Symptom Finder - Dilated Pupils ( Mydriasis)
DILATED PUPILS (MYDRIASIS)
Like that of myosis, the differential diagnosis of dilated pupils or mydriasis can best be developed by applying neuroanatomy
“Knowing where the lesion is, tells us what the lesion is.” One simply follows the nerve pathway from the end organ up the oculomotor nerve to the termination in the brainstem. A dilated pupil, however, may also signify a lesion of the optic nerve and its pathways.
1. Lesions of the oculomotor nerve and pathways
End organ: Lesions of the eye that cause dilated pupils include glaucoma, high myopia, anticholinergic drugs (e.g., atropine), and sympathomimetic drugs (such as Neo-Synephrine).
Peripheral portion of the oculomotor nerve: Important lesions here include aneurysms of the internal carotid artery and its branches; herniation of the brain in brain tumors, subdural hematomas, and other space-occupying lesions; cavernous sinus thrombosis; sellar and suprasellar tumors; tuberculosis and syphilitic meningitis; and sphenoid ridge meningiomas. Diabetic neuropathy of the third cranial nerve does not usually cause mydriasis. Most of these lesions are associated with ptosis and paralysis of the other extraocular muscles supplied by the oculomotor nerve.
Brainstem: Lesions here include MS, syphilis, encephalitis, Wernicke encephalopathy, brainstem gliomas, and Weber syndrome. Barbiturates and other drugs may cause dilated pupils by their central nervous system effects.
2. Optic nerve and pathways
End organ: Keratitis, cataracts, retinitis, and occlusion of the ophthalmic artery are included here.
Peripheral portion of the optic nerve: Aneurysms; optic neuritis; sellar and suprasellar tumors; optic nerve gliomas; primary optic atrophy from lues and other conditions; orbital
fractures; exophthalmos; and cavernous sinus thrombosis are recalled in this category.
Brainstem: The lesions involving the optic tract here are similar to those that involve the oculomotor nerve discussed above. Optic cortex (calcarine fissure) lesions may cause blindness, but there is no mydriasis.
Approach to the Diagnosis
The clinical picture will often help to pinpoint the diagnosis. A history of drug use (narcotics, amphetamines, etc.) will suggest drug intoxication.
Unilateral dilated pupil with ptosis would suggest oculomotor palsy, which may be due to a cerebral aneurysm or tumor or other space-occupying lesion. Early compression of the oculomotor nerve by a subdural hematoma or other mass may be indicated by a dilated pupil. Diabetic neuropathy may cause ptosis and extraocular muscle palsy without a
dilated pupil. Unilateral or bilateral dilated pupils with blurred vision may be due to glaucoma or iritis. Dilated pupils may also be associated with blindness
A dilated pupil with other neurologic findings is a clear indication for referral to a neurologist or neurosurgeon. He or she can best decide whether a CT scan or MRI is indicated.
Without focal neurologic signs the patient should have a drug screen. If that is negative, a referral to an ophthalmologist may be indicated. He or she may be able to do tonometry to rule out glaucoma and a slit lamp examination to evaluate for iritis and other conditions.
Other Useful Tests
1. Spinal tap (MS)
2. Visual evoked potentials (MS)
3. Arteriogram (cerebral aneurysm)
4. Visual field examination (MS, glaucoma)
5. Mecholyl test (Adie pupil)
Like that of myosis, the differential diagnosis of dilated pupils or mydriasis can best be developed by applying neuroanatomy
“Knowing where the lesion is, tells us what the lesion is.” One simply follows the nerve pathway from the end organ up the oculomotor nerve to the termination in the brainstem. A dilated pupil, however, may also signify a lesion of the optic nerve and its pathways.
1. Lesions of the oculomotor nerve and pathways
End organ: Lesions of the eye that cause dilated pupils include glaucoma, high myopia, anticholinergic drugs (e.g., atropine), and sympathomimetic drugs (such as Neo-Synephrine).
Peripheral portion of the oculomotor nerve: Important lesions here include aneurysms of the internal carotid artery and its branches; herniation of the brain in brain tumors, subdural hematomas, and other space-occupying lesions; cavernous sinus thrombosis; sellar and suprasellar tumors; tuberculosis and syphilitic meningitis; and sphenoid ridge meningiomas. Diabetic neuropathy of the third cranial nerve does not usually cause mydriasis. Most of these lesions are associated with ptosis and paralysis of the other extraocular muscles supplied by the oculomotor nerve.
Brainstem: Lesions here include MS, syphilis, encephalitis, Wernicke encephalopathy, brainstem gliomas, and Weber syndrome. Barbiturates and other drugs may cause dilated pupils by their central nervous system effects.
2. Optic nerve and pathways
End organ: Keratitis, cataracts, retinitis, and occlusion of the ophthalmic artery are included here.
Peripheral portion of the optic nerve: Aneurysms; optic neuritis; sellar and suprasellar tumors; optic nerve gliomas; primary optic atrophy from lues and other conditions; orbital
fractures; exophthalmos; and cavernous sinus thrombosis are recalled in this category.
Brainstem: The lesions involving the optic tract here are similar to those that involve the oculomotor nerve discussed above. Optic cortex (calcarine fissure) lesions may cause blindness, but there is no mydriasis.
Approach to the Diagnosis
The clinical picture will often help to pinpoint the diagnosis. A history of drug use (narcotics, amphetamines, etc.) will suggest drug intoxication.
Unilateral dilated pupil with ptosis would suggest oculomotor palsy, which may be due to a cerebral aneurysm or tumor or other space-occupying lesion. Early compression of the oculomotor nerve by a subdural hematoma or other mass may be indicated by a dilated pupil. Diabetic neuropathy may cause ptosis and extraocular muscle palsy without a
dilated pupil. Unilateral or bilateral dilated pupils with blurred vision may be due to glaucoma or iritis. Dilated pupils may also be associated with blindness
A dilated pupil with other neurologic findings is a clear indication for referral to a neurologist or neurosurgeon. He or she can best decide whether a CT scan or MRI is indicated.
Without focal neurologic signs the patient should have a drug screen. If that is negative, a referral to an ophthalmologist may be indicated. He or she may be able to do tonometry to rule out glaucoma and a slit lamp examination to evaluate for iritis and other conditions.
Other Useful Tests
1. Spinal tap (MS)
2. Visual evoked potentials (MS)
3. Arteriogram (cerebral aneurysm)
4. Visual field examination (MS, glaucoma)
5. Mecholyl test (Adie pupil)
