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 application s. Identify the lines of treatme nt of some eye diseases as glaucoma and conjunctivi tis. STRUCTURES OF THE EYES Anatomically eye composed of : i) Anterior chamber ii) Posterior chamber ANTERIOR CHAMBER INCLUDE: 1.CORNEA2.IRIS3.LENS4.AQUEOUS HUMOUR1. THE CORNEA CORNEAL OR CONJUNCTIVAL REFLEXThe 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.Diagnostic Dyes C.Topical Anti-Inflammatory D.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 ofIOP b. Removal of corneal foreign bodies 2. Profound anaesthesia by tetracaine eye drops for: Removal of cataracts B. DIAGNOSTIC DYES Fluorescein 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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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