Practical Pharmacology

3rd-year classPractical Pharmacology2010-2011

Lab.11

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.

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

Mydriasis

+ve

___

___

Pale

↑


Lignocaine

___

+ve

___

Lost

___

___

Procaine

___

+ve

___


___

___

___