Ocular Pharmacology Flashcards
Requirements for topical administration of drugs to the eyes?
Required to act on the surface
Require corneal penetration
Which drugs can effectively penetrate the cornea?
LMW drugs
Nature of the epithelium and which drugs can penetrate it?
Epithelium is lipophilic/hydrophobic
Lipid-soluble drugs penetrate the epithelium
Nature of the stroma and which drugs can penetrate it?
Stroma is lipophilic/hydrophilic
Water-soluble drugs
Which drugs have both lipophilic and hydrophilic properties?
Chloramphenicol; these drugs easily penetrate the cornea
How does ocular surface inflammation affect the epithelium?
Often REDUCES the hydrophobic nature of the endothelium
So which drugs are limited by which layer of the eye (in terms of penetration)?
Hydrophilic drugs are limited by the epithelium
Hydrophobic drugs are limited by the stroma
What chemical modifications can be made to topical steroids to alter their characteristics?
Alcohol or acetate - makes steroid more hydrophobic
Phosphate - makes steroid more hydrophilic
Uses of prednisolone acetate?
Hydrophobic and so achieves good penetration in an uninflamed cornea, i.e: it is not washed away by tears
It is used post-operatively
Uses of prednisolone phosphate?
Hydrophilic and so only achieves poor penetration in an uninflamed cornea, i.e: it is washed away in the tears
Used for corneal disease or for when low-dose steroids are desired
What is benzalkonium?
A preservative in eye products that disrupts the lipid later of tear film, causing dry eyes
It also aids the penetration of some drugs
What is Bimatoprost?
Drugs used to lower the intra-ocular pressure in glaucoma
How does systemic absorption of topical drugs occur?
Tears are pumped out of the lacrimal sac rapidly but the excess gains systemic absorption at the nasopharynx
How can systemic absorption of topical drugs be limited?
By punctal occlusion
Routes of administration of drugs
Subconjunctival
Subtenons
Routes of administration of ocular injections?
Intravitreal
Intracameral
Anti-inflammatory drugs that can be used?
Steroids
Topical NSAIDs (can be used for pain relief, e.g: post-refractive laser)
Anti-histamines (used in allergic conjunctivitis/hayfever)
Mast cell stabilisers
When are steroids used topically?
- Post-operative cataracts
- Uveitis
- Prevention of corneal graft injection
Local (ocular) side effects of steroids?
Cataract, glaucoma and exacerbation of viral infection
Systemic side effects of steroids?
Gastric ulceration
Immunosuppression
Osteoporosis
Weight gain, diabetes
Neuropsychiatric effects, etc
Varying strengths of topical steroids?
- Fluorometholone (FML)
- Predsol
- Betamethasone
- Dexamethasone/prednisolone
What is glaucoma?
Group of diseases characterised by progressive optic neuropathy, resulting in characteristic field defects
Cause is intra-ocular pressure
Symptoms of glaucoma?
Usually asymptomatic until advanced disease stage
How do glaucoma drops occur?
Drugs that either:
- Decrease aqueous humor production
- Increase aqueous humor outflow
Examples of drugs used in glaucoma treatment?
Prostanoids, e.g: latanoprost
β-blockers
Carbonic anhydrase inhibitors:
• Topical - Dorzolamide
• Systemic - Brimonidine
Parasympathetic, e.g: pilocarpine
Combination drugs (dorzolamide and timolol)
Uses of intravitreal injections?
Method of administration of antibiotics in endophthalmitis
To deliver intra-ocular steroids
Anti-VEGF (anti-vascular endothelial growth factor) - prevents growth of new vessels
Advantages and disadvantages of intravitreal injections?
Delivers effective concentration of drug at the target site instantly
BUT
Many drugs are toxic to the retina
Complication of endopthalmitis?
Blindness
What is dry macular degeneration?
ATROPHIC type
Unknown aetiology
What is wet macular degeneration?
New vessel membrane forms over the macula; these haemorrhage and leak, leading to damage of the macula
Mechanism of action of local anaesthetic in the eye?
Blocks Na+ channels and impedes nerve conduction
Uses of local anaesthetic?
- Foreign Body (FB) removal
- Tonometry (IOP measurement)
- Corneal scraping
- Comfort
Uses of diagnostic dyes?
Most commonly used is fluorescein
Uses include:
- Showing a corneal abrasion
- Tonometry
- Diagnosing a nasolacrimal duct obstruction
- Angiography
What are mydriatics?
Cause pupil dilatation by blocking the parasympathetic supply to the iris, e.g: tropicamide and cyclopentolate
Side effects of mydriatics?
Blurring
AACG (Acute Angle Closure Glaucoma)
How do sympathomimetics work?
Act to enhance the sympathetic nervous system, causing the pupils to dilate, e.g: phenylephrine, atropine
They do not affect ciliary muscle (accommodation)
Example of a drug that constricts the visual fields?
Vigabatrin
Example of a drug that can cause a cataract?
Steroids
Example of a drug that can cause optic neuropathy?
Ethambutol
Example of a drug that can cause maculopathy?
Chloroquine
Example of a drug that can cause corneal opacities in the eye?
Amiodarone - appears as a horizontal pigmented line
