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Dilatation (mydriasis) of pupil

Mydriasis is defined as Pupil size > 5 mm
Constrictors ol the pupil are supplied by parasympathetics via the oculomotor nerve while the dilator are controlled by sympathetic nervous system. Changes in the size of the pupil do not affect the vision

Unilateral mydriasis causes
  • Drugs—-anticholinergics -
  • Acute ciliary ganglionitis—following several days after infection/ trauma
  • 3rd nerve palsy.
  • Holmes-Adies pupil or myotonic pupil.
  • Blindness due to Optic atrophy 
  • Acute congestive glaucoma.
  • Head injury-Uncal herniation Unilateral pupillary dilatation is the most important physical sign in the unconscious patient, and until proved otherwise a dilated pupil indicates that a herniated temporal lobe is compressing-the ipsilatcral oculomotor nerve, and that immediate surgical action is required.
Bilateral mydriasis causes
  • Anxiety
  • Myopic eyes
  • Infancy 
  • Thyrotoxicosis 
  • Drug poisoning-antihistamine, phenolhiazinc, anticholinergics, Datura poisoning,Drugs like atropine and pethidine
  • Application of mydriatics(atropine)
  • Postictal state 
  • Parinaud’s syndrome
  • Coma.
  • Severe raised intracranial tension.
  • Cerebral anoxia.