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Pharmacology: Special Sense
DRUGS ACTING ON EYE
OBJECTIVES
List main groups of drugs applied on the eye and their clinical applications.
Discuss the local effects of autonomic drugs on their receptor sites in the eye with relevance
to their clinical applications.
Identify the lines of treatment of some eye diseases as glaucoma and conjunctivitis.
STRUCTURES OF THE EYES
Anatomically eye composed of : i) Anterior chamber
ii) Posterior chamber
ANTERIOR CHAMBER
INCLUDE:
1. CORNEA
2. IRIS
3. LENS
4. AQ UEOUS HUMOUR
1. THE CORNEA
CORNEAL OR CONJUNCTIVAL REFLEX
The cornea and the sclera are supplied by sensory nerves.
When the cornea is touched the corneal reflex is initiated i.e. the eye blinks on touching the
cornea with a piece of cotton
DRUGS ACTING ON CORNEA
Include:
A. Local Anaesthetics
B. DiagnosticDyes
C. Topical Anti-InflammatoryD. Topical Anti-Infective Drugs
E. Tear Substitutes & Lubricating Agents
A. LOCAL ANAESTHETIC DRUGS
Includes:
1. Surface anaesthesia by lidocaine eye drops for :
a. Tonometry: measurement of IOP
b. Removal of corneal foreign bodies
2. Profound anaesthesia by tetracaine eye drops for:
Removal of cataracts
B. DIAGNOSTIC DYESFluorescein 1%
- Used for diagnosis of corneal ulcers
- Denuded epithelium is stained bright green
Rose Bengal 1%
- Used for diagnosis dry eye
- Dead cells are stained red
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Pharmacology: Special Sense
C. TOPICAL ANTI-INFLAMMATORY DRUGS
Includes:
1. Steroidal anti-inflammatory drug
Used for anterior segment of eye inflammation as allergic conjunctivitis
Example: Dexamethasone
2. Non-steroidal anti-inflammatory drugs
Have anti-prostaglandins action Example: Ketophenac sodium
D. TOPICAL ANTI-INFECTIVE DRUGS
Include:
1. Topical Anti-Biotics (e.g. Neomycin, Chloramphenicol,Ciprofloxacin)
2. Topical Anti-Fungi (e.g. Nystatin Solution)
3. Topical Anti-ViralAgents (e.g. Acyclovir for dendritic corneal ulcer)
E. TEAR SUBSTITUTES AND LUBRICATING AGENTS
Example:
1. Methyl cellulose
2. Polyvinyl alcoholUses:
1. Formation of artificial tears in dry eye conditions as S jogrens syndrome
2. Contact lens solution
2. THE IRIS
Muscles include:
1) Sphincter Pupillae Muscle: Parasympathetic M3 Receptors
2) Dilator Pupillae Muscle: Sympathetic 1 Receptors
LIGHT REFLEX
PRINCIPLE
Narrowing of pupil (miosis) when the eye is stimulated by light
This miosis is due to contraction of constrictor pupillae muscle i.e. light reflex depends on
integrity of parasympathetic supply of the eye
Parasympatholytics abolish light reflex
3. THE LENS
ACCOMODATION REFLEX
It is the ability to increases the convexity of the crystalline lense to obtain a clear image of an
object at various distances
This is mediated through the parasympathetically innervated ciliary muscle, whose
contraction causes suspensory ligaments relaxation thus increasing the lense curvature and
diopteric power leading to accomodation for near vision
4. THE AQUEOUS HUMOUR
It is formed of highly vascularized ciliary body processes that absorb sodium selectively via
carbonic anhydrase enzyme(70%) and ATPase system
The aqueous humour circulates through the pupil and is drained in the canal of Schlemm
then to episcleral veins
Normally there is balance between aqueous homour formation and outflow and this keeps
intraocular pressure within normal range (10-21mmHg)
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AUTONOMIC DRUGS ACTING ON THE EYE
Includes:
A. Miotics
B. Mydriatics
A. MIOTICS
Includes:1. Parasympathomimetics
2. Sympatholytics (e.g. Guanethidine)
3. Morphine (by stimulation of Edinger-Westphal nuclei)
1. PARASYMPATHOMIMETICS
MECHANISM OF ACTION
They stimulate M3 receptors in ciliary muscle and constrictor pupillae muscle leading to:
a. Miosis: constriction of the pupil
b. Accomodation for near vision
c. Reduce intraocular pressure: as when the pupil is constricted, the anterior chamber angle
is widened and this facilitates the drainage through Canal of Schlemm
INCLUDES:
I) C holinesters
1. Carbachol 1%
2. Bethenecol 1%
II) C holinomimetic Alkaloids
Pilocarpine 2%
III) Anticholinesterases
A. Reversible
i. Physostigmine 1%
ii. Neostigmine 3%
B. Irriversible
i.AS
D
.F.P 0.1%
Parasymathomimetics
Pupil Size : Miosis
Light Reflex : Absent
Accommodation : For Near Vision
IOP : Reduced
Conjunctival BV : Congested
B. MYDRIATICS
CAUSE:
A. Passive Mydriasis
i.
