1.	What is the tentative diagnosis? a -- Horner's syndrome Although this patient does not have other findings for this syndrome (left upper lid ptosis, left lower lid ptosis, anhidrosis, etc.), the difference in pupil size being greater in dim light is typical for Horner's syndrome. Third nerve palsy affecting only the pupil is rare.  With third nerve palsy or an optic nerve lesion, the difference in pupil size would be greater in bright light.  The same goes with Adie's pupil. Simple central anisocoria, although rare in children, tends to have no difference in pupil size associated with lighting. (See:  Neuro-ophthalmology Minute, Volume I, No. 10)
2.	What is the next best action in confirming the diagnosis that can be performed in the office? c -- 4-10% cocaine drops to both eyes 4-10% cocaine drops to both eyes applied twice 2-5 minutes apart is a common test used to diagnose suspected Horner's syndrome. The patient's pupils should be checked 30 minutes later to see the amount of anisocoria. If the relative pupillary diameter difference is increased or the postcocaine anisocoria is at least 1.0mm, then the diagnosis of Horner's syndrome is confirmed.  To differentiate a third neuron lesion from a first or second neuron lesion, a drop of hydroxyamphetamine (paradrine) is placed on each eye 24 hours later.  If the pupil does not dilate, a third order neuron is affected.  If the pupil dilates, a first or second order neuron is affected.
3.	What other laboratory tests could be obtained for underlying asociated conditions?  c -- check for urine catecholamines In a paper by Jeffery, et. al. (Pediatric Horner syndrome. JAAPOS, June 1998;2:159-67), 73 children with Horner's syndrome were evaluated. In children with congenital Horner's syndrome and with no birth trauma history or any other underlying conditions, it was suggested that urine catecholamines be tested to rule out neuroblastoma. This condition was the only associated potentially life threatening condition in their patient population. For this reason, at least the urine test should be performed to rule out neuroblastoma. If a first or second order neuron is affected, a chest X-ray should be obtained.