Looking at the pupils can sometimes be helpful, particularly in an unconscious patient. There are many causes of dilated pupils but if you're lucky and a patient comes in with constricted pupils then this narrows down the possible causes significantly.
A constricted pupil is one that is less than 2mm under normal lighting conditions. Note that the pupils will constrict if you shine a torch into them!
Bilateral pinpoint pupils
- Opiates (Heroin, Fentanyl, Codeine, Methadone, Morphine) stimulate the parasympathetic side of the autonomic nervous system causing pupil constriction. Look for track marks and a past history of drug use.
- Pontine hemorrhage (brain stem)
- Organophosphate chemicals (pesticides, Sarin gas). Look for SLUDGE presentation (salivation, lacrimation, urination, defecation, emesis)
- Other drugs (neuroleptics, EtOH, benzos, isopropryl alcohol, lithium)
Bilateral dilated pupils
- Anticholinergic drugs (TCA)
- Adrenergic drugs (cocaine, amphetamines) - but these don't usually lead to coma unless complicated by seizures or cerebrovascular events.
- Other drugs (quinine, baclofen, barbiturates, other sedatives like carbamazepine)
- Raised ICP
- Brain death
References I used:
1) http://theemtspot.com/2009/04/23/rapid-diagnosis-pinpoint-pupils/
2) http://curriculum.toxicology.wikispaces.net/Pupil+Size+and+Reaction
There is also an online teaching syllabus for toxicology at WikiTox.
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