3rd-year class Practical Pharmacology 2010-2011 Lab.11 3rd-year class Practical Pharmacology 2010-2011

EFFECT OF DRUGS ON HUMAN EYE

Drugs used in this experiment 1.Adrenaline 2.Pilocarpine 3.Tropicamide 4.Phenylephrine 5.Lignocaine 6.Procaine 

Parameters 1.Size of pupil. 2.Reaction to light 3.Accomodation 4.Corneal sensation 5. Conjunctival vessles 6.Width of palpebral fissure

Adrenaline & phenylephrine: adrenaline is catecholamine while phenylephrine is sympathomimtic drug & both drugs have the same effect, but in topic use adrenaline differs from phenylephrine in that, adrenaline is poorly absorbed from mucous membrane, so it is not like the effect of phenylephrine which have more prominent in topic use .

Pilocarpine: cholinomimitic drug, used to produce miosis (only used topicaly).

Tropicamide atropine like agent, its max effect is about 40 min.

Lignocaine & procaine: both drugs are local anesthetics, but procaine doesn't work topically (act here as a distill water). Lignocaine anesthetizes the conjunctival membrane, so used in ophthalmology when we want to measure the intraocular pressure or we want to get out any foreign body from the eye.

Parameters: Size of the pupil: size of the pupil is kept normal by the action of 2 muscles which are circular & radial muscles. Circular mm try to constrict the pupil which is supplied by parasympathetic nerve while, radial mm try to dilate (mydriasis) which is supplied by sympathetic nerves. The size of pupil is dilated by tropicamide & phenylephrine while adrenaline has less effect because adrenaline is poorly absorbed by mucous membrane. Pilocarpine causes constriction of pupil (miosis). Lignocaine & procaine have no effect.

Reaction to light there're 2 types of reaction to light which are directly & indirectly reaction to light. Direct reaction to light is by applying the light to the eye & notice the effect or the response on the same eye, while indirect reaction to light is by applying the light to the eye & notice the response on the other eye. When we carry out this experiment in the lab., we'll apply only direct reaction to light.

Applying the light on the eye (normal eye) causes constriction of pupil. Adrenaline has (+ve) because adrenaline doesn't affect on circular m, also phenylephrine has the same effect of adrenaline. Pilocarpine causes constriction of pupil but will not show a clear reflex because pilocarpine causes full constriction & the pupil has no further constriction (+ve). Tropicamide has no direct reflex due to paralysis of circular muscle (-ve). While lignocaine & procaine has no effect(+ve) .

Accomodation near & far vision are the job of ciliary mm & paralysis of ciliary mm causes cycloplegia which accommodates for far vision, but stimulation of ciliary mm causes more accommodation for near vision. The accomodation is measured by near point which is (the distance between the eye & the object); normally 6cm. in cycloplega there is an increase in near point, while in the stimulation of ciliary mm there's a decrease in the near point. Ciliary mm are supplied mainly by parasympathetic nerve, while the sympathetic has a very little effect & has no significance. Pilocarpine causes decrease in near point. Tropicamide causes increase in near point (because paralysis of ciliary mm) while the rest drugs have no effect.

Corneal reflex only lignocaine has +ve effect anesthetizing the conjunctival membrane. We can examine this effect by the (blinking test) or corneal reflex by touching the cornea with a wisp of damp cotton wool .

Conjunctival vessels adrenaline & phenylephrine have an effect on alpha receptors, thus causes vasoconstriction (paler conjunctival appearance). Pilocarpine causes vasodilatation & inconsequence, causing what we call it congestion (injection) & redness conjunctival appearance.

Width of palpebral fissure: means the distance between the upper eyelid & lower eyelid, if we stimulate it there'll be more opening of upper eyelid & the eye will seem larger. Levator palpebrae superioris has also smooth muscles supplied by sympathetic fibres causing upper eyelid to elevate. Increasing the width of palpebral fissure is done by adrenaline & phenylephrine.  

Width of palpebral fissure Parameter Drug Size of pupil Reaction to light Accomoadtion Corneal sensation Conjunctival vessels Width of palpebral fissure Pilocarpine Miosis Present but not evident Near vision ___ injection Tropicamide Mydriasis Lost Far vision Adrenaline Mydriasis but slow +ve Pale ↑ Phenylphrine Lignocaine Procaine