Hi, Stroke is a condition related to reduced blood supply of the brain. It may be caused by many reasons like a bleed (in turn due to many reasons, hypertension being one the most common) or block in blood vessels etc. That part of the brain gets no blood during this time which leads to brain damage. The extent of brain damage manifests as what we see clinically as weakness of limbs and/or face. Dilated fixed pupils can also be seen as a part of the stroke. Haloperidol (haldol) is an antipsychotic drug that is very commonly used to control agitation in bed ridden or comatose patients. Its side effects are mainly stiffness, slowness of movement or very little movement, tremor, occasionally-abrupt onset sometimes bizarre muscular spasms affecting mainly the musculature of the head and neck, increased salivation etc. This drug is not known to cause dilatation of one pupil. You have not mentioned the GCS score of the patient nor the dose of the drug administered so i would not be able to comment further. It has varied effects in different individuals as far the extent of side effects are concerned. There are anticholinergic medications to reverse the side effects if severe. The safety of which will depend on the condition of the patient. Discuss it with the treating doctor, Wishing your father in law, best of health Dr A Rao