ParasympatholyticsB. Passive Mydriasis
i. Sympathomimetics
ii. Cocaine
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A i) PARASYMPATHOLYTICS
MECHANISM OF ACTION
They cause paralysis of sphincter pupillae muscle leading to:
a. Passive mydriasis
b. Abolish light reflex
c. Increase IOP: due to narrowing of anterior chamber angle
d. Loss of accomodation for near vision: as they produce cycloplegia
INCLUDES:
a. Atropine 1% (last for 10 days)
b. Atropine Substitutes
i. Homatropine 2% (for 24 hours)
ii. Eucatropine 2% (for 3-4 hours)
iii. Cyclopentolate 1% (2 hours)
iv. Tropicamide 1%
THERAPUTIC USES
1. Fundus examination and diagnosis of refractory errors
2.T
o break recent adhesions between the iris and the lense in anterior uveitis3. Treatment of acute iritis and iridocyclitis as they relief pain resulting from cilliary muscle spasm
Parasympatholytics
Pupil Size : Passive Mydriasis
Light Reflex : Absent Due To Paralysis Of Constrictor Pupillae Muscle
Accommodation : For Far Vision
IOP : Increased
Conjunctival BV : No Effect
B i) SYMPATHOMIMETICS
MECHANISM OF ACTION
They produce active mydriasis by sympathetic nerve fibers that are motor to radial muscle
through action on 1 receptor
They do not affect light reflex or accomodation
They are vasoconstrictors so the reduce vascular congestion of conjunctival blood vessels
EXAMPLE
Ephedrine sulphate, Phenylephrine and Dipivefrin
B ii) COCAINE
MECHANISM OF ACTION
1. It produces active mydriasis as it potentiates sympathetic response by:
a. Decreasing re-uptake of released catecholamines
b.Inhibits degradation of catecholamines by M
AO 2. It preserves light reflex
3. Abolishes corneal reflex by its local anaesthetic action
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TREATMENT OF SOME EYE DISEASES
A. CONJUNCTIVITIS
Includes:
1. Bacterial Conjunctivitis
2. Allergic Conjunctivitis
1. BACTERIAL CONJUNCTIVITIS
DEFINITION
It is inflammation of the conjunctiva associated with mucopurulent discharge, redness and eyelids
edema.
MANAGEMENT
Includes:
I) Eye Lotions
II) Hot Foments
III) Astringent Eye Drops
IV) Topical Antimicrobial Agents
I) EYE LOTIONS
To wash off the discharge
Example: Bland eye lotions
Boric acid lotion 4%
II) HOT FOMENTS
Are applied locally in order to relief edema and pain
III) ASTRINGENT EYE DROPS
Precipitate proteins so decrease capillary permeability
Example: Z inc sulphate 1%
IV) TOPICAL ANTIMICROBIAL AGENTS
Local eye drops every 1-2hrslday and eye ointment at night
Example: Neomycin
2. ALLERGIC CONJUNCTIVITIS
DEFINITION
It is acute allergy due to exposure to allergen .The patient present with redness of eyes with itching
and lacrimation.
