Nystagmus in a semiconscious patient may be due to any of these toxins but is most common with anticonvulsants (carbamazepine, phenytoin, valproate) and alcohols. Nystagmus is lost as the coma deepens, and its absence does not exclude these poisons.

Serotonin reuptake inhibitors can cause prominent ocular clonus that may be confused with nystagmus but are an uncommon cause of coma.

All patients with nystagmus (or extraocular palsies) should be given thiamine 300 mg IVI immediately.

Marked nystagmus suggests carbamazepine poisoning - this effect is lost with increasing sedation. SSRIs can produce an ocular clonus which may be mistaken for nystagmus.

Nystagmus occurs in alcohol intoxication, Wernicke's encephalopathy, sedative (e.g. benzodiazepine), and anticonvulsant drug (e.g. carbamazepine and phenytoin) poisoning.

Ocular clonus, a continuous rhythmical oscillatory movement, suggests the serotonergic syndrome.

ALL PATIENTS WITH NYSTAGMUS SHOULD BE GIVEN THIAMINE!