10. Pharmacology, Microbiology, Cataract Flashcards
What are considered to be commensal organisms of the eyelid and conjunctiva?
Staph epidermidis
Staph aureus
- Not usually responsible for serious pathology?
What are common pathological organisms for the eyelid/conjunctiva?
- Gram +ive (staph, strep)
- Gram –ive (pseudomonas, e. Coli, klebsiella)
- Viruses (adenovirus, herpes)
- Protozoa (acanthomoeba) (serious lens infections)
- Fungi
What are the defense mechanisms of the cornea?
- Intact epithelium
- Irrigation by tears
- Tear lysozyme
- Blinking
- Decreased ocular temperature
What are common pathologies which compromise corneal defenses?
Corneal abrasion,
Contact lenses,
Ocular surgery
What pathologies often result from compromised corneal defenses?
Conjunctivitis
Keratitis
Endophthalmitis
What are the main methods of administration for ocular medications?
- Topical (eye drops)
- Systemic (oral, IV)
- Periocular (peribulbar, rebrobulbar, subtenons)
- Intraocular (intravitreal)
What are the features of topical administration?
Good for delivering local antibiotics, steroids.
Lipid soluble for better penetration
Especially good for anterior chamber problems.
What are the features of systemic administration?
Good for Uveitis, GCA etc
eg steroids, antibiotics, acetazolamide.
Carbonic Anhydrase in AACG
What are the features of periocular administration?
(peribulbar, retrobulbar, subtenons) –
eg local anaesthetic, steroid
What are the features of intraocular administration?
(intravitreal) – eg intravitreal anti-
VEGF, antibiotics
What causes miosis?
Parasympathetic NS From EWN Via Inferior Division of CNIII To Ciliary Ganglion To Short Ciliary Nerves
Innervates iris sphincter = Miosis
What causes mydriasis?
Sympathetic NS From Hypothalamus Via Superior Cervical Ganglion To Cavernous Sinus Ophthalmic Division of CN V (Trig) To Nasociliary Nerve To long Ciliary Nerve
Innervates iris dilator = mydriasis
Give examples of dilating drops?
- Antimuscarinics
- tropicamide, cyclopentolate, atropine - Alpha-agonists
– phenylephrine
Give some uses of dilating eye drops?
Uses –
to facilitate examination,
therapeutic (useful in uveitis, hyphaema)
Give examples of constricting drops
Parasympathomimetic
– pilocarpine (muscarinic receptor agonist)
Give some uses of constricting drops?
Uses
– lowering IOP, acute angle closure glaucoma
Examples of Topical Anaesthetics?
Proxymethacaine, tetracaine
What are the potential S/E’ of topical anaesthetic? When are they indicated?
Warning: Can impair corneal healing.
Only used for purpose of examination. Do not prescribe.
Antibiotics used for conjunctivitis?
Chloramphenicol
Fucidic acid
Antibiotics used for Pseudomonal Inf (corneal lens inf)?
Ofloxacin/Floxin
Antibiotics for more severe infections eg severe bacterial keratitis, endophthalmitis?
Cephalosporins
Vancomycin
Gentamycin
Steroids used in treatment of ocular inflammatory conditions?
Prednisolone
Dexamethasone
Rx in allergic conjunctivitis?
Antihistamines
Mast cell stabilisers
What are the Rx’s in glaucoma?
Protaglandin analogues
• Increase aqueous outflow
• Risk of increased eyelash/iris pigmentation
Beta-blockers
• Reduce aqueous production
• Risk of bronchospasm in susceptible patients (avoid in asthma, CCF)
Carbonic anhydrase inhibitors
• Acetazolamide or topical versions
• Reduce aqueous production
Alpha-agonists
• Reduce aqueous production, increase outflow
• Can cause red eye
Which commonly used drugs have occular side effects? What are they?
- Steroids (increased IOP)– glaucoma, cataract
- Ethambutol, quinine (TB) – optic neuropathy
- Chloroquine (Antimalarial) – maculopathy
- Tamoxifen – pigmentary retinopathy
- Vigabitrin – visual field defects
- Amiodarone – Corneal deposits (vortex keratopathy)
What is Cataract?
Loss of transparency of the lens
What are the symptoms of cataract?
Gradual reduction in visual acuity
“a cloud”, “generalised blur”, “haze”,
“everything duller”
“Glare” from bright lights, sunshine – difficulty driving at night – glare from oncoming cars
Myopic shift – Induced Myopia
What are the clinical findings in cataracts?
Reduced visual acuity – which may improve with pinhole
Diminished red reflex (clouding)
NO RAPD (provided retina and optic nerve are healthy)
Note: As a cataract becomes very mature it become fatter, and can push the iris forward thus narrowing the
iridocorneal angle, which can predispose to angle closure.
glaucoma and high IOP
Common misconceptions about Cataract?
A cataract is NOT: • A film over the eye • Spread from one eye to the other • Caused by straining the eye • A cause of irreversible blindness • Is not fixed by laser (although newer techniques for cataract extraction do involve lasers – still intraocular)
What are the different types of cataracts?
Nuclear Sclerosis (most common)
Cortical
Posterior Sub capsular
What are the risk factors for cataracts?
• AGE
• Diabetes
• Family history
• Previous surgery or injury to the eye
• Certain medications, prolonged use of steroids
• Congenital cataracts associated with intrauterine
infections – rubella, toxo, CMV, herpes
• Associated with certain syndromes – myotonic dystrophy,
Down’s
What are the indications for surgery in cataracts?
- Operate for visual improvement
– when patient complains of difficulty seeing, performing daily tasks, reading, driving - Operate for medical reasons
– eg to improve view of fundus for monitoring diabetic retinopathy, to help treat high IOP.
Describe Cataract surgery? Efficacy? Risks?
Local anaesthetic for most cases (topical only, peribulbar, subtenons)
GA – for patients who can’t lie still, young, very anxious
Approx 20 minute procedure
90-95% chance of good-excellent vision post-op
2% chance of vision not improving much or deteriorating
1 in 1000 risk of vision loss (eg due to endophthalmitis)
What are the potential complications of Cataract Surgery?
Intraoperative:
• Rupture or tear of posterior capsule – the “bag”
• This means that vitreous could come forward; lens fragment could fall into posterior segment; ruptured “bag” can’t hold new lens implant – may need to put it into anterior chamber
Postoperative
• Increased IOP
• Corneal oedema
• Macular oedema
• Retinal detachment (higher risk in myopes)
• Induced astigmatism from wound
• Serious infection (endophthalmitis) – risk 1 in 1000
How is the risk of infection post-operative infection mitigated?
- Antiseptic – betadine (Broad spectrum microbicidal
Activity) - Intraoperative antibiotic
- 3rd gen cephalosporin, gentamycin (broad spectrum
spectrum – gram pos, gram neg, pseudomonas) - Postoperative antibiotic
– chloramphenicol, neomycin - Postoperative steroid
– dexamethasone
