Because the eye is an extension of the central nervous system, a neuro exam can lead to a vital diagnosis. Just ask Patricia Modica, O.D., F.A.A.O., clinical professor at SUNY College of Optometry.

“There are two incidences, in particular, in which a neuro exam can be incredibly helpful,” she explains. “The first is getting to the bottom of why a patient has VF loss. The second is when a patient presents with a cranial nerve palsy that affects the muscles of the eye. Determining whether these issues are problems with the nerve itself or nerve damage that occurred from the brain is critical in finding out the precise problem and, therefore, the most appropriate management.”

Something else to keep in mind: A brain-related visual impairment, initially thought of as rare in children, may actually affect one in every 30 children, reports a Feb. 3 study in Developmental Medicine and Child Neurology.

What follows is a discussion of the importance of the neuro exam and how to make it successful.

NEURO EXAM IMPORTANCE

Andrew G. Lee, M.D., chair of ophthalmology at Houston Methodist Eye Associates, ophthalmology at the Blanton Eye Institute, Houston Meth­odist Hospital, says neuro exams are important in ruling out whether something is an emergency — a critical obligation of the primary eye care practitioner.

“Key features of an emergent condition are acute and painful,” he says. “The combination of these two symptoms with any neuro-ophthalmic find should lead to prompt consideration that the hospital is the next step.”

Dr. Lee adds that past medical history comes into play, as the patient could present with an acute, painful and droopy eyelid or an acute, painful loss of vision.

“If the patient has a history of cancer, it should always be considered that these new symptoms are cancer until proven otherwise,” he says, as an example. “An emergency case might come to the eye doctor first because the chief complaint is something with their eye. It’s the doctor’s responsibility to recognize when it’s something else, even if they’re not the one making the ultimate diagnosis.”

John J. O’Donnell, O.D., of Harrisburg Premier Eye Care Group and a diplomate in the glaucoma section of the American Academy of Optometry, agrees that patient history is of critical importance. He cites it as the first step in any exam and the catalyst for possibly performing a thorough neuro exam in the first place. Does the patient have vision loss and if so, is that loss monocular or binocular? Also, does the patient have a history of double vision? Is there a patient history of headaches or a family history of stroke? Dr. O’Donnell says patient history questions can help set the diagnosis on the right track and determine whether the case could be an emergency.

He advises doctors also need to be clear about what their patients describe as “double vision,” as he’s often found that what patients are actually experiencing is blurred vision — something that can send the doctor on a different diagnostic path.

“True double vision goes away when you cover one eye,” he says. “If it doesn’t go away, it’s monocular diplopia — usually refractive in nature — and not a neuro eye disease.”

Following patient history, a vision check and a pupillary exam are important.

As a glaucoma specialist, he says that one of the best — but most-under-used — tests is a recheck of color vision. He says he has seen many patients who have been diagnosed with glaucoma but actually have another form of optic neuropathy, such as anterior ischemic optic neuropathy.

“Vision loss from glaucoma is not likely to have color loss, so if the patient has color vision loss, it may be optic nerve disease,” he says.

Glaucoma misdiagnoses are a concern during a neuro exam. Dr. O’Donnell says that the classic understanding that optic nerve cupping is a definite glaucoma diagnosis is problematic. Many practices still use the rudimentary rule that cupping means glaucoma, but Dr. O’Donnell says you must walk through the entire checklist of tests. Taking too quick of a leap in diagnostics can be a serious misstep.

Dr. Lee agrees. “The most common cause of VF loss is slow, progressive glaucoma,” he says. “But in some cases, a diagnosis can look like glaucoma when it’s really not. There are some red flags that should make the doctor question this. The most common is when the VF does not match the cupping in the nerve. In addition, most are not nasal, so if we have a temporal defect, it should raise a red flag. We have to have a structure and function map between cupping, nerve damage and the VFs.”

Dr. Lee says that the speed of the VF loss is also key. If it’s unilateral and really fast, it’s probably not glaucoma.

Both Drs. Lee and O’Donnell stress that any uncertainty should lead to a neuro-ophthalmologist referral.

“If I have a patient in my chair who has non-glaucoma atrophy — and I know they have it, but I don’t know why — that’s a referral,” Dr. O’Donnell says. “You don’t want to get caught with a patient [who has] temporal arteritis causing bilateral blindness. That can cause life-threatening complications if not treated. If you’re not comfortable or you’re unsure, you need to refer. I’m not shy about referring patients out.”

Dr. Lee concurs. “I think it’s important for the primary care doctor to recognize that limitation is not a sign of weakness but a sign of strength,” he says. “You can’t be everything to every patient, and knowing when to ask for help is critical.”

NEURO EXAM SUCCESS

• Revisit the anatomy. Dr. Modica advises that revisiting the anatomy is important for doctors who aren’t regularly involved in applying the concepts mentioned above.
  “A primary care optometry doctor is doing so many different types of things — from prescribing spectacles to contact lenses, to managing their patients’ regular ocular health — so the concepts of neuro-ophthalmology can get lost,” she says.
• Don’t be intimidated. The equipment used in neuro-ophthalmology is largely the same as that used in the primary care optometry practice, says Dr. Lee, so it does not take advanced technology to perform a neuro exam, and most primary care optometry practices are already set up to do so.
  “For example, the swinging-flashlight test [which assesses] pupillary function is one of our most valuable diagnostic tools for unexplained visual loss and is performed with a hand light,” he explains. “This tests for a relative afferent pupil defect and can be one of the first ways to differentiate something that is neuro-ophthalmic vs. a cataract or something benign.”
  Dr. Lee says that a neuro exam should also include testing VF and utilizing an OCT of the optic nerve. An OCT can assist in the diagnosis of neuro-ophthalmic diseases, such as optic neuritis, neuroretinitis and papilledema. In addition, an OCT exam can aid in the visual prognosis of compressive optic neuropathies.
• Focus on structure. DeAnn M. Fitzgerald, O.D., president of the Neuro-Ophthalmic Rehabilitation Association (NORA), who is also in private practice and specializes in evaluating patients who have brain injury, says optometrists should think about their role in a neuro exam as doing what they already do best: ruling out structural pathology or disease.
  “The No. 1 thing that we want to rule out beyond an immediate structural problem, like macular degeneration or a detached retina, is double vision,” she says. “Is that caused by a refractive error? By third, fourth, or sixth nerve palsy? Or could it be a spatial difficulty? We must determine whether this is a structural pathological problem or functional.” OM

 

 

Read more from Practicing Medical Optometry:

This iteration of Practicing Medical Optometry (PMO) is part of an ongoing series focusing on medical optometry offerings of glaucoma, AMD, dry eye, and more. You can find the previous issues of this section for download here.