Ординатура / Офтальмология / Английские материалы / Neuro-Ophthalmology_Kidd, Newman, Biousse_2008
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LEFT AFFERENT PUPIL DEFECT
Figure 1–25 The swinging flashlight test is used to test the integrity of the afferent visual pathway. In this example, the left optic nerve is not functioning properly and there is a paradoxical dilation of the left pupil as the light is directed into it (left relative afferent pupillary defect).
equally bleach both retinas. The swinging flashlight test is done rhythmically, holding the light on each eye for 1 to 2 seconds. It is important to cross the bridge of the nose quickly and equally stimulate both eyes. Some neuro-ophthalmologists use the following grading scheme for afferent pupillary defects:
1þ ¼ initial constriction followed by early release of the affected pupil 2þ ¼ no movement initially, followed by pupillary release
3þ ¼ immediate pupillary dilation
4þ ¼ amaurotic eye (no light perception vision)
Because an afferent pupillary defect is established by comparing the light reaction of one pupil versus the other, there is no such entity as “a bilateral afferent pupillary defect.” The examiner must be careful of the physiologic phenomenon known as hippus. In the case of marked pupillary unrest (hippus), it is best to look primarily at the initial constriction response of each pupil. A bright light
source should be used to assess the pupils, but occasionally a dim light will bring out an afferent defect not observed with a bright light.26,27 When one
is unsure if an afferent pupillary defect exists, the examiner may try to gather supporting evidence by:
1.Having each eye compare the intensity of a bright light
2.Comparing red bottle tops
3.Performing contrast sensitivity testing
4.Comparing color plate performance
5.Placing a small (0.3 log filter) neutral density filter over the suspected eye to see if it magnifies or brings out an afferent pupillary defect
The swinging flashlight test becomes a bit more difficult to interpret when one pupil is dilated as in a patient with a third nerve palsy. In this setting, one screens for an ipsilateral optic neuropathy by checking the response of the fellow pupil when light is directed into the dilated pupil. This is an indirect measure of the optic nerve function on the side of the dilated pupil.
The term anisocoria refers to asymmetric pupil size. The most common form of anisocoria is physiologic or essential. Patients with physiologic anisocoria
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should have normal pupillary responses to light and near. Most importantly, the amount of pupil inequality should be similar in light and dark conditions.
Pathologic anisocoria results from damage to the efferent part of the pupillary pathway. It should be remembered that damage to the afferent part of the pupillary pathway does not produce anisocoria. Anisocoria that is greatest in light suggests parasympathetic dysfunction. In contrast, anisocoria greatest in dark is consistent with oculosympathetic paresis (Horner’s syndrome). In oculosympathetic paresis, the affected pupil fails to dilate or dilates very slowly when the lights are turned off. This is called dilation lag and the anisocoria is most evident in the first 5 seconds after the lights are turned off.28 Pupillary disorders are covered in Chapter 11.
EYELID EXAMINATION
The examiner must be able to assess lid function. In normal individuals, the upper lid covers the superior 1 to 2 mm of the iris, and the lower lid borders the inferior aspect. The palpebral fissure is the opening that exists between the upper and lower lids and usually measures 9 to 12 mm in most normal individuals. Because lower lid position may vary, it may be best to measure the distance between the upper lid margin and pupillary light reflex. This measurement is known as the margin reflex distance and usually measures 4 to 5 mm.29
Measurement of lid function will help establish the cause of ptosis. Lid function is measured by manually neutralizing the ipsilateral brow with the hand while asking the patient to look downward30 (Fig. 1–26). A ruler is then placed at the lid margin and the number of millimeters of lid elevation is measured as the patient looks upward. Normal lid function exceeds 12 mm.29 Levator function is reduced in ptosis associated with myasthenia gravis, congenital ptosis, myopathic disorders such as myotonic dystrophy, chronic progressive ophthalmoparesis, and third nerve palsies. In contrast, levator function will be normal in patients with Horner’s syndrome and levator dehiscence.