MANGEMENT
Includes:
I) Treatment Of Acute Attack
a. Anti-Histaminic Eye Drops
b. Glucocorticoid Eye Drops
II) Prophylactic Treatment
a. Mast Cell Stabilizer
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I a) ANTI-HISTAMINIC EYE DROPS
y Example: Levocabastine
Antazoline
I b) GLUCOCORTECOIDS EYE DROPS
y Example: Dexamethasone
y Precaution:We must exclude viral dendritic ulcer and glaucoma
II a) MAST CELL STABILIZERS
Example: Na cromoglycate
B. GLAUCOMA
# DEFINITION
It is agroup of diseases that have in common a characteristic optic neuropathy with associated visual
field loss for which the elevated intraocular pressure is one of primary risk factors.
# CLASSIFICATIONIncludes:
1. Closed-Angle Glaucoma
2. Open-Angle Glaucoma
1. CLOSED-ANGLE GLAUCOMA
It is associated with a shallow anterior chamber, in which a dilated iris can occlude the
outflow drainage pathway at the angle between cornea and cilliary body
In this type, acute and painful rise of IOP is often precipitated that must be controlled on an
emergency basis with drugs or prevented by iridectomy
2. OPEN-ANGLE GLAUCOMA
The outflow of aqueous humour through the trabecular meshwork-Schlemms canal venous
system is impaired
It is a chronic condition and treated medically, aiming to slow the rate of disease progression
to prevent significant visual impairment
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# MEDICAL MANAGEMENT OF GLAUCOMA
I) -BLOCKERS
II) DIURETICS
III) SYMPATHOMIMETICS
IV) PROSTAGLANDIN ANALOGUES
V) PARASYMPATHOMIMETICS
I) - BLOCKERS
Includes:
A. Non-Selective -Blockers (e.g. T imolol Maleate Topical Eye Drops)
B. Selective 1 Blockers (e.g. Levobunolol HCL Topical Eye Drops)
Mechanism Of Action
Timolol blocks beta receptors on the cilliary processes resulting in decreasing aqueous production. It
is treatment of choice in open-angleglaucoma
II) DIURETICS
Includes:
1.
Hyper Osmotic Agentsa. Mannitol I.V.
2. Carbonic Anhydrase Inhibitors
a. Acetazolamide Oral (I.V. in emergency)
b. Dorzolamide Topical Eye Drops
Mechanism Of Action Of Hyperosmotic Agents
It acts by withdrawing fluid from the eye and reducing vitreous volume.
Mechanism Of Action Of Carbonic Anhydrase Inhibitors
They inhibit carbonic anhydrase in the cilliary body, which prevents bicarbonate synthesis resulting
in a fall in Na transport and aqueous flow.
III) SYMPATHOMIMETICS
Includes:
1. And Agonists
a. Dipiverfin HCL Topical Eye Drops
2. 2 Agonists
a. Brimonidine T artrate Topical Eye Drops
Mechanism Of Action Of And Agonists
It lowers the IOP by a balance between and adrenoreceptors stimulation
1. mediated VC of the cilliary BVs will decrease the aqueous flow
2. 2 mediated effect will increase trabecular meshwork drainage
Contraindication
Angle-closed glaucoma
Mechanism Of Action Of 2 Agonist
1. It reduces aqueous humour production
2. It increases uveoscleral outflow (secondary pathway for aqueous outflow 20%)
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IV) PROSTAGLANDIN ANALOGUES (F2)
Example And Form
Latanoprost solution: topical eye drops
Mechanism Of Action
1. It enhances the uveoscleral outflow of the aqueous2. It increases blood flow to the optic nerve that may contribute in retinal neuroprotection
V) PARASYMPATHOMIMETICS
Example And Form
Pilocarpine HCL: topical eye drops or gel
Mechanism Of Action
It increases aqueous outflow by contracting the ciliary muscle. Which pulls the scleral spur, resulting
in widening of the trabecular meshwork
Side EffectsBlurred vision and ache over the eye
# DRUGS CONTRAINDICATED IN GLAUCOMA
o Topical and systemic corticosteroids due to the possible increase in trabecular meshwork
inducible glucocorticoid response (TIGR) gene expression as an assumed mechanism for
outflow obstruction.
o Strong vasodilators (e.g. nitrites) because they may increase aqueous humour formation.
o Cycloplegic drugs as atropine.