Corpus: Mydriasis
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Synonym: pupil dilation
English:
Definition[Bearbeiten]
Mydriasis is the dilation of the pupil beyond a diameter of 5 mm. It is the opposite of miosis.
Physiology[Bearbeiten]
Physiological mydriasis is a reaction to dark adaptation and remote accommodation. This occurs via sympathetic fibres coming from the ciliospinal centre in the spinal cord. They are connected in the superior cervical ganglion (2nd neuron) and travel via the internal carotid plexus to the ciliary ganglion. From there they travel unconnected via the ciliary nerves to the pupillary dilator muscle.
Causes[Bearbeiten]
Mydriasis can be caused by the following factors, among others:
- Darkness
- Mydriatic drugs
- pain
- Psychological excitement
- oculomotor nerve palsy
- Cocaine
- Migraine attack
- Lesion in the midbrain
- Brain death
Pathophysiology[Bearbeiten]
- Mydriasis spastica: sympathetic stimulation with consecutive continuous contraction of the dilator pupillae muscle
- Mydriasis spinalis: irritation of the ciliospinal centre
- Mydriasis paralytica: Paralysis of the parasympathetic nervous system with consecutive relaxation of the sphincter pupillae muscle
- Mydriasis traumatica: laceration of the sphincter papillae
Special forms of mydriasis[Bearbeiten]
- The pupil (with damage to the ciliary ganglion)
- Argyll-Robertson pupil (in neurosyphilis)
- Pseudomydriasis