Pseudoptosis may be associated with blepharospasm. In this situation, the eyebrow will be dropped rather than elevated as seen in patients with true ptosis. A markedly hypotropic eye will also demonstrate pseudoptosis as the normal lid follows the globe downward. Lid retraction occurs when the upper lid rides too high. True lid retraction is usually obvious when the superior sclera becomes
Figure 1–26 A, To measure eyelid function a ruler is placed at the lid edge. B, The distance the lid travels to reach full upgaze is recorded as eyelid function.
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Figure 1–27 Patient with eyelid retraction from dorsal midbrain compression. Note that the superior sclera is exposed.
exposed (Fig. 1–27). Common causes of eyelid retraction include thyroid eye disease, topically administered sympathomimetic drugs, and a dorsal midbrain syndrome.
OCULAR MOTILITY
The objective of the motility examination is to assess the integrity of the supranuclear pathways, ocular motor nuclei, ocular motor nerves, and their muscles. Saccades or fast eye movements are tested by having the patient refixate between two targets. This can be easily accomplished by having the patient look at the examiner’s nose and then at an eccentrically placed finger (Fig. 1–28). Saccades may be recorded as follows: 1 ¼ normal, 2 ¼ hypometric when the patient undershoots the target, 3 ¼ hypermetric when the patient overshoots the target, 4 ¼ slow when the examiner can observe the full trajectory. To test the pursuit system, one needs an object of regard. The examiner’s finger may be an adequate target provided that one does not exceed the limits of the pursuit system (40 degrees per second). Alternatively, one can swing a reflex hammer from side to side to induce pursuit eye movements (Fig. 1–29). Defective pursuit is “saccadic” because the fast eye system has to be activated to keep up with the target. The vestibular ocular reflex (VOR) can be tested in the awake patient by having the patient fixate on the examiner’s finger as the examiner rotates the patient’s head from side to side. Once again, a defective VOR results in catch up saccadic eye movements. Cancellation of the VOR usually requires an intact pursuit system. Failure to cancel the VOR properly may be detected when the patient is slowly rotated while focusing on the outstretched thumb. The patient with defective cancellation of the VOR shows catch up saccades.
Figure 1–28 Testing saccades may be accomplished by having the patient look quickly between two fingers.
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Figure 1–29 Smooth pursuit may be tested by slowly oscillating a neurologic hammer across the midline.
When diplopia is binocular, it usually results from dysfunction of the ocular motor nerves, neuromuscular junction, or extraocular muscles. Monocular diplopia is usually caused by early cataract formation or astigmatism and is usually relieved by viewing through a pinhole device (Fig. 1–14). Monocular diplopia not alleviated by a pinhole suggests a functional etiology. The diplopia assessment is begun by finding out whether the double vision is vertical or horizontal. Is it worse at distance or near, and in what gaze is the double vision worse? For example, a patient with a right sixth nerve palsy might be able to discern that the diplopia is horizontal, worse at a distance (the eyes need to diverge at distance), and increased by right gaze. In the diplopia evaluation, review of old photographs is essential to check for an old strabismus, face turn, or a head tilt. For example, the patient with a long-standing right fourth nerve palsy will often have a left head tilt in old photographs. Chin depression to keep the eyes in upgaze and a left face turn to keep the eyes in right gaze may also be apparent.
Before taking the patient through the cardinal positions of gaze, one should examine the lids carefully. Lid retraction might suggest thyroid eye disease or a dorsal midbrain syndrome depending on the associated findings. Fatigueable ptosis or Cogan’s lid twitch sign (transient improvement of lid function after sustained downgaze) suggests myasthenia gravis (Chapter 13). Next check the eyes in the cardinal positions of gaze. In most individuals, the sclera is covered by the lids in eccentric gaze. One should assess the ocular rotation by recording it as a percentage of normal (i.e., 70% of normal). This may be recorded in the chart from the examiner’s perspective (Fig. 1–30).
