Phenylephrine

Mechanisms of action:
Stimulates post-synaptic alpha receptors which constricts the dilator muscle, hence causing mydriasis.

Clinical Uses:

Used as an eye drop to dilate the pupil which can be also used as an aid in viewing the fundus in adults. It is often used in combination with tropicamide, an anti-cholinergic drug.

Phenylephrine can also be used in the diagnostic test of horner’s syndrome to determine the site of the neurologic damage.

Phenylephrine is also used to break synaechiae to prevent glaucoma caused by pupil block.

Ocular side effects:

Use of phenylephrine may cause widening of the palpebral aperture and blanching of the conjunctival blood vessels because alpha receptors are also found in those areas.

Systemic effects:

Central Nervous System – Headache, Dizziness

Respiratory System – Respiratory Distress

Cardiovascular System – Bradycardia

Contraindications:

Phenylephrine should not be used in patients with severe hypertension or tachycardia(fast heart rate) or should they be hypersensitive to any of the components in the drugs.

Intraocular Pressure(IOP):

Phenylephrine has little effect on IOP and if safe to be taken in patients with glaucoma