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, or 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.
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.
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Constricted pupils (miosis) |
Other Useful Tests
1. Venereal disease research laboratory (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)
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Constricted pupils (miosis) |
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TABLE 19. Convulsions |
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Case Presentation #11
A 24-year-old white male medical student was found to have miosis, partial ptosis, and enopthalmos of the left eye on a routine life insurance examination. On further questioning, he admitted he had intermittent weakness of his left arm and hand.
Question #1. Applying the methods from the above discussion, what are your diagnostic possibilities at this point?
Complete neurologic examination was normal except for a weak left radial pulse.
Question #2. What are your diagnoses now?
