Ophth - Special senses pharmacology Flashcards
What are some inherent ocular defences?
Lacrimal functional unit
Internal ocular homeostasis
What is the name for increased tearing?
Epiphora
What is the nmae for increased blinking?
Blepharospasm
What is the function of the functional lacrimal unit?
Physical and chemical barrier to infectious agents
What makes up the functional lacrimal unit?
Normal eyelids
Normal tear film
Corneal epithelium
Functional tear drainage
Conjunctival associated lymphoid tissue
What is conjunctival associated lymphoid tissue?
Very diffuse lymph gland under epithelium
Recruits immune cells with chemical mediators to remove foreign substances by WBCs
What makes up the ocular surface response?
Epiphora
Mucoid discharge
Purulent discharge
Blepharospasm
What is the function of internal ocular homeostasis?
Maintains the clarity of ocular media (aqueous and vitreous humour) for vision
What helps to maintain the internal ocular homeostasis?
Blood ocular barrier
immune priveliged site
Intraocular pressure maintained locally
What is the blood ocular barrier?
Second line physical and chemical barrier - tight junctions that act as a filter to keep drugs and infectious agents out of eye
What does it mean that the eye is an immune privileged site?
No immune cells are in the eye as they can damage the eye
There is no lymphatic drainage
What is the general rule for treating the eye with drugs?
Surface and anterior segment - topical drugs needed
Posterior segment - systemic drugs needed
What are the barriers to topical penetration?
Tear dilution
Blinking
Lacrimal drainage
Permeability of tissues - cornea, conjunctiva, sclera
What is the best pH for drugs used in the eye?
pH 7.4 - same as normal tears so non-irritant
Between 4.5 and 9 for comfort
What are the two main routes of penetration?
Transcellular - across the corneal epithelial cell
Paracellular - between individual cells
What is the structure of the cornea? What are the layers?
Corneal epithelium - lipophilic barrier
Corneal stroma - hyprophilic
Descemet’s membrane (endothelium) - lipophilic barrier
What is required for a drug to be able to go the transcellular route for topical eye treatment?
Lipophilic-hydrophilic balance of the drug
What is required for a drug to be able to go the paracellular route for topical eye treatment?
Small molecular weight - to pass between the tight junctions
What is an example of a drug that go via the transcellular route?
Chloramphenicol
How do topical solutions for eye treatment work?
Treat the ocular surface without needing to penetrate deeply
What is an example of an optical topical solution?
Prednisolone sulphate
How can you improve topical penetration?
Combine drugs with organic salts
Add preservatives that disrupt the corneal epithelial barrier
Use suspension
How do topical suspensions aid with drug absorption?
They improve tear retention by micronizing the particles to prevent irritation
Why are topical ointments good for drug retention and absorption?
Have a lipophilic character so are retained in the tearfilm
What is the topical dose/drop volume to use
1 drop! Palpebral fissure can hold max 25/30 ul
How often do you need to give topical eye treatments?
As often as possible - 1 drop cleared in 10 mins
Wait 10 mins in between applications of different drops or will dilute each other
What order should you put different eye treatments in?
Aqueous drop>suspension>gel>ointment
What periocular injections can you give?
Subconjunctival injection - for absrobing across the sclera
Retrobulbar injection - for removing an eye
When do you use sustained release implants in eyes?
For immun emediated conditions
What do systemic medications need to penetrate the eye?
Lipid solubility
Low molecular weight molecules
Protein binding
What are the most commonly used systemic drugs for eyes?
Chloramphenicol, doxycycline
What anti-inflammatory drugs are used for eyes?
Corticosteroids
NSAIDs
What are the contraindications for corticosteroids?
Dont use in infections - immunosuppressive
Dont use in corneal ulceration
What are the antiglaucoma drugs?
Prostaglandin analogues
Carbonic anhydrase inhibitors
Beta blockers
How do prostaglandin analogues act as anti-glaucoma drugs?
The increase the outflow of aqueous humour so reduce the pressure in the eye
When do prostaglandin analogues not work to prevent glaucoma?
In cats
What is a side effect of prostaglandin analogues as anti-glaucoma drugs?
Cause a profound myosis - small pupil
How do carbonic anhydrase
inhibitors and beta blockers act as anti-glaucoma drugs?
They decrease aqueous humour production
What are the two main mydriatic drugs?
Atropine
Tropicamide
What are the features of atropine and when should it be used?
Atropine has a slower onset but longer duration
So use for clinical indication to dilate the pupil eg. spasming
Tastes bitter
When should you not use atropine?
In glaucoma or keratoconjunctivitis secca cases
What are the main features of tropicamide and when should it be used?
Rapid onset, quicker wear off
Reduces tears in cats
What local anaesthetics can be used in the eye?
Proxymetacaine
What should you use for tear replacement?
Hyaluronic acid (clinitas) - holds water well, good lubricant
Lipid based substitutes
Aqueous based substitutes
What are anti-collagenases used for in the eyes?
They stop the cornea melting from collagenase enzymes produced by bacteria
What are the best anti-collagenases?
Serum and plasma from the patients own blood
Acetylcysteine
Tetracyclines
