10. Pharmacology, Microbiology, Cataract

Question 1

What are considered to be commensal organisms of the eyelid and conjunctiva?

Answer 1

Staph epidermidis
Staph aureus

• Not usually responsible for serious pathology?

Question 2

What are common pathological organisms for the eyelid/conjunctiva?

Answer 2

• Gram +ive (staph, strep)
• Gram –ive (pseudomonas, e. Coli, klebsiella)
• Viruses (adenovirus, herpes)
• Protozoa (acanthomoeba) (serious lens infections)
• Fungi

Question 3

What are the defense mechanisms of the cornea?

Answer 3

• Intact epithelium
• Irrigation by tears
• Tear lysozyme
• Blinking
• Decreased ocular temperature

Question 4

What are common pathologies which compromise corneal defenses?

Answer 4

Corneal abrasion,
Contact lenses,
Ocular surgery

Question 5

What pathologies often result from compromised corneal defenses?

Answer 5

Conjunctivitis
Keratitis
Endophthalmitis

Question 6

What are the main methods of administration for ocular medications?

Answer 6

1. Topical (eye drops)
2. Systemic (oral, IV)
3. Periocular (peribulbar, rebrobulbar, subtenons)
4. Intraocular (intravitreal)

Question 7

What are the features of topical administration?

Answer 7

Good for delivering local antibiotics, steroids.

Lipid soluble for better penetration

Especially good for anterior chamber problems.

Question 8

What are the features of systemic administration?

Answer 8

Good for Uveitis, GCA etc

eg steroids, antibiotics, acetazolamide.

Carbonic Anhydrase in AACG

Question 9

What are the features of periocular administration?

Answer 9

(peribulbar, retrobulbar, subtenons) –

eg local anaesthetic, steroid

Question 10

What are the features of intraocular administration?

Answer 10

(intravitreal) – eg intravitreal anti-

VEGF, antibiotics

Question 11

What causes miosis?

Answer 11

Parasympathetic NS 
From EWN
Via Inferior Division of CNIII
To Ciliary Ganglion
To Short Ciliary Nerves

Innervates iris sphincter = Miosis

Question 12

What causes mydriasis?

Answer 12

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

Question 13

Give examples of dilating drops?

Answer 13

1. Antimuscarinics
   - tropicamide, cyclopentolate, atropine
2. Alpha-agonists
   – phenylephrine

Question 14

Give some uses of dilating eye drops?

Answer 14

Uses –
to facilitate examination,
therapeutic (useful in uveitis, hyphaema)

Question 15

Give examples of constricting drops

Answer 15

Parasympathomimetic

– pilocarpine (muscarinic receptor agonist)

Question 16

Give some uses of constricting drops?

Answer 16

Uses

– lowering IOP, acute angle closure glaucoma

Question 17

Examples of Topical Anaesthetics?

Answer 17

Proxymethacaine, tetracaine

Question 18

What are the potential S/E’ of topical anaesthetic? When are they indicated?

Answer 18

Warning: Can impair corneal healing.

Only used for purpose of examination. Do not prescribe.

Question 19

Antibiotics used for conjunctivitis?

Answer 19

Chloramphenicol

Fucidic acid

Question 20

Antibiotics used for Pseudomonal Inf (corneal lens inf)?

Answer 20

Ofloxacin/Floxin

Question 21

Antibiotics for more severe infections eg severe bacterial keratitis, endophthalmitis?

Answer 21

Cephalosporins
Vancomycin
Gentamycin

Question 22

Steroids used in treatment of ocular inflammatory conditions?

Answer 22

Prednisolone

Dexamethasone

Question 23

Rx in allergic conjunctivitis?

Answer 23

Antihistamines

Mast cell stabilisers

Question 24

What are the Rx’s in glaucoma?

Answer 24

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

Question 25

Which commonly used drugs have occular side effects? What are they?

Answer 25

* 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)

Question 26

What is Cataract?

Answer 26

Loss of transparency of the lens

Question 27

What are the symptoms of cataract?

Answer 27

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

Question 28

What are the clinical findings in cataracts?

Answer 28

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

Question 29

Common misconceptions about Cataract?

Answer 29

``` 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) ```

Question 30

What are the different types of cataracts?

Answer 30

Nuclear Sclerosis (most common) Cortical Posterior Sub capsular

Question 31

What are the risk factors for cataracts?

Answer 31

• 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

Question 32

What are the indications for surgery in cataracts?

Answer 32

1. Operate for visual improvement – when patient complains of difficulty seeing, performing daily tasks, reading, driving 2. Operate for medical reasons – eg to improve view of fundus for monitoring diabetic retinopathy, to help treat high IOP.

Question 33

Describe Cataract surgery? Efficacy? Risks?

Answer 33

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)

Question 34

What are the potential complications of Cataract Surgery?

Answer 34

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

Question 35

How is the risk of infection post-operative infection mitigated?

Answer 35

1. Antiseptic – betadine (Broad spectrum microbicidal Activity) 2. Intraoperative antibiotic - 3rd gen cephalosporin, gentamycin (broad spectrum spectrum – gram pos, gram neg, pseudomonas) 3. Postoperative antibiotic – chloramphenicol, neomycin 4. Postoperative steroid – dexamethasone