Figure 1–30 Ductions are recorded from the examiner’s perspective as a percentage of a normal eye excursion. In the example provided, there is a right abduction deficit with an eye movement that is 80% of normal.
Examiner’s view: Right abduction deficit
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Although the appearance of sclera in end gaze is usually pathologic, some patients have shallow orbits and no true ocular deviation exists. In this instance, proof of an ocular deviation requires quantitation of the patient’s ocular misalignment. For example, when the examiner suspects an abduction deficit, confirmation comes from demonstrating an inward strabismus. When an eye is deviated inward, it is called an esotropia, outward deviation is called an exotropia, and vertical displacement is called a hypertropia. Regardless of which eye is vertically impaired, the hypertropia is denoted by the higher eye.
Quantitation of the ocular deviation may be made using the cross-cover method, the Maddox rod, or red glass test. In the cross-cover method one eye is covered and the deviated eye will need to pick up the fixation target. For example, an eye that is exotropic will need to move inward to pick up the target when the fixating eye has been covered. The amount of ocular deviation can be neutralized by placing a prism over one eye. Each eye is then alternately covered as the amount of prism is slowly increased. When the eyes no longer move on alternate cover testing, the deviation has been neutralized and the amount of prism required can be read off of the prism bar. A Maddox rod can also be used to quantify the amount of ocular deviation. The Maddox rod is a series of red cylinders that create a bar of red light when a light is directed at it. By convention, the patient places the Maddox rod over the right eye (Fig. 1–31). Holding the bar with the cylinders horizontal provides a single vertical line. This is the orientation required to test horizontal deviations. The patient is then asked which side is the red bar on (relative to the white light). If the patient tells the examiner that the red bar is to the right of the white light, this is an esodeviation (Fig. 1–32). The patient is then taken into right and left gaze to see if the amount of separation increases in the field of action of either the right or left
Patient’s view: Esotropia
Red
line
White light |
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Right gaze: |
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right 6th nerve palsy |
Figure 1–31 A Maddox rod is placed over the right eye by convention. To test for a horizontal deviation of the eyes, the bars are placed horizontally as shown. This Maddox rod orientation generates a single red vertical line viewed by the patient. The examiner then asks the patient where the red bar lies in relationship to the white light that is viewed by the left eye.
Figure 1–32 If the red bar lies to the right of the white light from the patient’s perspective, the patient has an esodeviation.
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lateral rectus muscle. If prisms are unavailable, one can get a reasonable estimate of the ocular deviation by asking the patient to show the examiner the extent of separation by spreading his or her fingers apart. An esotropia, which increases in right gaze, is consistent with a right sixth nerve palsy. If the patient sees the red bar to the left of the white light, this represents an exodeviation (Fig. 1–33). This might be remembered by the statement “There is an “x” in exo.” This means that the red bar seen by the right eye crosses to the left of the white light (crossed diplopia).
To examine a vertical deviation, the cylinders are placed over the right eye with a vertical orientation. This will give the patient a red horizontal bar when light is directed at him or her. In a right hypertropia (the right eye is higher than the left) the patient will see the red bar below the white light. The patient with a right hypertropia either has a problem with the depressors of the right eye (right inferior rectus or right superior oblique) or the elevators of the left eye (left superior rectus and left inferior oblique). When the red bar appears above the white light, the patient has a left hypertropia. The patient with a left hypertropia either has a problem with the depressors of the left eye or the elevators of the right eye. If the deviation or separation of the bar and light is greater in downgaze with a left hypertropia, then one of the depressors is implicated (left inferior rectus or left superior oblique). The patient is then taken into the cardinal fields of gaze to better localize the involved nerve or muscle. For example, a patient with a left fourth nerve palsy will have a left hypertropia that is worse in downgaze and in right gaze (Fig. 1–34). The deviation associated with a left fourth nerve palsy will increase with left head tilt and lessen with right head tilt. If a right hypertropia appears with right head tilt, this suggests a superimposed
Figure 1–33 If the red bar lies to the left of the white light from the patient’s perspective, the patient has an exodeviation. In this example, the separation of the bar and light was greatest in right gaze consistent with a left internuclear ophthalmoparesis.
