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BASICS IN NEURO-OPHTHALMOLOGY

Kathleen B. Digre, M.D.

DEPARTMENTS OF NEUROLOGY AND OPHTHALMOLOGY UNIVERSITY OF UTAH MEDICAL CENTER

Objectives:

1. Know the pathways for pupillary responses.

2. Know how to diagnose a Horner's Syndrome; Adies Syndrome; How do you approach anisocoria?
What are causes of light near dissociation?

3. Know the pattern of visual field defects and their neuro-anatomical localization.

4. Know the principal disorders of ocular motility.

I. Introduction: Neuro-ophthalmology is the study of the eye and its relationship to the nervous system. As with any problem in neurology, the history is probably one of the most important parts of the neuro-ophthalmic examination.

The neuro-ophthalmic examination consists of:

1. Best corrected visual acuity using either a Snellen acuity chart at 20 ft. or a near card equivalent for each eye (OD = R eye; OS = L eye).

2. Pupil examination.

3. Visual field examination

4. Extraocular motility examination

5. Funduscopic examination—this will be covered in a separate lecture

We will approach each part of the examination emphasizing how to test the patient, the anatomy of the area tested and understanding the pathologic defects in this testing process.

II. Visual Acuity Testing: Near card

Patient wears corrective lenses,

cover each eye individually,

read to the lowest line possible.

III. Pupils:

A. Anatomy:

The pupils are important to test due to the long pathways involved. They are innervated both by the sympathetic and parasympathetic systems and can give a general indication of the neurologic condition.

Constrictor of Pupil—Parasympathetic input into the pupil and the pupillary light reflex.

The pupillary light reflex: Light stimulates the retinal photo receptor and initiates pupillo-constriction as well as visual impulses. Pupil motorfibers are transmitted via the optic nerves; they undergo a hemi-decussation at the chiasm. They exit from the optic tracts before the lateral geniculated body and enter the brainstem via the brachium of the superior colliculus. After synapsing in the prectectal area, fibers are distributed to the ipsilateral and contralateral Edinger Westphal nuclei. The efferent pupillary fibers travel via the III nerve to synapse in the ciliary ganglia after exiting the ciliary ganglion. Short ciliary nerves then go the iris sphincter and ciliary body.

Dilator of the Pupil Sympathetic Pathway

The sympathetic system also supplies the pupil. This pathway is perhaps less well defined but probably originates in the hypothalamus. It descends uncrossed, to the level of C8-T2 and it exits from the spinal cord via the perivertebral sympathetic chain to synapse in the superior cervical ganglion and follow the carotid plexus to join the ophthalmic division of the trigeminal nerve. It reaches the ciliary body and the dilator of the iris, via the long ciliary nerves.

B. Examination of the pupils:

1. Note the size and shape in darkness and in light.

2. Check for the light reflex in each eye individually.

3. Look for an afferent pupillary defect (RAPD - also known as Marcus Gunn Pupil) by:

a. The Swinging Flash Light Test

b. The pupils must react to light in order to perform the test

c. Not a test of the pupil per se—but we do the test when we look at the pupil

d. Tests the optic nerve function

e. Relies on a difference between the two optic nerves—one must be different from each other

4.Check the near reflex by bringing the patients own finger toward his nose.

C. Recording the pupils examination:

1. Record the actual size of the pupil OD (right eye) and OS (left eye). For example: pupils in darkness 8 mm OU (both eyes), in light 3 mm OD and 2.5 mm OS. No relative afferent pupillary defect (no RAPD). Good near reflex.

D. The pathology involving the pupil.

1. Lesions of the parasympathetic system cause a dilated pupil (greater anisocoria in light).

a. An acute third nerve palsy: may signal compression of the third nerve due to a posterior communicating artery aneurysm. A third nerve palsy will be usually associated with other signs of dysfunction including ocular motility disturbances and ptosis. An isolated dilated pupil does not usually signify a III nerve palsy.

b. Tonic pupil or Adie's pupil is characterized by a dilated pupil with very poor or no light reaction with tonic constriction to near and tonic redilation. Under the slit lamp sectoral palsies of pupillary sphincter may be seen with light stimulation. Because the abnormality is post-ganglionic (that is, damage to the ciliary ganglion), one can demonstrate supersensitivity of the sphincter muscle to pilocarpine 1/10%. An acute Tonic pupil usually a condition seen in young women who have asymptomatic anisocoria. Adie's syndrome consists of a tonic pupil and loss of deep tendon reflexes. The lesion causing pupillary dysfunction is generally thought to be in the ciliary ganglion and the cause is basically unknown.

c. Argyll Robertson pupil is characterized by small and unreactive pupils (usually bilateral). "Light-near" dissociation exists, i.e.; the pupil does not react to light but will react to near (frequently the pupils are irregular). This pupil is associated with syphilis. In order to diagnosis this a VDRL and FTA be drawn. The anatomic cause is unknown. A long-standing Adie's Tonic pupil can occasionally be confused with this pupil.

d. Light-near dissociation can be seen in lesions in the mid-brain.

