Understanding the anatomy and physiology of the eye, the orbit, and the central connections is key to understanding neuro-ophthalmologic emergencies. Anisocoria is an important sign that requires a systematic approach to avoid misdiagnosis of serious conditions, including carotid dissection (miosis) and aneurysmal third nerve palsy (mydriasis). Ptosis may be a sign of either Horner syndrome or third nerve palsy. An explanation should be pursued for diplopia since the differential diagnosis ranges from the trivial to life-threatening causes.
Key points
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Understanding the anatomy and physiology of the eye, the orbit, and the central connections is key to understanding neuro-ophthalmologic emergencies.
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Anisocoria is an important sign that requires a systematic approach to avoid misdiagnosis of serious conditions, including carotid dissection (miosis) and aneurysmal third nerve palsy (mydriasis).
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Ptosis may be a sign of either Horner syndrome or third nerve palsy.
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An explanation should be pursued for diplopia since the differential diagnosis ranges from the trivial to life-threatening causes.
Introduction
Neuro-ophthalmologic emergencies are inexactly defined but may be thought of as neurologic emergencies where findings of the eyes or vision predominate and there is some urgency for evaluation or treatment. There is overlap with other neurologic and ophthalmologic disorders. This discussion is a brief overview directed at the emergency physician. Findings on the neuro-ophthalmologic system do not exist in isolation and must be viewed in context of the entire presentation of the patient. A patient’s level of consciousness, comorbidities, and associated conditions or injuries frequently direct the tempo of evaluation.
Examination of the neuro-ophthalmologic system allows a sampling of the general neurologic examination. Motor function, sensory findings, coordination, several of the cranial nerves, and even cortical and higher cerebral functions are tested. Although the neuro-ophthalmologic examination is often straightforward, it is occasionally perplexing. Like the general neurologic examination, the history informs the key portions of the physical examination and these clinical findings together suggest the anatomic localization of abnormalities within the central nervous system, which is critical to determine if addition work-up is necessary. Funduscopic examination allows visualization of blood vessels and the neural tissue in the optic disc.
With neuro-ophthalmologic emergencies, the emergency physician is faced with determining the need for prompt consultation, imaging, or hospital admission. This article presents examination techniques and findings as well as summaries of several clinical entities that are encountered in emergency medicine practice. Emphasis is on do-not-miss causes.
Introduction
Neuro-ophthalmologic emergencies are inexactly defined but may be thought of as neurologic emergencies where findings of the eyes or vision predominate and there is some urgency for evaluation or treatment. There is overlap with other neurologic and ophthalmologic disorders. This discussion is a brief overview directed at the emergency physician. Findings on the neuro-ophthalmologic system do not exist in isolation and must be viewed in context of the entire presentation of the patient. A patient’s level of consciousness, comorbidities, and associated conditions or injuries frequently direct the tempo of evaluation.
Examination of the neuro-ophthalmologic system allows a sampling of the general neurologic examination. Motor function, sensory findings, coordination, several of the cranial nerves, and even cortical and higher cerebral functions are tested. Although the neuro-ophthalmologic examination is often straightforward, it is occasionally perplexing. Like the general neurologic examination, the history informs the key portions of the physical examination and these clinical findings together suggest the anatomic localization of abnormalities within the central nervous system, which is critical to determine if addition work-up is necessary. Funduscopic examination allows visualization of blood vessels and the neural tissue in the optic disc.
With neuro-ophthalmologic emergencies, the emergency physician is faced with determining the need for prompt consultation, imaging, or hospital admission. This article presents examination techniques and findings as well as summaries of several clinical entities that are encountered in emergency medicine practice. Emphasis is on do-not-miss causes.
Anatomy and physiology
An understanding of anatomy aids both with examination and formulation of a clinical impression. The eye developmentally is an amalgam of neural elements and connective tissues. The globes are moved by the extraocular muscles, and disorders of muscles or the neuromuscular junction may affect eye movements. Because muscles are controlled by the nervous system, disorders of cranial nerves, the cranial nerve nuclei, and neural systems controlling the cranial nerve nuclei may also affect eye movements. The coordination needed to maintain visual fixation of 2 eyes simultaneously in a moving environment is complex, and the interaction and coordination of extraocular movements and conscious interpretation of visual information is complex as well as involving extra-ocular muscles, their innervation, cerebellum and cerebellar pathways, and cortical and subcortical structures.
