![]() Coma or brain death: Severe brain damage may cause a change in the size and reactivity of the pupils.Dilute pilocarpine (0.21 solution) is a parasympathomimetic alkaloid that may be used to differentiate iris atrophy and other lesions of the iris, such as posterior synechia, from a lesion of the parasympathetic system. Injuries to the eyes and head can cause scarring or blindness. Constriction of the pupil is a common reaction by an injured eye, and it can add to the pain of a damaged cornea. In a normal eye, administration of physostigmine (and pilocarpine, below) causes slow or delayed constriction of the pupil. Surgery: Eye surgery may result in alterations in pupil size, which can be permanent. One of the most common causes of eye issues in dogs is a scratch to the lens of their eye.Seizure: Sometimes seizures (a disruption of electrical activity in the brain) can cause changes in the pupils, which may be equal or unequal. Unilateral blindness from a retinal disorder may cause only a mild dilation of the affected eye in dogs and cats because of weaker consensual stimulation.The ability of the pupil to either dilate or constrict is medically known as pupillary response. If the pupils are asymmetric, one pupil is larger than the other, the condition is known as anisocoria. When the pupils are dilated, the condition is known as mydriasis. Absent or poor tendon reflexes are also associated with this disorder. In most patients the pupil is larger than normal (dilated) and slow to react in response to direct light. Migraine: While it is not common, migraines can cause anisocoria. When the pupils are constricted, the condition is known as miosis. Adie syndrome, or Holmes-Adie syndrome, is a rare neurological disorder affecting the pupil of the eye.Vision loss: Significant vision defects can affect pupil size and reactivity.Increased intracranial pressure: This can result from a brain tumor, meningitis (inflammation of the fluid around the brain), or a stroke.Trauma: An injury affecting the eye or the brain may cause the pupils to be unequal.Inflammatory conditions, such as MS and sarcoidosis, also can do this. Inflammation: An infection affecting the eye or the cranial nerves can cause anisocoria.Cranial nerve damage: This can occur due to a stroke (a blockage of blood flow or bleeding in the brain), brain aneurysm (defect in a blood vessel), or a brain tumor.Multiple sclerosis (MS): MS is a chronic neurological disorder that causes symptoms affecting vision, movement, sensation, and more.
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