Pharmacology of the Eye Flashcards
Alpha 1
Pupillary Dilator (radial) muscle in the iris contracts and causes mydriasis.
M3
Pupillary Constrictor (sphincter, circular) muscle in the iris contracts and causes miosis.
Ciliary muscle contracts in order to accommodate the eye to short range focus. Relaxation adapts to long range focus.
B2
The Ciliary epithelium produces aqueous humour. Its production is decreased via Alpha-2
Muscarinic Effects
Contraction of the pupillary constrictor muscle causes miosis (reduction in pupil size).
Contraction of the ciliary muscle (cyclospasm) facilitates outflow of the aqueous humour into the canal of Schlemm. This reduces intraocular pressure which makes these drugs useful in Glaucoma.
Ciliary muscle contraction in response to activation of muscarinic receptors causes accommodation of focus for near vision. This parasympathetic reflex is thus necessary to accommodate the eye for near vision. Marked contraction of the ciliary muscle is called cyclospasm. Ciliary muscle contraction also puts tension on the trabecular meshwork, opening its pores and facilitating outflow of the aqueous humour into the canal of Schlemm.
Increased outflow reduces intraocular pressure: useful in glaucoma. All these effects can be reversed by muscarinic blocking drugs such as atropine.
Antimuscarinic Effects
They cause mydriasis via relaxation of the pupillary constrictor muscle (sphincter) and accommodation of focus for long distance vision (cycloplegia) via relaxation of the ciliary muscle.
An example is Atropine.
Adrenergic Effects
Activation of Alpha-1 causes mydriasis. Like Phenylephrine. Contraindicated in Glaucoma. Anything that causes mydriasis is contraindicated like anticholinergic and adrenergic drugs.
Activation of B2 receptors on the ciliary epithelium facilitate secretion of aqueous humour. Therefore blocking these receptors with B-blockers reduce secretion, reducing intraocular pressure, also helpful in Glaucoma therapies.
