Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
Ophthalmologic evaluation of idiopathic intracranial hypertension
Introduction
The term idiopathic intracranial hypertension (IIH) was first introduced by Corbett and Thompson in the late 1980s, nearly 100 years after the disease was first identified. By definition, IIH refers to intracranial hypertension in the absence of all secondary causes, including intracranial or spinal neoplasms and non-neoplastic causes such as trauma, intracerebral thrombosis or vascular malformations, infections, or medications. Although the pathogenesis of IIH remains unclear, disordered cerebrospinal fluid (CSF) dynamics such as hypersecretion and outflow obstruction and increased venous sinus pressure have been implicated. The strong association between weight gain and IIH is not completely understood, but hormonal, metabolic, and mechanical factors have been implicated most recently. National data from the United Kingdom suggest a rising rate of IIH over the past 20 years, with nearly doubling of the prevalence between 2002 and 2016.
A complete ophthalmic examination is required in patients with a documented or suspected IIH diagnosis because of its high potential for visual morbidity. Visual symptoms occur in more than 90% of patients with IIH and result in blindness in 5% to 10%. , Timely ophthalmic examination can prevent misdiagnosis of IIH, which may occur in up to 25% of patients, and can aid in identification of potential vision-threatening complications. Although papilledema is the most common ocular feature of IIH, it need not be present in all patients with IIH, and it may be accompanied by many other ocular findings, including cranial nerve palsies, retinal and choroidal findings, optic disc pallor, or hemorrhages. Some patients with IIH report other ocular symptoms that lack structural correlates, including photophobia and eye pain.
Patient history
Evaluation of a patient with suspected IIH begins with a thorough history, medication review, and physical examination. Patient demographics can raise suspicion for IIH, with female gender, obesity, and weight gain being strong epidemiologic risk factors for this condition ; however IIH can also occur outside of these demographics. The largest rigorous study of patients with IIH occurred during the IIH Treatment Trial (IIHTT), which assessed symptoms in 165 patients with IIH and mild vision loss, finding headache to be the most common symptom in IIH, occurring in 84% of patients. Headache in IIH is highly variable in character but is often migraine or tension-like, and may be positional and worse in the morning. Tinnitus (pulsatile and nonpulsatile), dizziness, neck and back pain, and cognitive disturbances are other common symptoms identified in patients with IIH. In the IIHTT cohort, the most common visual symptom was transient visual obscurations, lasting for seconds and then resolving, which occurred in 68% of patients. Dimming or blacking out of vision may occur in one or both eyes, often during Valsalva maneuvers or postural changes. Other visual symptoms experienced less often include periodic sparkling or flashing, photophobia (48%), diplopia (18%), and vision loss (32%). Patients may complain of nonspecific eye pain or pressure, although this is likely to be more related to headache than an intrinsic ocular issue. Although most patients with IIH have subtle symptoms, visual or other neurologic, it is important to note that some patients are asymptomatic and diagnosed incidentally at the time of eye examination or neuroimaging for other reasons. For this reason all patients, with or without visual symptoms should undergo a thorough ophthalmic evaluation.
Finally, a thorough review of past medical history and medications can also be useful to identify possible secondary causes of increased intracranial pressure (ICP). Several commonly used medications, including tetracyclines, vitamin A, lithium, and corticosteroid withdrawal, have been demonstrated to increase ICP. In addition, various medical conditions, including thyroid disease, sleep apnea, anemia, and chronic respiratory disease, have also been associated with increased ICP.
Ocular examination
After a thorough patient history, ocular examination should be initiated. In the ideal circumstance, this examination should be conducted in an ophthalmic clinic setting with the availability of a slit lamp to facilitate careful anterior and posterior examination of the eye, particularly of the optic nerve. Although moderate to severe papilledema can be identified using standard ophthalmoscopy, more subtle disc edema is more readily appreciated with a stereoscopic view of the nerve. In addition, access to clinic-based examination facilitates important ancillary testing that allows assessment structure and function of the optic nerve and retina. The ocular examination in IIH should involve standard components that are done for all patients, including visual acuity (VA), confrontational visual fields, extraocular motility, careful pupillary examination, and intraocular pressure (IOP) measurement. Additional examination components that are useful in patients with known or suspected IIH include measurement of color vision and assessment of other cranial nerves, as well as select ancillary testing.
