CONSTRICTED PUPILS (MIOSIS)

The best method to develop a list of the causes of a constricted pupil is to use neuroanatomy. one simply follows the nerve pathways from the end organ (iris) through the peripheral portion of the nerves to the central nervous system (brainstem) (Table 18).

1. End organ. Iritis, keratitis, and the cholinergic drugs may be the cause of the constricted pupil in this location. Hyperopia and presbyopia are also possible causes.
2. Peripheral nerves. Constriction of the pupil may occur from lesions anywhere along the sympathetic pathway as it branches around the internal carotid artery (aneurysms, thrombosis, and migraine), enters the stellate ganglion in the neck (scalenus anticus syndrome, tumors or adenopathy in the neck), and follows the preganglionic pathway into the spinal cord (aneurysm of the aorta, mediastinal tumors, spinal cord tumors, or other space-occupying lesions).
3. Central nervous system. Lesions involving the sympathetic pathways of the brainstem (posterior inferior cerebellar tumors, occlusion, brainstem tumors, hemorrhages, encephalitis, or toxic encephalopathy) will cause miosis. Both pupils are constricted in the Argyll Robertson pupil of neurosyphilis in which the damage is located in the pretectal nucleus of the midbrain. Morphine characteristically causes bilateral constriction of the pupils, probably based on its central nervous system effects.

CONSTRICTED PUPILS (MIOSIS)

CONSTRICTED PUPILS (MIOSIS)

Approach to the Diagnosis

In unilateral miosis, the clinician must look for local conditions such as iritis and keratitis. If there is an associated ptosis and enophthalmos, Horner syndrome is present. The lesion is undoubtedly located somewhere along the sympathetic pathway. Miosis alone, however, may be due to a sympathetic lesion. Bilateral miosis and coma should suggest narcotic intoxication or a brain stem lesion (possibly a pontine hemorrhage). Bilateral miosis in an alert individual with pupils that fail to react to light but react to accommodation is clear evidence of an Argyll Robertson pupil. Partial Argyll Robertson pupils do occur. Bilateral miosis in older individuals without loss of the light reflexes suggests hyperopia or arteriosclerosis.

The laboratory workup may include an x-ray film of the cervical spine, chest and skull roentgenogram, a CT scan or MRI of the brain, and a spinal tap or arteriograms, depending on the association of other symptoms and signs. A starch test to determine if sweating function is lost on the side of the lesion will help locate the level of the sympathetic nerve lesion.

Other Useful Tests

1. VDRL test (neurosyphilis)
2. Histoplasmin skin test (iriditis)
3. Toxoplasma serology (iridocyclitis)
4. Epinephrine test (Horner syndrome)
5. Slit lamp examination (iriditis, keratitis)
6. Tonometry (glaucoma)
7. Mecholyl test (Argyll Robertson pupil)

Book Source Details

• Book Title: Differential Diagnosis in Primary Care
• Author(s): R. Douglas Collins
• Year of Publication: 2007
• Copyright Details: Differential Diagnosis in Primary Care, Copyright © 2007 Lippincott Williams & Wilkins.

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Copyright Details: Differential Diagnosis in Primary Care, Copyright © 2008 Williams & Wilkins.

More About Causes of Pupil symptoms

• Back to symptom: Pupil symptoms: Introduction (review 164 causes)
• Next Book Extract About Pupil symptoms: Mydriasis (Handbook of Signs & Symptoms (Third Edition))
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More About This Book: Title: Differential Diagnosis in Primary Care Authors: R. Douglas Collins Publisher: Lippincott Williams & Wilkins Copyright: 2007 ISBN: 0-7817-6812-8

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