Pharmacology on Eye

8/3/2019 Pharmacology on Eye

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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




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)




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




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




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




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




# 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%)




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.

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Pharmacology on Eye