Ciliospinal reflex

The ciliospinal reflex (pupillary-skin reflex) consists of dilation of the pupil ipsilateral to a pain stimulus applied to the neck. Therefore, if scratch the right side of the neck with a sharp pin, the right pupil should dilate. This reflex is absent in Horner's syndrome.

References: http://medical-dictionary.thefreedictionary.com/ciliospinal+reflex

http://cancerweb.ncl.ac.uk/cgi-bin/omd?ciliospinal+reflex