2. Lesions of the sympathetic system cause a small pupil (increased anisocoria in darkness) Horner’s Synd.

a. Horner's Syndrome, consists of pupillary meiosis which is more accentuated in darkness; light and near reactions are intact. There is ipsilateral ptosis due to paresis of Muller's muscle (not the levator muscle of the eyelid). There is an apparent enophthalmos because there is also an upside/down ptosis. Occasionally anhydrosis of the face will also be seen.

b. Pharmacologic testing, to confirm the diagnosis of a Horner's syndrome, a pharmacologic test may be done.

1) Cocaine test, ten percent cocaine is instilled into the eye. The cocaine prevents the re-uptake of norepinephrine into the normal nerve and hence the norepinephrine will cause dilation of the pupil. If there is a lesion anywhere along the sympathetic pathway, there will be less norepinephrine coming down the nerve to be released; therefore cocaine will not dilate the eye with a sympathetic defect.

2) Hydroxyamphetamine test, to localize whether the Horner's syndrome is preganglionic (that is before the superior cervical ganglion) or postganglionic (after the cervical ganglion), Hydroxyamphetamine (Paredrine) is instilled into both eyes at another time. Hydroxyamphetamine actively releases norepinephrine from the nerve endings. If the lesion is preganglionic, there will be normal norepinephrine store present at the iris and therefore the pupil dilates. A dilation to Hydroxyamphetamine in a Horner's eye means the lesion is preganglionic. If the pupil does not dilate, the lesion is postganglionic because there is no norepinephrine to be released.

c. Causes of pre-ganglionic Horner's:

Central: Stroke (Wallenburg syndrome)

Dissection of vertebral artery with brain stem

Pre-ganglionic: Apex of lung mass

Cervical spine abnormality

In children, neuroblastoma

d. Causes of post-ganglionic Horner's:

Dissection of carotid artery

Cluster Headache

3. Pharmacologic Blocade.

a. Can occur due to accidental exposure of the iris to a dilating agent (e.g. Jimson weed; scopolamine patch)

b. Test with pupillary constricting drug—Pilocarpine 1%--if no reaction—likely pharmacologic blockade

III. VISUAL FIELDS

Visual fields can localize a lesion in the visual sensory pathway.

A. Testing the visual field.

1. Visual fields to confrontation

a. Each eye is covered separately. You tell the patient to cover the untested eye with the palm of the hand. Be sure the patient is not peeking through the fingers. Ask the patient to fixate on your nose and then you present fingers rapidly in all four quadrants of his vision while he is fixating on your nose and he counts the fingers.

b. Hand-to-hand comparison when both hands are presented in the inferior field or the superior field. Ask the patient which he sees better.

c. One can test the field with a red object and ask the patient if he/she sees both objects as red in both the superior and inferior fields.

d. Double simultaneous stimulation. One can test double simultaneous stimulation by having the patient fixating on the nose with both eyes open and by wiggling the fingers in the outside quadrants. Obviously one can pick up a gross hemianopia or and extinction to simultaneous stimulation. However, this form of visual field testing is not adequate for the routine examination. Each eye must be tested separately.

2. When testing the visual field in the lethargic patient, the examiner may use a light or hand to elicit a blink.

3. Other ways of visual field testing:

a. Tangent screen

b. Goldmann visual field perimetry

c. Automated perimetry

B. Recording the visual field

Pretend you are superman, burning the patient's visual field into the page. By convention, we recorded the left eye on the left and the right eye on the right (CF= count fingers).

C. Anatomy and Lesions:

Anatomy of the visual field afferent system. The afferent system starts at the retina, progresses through the optic disc, optic nerve, optic chiasm, lateral geniculate body, optic radiation's to the occipital cortex. Lesions along this pathway cause characteristic visual field defects.

