It is rare in brachiocephalic breeds (short noses) like the Pug or Boston Terrier. (lowchensaustralia.com)
Dogs with «smushed - in» faces (i.e. brachiocephalic dogs like bulldogs, pugs, Shih Tzus, etc) are more prone to epiphora because their facial structure prevents the tear ducts from draining effectively. (smartdogowners.com)
In addition, some breeds with brachiocephalic skulls seem to have a much greater than 25 percent incidence of orchidism when «supposed» (phenotypically) normal dogs (who are actually carriers) are bred. (siriusdog.com)