Pupillary Syndromes Anisocoria

It is commonly written that 20 percent of the population has anisocoria of at least 0.4 mm in dim light, although published series cite highly variable percentages from 2 to 60 percent. The most common sort of variable anisocoria among healthy people has been called see-saw anisocoria or simple central anisocoria whereas the mechanism is indeterminate, this benign condition may vary from one examination to the next or even reverse sides. Light stimulation of one or both eyes decreases the anisocoria, and the pupillary reactions to light, near, and psychosensory stimulation are all normal. A different sort of anisocoria among seemingly healthy normal people results when the consensual response is weaker than the direct response. This type of anisocoria is present only when either eye is stimulated individually with light and alternates sides because the illuminated pupil is always the smaller one. This characteristic may result from the selective dysfunction of the intercalated neuron that connects the midbrain pretectal nuclei and the Edinger-Westphal subnucleus of cranial nerve III. These and other normal pupillary phenomena, such as hippus (pupillary unrest) and early release after maximum light response, may confound detection of a relative afferent pupillary defect. Finally, it is important to note that with age, the pupils normally become smaller, and the average diameter of the pupils in darkness decreases at approximately 0.5 mm per decade after the second decade of life. Neurologically significant anisocoria occurs with lesions affecting parasympathetic components in cranial nerve III and with disorders of the ocular sympathetic system.

Ocular Parasympathetic Syndrome, Preganglionic. Lesions affecting cranial nerve III often cause anisocoria in which the pupil is larger in the affected eye and the degree of anisocoria (difference in size) is greater in bright than in dim light. The important causes of cranial nerve III lesions in this setting include intracranial aneurysms (typically those of the posterior communicating artery at its junction with the internal carotid artery) y and small vessel disease with resulting ischemic nerve lesions, such as that associated with diabetes. The pupillary sphincter is usually involved in the setting of an aneurysm or other extra-axial compression like temporal lobe herniation, because the pupillomotor fibers are arranged on the outside of the nerve. In contrast, pupillary function is most often spared when ischemic lesions of the third nerve are present. y , y As a rule, the pupil is not solely affected in cranial nerve III lesions, because the autonomic component fibers are intimately associated with axons carrying motor innervation to the other muscles innervated by that nerve.

Ocular Parasympathetic Syndrome, Postganglionic (Adie's Pupil). Damage to the postganglionic parasympathetic pathways in the long posterior ciliary nerves produces the condition known as tonic pup/l.y , y This type of pupil is large and reacts very little to light when the stimulus is presented briefly but may contract slowly if the light stimulus is maintained for up to 30 to 40 seconds. Redilatation after the light is turned off is also very slow on the involved side. There is a greater pupillary constriction when the patient looks at a near object, and this difference is referred to as light-near dissociation. Tonic pupils are associated with patchy or generalized loss of deep tendon reflexes in Adie's syndrome. y This disorder is more common in women and is pathologically characterized by an idiopathic degeneration of spinal root and ciliary ganglia. It does not result in any clinically important sensory or motor defect apart from the areflexia. In Adie's tonic pupil, the axons of the postganglionic nerve degenerate one by one, producing paralysis of progressively more segments of the iris sphincter muscle. y Examination of the iris under magnification allows the examiner to perceive the segmental loss of constriction around the margin of the pupil in the early and intermediate stages of the disease. When a tonic pupil has been present for a period of time, all sectors become involved and, in general, the pupil becomes fixed at a small diameter.

Ocular Sympathetic Syndromes. With ocular sympathetic lesions (Horner's or Claude Bernard's syndrome), the pathological pupil is the smaller one, and the anisocoria is greater in dim than in bright light. The light reflex is

TABLE 9-5 -- SELECTED ETIOLOGIES ASSOCIATED WITH DISORDERS OF CRANIAL NERVES 111, IV, AND Vl

Etiological Category

Specific Etiologies

Chapter

STRUCTURAL DISORDERS

Developmental structural disorders

Arnold-Chiari malformation, cerebellar ectopias, basilar invagination

28

HEREDITODEGENERATIVE DISORDERS

Storage diseases: lipidoses, glycogen disorders, and leukoencephalopathies

Tay-Sachs', Gaucher's, Nieman-Pick C, and Pelizaeus-Merzbacher diseases

30

Aminoacidopathies/organic acidopathies, mitochondrial enzyme defects, and other metabolic errors

