Ciliary muscles

The alkaloid is principally used in medicine to cause dilatation of the pupil of the eye (mydriasis), due to paralysis of the circular muscle of the ns. The accommodation is also paralysed as a result of action on the ciliary muscle (cycloplegia). Atropine is also used in conditions where... 

Radial muscle of iris 2. 5hincter muscle of iris 3. Ciliary muscle Skin Contraction (pupil dilates) a Contraction (pupil constricts) Contraction... 

Cycloplegic mydriatics cause mydriasis and cyclople-gia (paralysis of the ciliary muscle, resulting in an inability to focus the eye). These drugs (see Chap. 25) are used in the treatment of inflammatory conditions of the iris and uveal tract of the eye and for examination of the eye... 

Eighty percent of aqueous humor drains through the trabecular meshwork, which is a lattice of connective tissue that surrounds the anterior chamber. The size of the trabecular meshwork can be altered by the contraction or the relaxation of the ciliary muscle. Stimulation of muscarinic receptors on the ciliary muscle causes contraction, which in turn causes the pores of the trabecular meshwork to open, increasing aqueous humor outflow. 

A second pathway, uveoscleral outflow, comprises the other 20% of aqueous humor drainage. In the uveoscleral pathway, aqueous humor exits the anterior chamber through the iris root and through spaces in the ciliary muscles, which then drains into suprachoroidal space. Uveoscleral outflow can be pharmacologically modulated by adrenoceptors, prostanoid receptors, and prostamide receptors.4,10,12-15... 

Pilocarpine directly stimulates the muscarinic (M3) receptors of the ciliary body which causes contraction of the ciliary muscle. This results in widening of the spaces in the trabecular meshwork, which causes an increase in aqueous humor outflow and reduces IOP by 20% to 30%. 

The adverse effects of pilocarpine are caused by the induction of miosis. The contraction of the ciliary muscle causes the lens to displace forward, which can lead to accommodation spasm, myopia, and brow ache. Pupillary constriction can also affect night vision. Pilocarpine should be avoided in patients with severe myopia, as it increases the risk of developing retinal detachment. Systemic effects may occur at higher concentrations and include, nausea, vomiting, diarrhea, and bradycardia. 

Parasympatheti c Muscarinic Eye Iris muscle Ciliary muscle Contraction Contraction Miosis Blurred vision... 

Ciliary muscle P2 Relaxation for far vision Contraction for near vision... 

Multiunit smooth muscle is located in the large blood vessels, eyes (iris and ciliary muscle of the lens), and piloerector muscles at the base of hair follicles. This type of muscle consists of discrete smooth muscle cells or units that function independently. Each of these units is innervated by the... 

Eye iris (pupillae sphincter muscle) Ciliary muscle... 

Impairment in visual accommodation results from paresis of ciliary muscles. Photophobia may also result. If severe, pilocarpine ophthalmic solution may be necessary. 

Accommodation (fig. 9). The lens of the eye is suspended by the zonula (suspensory ligament) consisting of delicate transparent fibres attached on the one hand to the ciliary body and on the other to the elastic capsule covering the lens. At rest, this zonula is under tension and in consequence the lens assumes a flattened form. When the ciliary muscle contracts it pulls the... 

Effect on the eye. Leopold and Comroe4 recorded the actions of D.F.P. on the normal eye, expanding the earlier British work (pp. 2, 43). They confirmed the prolonged myosis lasting up to 3 weeks with a spasm of the ciliary muscle for 3-7 days. There is usually a decrease in the intra-ocular tension, although occasionally there may be a slight rise before a fall in pressure. The action outlasts that of common myotics, and a 0-1 per... 

Muscarine-like action causing bronchospasm atropine and ephedrine are antagonists. Other parasympathetic effects include constriction of the pupil and of the ciliary muscles of the eye both effects are antagonized by atropine. 

Mild symptoms are relieved by 0-5 per cent atropine ointment in the eye, aspirin as a mild analgesic for pains in the ciliary muscles and headache, ephedrine to deal with bronchospasm. 

Suzuki H, Ishikawa S. 1974. Ultrastrcture of the ciliary muscle treated by organophosphate pesticide in beagle dogs. Br J Ophthalmol 58 931-940. 

The 5 groups of agents used in therapy of primary open-angle glaucoma are listed in the table, which summarizes their mechanism of decreasing lOP, effects on pupil size and ciliary muscle and duration of action. 

Pharmacology Direct-acting miotics are parasympathomimetic (cholinergic) drugs which duplicate the muscarinic effects of acetylcholine. When applied topically, these drugs produce pupillary constriction, stimulate ciliary muscles, and increase aqueous humor outflow facility. With the increase in outflow facility, there is a decrease in lOP. Topical ophthalmic instillation of acetylcholine causes no discernible P.1248... 

Pupil size Accommodation i Constriction of radial muscle causing dilation (mydriasis) No innervation Contraction of circular muscle (miosis) Contraction of ciliary muscle producing accommodation for near vision... 

When solutions of directly acting choUnomimetics are applied to the eye (i.e., conjunctival sac), they cause contraction of the smooth muscle in two important structures, the iris sphincter and the ciliary muscles (Fig. 12.3). Contraction of the iris sphincter decreases the diameter of the pupil (miosis). Contraction of the circular fibers of the ciliary muscle, which encircles the lens, reduces the tension on the suspensory ligaments that normally stretch and flatten the lens, allowing the highly elastic lens to spontaneously round up and focus for near vision (accommodation to near vision). 

Diagram of eye depicting major pathway for outflow of aqueous humor (arrow) and ocular smooth muscles, which contract in response to parasympathomimetics or cholinesterase inhibitors (i.e., iris sphincter and ciliary muscle). 

Visual Cycloplegia (relaxation of ciliary muscle) mydriasis (relaxation of sphincter pupillae muscle) increase in aqueous outflow resistance (increases intraocular pressure in many cases of glaucoma)... 

Antimuscarinic drugs block contraction of the iris sphincter and ciliary muscles of the eye produced by ACh. This results in dilation of the pupil (mydriasis) and paralysis of accommodation (cycloplegia), responses that cause photophobia and inability to focus on nearby objects. Ocular effects are produced only after higher parenteral doses. Atropine and scopolamine produce responses lasting several days when applied directly to the eyes. 

The principal determinants of lOP are the rate of aqueous fluid production by the ciliary epithelium and the rate of fluid drainage (outflow) in the canal of Schlemm. Aqueous fluid production involves passive, near-isosmolar fluid secretion driven by active salt transport across the ciliary epithelium. Ion and solute transporters have been identified on pigmented and non-pigmented layers of the ciliary epithelium that probably facilitate active solute secretion. Aqueous fluid drainage is believed to involve pressure-driven bulk fluid flow in the canal of Schlemm, as well as fluid movement through the sclera by seepage across the ciliary muscle and supraciliary space. 

Overdose may produce temporary paralysis of ciliary muscle pupillary dilation tachycardia palpitations hot, dry, or flushed skin absence of bowel sounds hyperthermia increased respiratory rate EGG abnormalities nausea vomiting rash over face or upper trunk CNS stimulation and psychosis (marked by agitation, restlessness, rambling speech, visual hallucinations, paranoid behavior, and delusions, followed by depression). 

---