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Sunday / November 3.
HomemipatientFocussing to See the Light Top Tips in Neuro-Ophthalmology

Focussing to See the Light Top Tips in Neuro-Ophthalmology

As the only practitioner in Australia to hold the dual specialties of neurologist and ophthalmic surgeon, Dr Dennis Lowe has a unique perspective on diagnosing challenging neurology and ophthalmology cases. Dr Margaret Lam recently asked Dr Lowe to share his top tips for eye care professionals.

Q. What are the most important, common conditions that eye care professionals should be knowledgeable about when working up cases that indicate a neurological cause?

‘Visual blur’ is one condition. When cases indicate a neurological cause, it’s important to be able to assess the visual blur your patient describes. During history taking, document exactly what the blurred vision is, identify the time of onset, and any changes. For example, is it transient, chronic or acute? Has it been the same since onset, or is it progressive?

If it is acute, an optometrist or ophthalmologist should immediately think of vascular causes for the reported blurriness.

If it is a transient visual loss – over seconds or minutes as opposed to hours or days – then the pathological cause can be very different. For example, transient obscurations in vision lasting seconds may indicate disc swelling in benign intracranial hypertension.

Another important diagnostic clue is the optic nerve function. It’s best to assess this by looking at the optic disc using ophthalmoscopy or fundoscopy rather than imaging per se.

Despite all the advanced imaging techniques we have access to now – like optical coherence tomography (OCT), visual fields testing, and sophisticated mapping analyses – nothing beats looking directly at the optic nerve to assess optic nerve function. Although these sophisticated new instruments give us a great view of the broader picture, looking directly at the optic nerve gives us much richer information on assessing things such as optic disc swelling and pallor.

The appearance of optic disc swelling due to the presence of fluid, for example, indicates papilloedema. Other causes include infiltration, sarcoid, lymphoma, and deposits (drusen), and are also best viewed directly in these ways.

Q. What else should an eye care professional be looking for?

It is helpful to look for areas of ischaemia, pallor, and the pattern of optic disc changes.

Assessing the presence of pallor on the optic nerve is very important. If the pallor is temporal, it is indicative of a centrocecal condition, such as vitamin deficiency or optic neuritis. If the pallor is in the presence of optic disc cupping, then glaucoma, giant cell arteritis (GCA), and methanol poisoning are worth investigating.

In summary, looking directly at the optic disc can more clearly indicate diagnostic pathophysiological conditions. And, of course, a thorough history is critical to providing excellent diagnostic clues as to the cause of the pathophysiology and the diagnosis.

Q. How should we manage these patients?

We must be mindful that conditions such as optic nerve head drusen can be responsible for progressive field loss from crowding of the disc, which leads to retinal ischaemia and atrophic changes, resulting in acute ischaemic neuropathy.

We need to advise these patients to avoid scuba diving beyond 20 m, avoid episodes of dehydration, and to avoid taking Viagra. Interestingly, Viagra causes two optic nerve side effects: although rare, it can cause anterior ischaemic optic neuropathy (AION) and ‘blue vision’, an overrepresentation of blue in the patient’s colour perception.

AION is rare, but much more common in a person over 70 years of age. It is important to establish whether AION is caused by inflammation, e.g., GCA, systemic lupus erythematosus (SLE), or a degenerative cause, such as degenerative atherosclerosis (i.e., hypertension, hyperglycaemia, or hyperlipidaemia).

Acute loss of vision i.e., infarction, can present from posterior ischaemic optic neuropathy (PION), an acute optic neuropathy due to ischemia in the posterior (retrobulbar) portion of the optic nerve. In these cases, the patient presents with loss of vision, however the optic disc initially looks normal.

PION is one of two conditions to rule out when we can’t see anything wrong with the optic disc; the other is acute retrobulbar neuritis. Both these patient groups require careful management to avoid progressive field loss. And invariably, anyone with optic disc swelling needs magnetic resonance imaging.

Q. What are the unmissable clinical signs and symptoms an eye care professional should look for in neurological presentations?

There are several, the most important of which I have set out in Table 1 for easy reference.

When considering cranial nerve palsies, it is important for eye care professionals to consider the following, often overlooked areas that are controlled by the cranial nerves:

CN3: for convergence, accommodation and medial rectus control; it helps us to look at the computer.

CN4: for adduction and intorsion, e.g., walking down stairs.

CN6: for driving a car and abduction.

When examining for diplopia, the first thing to determine is, is it in one eye or two eyes? Then we need to ask the patient, “What do you mean by diplopia: is it one image superimposed on the other?”

If it is two separate images superimposed, then you can be certain that monocular diplopia will always indicate an ocular cause (e.g., a dislocated lens), whereas binocular diplopia will always indicate a neurological cause.

Pupil assessment involves determining pupil changes, looking for simple anisocoria, Horner’s syndrome, and afferent pupillary defect (APD).

Q. What are the common causes of ophthalmic neurological conditions for patients in their late teens and early 20s?

Patients can present with ptosis caused by contact lens or orthokeratology (OK) overwear. When this occurs, we need to establish the length of contact lens wear.

After that, assess for myasthenia gravis, and unilateral and bilateral ptosis.

If it is a unilateral ptosis, determine whether it is bilateral or asymmetric using Herring’s law. To do this, put your finger on the opposite side of the ptosis.

If the eyelid drops, the eyelid with the ptosis will appear normal, because the eye is being ‘unnaturally’ forced up. This indicates bilateral asymmetric ptosis, which means you need to look for the neurological cause.

