Causes of Miosis

Miosis is defined as Pupil size is < 2 mm
Following are the common causes of miosis

• Old age
• Homer's syndrome
• Drugs or toxins
• Neostigmine
• Morphine
• Organophosphorous poisoning
• Pontine haemorrhage.

Unilateral miosis causes

• Homer’s syndrome• Paralysis of cervical sympathetic - Horner's syndrome
• Drugs
• Irritation of parasympathetic system
• Drugs - Morphine, organophosphate poisoning, levodopa
• Deep coma, increased-OLpontine hemorrhage
• Rowland Payne syndrome - Consists of Horner's syndrome, phrenic nerve and recurrent laryngeal nerve involvement. It is caused in metastatic tumor at neck from malignancy like carcinoma breast.
• Old age.
• Argyll Robertson pupil.
• Application of pilocarpine drops : overdose of neostigmine.
• Iritis.

Bilateral miosis causes

Pin-point pupil.

• Morphine or barbiturate poisoning, 
• heat stroke (hyperpyrexia)

How to differentiate between patients with pin point pupil

• Pontine haemorrhage—There is coma, hyperpyrexia and long tract signs (ie. sings ol pyramidal tract lesion).
• Organophosphorus poisoning— It is diagnosed by history, absense of long tract signs, and sign of respiratory depression. The patient may be unconscious but there is absense of pyrexia.

Irregular pupils are due to 

• Coloboma.
• Neurosyphilis
• followlng eye operation.
• Sometimes, it is seen in normal healthy subjects.