Vision involves light entering the pupil, having an impact on the retina with photochemical conversion of light energy to electrical impulses and transmission of the visual information by the optic nerves via the optic chasm and optic tracts to the thalamus. At the optic chiasm, partially crossing fibers form the optic tracts in route to the lateral geniculate bodies of the thalamus ( Fig. 1 ). Pupillary reactivity with efferent responses through parasympathetic and sympathetic systems is supplied by specialized ganglion cells, which leave the optic tract to reach the pupillary centers in the dorsal midbrain. Transmission via the optic radiations through the temporal lobes to the occipital cortex is the pathway for conscious awareness of vision and higher cerebral processing. Interpretation of the imagery involves interaction with other cortical areas.
Pupillary testing involves provoking a reflex arc involving receptors on the retina, the afferent optic nerve (cranial nerve II), and fibers to the midbrain pupillary nuclei, brainstem interneuronal connections, and then efferent parasympathetic response. The parasympathetic pupilloconstrictors originating in the Edinger-Westphal complex of the third nerve nucleus take a direct route from the midbrain to the globes along the third cranial nerves (inferior division). The proximity of the third nerve with its pupilloconstrictors to the tentorium cerebelli is the basis for the pupillary dilatation in patients with uncal herniation. The sympathetic pupillodilators take a circuitous route from the supraoptic nuclei in the hypothalamus via the intermediolateral column through the brainstem, along the intermediolateral portion of the cervical and upper thoracic spinal cord, and reach the orbit along blood vessels ( Fig. 2 ).
Clinical findings/physical examination techniques
The sequence of the neuro-ophthalmologic examination varies from patient to patient. In most patients, the best fit is with cranial nerves testing during the neurologic examination. For primary ophthalmologic issues, a physician might start with examination directed at the visual system. It is axiomatic that visual acuity should be tested and recorded in every patient with a visual problem. Best corrected visual acuity using glasses or a pinhole (if patients do not have their glasses) should be obtained. The eye does not exist in isolation. Each of these findings must be interpreted in context. For example, the clinical implication of a large, nonreactive pupil is much different in an alert interactive patient than in a comatose patient.
Inspection of the Pupils and Pupillary Reactivity
The jargon PERRLA (pupils equal, round, reactive to light and accommodation) should be broken down to different components. First of all, are the pupils equal? Physiologic anisocoria is common in the population. One millimeter of asymmetry may occur but in less than 5% of the population. It is equally important to determine whether both pupils react normally. A sluggish reaction (or no reaction) may be important especially if involving the larger pupil. The ability of casual observers to note differences in pupillary size is not clear. It is a common occurrence in the resuscitation area for 1 caregiver to be calling out pupillary sizes that on closer inspection are simply not accurate. Additionally, pupillary size and asymmetry vary with lighting, becoming more noticeable in lower ambient lighting. The dim room phenomena may explain some of the different assessments at different times by observers because pupillary asymmetry often becomes more noticeable in low ambient lighting.
The response of the pupil to light has both a direct and consensual component. A bright light directed at 1 pupil should cause constriction of that pupil (the direct response) as well as constriction of the other pupil (the consensual response). Failure of a pupil to constrict to direct stimulation may represent a problem of light conduction or reception by the retina; dysfunction of the optic nerve, tract, or chiasm; brainstem interneurons; cranial nerve nuclei; or the efferent limb of the reflex with cranial nerve III. The magnitude of constriction of both pupils should be relatively similar; this is the basis of the so-called swinging flashlight test. A bright light directed at 1 pupil should cause constriction; after the light is shifted to stimulate the other eye, that pupil should remain the same size. If that pupil enlarges after the light is swung to it, seemingly paradoxically dilating in the face of a bright light, this is a positive swinging flashlight test ( Fig. 3 ). This is indicative of an afferent pupillary defect, most frequently indicating a problem with that optic nerve.
The “A” in PERRLA, stands for accommodation. If a visual target is moved closer to the patient while the patient continues to track the target, the pupil is observed constrict. There currently is interest in convergence pupilloconstriction in concussion evaluation. Because this is infrequently tested in common practice, the “A” in that acronym should be a dropped if not performed. In common practice, testing a pupil accommodative response is only indicated if the pupil does not react to light. If it does react to a near stimulus, then the differential of light-near dissociation should be explored.
Examination of the optic disc is frequently perplexing to emergency physicians. This examination is limited by time, confidence, and experience of the examiner and because in most ED settings it is performed with a pupil that has not been pharmacologically dilated. Funduscopic detail is difficult to discern in patients given these limitations. With practice, an emergency physician should be able to make some assessment of the quality of the view of the posterior pole (possibly indicating a cataract or other media problem), sharpness of the optic disc, possible presence of disc edema or optic atrophy, a comment on the blood vessels (narrowed, dilated, or sclerotic), the presence of exudate, or the presence of hemorrhage. With practice, the presence of retinal venous pulsations may be appreciated, which has implications regarding intracranial pressure (ICP). Portable retinal cameras may have an impact on funduscopic assessment in the future.
