.35, trace epiretinal membrane in the right eye and mild asteroid bodies in the left eye.
On external exam, the patient’s palpebral fissures measured 9 mm OD and 11 mm OS. In primary gaze, there was a marked exotropia with the left eye. Cover test demonstrated an alternating exotropia (AXT) that measured 24 prism diopters OS when the patient fixated with his right eye and reduced substantially when made to fixate with the left. There was mild restriction in extraocular muscle movement in his right eye when looking up, down and into left gaze (adduction). Ductions were full in the left eye. The Humphrey 24-2 visual field (Carl Zeiss Meditec) performed was unremarkable for neurological field defects.
The differential diagnoses are relatively limited for a complaint of new-onset diplopia in adults. The most likely differentials include palsy of the third, fourth or sixth cranial nerve. Internuclear ophthalmoplegia and decompensated phoria should also be considered.
Third cranial nerve
The third cranial nerve (CN III), or oculomotor nerve, originates in the oculomotor and Edinger-Westphal nuclei located within the midbrain, then travels in close proximity to the posterior communicating artery before passing along the lateral wall of the cavernous sinus, entering the superior orbital fissure and accessing the orbit. The nerve is made up of fibers controlling voluntary motor function for the superior, inferior and medial rectus and superior levator palpebrae muscles, as well as parasympathetic fibers, which play a role in pupillary constriction and run superficially along the nerve, leaving them particularly vulnerable to injury from compressive lesions. Signs of a third nerve palsy include predominantly horizontal diplopia and ptosis, with or without mydriasis.
Top photo shows primary gaze with fixation in the right eye. Bottom photo shows primary gaze with fixation in the left eye.
Ischemic third nerve palsies are often pupil-sparing, especially in early stages. This means that the outer, parasympathetic fibers of the nerve are not involved and, therefore, no changes occur in the patient’s pupillary size or function. Compressive lesions, however, are typically non-pupil sparing, leading to a fixed, dilated pupil in the affected eye. CN III palsies are the cause of the classic so-called “down and out” presentation.
Fourth cranial nerve
Like CN III, the trochlear nerve (CN IV) has its nucleus within the midbrain. It is the only cranial nerve to decussate then exit the brainstem dorsally. The nerve travels through the subarachnoid space, extends through the cavernous sinus and enters the orbit through the superior orbital fissure. It is the thinnest and longest cranial nerve. These characteristics and its dorsal pathway leave the trochlear nerve at increased risk for damage from trauma to the back of the head or brainstem.
Extraocular movements in upgaze, downgaze, right gaze and left gaze.
Images: Fulmer P
Due to its role in controlling motor function of the superior oblique muscle, deficit results in vertical diplopia. Patients will often develop a contralateral head tilt in an attempt to compensate. Fourth nerve palsies are most frequently due to trauma or ischemic vasculopathy, making a thorough history imperative. This diagnosis was not the case for our patient.
Sixth cranial nerve
The abducens nerve (CN VI) begins in the abducens nucleus located in the pons. It makes a tight bend over the petrous ridge of the temporal bone as it travels toward the cavernous sinus and passes lateral to the internal carotid artery prior to entering the superior orbital fissure. Because CN VI controls lateral rectus function, patients with sixth nerve palsy will have horizontal uncrossed diplopia and esotropia or esophoria that will be worse at distance and in right or left gaze. Increased intracranial pressure and internal carotid aneurysms are common causes of CN VI palsy; therefore, imaging of these patients is crucial.
Isolated VI nerve palsy was unlikely in this case.
Internuclear ophthalmoplegia
Internuclear ophthalmoplegia (INO) is a result of damage to one medial longitudinal fasciculus (MLF), which makes excitatory synapses on medial rectus motor neurons when the contralateral abducens nucleus is activated. Patients present with diplopia in horizontal gaze and inability to adduct on the side ipsilateral to the affected MLF. The medial rectus will be able to function when the opposite lateral rectus is not involved, such as during convergence.
This patient’s presentation excluded this diagnosis.
Decompensated phoria
Decompensated phoria is a condition in which a patient is no longer able to fuse a longstanding phoria. Presentation is typically in older patients and worsens with fatigue. Diplopia in this condition can present as horizontal, vertical or diagonal.
The sudden onset nature of this case, coupled with the clinical findings, made the diagnosis of decompensated phoria doubtful.
This patient’s management
In this case, the patient was experiencing an early third nerve palsy in the right eye. The apparent left exotropia initially suggested a problem with the left eye. However, his left eye was able to demonstrate full motility, while the right eye was restricted in upgaze, downgaze and adduction. In addition, right upper lid ptosis was present. Strain induced by use of the weakened third nerve when fixating with his right eye caused the patient to develop an overshoot in his left eye, perceived as a left exotropia.
Early CN III palsies are likely to progress before resolving, causing the patient to become alarmed if not made aware of this probability. Therefore, patient education is paramount. Progression in this patient resulted in full lid ptosis and severe EOM restriction in the right eye within 1 week of initial presentation. Pupil involvement remained absent as of last follow-up.
In any third nerve palsy, it is important to discern whether the etiology is compressive or ischemic. Lack of pupil involvement suggested that this case was likely ischemic. Additionally, the patient’s report of a previous memory loss event supported the likelihood of an overall systemic problem with blood flow.
Regardless, a scan of the head and orbits was ordered to evaluate for lesions or other compressive abnormalities, such as an aneurysm. While MRI/MRA is preferred, a CT was required due to this patient’s pacemaker. Blood work was ordered to assess markers for systemic inflammation, infection or other contributory factors such as diabetes.
The patient’s ANA and HLA-B27 returned positive, and his lipid panel was slightly elevated. The rest of his blood work was normal, including his HbA1C. His CT revealed a remote lacunar type infarct in the left basal ganglia, no intracranial abnormality and no abnormal enhancement.
After receiving these results, a carotid Doppler was obtained, which returned normal, with less than 39% stenosis in each artery. A referral to rheumatology, neurology and cardiology was made to further investigate the ischemic event, leading to identification of an MTHFR mutation. A hematology consult was recommended secondary to increased risk of aneurysm in some patients with an MTHFR mutation. Results of this consult are pending.
Three months after onset, efforts are still underway to identify the root of this patient’s ischemia. He is showing marked overall improvement, and patching is successful when his diplopia is bothersome. In most ischemic third nerve palsies, significant to full resolution is seen within 3 to 6 months. If this does not occur, imaging should be repeated to re-evaluate for compressive lesions.