Patient’s view: Exotropia
White light
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Figure 1–34 When testing for a vertical separation of the eyes, the Maddox rod bars are placed over the right eye in a vertical orientation. This orientation generates a horizontal red bar. In a patient with a right fourth nerve palsy, the red bar sits below the white light. In left and down gaze, the separation between the red bar and white light should become even greater.
Patient’s view: Right fourth nerve palsy
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right fourth nerve palsy. Bilateral fourth nerve palsies (one which may be subtle or “masked”) are common with head trauma. In long-standing (congenital) fourth nerve palsies, there may be hypertrophy of the neck muscles contralateral to the head tilt. The diagnosis of a congenital fourth nerve palsy is suggested when the patient can fuse a very large amount of vertical deviation (a large fusional amplitude). Again, old photographs are extremely helpful to document the duration of a head tilt when a congenital fourth nerve palsy is suspected.
A third nerve palsy is characterized by a hypertropia that changes sides in upgaze when compared with downgaze. For example, a right third nerve palsy will show a left hypertropia in upgaze (right superior rectus weakness) and a right in downgaze (right inferior rectus weakness).
An ocular deviation may be concomitant, meaning that the deviation is the same in all fields of gaze. Concomitant deviations may be seen with the following:
1.Strabismus
2.Skew deviation
3.A long-standing nerve or muscle palsy
4.Convergence or divergence insufficiency
5.Myasthenia or thyroid eye disease
In contrast, inconcomitant deviations have a variable ocular deviation depending on the position of gaze. Inconcomitant deviations are seen with the following:
1.Acute ocular motor palsy
2.Skew deviation
3.Myasthenia or thyroid eye disease
4.Internuclear ophthalmoplegia
Because both thyroid eye disease and myasthenia gravis may mimic any ocular motor palsy, it is important to always consider these entities. A forced duction test can be easily carried out in the office or at the bedside (Fig. 1–35). The inability to move the eye passively with a cotton tip applicator (after topical anesthesia) suggests a restrictive process such as thyroid eye disease. A Tensilon test may be carried out when myasthenia is suspected. We use 2-mg increments (every 30 to 60 seconds) to avoid overmedicating the patient and occasionally missing the point of ocular recovery. The test can be terminated at any point or after the patient has received the full 10-mg dose if no response has occurred to that point.
The red glass test is an analogous to the Maddox rod test except that the patient perceives a red circle rather than a red line in the red glass test. If a red glass or Maddox rod is unavailable, one could perform the cover-uncover
Figure 1–35 Forced duction testing. After topical anesthesia, one may assess the freedom of eye movement using a cotton tip applicator. The patient is instructed to look into one direction as the examiner gently pushes on the eye to determine restriction.
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test with the hand or a paddle. The cover-uncover test is used to detect overt ocular misalignments (tropias). For instance, if the examiner covers the right eye and the left eye moves out, there is an esotropia, and, if acquired, an abduction deficit is suggested (i.e., sixth nerve palsy). On the other hand, inward movement of the uncovered eye is consistent with an exotropia (third nerve palsy, internuclear ophthalmoparesis, and strabismus). If the uncovered eye moves down, hypertropia is present (i.e., fourth nerve palsy, skew deviation, or myasthenia).
