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Phenylephrine eyedrops as a diagnostic test in equine grass sickness
  1. C. N. Hahn, BS, DVM, MSc, MRCVS1 and
  2. I. G. Mayhew, BVSc, PhD, DipACVIM, DipECVN FRCVS1
  1. 1 Department of Veterinary Clinical Studies, Royal (Dick) School of Veterinary Studies, Easter Bush Veterinary Centre, Easter Bush, Roslin, Midlothian EH25 9RG


The effect of an ocular administration of the α-1 adrenergic agonist phenylephrine was studied in 23 cases of grass sickness and 12 control horses. In the horses with grass sickness there was a significantly greater mean increase in the size of the palpebral fissure, as measured by the change in the angle of the eyelashes to the head observed from a frontal view.

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