Maple syrup urine disease, nonketotic hyperglycinemia; Leigh's disease mitochondrial myopathies

31

Chromosomal abnormalities and neurocutaneous disorders

Ataxia-telangiectasia

32

The degenerative dementias

Alzheimer's disease

33

Movement disorders

Parkinson's disease, progressive supranuclear palsy, Wilson's disease, Shy-Drager syndrome

34

Ataxias

Friedreich's ataxia, autosomal dominant cerebellar degeneration

35

Degenerative motor, sensory, and autonomic disorders

Parasympathetic dysautonomia, Shy-Drager-syndrome, acute pandysautonomia

36

ACQUIRED METABOLIC AND NUTRITIONAL DISORDERS

Endogenous metabolic disorders

Diabetes, hypomagnesemia

38

Exogenous acquired metabolic disorders of the nervous system: toxins and illicit drugs

Botulism

39

Nutritional deficiencies and syndromes associated with alcoholism

Wernicke-Korsakoff syndrome, vitamin E deficiency

40

INFECTIOUS DISORDERS

Viral infections

Brain stem encephalitis

41

Nonviral infections

Mucormycosis (diabeties), fungal meningitis

42

NEUROVASCULAR DISORDERS

Small vessel arteriosclerosis, berry aneurysm, artery dissection

45

NEOPLASTIC DISORDERS

Primary neurological tumors

Brain stem glioma, medial sphenoid ridge and parasellar meningioma; Pancoast's carcinoma (lung), lymph node metastases (cervical)

46

Metastatic neoplasms and paraneoplastic syndromes

Paraneoplastic brain stem encephalitis; meningeal carcinomatosis, neuroblastoma, ovarian carcinoma

47

DEMYELINATING DISORDERS

Demyelinating disorders of the central nervous system

Multiple sclerosis

48

AUTOIMMUNE AND INFLAMMATORY DISORDERS

Systemic lupus erythematosus, penarteritis nodosa, vasculitis, myasthenia gravis

50

TRAUMATIC DISORDERS

Blunt, penetrating head trauma

51

EPILEPSY

Seizures (nystagmoid movements)

52

HEADACHE AND FACIAL PAIN

Migraine, cluster headaches

53

DRUG-INDUCED AND IATROGENIC NEUROLOGICAL DISORDERS

Anticholinergics, phenytoin, carbamazepine, aminoglycosides

55

usually not perceptibly altered. This anisocoria is usually asymptomatic. Another finding in Horner's syndrome is mild ptosis of the upper eyelid from weakness of Muller's smooth muscle in the lids. Less well recognized, however, is that weakness of Muller's muscle in the lower lid also causes the lower lid to elevate. Upper lid ptosis and elevation of the lower lid together cause narrowing of the palpebral fissure. This contributes to an illusion that the involved eye is displaced backward in the orbit, which is the so-called apparent enophthalmos described with Horner's syndrome. A third component of Horner's syndrome involves sympathetic fibers serving the skin of the forehead just above the brow that travel with the nasociliary branch of the first (ophthalmic) division of the trigeminal nerve. With intracranial postganglionic sympathetic lesions, altered vasomotor tone and decreased sweating may be limited to a triangular patch of skin just above the brow extending to the midline. The sudomotor and vasomotor fibers to the skin of the lower face travel with branches of the external carotid artery after leaving the sympathetic paravertebral chain near the skull base and are spared with lesions rostral to this point of divergence.

The most important disorder that produces Horner's syndrome is malignancy involving the preganglionic sympathetic pathways in the neck or next to the apex of the lung. A minority of these preganglionic Horner's syndrome cases are secondary to trauma, usually resulting from penetrating neck wounds and root involvement in spinal injuries, and they should be obvious from the history and physical findings. In stellate ganglia anesthetic blocks, a transient Horner's syndrome predictably occurs because the preganglionic ocular sympathetic fibers go through this area. Inflammation, caused by suppurative infections and granulomatous diseases such as sarcoidosis or tuberculosis in cervical lymph nodes, is an occasional nonmalignant cause for preganglionic ocular sympathetic palsy. This etiology

has become more prevalent in the AIDS era. Another important cause is carotid artery dissection, which presents with pain in the neck along with signs of ipsilateral cerebral hemisphere ischemia.