Extraocular Movements
Evaluation of extraocular movements is sometimes thought to only test different cranial nerve functions. Because there are multiple other causes of motility disruption, start by examining movement of each eye (ductions) in all directions. Assessment of versions examines whether the 2 eyes move together. Assessment of cranial nerves, in particular, cranial nerves III and VI, are commonly done during evaluation of extraocular movements testing. By way of review, the sixth cranial nerve innervates the lateral rectus of each globe, responsible for lateral movement or abduction of each globe. The fourth cranial nerve (the most difficult to assess) innervates the superior oblique muscle responsible for depression in adduction and intorsion of each globe. The third cranial nerve innervates the other extraocular muscles and controls adduction, elevation, and depression of each globe. Associated parasympathetic fibers with cranial nerve III are involved with pupilloconstriction. Frequently, several cranial nerves and extraocular muscles are involved with eye motions. The H-shaped tracing examination pattern and knowledge of the principal direction of movement of the individual muscles attempts to isolate these different motions, allowing assessment of specific extraocular muscles and cranial nerve functions ( Fig. 4 ).
Like other voluntary muscle movements, some assessment of coordination is possible analogous to assessing cerebellar functions. Asking a cooperative patient to slowly track a moving finger or other object assesses smooth pursuit functions. An observation of breakup or irregularity of smooth pursuit movement may indicate a cerebellar system problem. Directing patients to direct their eyes back-and-forth between different objects — typically an examiner’s nose and finger — may show over or undershoot phenomena (saccadic dysmetria) — the eyes are seen to overshoot the target then quickly correct. Again, this frequently represents a cerebellar system lesion. These fast movements are part of the saccadic system. Saccades are rapid eye movements that shift the line of sight between successive points of fixation. Abnormalities of saccadic movements may occur from cerebellar or cerebellar pathway lesions but also occur from midbrain or other problems in the nervous system.
Vestibular-Ocular and Caloric Testing
Extraocular movements can also be assessed with rapid motion of the head or by irrigation of the auditory canal, provoking thermal stimulation to the vestibular system. Probably the most common use of this in contemporary practice is for brain death determination. Focusing on cold water irrigation of the right auditory canal, the response for a comatose patient with a functional vestibular system, efferent cranial VIII intact, functional interneurons and pathways, and functional cranial nerves III and VI is for tonic deviation of the eyes toward the side of cold water irrigation ( Fig. 5 ). Nystagmus is not observed in the comatose patient because this requires a functioning cerebral cortex. Should nystagmus be observed in a seemingly comatose patient, this is evidence of a functional cortex and suggests pseudocoma. The old mnemonic, cold opposite, warm same (COWS), refers to the direction of induced nystagmus for the alert patient, not eye movement direction in the patient with altered mental status. More useful in emergency practice is cold same, warm opposite (CSWO), the direction of the slow, tonic movement of eye direction in a comatose patient. In a patient with brain death or severely depressed brainstem functioning from any cause, including some toxicologic or metabolic causes, there is no reaction.
Corneal Reflex
Sensation to the globe is supplied by cranial nerve V; the corneal reflex reflects a cranial V–VII reflex arc. Although not strictly a neuro-ophthalmologic test, it may be useful in some patients. Much like the pupillary response, the corneal reflex has both direct and consensual responses. Abnormalities may result from the afferent cranial nerve V, interneuron connections, or from the efferent motor function of cranial nerve VII.
Visual Fields
Visual field testing is often used to detect cortical abnormalities, but lesions anywhere along the optic paths may cause different patterns of visual field loss. Bedside testing performed with confrontation maneuvers, 1 eye at a time, comparing an examiner’s fields to those of the patient, is the usual method in the ED. Visual field testing with confrontation maneuvers has limitations compared with quantitative perimetric testing. Even so, some distinctive patterns may be detected. The classic bitemporal hemianopsia pattern results from chiasmal lesions reflecting the partial decussation of fibers at the optic chiasm. Pathologic processes between the optic chiasm and the occipital cortex cause variable degrees of homonymous visual field losses. Unilateral occipital cortex lesions show contralateral homonymous hemianopsia. A summary is presented in ( Fig. 6 ). In some patients, the visual field deficit may seem pronounced if a parietal lobe lesion adds an element of cortical neglect to the visual field loss.
