Regardless of subspecialty, all eye care providers will encounter patients with neuro-ophthalmic disorders. Most diseases with potential for rapid vision loss or serious systemic morbidity are neuro-ophthalmic conditions and are often challenging to diagnose. As a result, neuro-ophthalmology represents a source of anxiety and frustration for many providers.
Here are seven practical and easy-to-implement ways for all eye care providers to improve their neuro-ophthalmology diagnostic acumen.
1. Use your color plates. While color-plate testing, such as with the Ishihara color plates, can be useful to evaluate and follow maculopathies and optic neuropathies, they are also great screening tools for simultanagnosia.
Simultanagnosia is a visual-processing disorder marked by the inability to process multiple visual stimuli at the same time. Some elderly patients with vague visual complaints — despite a normal structural eye exam and visual acuity — actually suffer from simultanagnosia. When the symptoms are insidious in onset, they are typically related to neurodegenerative diseases such as Alzheimer disease that predominately affect the posterior brain. Such patients may not show other signs of dementia.
Abnormal color-plate testing in this setting often provides the best clue that the vision loss may be due to a disorder of higher visual processing. Such results should prompt a referral to a neuro-ophthalmologist.
2. Order neuroimaging wisely. One study found that approximately 40 percent of neuroimaging studies performed on patients at an academic neuro-ophthalmology clinic were inappropriate. The most common errors included ordering the wrong study type (usually computed tomography instead of magnetic resonance imaging [MRI]), failing to use contrast and performing incomplete neuroimaging (e.g., a lack of dedicated orbital sequences when needed).
In general, trauma cases excluded, MRI remains the strongly preferred imaging modality for patients with visual complaints. You should always order intravenous gadolinium contrast unless the patient has renal failure. Don’t worry; imaging centers routinely confirm renal function before giving gadolinium. If you are unsure what exact test to order, call your local neuro-ophthalmologist or radiologist to confirm.
Finally, always take the time to list as clearly and precisely as possible the indication for the study. “New onset right cranial nerve 6 palsy” is a much more helpful description to the radiologist than “double vision.”
3. Avoid papilledema pitfalls. Ambulating, coherent patients who walk into your clinic with papilledema very rarely represent a true emergency.
The majority of patients with papilledema can and should wait for an expedited outpatient work-up, starting with an MRI brain with and without IV contrast. Patients with rapid onset of symptoms or known hypercoaguable disorders or who do not fit the typical pseudotumor cerebri demographic (reproductive-age, overweight women) also require a magnetic resonance venography to rule out a dural venous sinus thrombosis that could be missed on an MRI brain. Nonemergent patients who are referred from the eye clinic to the ER for papilledema often have a suboptimal work-up performed.
Signs or symptoms in a patient with papilledema that should prompt immediate referral to the ER include associated fever, mental status changes, other neurologic deficits, meningismus signs, hyperacute onset of intracranial pressure elevation symptoms, rapid severe vision loss or hypertensive crisis.
4. Use fluorescein angiography for giant cell arteritis (GCA). Most eye care providers know what questions to ask and labs to draw (erythrocyte sedimentation rate, C-reactive protein, complete blood count) when working up a patient for GCA.
Fluorescein is another powerful tool in diagnosing GCA. Patients with GCA-associated vision loss often demonstrate markedly delayed and patchy choroidal filling on fluorescein. Choroidal filling times, commonly defined as the time from initial to complete filling of the choroid, lasting longer than 20 seconds are highly suggestive of GCA.
5. Ask the best screening question for GCA. Many cases of GCA are missed initially due to an expedited and sloppy history. Important questions include recent onset of headaches, temple tenderness, jaw claudication, unintended weight loss, neck pain, low-grade fevers and proximal muscle myalgias.
However, jaw claudication is by far the most specific symptom of GCA and should prompt immediate steroid treatment and temporal artery biopsy in any patient who otherwise fits the demographic for GCA. “Do you have jaw pain?” is not an ideal screening question because many patients without GCA have temporomandibular joint disorder, and many patients with GCA and jaw claudication will deny “pain.” “Does your jaw ache or get tired when you eat?” is a much better GCA screening question.
6. Look for an eyelid that won’t stay open or closed. One helpful exam technique that strongly suggests ocular involvement by myasthenia gravis is orbicularis oculi-strength testing. Patients with intermittent ptosis or diplopia who have myasthenia gravis often exhibit prominent weakness or fatigue of the orbicularis oculi muscles.
Patients will not volunteer orbicularis oculi weakness as a symptom, so you must remember to check for it routinely. To check, ask the patient to close his/her eyes tightly. Using your thumb and index finger, attempt to open the patient’s eyelids. Normal patients will offer great resistance, while in myasthenics, the eyelids will often easily open.
7. Beware of severe optic neuritis. Demyelinating optic neuritis (DON) associated with multiple sclerosis typically causes painful subacute vision loss that recovers well within months.
Most patients with typical DON have mild or moderate vision loss. While severe vision loss (less than 20/200) can occur in DON, it raises concern for optic neuritis associated with neuromyelitis optica (NMO) and should prompt consideration of this severe form of demyelinating disease. NMO-associated optic neuritis is more often severe at onset, bilateral, painless and less responsive to steroids than typical DON.
Because up to one-third of optic neuritis patients with vision less than 20/200 are NMO associated, this scenario should prompt serum testing for the NMO anti-aquaporin 4 antibody and evaluation by a neuro-ophthalmologist or neurologist familiar with NMO.
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|About the author: Collin M. McClelland, MD, is a board-certified neuro-ophthalmologist and assistant professor of ophthalmology and visual sciences at Washington University in St. Louis. He is director of medical student education for ophthalmology and is an active teacher in the residency training program.