OPHTHALMOSCOPY
In an undilated patient, the optic nerve and retina may be viewed with a direct ophthalmoscope. The examiner should make note of the color, contour, and the cup to disc ratio of the optic nerve. The retinal vasculature should be evaluated observing the caliber of the veins and arteries in all four quadrants. The macula can be viewed by moving the ophthalmoscope temporally from the disc or by having the patient directly look at the light of the ophthalmoscope. It is important for the examiner to recognize some of the early features of papilledema. They include
(1) blurred disc margins particularly superiorly and inferiorly; (2) disc hyperemia; (3) nerve fiber layer hemorrhages; (4) venous distention; and (5) absence of the spontaneous venous pulse. It is the combination of these features that most convincingly establishes the presence of papilledema. Papilledema is also discussed in the coma section.
Pharmacologic dilation of the pupil may be accomplished by topical administration of 1% tropicamide (an anticholinergic) and 2.5% phenylephrine (sympathomimetic). The dilating effect of tropicamide peaks at 20 to 40 minutes and lasts 2 to 6 hours, whereas phenylephrine works in 20 minutes and lasts 2 to 3 hours.
Neuro-Ophthalmologic Examination in
Comatose Patients
Comatose patients are unresponsive to all external stimuli, noxious or otherwise. The eyes are closed, but there may be nonpurposeful movements or posturing of the limbs. Coma may be caused by a number of insults, including herniation, hydrocephalus, intracranial hemorrhage, hypoxic-ischemic injury, trauma, infection, and toxic or metabolic insult. The neuroanatomic correlates of coma include either (1) direct brainstem-diencephalic involvement disrupting the reticular formation or nuclei or (2) bilateral cerebral dysfunction.31
When physicians in the emergency department evaluate individuals with unexplained coma, the ability to differentiate between structural and toxic or metabolic causes heavily influences diagnostic and treatment considerations. The history often provides the most important clues, especially when trauma or drug ingestion are suspected. However, often the history is unavailable, and the examination findings may offer the initial clues. Furthermore, daily assessment of the comatose patients in the critical care setting requires a working knowledge of examination techniques and clinicoanatomic correlation.
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APPROACH TO THE COMATOSE PATIENT
Plum and Posner31 emphasize the evaluation of breathing pattern, pupillary function, eye movements, and motor responses in the neurologic assessment of comatose patients, especially with regard to brainstem localization and diagnosis. Thus, neuro-ophthalmic techniques are paramount in this clinical setting. The ocular motility examination is especially important, because the pathways governing ocular motility traverse the entire brainstem, so pathology in this region often produces recognizable eye movement abnormalities. Conversely, if the eye movements are all normal, it is likely that the entire brainstem is normal as well. This review concentrates on the pupillary, eye movement, and funduscopic abnormalities in coma.
The examiner of a comatose patient should decide, in a rostral-caudal fashion, which neuroanatomic structures have been affected by the disease process. In general, if the brainstem is intact in a comatose patient, bilateral hemispheric or thalamic disease should be suspected. If the brainstem is injured, the dysfunction should be localized to the midbrain, pons, or medulla.
EXAMINATION IN COMATOSE PATIENTS
In the neuro-ophthalmic assessment, pupillary size, shape, and reactivity to light should be evaluated first. If suspected, the absence of pupillary reaction to light should be confirmed with a magnifying lens. Next, eye position and spontaneous eye movements should be observed. Any overt misalignment, such as an esotropia, vertical or oblique misalignment, or conjugate eye deviation, should be noted. The examiner should also look for spontaneous roving or rhythmic, repetitive vertical movements.32
When spontaneous eye movements are absent, doll’s eye or oculocephalic eye movements can be elicited by turning the head horizontally then vertically. The eyes should deviate in the direction opposite to the head turn. Oculocephalic maneuvers should not be performed in trauma patients with possible cervical spine injury.