Postganglionic ocular sympathetic palsy is commonly associated with pain in the ipsilateral orbit and eye. In the early part of this century, a Norwegian ophthalmologist named Raeder reported this combination of pain, meiosis, and ptosis as a paratrigeminal syndrome with localizing value for mass lesions in the middle cranial fossa.y It is important to note that all four of his patients had, in addition to ocular sympathetic palsy, findings referable to the ipsilateral cranial nerves III through VI, either singly or in combination. During the past 2 decades, there has been growing awareness of patients with painful ocular sympathetic palsy without demonstrable middle fossa mass lesions. These patients often have histories of episodic retrobulbar and orbital pain that, in many cases, is typical of cluster or histamine headache (see Chaptei.53, ) [19' The ocular sympathetic lesion occurs during a cluster of headaches and sometimes resolves spontaneously after the cluster has ended, although at times, it remains as a permanent sequel. This benign condition, considered a migraine variant, has been referred to as Raeder's paratrigeminal syndrome, type II, and to qualify for this diagnosis, patients must have no objective neurological deficits of cranial nerves III through VI. It has been speculated that in type II Raeder's syndrome, the postganglionic ocular sympathetic fibers are affected by edema in the wall of the carotid artery.

CNS (hypothalamus, brain, or spinal cord) lesions are an uncommon cause of Horner's syndrome and are almost always recognizable by the associated cranial nerve, cerebellar, motor, or sensory findings. A classic example is Wallenberg's lateral medullary syndrome, which is usually caused by occlusion of one vertebral artery with infarction in the distribution of the posterior inferior cerebellar artery (see C.haptĀ§L..2.2 and Chapter.45 ). The attendant dorsolateral medullary lesion produces a syndrome that includes ocular sympathetic palsy along with facial numbness ipsilateral to the lesion, pain and temperature loss in the contralateral extremities, vertigo, dysphagia, and dysarthria.

LIGHT-NEAR DISSOCIATION

Light-near dissociation became a clinical sign relevant to etiological diagnosis when Argyll Robertson described it as a sign of neurosyphilis. y , y The features of the Argyll Robertson pupil include (1) meiosis, (2) a normal afferent visual system (retina, optic nerve, chiasm, optic tract), and (3) failure of pupillary meiosis to light stimulation but normal pupillary constriction in response to accommodation and convergence with near viewing. In the original description, patients with this phenomenon had tabes dorsalis as well, and the pupil became an invaluable aid to the diagnosis of neurosyphilis. Light-near dissociation is not specific for neurosyphilis, however, and merely refers to the phenomenon in which the pupillary constriction in response to looking at near objects is greater than that in response to a bright light stimulus. The definition is imprecise because there is no way to quantify the degree of near effort that determines the amount of pupillary constrictor tone that is produced by the near stimulus. Many individuals make a poor effort when looking close up, and this may mask the presence of light-near dissociation.

Light-near dissociation may be due to input or output failure. Input failure occurs in bilateral prechiasmal lesions of the optic nerve or retina, chiasmal lesions, and bilateral optic tract lesions. As such, the examiner should establish whether the afferent visual system is functioning normally. If these conditions are present, the light reaction may be reduced and the near reaction left unaffected, creating a false light-near dissociation. Output failure can be the cause of Argyll Robertson pupil and occurs in the setting of diabetes mellitus, peripheral neuropathies, Adie's pupil (see earlier), and the Miller-Fisher variant of acute idiopathic demyelinating polyradiculopathy (see Chapter.49 ). Patients with midbrain compressive and ischemic lesions generally demonstrate large, light-near dissociated pupils, in contrast to the classic description of Argyll Robertson, in which the pupils are small. y The mechanism of neurosyphilis-related Argyll Robertson pupil remains unknown.

BILATERAL UNREACTIVE PUPILS

Failure of both pupils to react to both light and near stimuli has been described in cases of dorsal or rostral midbrain lesions, sometimes before the development of vertical gaze palsy or other ocular motility impairment. y y An isolated unilateral (or bilateral) dilated, fixed pupil should also raise suspicion of pharmacological mydriasis. Patients or medical personnel may deliberately or inadvertently instill medications with parasympatholytic or anticholinergic activity into the eye. Pupils in this state will fail to constrict in the presence of pilocarpine (1 to 4 percent), whereas all fixed pupils from CNS or peripheral nervous system lesions become extremely meiotic in response to these concentrations of the drug.

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