Mydriase

Mydriasis is the dilation of the pupil of the eye. It is the opposite of miosis (pupillary constriction). Mydriasis can be a physiological response, a pathological condition, or induced pharmacologically.

Causes:

• Physiological:

  • Low ambient light: In dim or dark environments, the pupils dilate to allow more light to enter the eye and improve vision.
  • Emotional or psychological arousal: Activation of the sympathetic nervous system, as in response to fear, excitement, or pain, can cause pupillary dilation.
  • Accommodation: When focusing on distant objects, the pupils may dilate slightly.

• Pathological:

  • Brain injury or disease: Conditions affecting the brainstem, such as stroke, hemorrhage, or tumors, can disrupt pupillary control and lead to mydriasis.
  • Glaucoma: Angle-closure glaucoma can sometimes cause pupillary dilation due to increased intraocular pressure.
  • Adie's tonic pupil: A neurological condition causing a slowly reactive, dilated pupil.
  • Third nerve palsy: Paralysis of the oculomotor nerve can lead to mydriasis, ptosis (drooping eyelid), and impaired eye movements.
  • Certain systemic illnesses: Some diseases, such as botulism, can cause mydriasis.

• Pharmacological:

  • Mydriatic drugs: Certain medications, such as atropine, tropicamide, and cyclopentolate, are used to dilate the pupils for diagnostic eye examinations or to treat certain eye conditions.
  • Other drugs: Some antihistamines, antidepressants, and decongestants can have mydriatic side effects.
  • Illicit drug use: Substances like cocaine, amphetamines, and LSD can cause pupillary dilation.

Diagnosis:

Diagnosis of the cause of mydriasis involves a thorough medical history, physical examination, and neurological assessment. Pupillary response to light, accommodation, and other stimuli are carefully evaluated. Imaging studies, such as CT scans or MRI, may be necessary to rule out underlying brain abnormalities. Pharmacological testing may be used to differentiate between different types of mydriasis.

Treatment:

Treatment for mydriasis depends on the underlying cause. Physiological mydriasis requires no treatment. Pathological mydriasis requires addressing the underlying condition. Drug-induced mydriasis typically resolves when the offending medication is discontinued. Protective measures, such as wearing sunglasses, may be recommended to reduce light sensitivity while the pupils are dilated.