Pharmacology And The Eye Flashcards
What prevents many systemic medications from reaching the intra-ocular tissues?
The blood-ocular barrier
What is the result of most chemotherapeutic agents not being able to enter the eye?
Makes it a sanctuary site for cancer, particularly ALL
Is absorption of topical therapy through the cornea good?
Yes
What is the result of absorption of topical therapy through the cornea being good?
Most anterior segment problems can be treated with drops
When is systemic therapy required for ocular problems?
Posterior segment disease
When might drops not be tolerated?
When applied intensively, or when contact lenses are worn
Why are many drops not tolerated when applied intensively or when contact lenses worn?
Due to preservatives in the drops
What % of the active drug is absorbed into the eye when a drop is instilled in the eye?
10%
What happens to the drug that is not absorbed into the eye when using drops?
- Spills
- Enters the systemic circulation via the conjunctival vessels
- Enters nasal mucosa via the nasolacrimal ducts
After what time is the peak plasma concentration of drugs administered by eye drops?
Within 30 mins
Can drugs administered through eye drops cause systemic side effects?
Yes, particularly in neonates
How should systemic side effects caused by eye drops be minimised?
The lowest concentration of active ingredient should be used, and the nasolacrimal duct was occluded with a fingertip for a couple of minutes after drop instillation
What can prevent adequate examination of the eye?
Severe eye pain and blephrospasm
What might be helpful when examining the eye when there is severe pain or blepharospasm?
Topical anaesthetics
Should topical anaesthetics for the eye be used on a routine basis?
No
Why should topical anaesthetics for the eye not be used on a routine basis?
Corneal anaesthesia prevents epithelial healing and risks infection
What topical anaesthetics for the eye are in common use?
- Proxymetacaine 0.5%
- Tetracaine 0.5%
How long does proxymetacaine 0.5% last for?
10 minutes
Why is proxymetacaine a good choice for children?
Does not sting
What is the advantage of tetracaine 0.5%?
Longer lasting
What is tetracaine useful for?
Surgical procedures
What is the disadvantage of tetracaine 0.5%?
Severe stinging on instillation
Why is flourescein useful for diagnosis?
It lights up areas of conjunctival and corneal epithelial loss if illuminated with blue lights
Why can fluorescein light up areas of corneal and conjunctival epithelial loss?
Because it absorbs blue light and re-emits it in the green spectrum
In what forms is fluorescein available?
- Fluoret impregnated strip
- Eye drops
What do anti-muscarinic eye drops do?
Block the parasympathetic innervation of the ciliary muscle and pupil sphincter
What are anti-muscarinic eye drops commonly used for?
To allow accurate objective refraction in clinic
What are the side effects of anti-muscarinic eye drops?
- Stinging
- Blurred vision
- Photosensitivity
- Flushing
- Dry mouth
What anti-muscarinic eye drops are used?
- Tropicamide 1%
- Cyclopentolate 1% (0.5% for infants)
- Atropine 1%
What is the onset of tropicamide 1%?
15 minutes
How long does tropicamide active for?
3-6 months
What is the onset of action of cyclopentolate?
20 minutes
What is the duration of action of cyclopentolate?
24 hours
What is the onset of action of atropine?
30 minutes
What is the duration of action of atropine?
7 days
What are sympathomimetic eye drops used for?
Used synergistically with anti-muscarinic eye drops for intense mydriasis needed for intra-ocular surgery or ROP screening and treatment
What are the side effects of sympathomimetic eye drops?
- Stinging
- Blurred vision
- Sensitivity to light
Rarely, tachycardia and hypertension can occur
