Formally, this is an interrogation of the third, fourth and sixth nerves, However, examination of the eye movements tends to also reveal cerebellar pathology (as nystagmus). The gaze palsies are a difficult bunch of disorders, and for the purposes of the CICM fellowship exam one should become familiar with the main ones, but one should not feel compelled to become a master of this area. One should be able to recognise a third nerve palsy, a fourth nerve palsy and a sixth nerve palsy. If one is able to recognise internuclear ophthalmoplegia, one is ahead of the herd. If one is able to discourse intelligently about the disorders of conjugate gaze, then one has probably wasted their time with neurology, because the large swaths of cognitive real estate occupied by these complex topics could be better used on issues which are worth more marks. One's performance in the written paper or in the hot case is unlikely to hinge on the ability to discriminate between causes of pendular nystagmus.
Past paper SAQs on this topic include the following:
- Question 21.2 from the first paper of 2014 - CN IX, CN XII, CN VII, CN VI.
- Question 21.3 from the first paper of 2014 - CN VI
- Question 26.2 from the second paper of 2011 - localisation of a midbrain lesion by a CN III palsy.
- Question 25.4 from the first paper of 2011 - Oculocephalic reflex (CN III, IV, VI and VIII)
- Question 24.4 from the first paper of 2009 - Examination of eye movements
The ideal reference for this is "Cranial Nerves III, IV, and VI: The Oculomotor, Trochlear, and Abducens Nerves" - Chapter 60 from "Clinical methods." (1990)- by J. Donald Fite and H. Kenneth Walker.
The Conscious Patient
This one is easy.
Ask the patient to track a convenient object. The physician's exam candidate will have a brightly coloured hat pin. The hat pin, of course, is anachronistic wankery. Some of you might have a briefcase full of such detritus, and you might even be proud of it. The ICU fellowship candidate has no time for such nonsense.
Get the patient to follow your finger. The finger should ideally be held at least 1m away from the eye, otherwise non-pathological nystagmus might be elicited.
Using your finger, trace an imaginary H. The idea is to test all six movements of the eyes, as depicted above.
The specific lesions are discussed in following chapters, dedicated to each nerve individually:
- Lesions of the third cranial nerve (CN III)
- Lesions of the fourth cranial nerve (CN IV)
- Lesions of the sixths cranial nerve (CN VI)
- Additionally, a disorder of conjugate gaze might be discovered in this fashion.
The Unconscious Patient
One cannot get the comatose patient to track one's finger, but one can still test eye movements by testing the Oculocephalic and cold caloric reflexes. This is discussed elsewhere, as it has specific meaning associated with testing the 8th nerve (CN VII, the vestibulocochlear nerve).
Before you grab the head and start rotating it violently, it is also possible to derive meaning from simply looking at the unconscious patient's eyes, and watching their spontaneous position and movement.
Peel back the lids. You will see one of three things.
- The eyes are fixed and midline.
- The eyes are roving randomly.
- The eyes are deviated in some direction:
- Strabismus (eyes pointing in opposite directions)
- Conjugate lateral deviation (both eyes pointing left or right)
- Conjugate vertical deviation (both eyes rolled up or rolled down)
- Non-conjugate lateral deviation (one eye pointing left or right, with the other fixed and central)
- Non-conjugate vertical deviation ("skew deviation"; one eye points up and the other down)
These things have meaning, as discussed below.
First, in brief:
- Fixed eyes: non-specific finding.
- Strabismus: non-specific finding.
- Roving eyes: likely, metabolic cause of coma
- Conjugate lateral deviation:
- The eyes look towards a frontal eye field cortical lesion (eg. large MCA stroke)
- The eyes look towards a pontine infarct
- The eyes look away from a focus of epilepsy
- The eyes look away from a massive thalamic bleed.
- Conjugate vertical deviation (both eyes rolled up or rolled down)
- Both eyes up: "oculogyric crisis" of dystonia, or bilateral basal ganglia lesions.
- Both eyes down: pineal mass or bilateral thalamic haemorrhage.
- Non-conjugate vertical deviation ("skew deviation"):
- A lateral rostral medulla lesion on the side of the inferior eye
- A lower pontine lesion on the side of the inferior eye
- A vestibulo-cerebellar lesion on the side of the inferior eye
- An MLF lesion on the side of the superior eye
Now, in detail:
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Whatever the findings, one should go on to test the oculocephalic and cold caloric (oculovestibular) reflexes.
References
The LITFL summary of cranial nerve lesions is without peer in terms of useful information density.
Walker, H. Kenneth, W. Dallas Hall, and J. Willis Hurst. "Clinical methods." 3rd edition.(1990).Chapter 60 Cranial Nerves III, IV, and VI: The Oculomotor, Trochlear, and Abducens Nerves - by J. Donald Fite and H. Kenneth Walker.
Twenty five years out of date, but still relevant.
These authors, in turn, reference even more ancient vellum:
Leigh RJ, Zee DS. The neurology of eye movements. Philadelphia: FA Davis, 1983.
Miller NR. Walsh and Hoyt's clinical neuro-ophthalmology. Vol 2. 4th ed. Baltimore: Williams and Wilkins, 1985.
Broadway, David C. "How to test for a relative afferent pupillary defect (RAPD)."Community Eye Health 25.79-80 (2012): 58.
Fincham, Edgar F. "The accommodation reflex and its stimulus." The British journal of ophthalmology 35.7 (1951): 381.
Maramattom, Boby Varkey, and Eelco FM Wijdicks. "Uncal herniation."Archives of neurology 62.12 (2005): 1932-1935.
Karatas, Mehmet. "Internuclear and supranuclear disorders of eye movements: clinical features and causes." European Journal of Neurology 16.12 (2009): 1265-1277.