Other presentations can include pain behind the eye and headaches, which can be caused by conditions such as pituitary apoplexy, orbital apex, and cavernous sinus syndromes, Horner’s syndrome, and trigeminal nerve pathology.

When assessing for trigeminal sensory loss, it is important to realise that the trigeminal nerve innervates the eyeball and periocular areas.

While you can use a cotton bud technique to touch the centre of the eye, the best place to test for trigeminal sensory loss is in the conjunctival area at the 12 o’clock position under the eye lid, an area which is not normally exposed.

Test the reflex at the 11 or one o’clock position under the eyelid on the conjunctiva and if they’ve lost both the cornea and conjunctival reflex, the cause is very different. If this is the case, look along that pathway, i.e., the retrobulbar and apex of the orbit and cavernous sinus for a cause.

When interpreting visual fields, especially the optic nerve and cerebral cortex, some important tips to remember include:

  • Horizontal visual field loss, also known as altitudinal field loss, identifies a retinal or optic nerve cause,
  • A vertical visual field defect is always a neurological cause,
  • Quadrantanopic visual field loss (including a bitemporal or binasal field loss) always has a neurological cause until proven otherwise, and
  • The most common condition in neurological presentations that you will see as an optometrist will be a pituitary tumour, and this will present as a bitemporal field loss.

Asking questions about hormonal change can also aid in diagnosis. If the patient is female, enquire about any changes in menstruation and if the patient is experiencing amenorrhea (absence of menstruation) or galactorrhea (abnormal production of breast milk). If the patient is male, ask about hair loss and impotence.

Q. What conditions are most often underdiagnosed or misdiagnosed by eye care professionals, and how can we improve this situation?

From a neuro-ophthalmic point of view, I often see misdiagnosis due to errors in the assessment of pupil, visual field, and eye movement changes, as well as in testing for trigeminal loss, and optic disc appearance. Don’t rely solely on OCT in interpretation of optic nerve pathology. One still needs to look at the physical optic disc changes.

Q. Where do you see neuro-ophthalmology going in the next few years?

Neuro-ophthalmology relies heavily on not only clinical signs but also neuro-imaging including magnetic resonance imaging, angiography, and venography (MRI/MRA/MRV), as well as progression identified in OCT technology and angiography. As these technologies progress, so may our diagnostic capabilities. Electrophysiology such as electroretinogram (ERG) and electro-oculogram (EOG) is likely to become more refined. Detection of cerebrospinal fluid (CSF) abnormalities via CSF studies may also develop further.

In terms of treatments, I expect we will see advancements in immunotherapy, e.g., treatments using monoclonal antibodies for multiple sclerosis, and chemo-therapeutic/ radiotherapy treatments for pituitary tumour and optic nerve gliomas.

Q. What drives you in your day-to-day work?

Mary Anne Radmacher, a writer and artist, said, “As we work to create light for others, we naturally light our own way”.

As eye care practitioners, it is important to pick up treatable pathology early, so that we can manage our patients in a very objective way, to prevent blindness and improve their quality of life.

I hope the tips I’ve offered shed some light along your diagnostic journey in helping your patients.

Dr Margaret Lam BOptom UNSW Post Grad OcTherapy is the National President of Optometry Australia. She practises optometry at 1001 Optical in Bondi Junction in Sydney and teaches at the School of Optometry at the University of New South Wales (UNSW) as an Adjunct Senior Lecturer.

Dr Dennis Lowe MBBS FRACP FRACS FRANZCO trained as neurologist, before training to become an ophthalmic surgeon. He is the only practitioner in Australia to hold these dual specialties. Dr Lowe has particular interests in ophthalmic surgery, medical retina, neurologically related eye disease, and general ophthalmology. He completed his specialist training through Sydney Eye Hospital and Moorfields Eye Hospital in the UK. He currently holds teaching positions at Sydney University and UNSW affiliated hospitals and Visiting Medical Officer positions at Royal Prince Alfred, St Vincent’s and Sydney Eye hospitals.

He practises as an ophthalmic surgeon and consultant neurologist at Sydney CBD Eye Clinic.

CASE STUDY

A 64-year-old female presented with a 2.5 year history of blurred vision in the left eye. She had left eye cataract surgery overseas two years prior, with little subjective improvement and subsequently had YAG capsulotomy (also overseas), with no improvement.

When the patient presented to the optometrist, her uncorrected vision was 6/9 right and 6/18-2 left. Using her left eye, she was only able to read the right side of the chart. The optometrist noted slight temporal pallor of the left optic disc. Visual field testing showed a bitemporal visual field defect R>L.

On ophthalmology review, vision of 6/9 right and 6/18-2 left was again noted. Temporal disc pallor was noted L>R and visual field defect was repeatable. She had no other significant medical history, and no symptoms of hormonal changes.

An urgent MRI was ordered, which showed a large sellar and suprasellar mass lesion with impingement on the optic chiasm and invasion into the left cavernous sinus (radiological differential diagnosis of a craniopharyngioma or pituitary macroadenoma). The patient was referred for urgent neuro-ophthalmic opinion.

This case presents a good example of the optometrist looking at the optic disc and identifying disc pallor, then ensuring optimal management by providing a timely referral to the neuro-ophthalmologist. A close working relationship allows an optometrist and neuro-ophthalmologist to collaboratively identify and treat patients promptly, to mitigate any further sight loss.

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