Visual acuity, color vision, and intraocular pressure
Although changes in VA typically only occur in advanced cases of IIH, an ophthalmic examination in any patient with IIH begins with distance VA measurement. When possible, the patient should undergo refraction to obtain best corrected VA because early visual changes in IIH may be subtle and can be missed without refraction. When refraction is not possible, as in the emergency department or inpatient settings, the patient’s current spectacles or a pinhole can be used. Although measurement of distance VA is preferred, there are cases when this is not feasible as in nonambulatory patients, and a near card can be used to obtain near VA in these cases. It is important to remember to utilize a reading aid in patients older than 40 years of age because of the high prevalence of presbyopia in this age group. Color vision, most commonly assessed using Ishihara plates, can indicate subtle optic nerve damage and should be checked at presentation and follow-up in all patients with IIH.
There are currently no convincing data to support a clinical correlation between ICP and IOP. , Despite this, measurement of IOP is an important part of a comprehensive eye examination in IIH patients because IOP elevation, like IIH, can also have effects on the optic nerve, possibly complicating the diagnosis or monitoring of IIH patients. Glaucoma, the most common cause of raised IOP, can lead to optic disc pallor or optic disc hemorrhages, both of which can also be seen in patients with chronic or resolved IIH. Furthermore, glaucoma, like IIH, can cause peripheral vision loss on confrontation and on automated perimetry. Knowledge of these ocular comorbidities is important to facilitate accurate diagnosis and appropriate metrics for patient-specific monitoring.
Pupillary examination
All patients with a suspected or confirmed IIH should have a thorough pupillary examination. In cases of IIH, pupillary size and symmetry are preserved; anisocoria should raise concern for an alternate intracranial processes. The swinging flashlight test is used to assess for the presence of a relative afferent pupillary defect (RAPD), which, when present, indicates asymmetric optic nerve disease. To perform this test, a bright light is swung between the two eyes ( Fig. 18.1 ). In a healthy individual, pupillary constriction occurs as the light is shone on either eye, but individuals with optic nerve disease have paradoxical dilation in the affected eye as the flashlight is swung back and forth. It is important to understand that severe optic nerve damage that is relatively symmetric does not cause an RAPD; therefore, the absence of an RAPD does not rule out symmetric optic nerve damage.
Confrontation visual field examination
Visual field changes are often the first sign of functional damage in IIH, and the importance of visual field examination and monitoring in IIH patients should be underscored. Visual field changes in IIH range from enlarged blind spot, scotomas, altitudinal changes, or constriction of isopters. However, confrontation visual fields, performed monocularly by presentation of fingers in different quadrants either simultaneously or individually, despite being a standard component of the ocular examination, have poor sensitivity for detection of subtle visual field changes, making them a poor screening test. When formal visual field examination cannot be obtained (e.g., in hospitalized patients or those in whom positioning issues preclude testing), different types of confrontation visual field tests can be combined to improve the sensitivity of bedside testing.
Cranial nerve and ocular motility examination
A thorough motility examination can help identify IIH-related cranial nerve palsies and other preexisting disorders of extraocular movement and alignment. Cranial nerve VI palsies are the most common cranial nerve palsy in IIH patients, occurring in up to 12% of adults with IIH and up to 48% of pediatric IIH patients. Cranial nerve VI palsies present with binocular (occurring only when both eyes open, disappearing with either eye covered) horizontal diplopia worse at distance and can be unilateral or bilateral in nature. Other cranial nerves have been described in patients with IIH, albeit rarely, and the presence of an additional cranial nerve palsy should raise suspicion for a secondary cause for increased ICP. Cranial nerve III, IV, VII, IX, and XII palsies have been described in patients with IIH. Other ocular motility disorders such as intranuclear ophthalmoplegia, ophthalmoplegia, and nystagmus have also been described. Although their pathogenesis in IIH is not completely understood, traction at the level of the brainstem or cranial nerve is thought to be the cause.
It is important to note that ocular misalignment does not necessarily indicate the presence of a cranial nerve palsy. Patients may have longstanding tropias that are manifest (usually reported on history) or phorias that can decompensate acutely during times of medical instability or in cases of profound vision loss in one or both eyes. However, cranial nerve palsies typically produce incomitant deviations that vary significantly in different directions of gaze, in which long-standing tropias and phorias are typically comitant, remaining roughly similar in magnitude in different directions of gaze. A notable exception is bilateral cranial nerve VI palsy, which can rarely present as a comitant esotropia without obvious abduction deficits (“divergence paresis”), which can be indistinguishable from a congenital esotropia in children other than its resolution with normalization of ICP.
You're Reading a Preview
Become a Clinical Tree membership for Full access and enjoy Unlimited articles
If you are a member. Log in here