Effect Of Autonomic Drugs On Rabbit Eye PDF

EFFECT OF AUTONOMIC DRUGS ON RABBIT EYE D E PA R T M E N T O F P H A R M A C O L O G Y, FA C U LT Y O F P H A R M A C Y, M I N I A U N I V E R S I T Y OUTLINES: Eye structure Autonomic supply to the eye  Pupil  Ciliary body Effect of autonomic drugs on : 1-Pupil size 2-A...

EFFECT OF AUTONOMIC DRUGS ON RABBIT EYE D E PA R T M E N T O F P H A R M A C O L O G Y, FA C U LT Y O F P H A R M A C Y, M I N I A U N I V E R S I T Y OUTLINES: Eye structure Autonomic supply to the eye  Pupil  Ciliary body Effect of autonomic drugs on : 1-Pupil size 2-Accomodation 3-Intraocular pressure Light reflex Corneal reflex Movement of eyeball EYE STRUCTURE  AUTONOMIC SUPPLY TO THE EYE The eye is innervated by both symp.(through cervical ganglia) and parasymp.(cranial nerve III) nerve fibers. I-The iris: It controls the size of pupil and amount of light entering the eye and consists of 2 types of smooth muscles: Radial muscles Circular muscles  AUTONOMIC SUPPLY TO THE EYE 1-Circular muscles : (sphincter pupilary muscles) parasympathetically innervated & contain M3 receptors Activation of M3 receptors by a parasympathomimetic (pilocarpine) causes miosis ( decrease pupil size)  AUTONOMIC SUPPLY TO THE EYE 2- Radial muscles (dilator pupillary muscles) : sympathetically innervated and contains alpha1 receptors Activation of alpha1 receptors by a sympathomimetc (epinephrine) causes mydriasis (increase pupil size)  AUTONOMIC SUPPLY TO THE EYE II-Ciliary body Consists of smooth ms and responsible for the production of aqueous humor and the thickness of the lens (accomodation) Parasympatheticaly innervated and contains M3 receptors on the smooth muscles and alpha and beta receptors on the blood vessels.  EFFECT OF AUTONOMIC DRUGS ON PUPIL SIZE Pupil size is controlled by the movement of 2 musles, circular and radial muscles of the iris Parasympathomimetics (pilocarpine) activate M3 of circular muscles >>>> contrction >>>>> miosis Parasympatholytics (atropine) blocks M3 of circular muscles so, effect of sympathetic innervation to the radial muscles predominates >>>> passive mydriasis EFFECT OF AUTONOMIC DRUGS ON PUPIL SIZE Sympathomimetics activate alpha1 RC of radial ms>>>>> contraction >>>> active mydriasis Sympatholytics block alpha1 RC of radial ms >>>> miosis Drug Effect on pupil size Parasympathomimetics Miosis (Pilocarpine, Acetylcholine, physostigmine) Parasympatholytics Passive mydryasis (Atropine, cyclpentolate) Sympathomimetics Active mydriasis (Epinephrine, phenylephrine) Sympatholytics Miosis (Phenoxybezamine, prazocin)  EFFECT OF AUTONOMIC DRUGS ON ACCOMMODATION Accommodation is the process by which the eye changes the lens convexity acc. to distance of the object to obtain a clear image. Ciliary body is responsible for accommodation Upon activation of M3 RC >>>> contraction of the sm. ms. of the ciliary body (muscles become thicker) >>>>tension reduction upon suspensory ligaments >>>> lens become rounded (increase the convexity of the anterior surface of the lens) >>> accommodation for near vision.  EFFECT OF AUTONOMIC DRUGS ON ACCOMMODATION Blocking M3 RC with atropine >>>> relaxation of the ciliary body >>>> increase tension on suspensory ligaments >>>> lens becomes flat (decrease the convexity of the anterior surface of the lens) >>>> accommodation for far vision. Cycloplegia : loss of accommdation for near vision, caused by parasympatholytics. Accommodation Drug Effect on accommodation Parasympathomimetics + (Pilocarpine, Acetylcholine, physostigmine) Prarsympatholytics _ (cycloplegia) (Atropine, cyclpentolate) Sympathomimetics No effect (Epinephrine, phenylephrine) Sympatholytics No effect (Phenoxybezamine, prazocin, naphazoline) EFFECT OF AUTONOMIC DRUGS ON IOP IOP is the pressure exerted by aqueous humor on the internal structures of the eye. It`s controlled by rate of formation and drainage of aqueous humor. Normal IOP : 10-21 mm Hg Aqueous humor is formed by the ciliary body and drained through canal of Schlemm. EFFECT OF AUTONOMIC DRUGS ON IOP Miotics decrease IOP by 2 mechanisms 1- Miosis (either by parasympathomimetic or sympatholytics) widen the angle of drainage >>>> rate of drainage 2-Parasympathomimetic cause accomodation for near vision >>> increase the thickness of the lens >>>> exert pressure on aqueous humor >>>> increase rate of drainage EFFECT OF AUTONOMIC DRUGS ON IOP Mydriatics increase IOP also by two mechanisms 1. Mydriasis (Either by parasympatholytics or sympathomimetics) >>>>> narrowing of drainage angle >>>> decrease rate of drainage 2. Sympathomimetics increase the rate of formation of aqueous humor Drug Effect on IOP Parasympathomimetics Decrease (miosis and (Pilocarpine, Acetylcholine, accommdation) physostigmine) Parasympatholytics Increase (mydriasis) (Atropine, cyclpentolate) Sympathomimetics Increase (mydriasis and increase (Epinephrine, phenylephrine) rate of formation) Sympatholytics Decrease (decrease rate of (beta blockers as Timolol) formation)  LIGHT REFLEX When a shining light is directed towards one eye, miosis occurs in both eyes. Circular muscles of the iris are responsible for it so, if M3 RC `re blocked >>>> passive mydriasis and loss of light reflex. While active mydriasis is not accompanied by loss of light reflex. How to differentiate between active and passive mydriasis. Drug Effect on light reflex Parasympathomimetics no effect (Pilocarpine, Acetylcholine, physostigmine) Parasympatholytics loss (Atropine, cyclpentolate) Sympathomimetics no effect (Epinephrine, phenylephrine) Sympatholytics no effect (beta blockers as Timolol)  CORNEAL REFLEX When a cotton swap or hair touches cornea, eyelids close spontaneously Sensory nerve terminals in the cornea `re responsible for corneal reflex Local anesthetics inhibit corneal reflex. e.g. : lidocaine  MOVEMENT OF THE EYEBALL Controlled by external ocular skeletal muscles innervated with somatic nerve fibers and can be inhibited by skeletal muscle relaxants >>>> fixation of the eyeball