Diagram showing the effects on the fields of vision produced by lesions at various points along the optic pathway: A: Complete blindness in left eye; B: The usual effect is a left junction scotoma in association with a right upper quadrantanopia. The later results from interruption of right retinal nasal fibers that project into the base of the left optic nerve (Wilbrand's knee). A left nasal hemianopia could occur from a lesion at this point but is exceedingly rare; C: Bitemporal hemianopia; D: Right homonymous hemianopia; E and F: Right upper and lower quadrant hemianopia; and G: Right homonymous hemianopia. From Victor & Adams: Neurology

IV. OCULAR MOTILITY

A. Testing extra-ocular muscles and motility.

1. Extra-ocular movements, observe the normal relationships of the eyes to the head and lids to the cornea and look for ptosis. Look for spontaneous movements of the eye. Then test the cardinal directions of gaze saying, "Follow my finger with just your eyes" and present your finger in the form of the letter H.

Remember that the third nerve supplies the following muscles: Inferior, oblique, superior rectus, inferior rectus and medial rectus as well as the levator of the lid. The fourth supplies the superior oblique. The sixth nerve supplies lateral rectus muscles.

(a) Recording the extra ocular movements, this should be done on a diagram showing any limitation of function. For example:

B. Disorders of ocular motility include third, fourth, and sixth nerve palsies, internuclear ophthalmoplegia, and 1½ syndrome .

1. Third Nerve Disorder

a. A third nerve palsy will frequently present as diplopia or ptosis. The patient will have a dilated pupil, ptosis on the same side and ophthalmoplegia of all muscles except for the lateral rectus on that side and superior oblique.

b. Sudden onset of a third nerve palsy: Be sure that an aneurysm is not present.

c. There are many other causers of third nerve palsies, such as brainstem or midbrain infarction. These syndromes will give other neurologic findings such as ipsilateral third nerve paresis with contralateral hemiparesis (Weber's syndrome), or ipsilateral third nerve paresis with contralateral hemitremor expanding mass in the temporal lobe because the third nerve caught between the edge of the tentorium cerebelli and the uncus of the temporal lobe in Uncal Herniation Syndrome. Cavernous sinus lesions and superior orbital fissure masses can also cause third nerve lesions.

d. Isolated third nerve palsies:

Ischemic (from diabetes)

Aneurysmal compression (look for pupil enlargement)

Trauma

Tumor (check for aberrant regeneration)

Infection

Inflammation

Idiopathic

The III Nerve Pathway

(From Bajandas, Kline: Neuro-Ophthalmology)

2. Fourth nerve palsy. The fourth cranial nerve or the trochlear nerve has its nucleus in the periaqueductial gray. Fibers of this nerve cross around the periaqueductial gray, and are the only cranial nerves to emerge on the dorsal surface of the brainstem. The trochlear nerve passes around the brainstem, across the tentorium and goes into the dura of the cavernous sinus lateral and inferior to the third nerve. It passes through the superior orbital fissure and supplies the superior oblique muscles. This nerve has the longest course of any cranial nerve in the subarachnoid space. The superior oblique muscle is a depressor in adduction. It is also a rotator.

a. Dysfunction of the fourth nerve causes the patient to complain of vertical diplopia.

b. The most common causes of fourth cranial nerve palsy is trauma. Since this is a long and very delicate nerve, it is easily disrupted even by small head trauma.

c. Isolated IV palsies

1) Trauma

2) Ischemic

3) Masses (along the clivus)

The IV Nerve Pathway

(from Bajandas, Kline: Neuro-Ophthalmology)

3. The sixth nerve. The sixth nerve or the abducens nerve nucleus lies in the dorsal portion of the pons near the midline, just underneath the fourth ventricle (see diagram). The sixth nerve leaves the brainstem at the pontomedullary junction, it runs in the subarachnoid space along the base of the pons where it is closely associated with the clivus bone. It pierces the dura and runs in the cavernous sinus and enters the orbit through the superior orbital fissure.

The VI Nerve Pathway

(from Bajandas, Kline: Neuro-Ophthalmology)

a. Pathology:

Isolated sixth nerve palsies have no localizing value. If they are associated with other neurologic signs such as fifth nerve palsy, seventh nerve palsy, or eighth nerve palsy, they may be of localizing value. Isolated sixth nerve palsies are commonly due to small occlusive disease in older individuals, trauma in all age groups or underlying tumors. Chronic sixth nerve palsies should be evaluated.

b. Isolated VI nerve palsy:

1) Idiopathic

2) Ischemic

3) Traumatic

4) Inflammation

5) Tumor

6) Cavernous sinus thrombosis

4. Internuclear ophthalmoplegia:

a. The PPRF or parapontine reticular formation is called the conjugate gaze center (horizontal gaze lies in the pons). The PPRF makes internuclear connections to the sixth nerve as well as to the third nerve. Its connection to the third nerve is called the medial longitudinal fasciculus which crosses to the contralateral third nerve. An MLF lesions blocks the information going from the PPRF to the third nerve nucleus. This results in the internuclear ophthalmoplegias (INO). Since MLF fibers originate in one PPRF and cross immediately to the other side, before ascending to the third nerve nucleus, an MLF lesion is on the same side as the eye with the medial rectus or adduction weakness. The INO is named by the side of the MLF lesion or the side of the adduction deficit. Internuclear ophthalmoplegia are frequently seen in vascular disease, but also can be seen in demyelinating diseases such as Multiple Sclerosis.

b. The clinical picture of a left INO or left MLF lesion: when looking to the right there is a failure of adduction of the left eye and abducting nystagmus of the right eye. A slowed adducting saccade is another sign of an INO.

(from Bajandas, Kline: Neuro-Ophthalmology)

5. 1½ syndrome:

a. A lesion of the PPRF

b. Gaze palsy and INO

c. E.G. a RPPRF lesion gives a right

gaze palsy and right INO

e.g. A right PPRF gives a right gaze palsy (the one) and a right INO (the one-half)

C. Other Eye Movements

1. Testing for saccades. Saccades are a rapid eye movements system which serves to refoviate the eye on an object of regard. The movement is demonstrated to command by presenting a target, “Look at my finger, look at my nose”. Saccades are fast 200-400 degrees per second. Disorders of the saccades include hypometric saccades (multiple small eye movements between two targets), hypermetric saccades (saccades that overshoot the endpoint and then go back to the desired object), and slow or absent saccades (no fast movement). Saccades are generated in the frontal eye fields.

b) Rapid eye movements to get to a new target

c) Starts in the Frontal eye field (contralateral)> to the PPRF (burst neurons)> project to abducens, and via MLF to III nerve

d) Disorders in saccades: Frontal gaze palsy due to frontal lobe injury; dysmetria; saccadic intrusions (square wave jerks); opsoclonus (saccadomania)

2. The pursuit system allows the eye to follow a target without saccades. We are able to maintain acuity during pursuit and pursuit will break down at speeds exceeding 30-35 degrees per second. Defective pursuit is seen when pursuit is broken up by saccades (saccadic pursuit). Pursuit lies in parietal occipital areas.

3. The vestibular ocular reflex (VOR) is a complicated pathway which can be affected by many disease processes. We test the reflex in two ways. First, in an alert patient we can ask them to fixate on a distant target while moving them in a swivel chair. The eyes should move smoothly side to side. A normal healthy individual should be able to suppress the reflex by fixating on his/her thumb while he/she is moved in the swivel chair. The eye should remain on the thumb without nystagmus or moving from the target.

4. Dorsal midbrain Syndrome—Parinaud’s Syndrome

a) Vertical gaze disorder

1. Complex pathways involving Frontal eye fields, parieto-occipital temporal junction, superior colliculus, ri MLF, PPRF and INC

2. Disorders of vertical gaze important: Up gaze paralysis (dorsal midbrain syndrome), Down gaze paralysis, progressive supranuclear palsy

b) Characteristic findings in dorsal midbrain syndrome

1. up-gaze paralysis

2. lid-retraction

3. light-near pupillary dissociation

4. convergence retraction nystagmus

5. Nystagmus:

a) Nystagmus is a rhythmic oscillation of the eyes

1. Jerk Nystagmus (initial slow; fast phase). The fast phase names the nystagmus; the pathology is the slow drift

2. Pendular nystagmus—phases opposite in direction but equal velocity

b) Nystagmus--what to look for

1. One eye or both

2. Jerk or pendular

3. Horizontal, vertical or both

4. Conjugate or dissociated

5. Primary position or eccentric gaze

6. Change with gaze position

c) Symptoms

1. Oscillopsia, blur, vertigo

d) Nystagmus has basically two parts: a slow phase and a rapid recovery phase. The slow phase which is the initial phase is considered to be the abnormal movement. The rapid phase is corrective. Nystagmus, however, it is names by side of the fast or corrective phase. Some nystagmus has localizing value.

1) Downbeat nystagmus can be seen with lesions of the cervical medullary junction.

2) Upbeat nystagmus (fast phase is up while the eyes are in primary position) can be seen with cerebellar or medullary tumors such as medulloblastoma.

3) Lateral nystagmus can be due to drugs or structural lesions in the cerebellum

6. There are many other abnormal eye movements which are not nystagmus: For example, square wave jerks, flutter, opsoclonus.

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