If there are no oculocephalic eye movements, a stronger stimulus can be provided by applying ice cold water against the tympanic membranes, which provokes the vestibulo-ocular reflex (cold caloric test). The patient’s head should be angled at 30 degrees to align the horizontal semicircular canals perpendicularly to the floor. After visual inspection to exclude rupture of the tympanic membrane, 30 to 60 ml of ice water can be irrigated into the external auditory canal using a large syringe and the tubing from a butterfly catheter or an Angiocath without the needle. A kidney basin should be placed under the ear to contain the overflow of ice water. The cold water creates convection currents in the endolymph of the horizontal semicircular canals and inhibits the ipsilateral vestibular system. In the normal caloric response, the eyes move slowly and conjugately toward the tested ear, followed by a fast corrective phase in the opposite direction to reset the eyes, then the cycle repeats. The slow phase is produced by vestibulo-ocular connections from the unopposed contralateral ear, whereas the fast phase is mediated by the frontal eye fields. Warm water stimulation produces a contralateral slow phase and ipsilateral fast phase. The direction of the caloric response is named after the fast phase, and normal responses can be summarized in the mnemonic
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“COWS,” which stands for “cold-opposite, warm-same.” Caloric stimulation in the setting of a normal brainstem but bilateral hemispheric dysfunction would produce only an ipsilateral tonic slow phase. Complete brainstem injury would result in no slow or fast eye movements. The other ear can be tested after an interval of a few minutes. Bilateral caloric stimulation with cold water produces a downward slow phase, whereas stimulation with warm water bilaterally results in an upward slow phase.
Other important neuro-ophthalmic observations in comatose patients include testing of the corneal reflexes and the funduscopic examination. The corneal reflexes can be evaluated with a sterile cotton swab. Bilateral eyelid closure should be observed, but asymmetric contracture of the orbicularis oculi may result if a facial nerve palsy is present. Completely absent corneal reflexes suggest pontine dysfunction. The funduscopic examination is often normal, but papilledema would indicate elevated intracranial pressure, for instance, whereas a vitreous hemorrhage (Terson’s syndrome) may signify an aneurysmal subarachnoid hemorrhage. Because frequent monitoring of the pupils is important in comatose patients, pharmacologic dilation of the pupils prior to funduscopic examination is not routinely recommended.
The Glasgow Coma Scale assigns a number to the level of dysfunction in a patient following head injury. Patients can receive a score of 1 to 5 for level of their verbal response, 1 to 4 for spontaneity of eye opening (4 ¼ spontaneous, 3 ¼ to speech, 2 ¼ to pain, 1 ¼ none) and 1 to 6 for motor function. A total score of 3 to 8 is consistent with severe trauma, 9 to 13 indicates moderate trauma, and 14 or 15 reflects only mild trauma.33
PUPILLARY ABNORMALITIES IN COMA
Hypothalamic lesions may cause small but reactive pupils because of oculosympathetic paresis, whereas thalamic and mesencephalic lesions may result in third nerve palsies; midposition or large pupils; or, less likely, pupillary corectopia. Destructive lesions of the pons may disrupt the descending oculosympathetic pathways and result in bilateral pinpoint pupils. Diffuse anoxic brain damage
can cause midbrain dysfunction and dilated pupils. Initially in brain death, the pupils can be midposition or dilated and unreactive to light.34,35 With more
time after death, however, all pupils become midposition, reflecting the equal parasympathetic and sympathetic dysfunction.
As a rule, metabolic coma is more likely to be associated with normoreactive pupils than with coma resulting from a structural lesion, although there are exceptions.31
EYE MOVEMENT ABNORMALITIES IN COMA
In comatose patients, any abnormality in the positions of the eyes and any spontaneous movements should be noted first. Conjugate lateral eye deviation may indicate a destructive lesion in the ipsilateral frontal lobe or contralateral pons or a seizure focus in the contralateral cerebral hemisphere. Rarely, a thalamic lesion causes “wrong-way eyes,” with contraversive horizontal eye deviation. Conjugate downward eye deviation implies a dorsal midbrain lesion or hydrocephalus.
Dysconjugate eyes might suggest an extraocular muscle palsy, although depressed mentation often uncovers a latent esotropia or exotropia. A pupil involving third