The Cornea, Lens and Intra-Ocular Pressure

Question 1

What is the cornea?

Answer 1

Avascular transparent structure that separate anterior chamber from tear film

Question 2

What are the 3 main roles of the cornea?

Answer 2

Maintain transparency
Ocular protection
Refract light

Question 3

Describe the epithelium of the cornea

Answer 3

5-7 cell layer thick non keratinized stratified squamous layer.

Cells migrate from basal layer to surface then sloughed off into tar film

Question 4

How is corneal oedema seen?

Answer 4

Visible lines in the stroma

Question 5

What happens to endothelial cell number with age?

Answer 5

Falls

Question 6

What nerve supplies the cornea?

Answer 6

Opthalmic branch of the trigeminal nerve –> via long ciliary nerve

Question 7

What can trigger an infection of the cornea?

Answer 7

Disruption of the epithelial surface caused by:

Trauma
Contact lens wear
Dry eyes
Pre-existing corneal disease
Systemic conditions - immunocompromised

Question 8

What symptoms would a patient with infective keratitis present with?

Answer 8

Severe pain
Red eye
Epiphora - excess eye watering

possible reduced visual acuity
Photophobia
Mucus discharge

Question 9

What would you expect to see on examination if you suspect infective keratitis?

Answer 9

White deposits in cornea - corneal infiltrate
Hypopyon - pus collect in anterior chamber

Anterior chamber may show cells and flare - leucocytes and protein respectively due to leaky blood vessels

Question 10

What is the aqueous humour pathway?

Answer 10

Ciliary processes in ciliary body –> iris and anterior surface of lens –> pupil –> through iridocorneal angle –> trabecular meshwork –> Canal of Schlemm –> episcleral vessels –> systemic venous circulation

Question 11

What is the unconventional drainage route for aqueous humour?

Answer 11

Uveaoscleral route - drain into root of iris and ciliary muscle –> scleral vascular system

10-20%

Question 12

How is intraocular pressure measured?

Answer 12

Force needed to flatten corneal surface using tanometer - pressure at which green lines match

Must correct for corneal thickness

Question 13

What is the normal intraocular pressure?

Answer 13

11-21mmHg

Question 14

What does ocular hypertension put you at higher risk of?

Answer 14

Developing glaucoma

Question 15

Which autonomic receptors control intra-ocular pressure?

Answer 15

Adrenergic - alpha 2 and beta 2

Cholinergic have little direct effect

Question 16

What effect does alpha 2 have on intraocular pressure?

Answer 16

Reduce IOP by reducing aqueous production

May increase uveoscleral outflow

Question 17

What effect does beta 2 have on intraocular pressure?

Answer 17

Increase IOP by increasing aqueous production

Question 18

What drug classes are used to target intraocular pressure?

Answer 18

Beta-blockers
Alpha antagonists
Prostaglandin analogues
Carbonic anhydrase inhibitors
Parasympathomimetics

Question 19

Give examples of beta blockers and their MoA for intraocular pressure

Answer 19

Timolol, Carteolol

Reduce aqueous humour - block beta 2 receptors

Question 20

Give examples of alpha agonists and their MoA for intraocular pressure

Answer 20

Apraclonidine, brimonidine

Reduce production of aqueous and slight increase in drainage

Question 21

Give examples of prostaglandin analogues and their MoA for intraocular pressure

Answer 21

Latanoprost, Bimataprost

Increase uveoscleral outflow of aqueous humour

Question 22

Give examples of carbonic anhydrase inhibitors and their MoA for intraocular pressure

Answer 22

Dorzolamid, Brinzolamide

Reduce production of aqueous humour by decreasing fluid transport in ciliary body

Question 23

Give examples of parasympathomimetics and their MoA for intraocular pressure

Answer 23

Pilocarpine

Increase outflow by ciliary muscle contraction causing trabecular meshwork to open

Question 24

What topical preparations are used in raised IOP?

Answer 24

Cosopt - timolol and dorzolamide

Question 25

What is the main function of the lens and how powerful is it?

Answer 25

Refraction Refractive power less than cornea

Question 26

How does the lens change refractive power?

Answer 26

Changes shape (accommodation)

Question 27

How does the lens change shape?

Answer 27

Ciliary body contract --> pull suspensory ligaments --> flatten lens --> less refraction vice versa if ciliary body relax

Question 28

What is presbyopia?

Answer 28

Lens' ability to accomodate diminish with age

Question 29

What causes presbyopia?

Answer 29

Atrophy of ciliary muscle Loss of lens elasticity

Question 30

How do inner lens fibres vary from outer lens fibres?

Answer 30

Inner fibres older and much harder then newer fibres on outside

Question 31

How does a lens maintain transparency?

Answer 31

Fibres are tightly packed and highly organised

Question 32

What is a cataract?

Answer 32

Loss of transparency of the lens

Question 33

What is the most common cause for cataracts?

Answer 33

Increasing age

Question 34

Why is early detection of cataracts crucial in newborns?

Answer 34

To salvage best vision possible

Question 35

What are common causes of cataracts in younger patients?

Answer 35

Trauma Drugs - steroids, amiodarone, allopurinol Systemic disease - Diabetes, myotonic dystrophy, neurofibromatosis type 2

Question 36

What are general symptoms of cataracts?

Answer 36

Painless loss of vision Diplopia Loss of red reflex Difficulty with every day tasks

Question 37

What is the most common technique for cataract surgery?

Answer 37

Phacoemulsification

Question 38

What is the management for infectious keratitis?

Answer 38

Topical broad spectrum quinolone

Question 39

What is the prognosis for infectious keratitis?

Answer 39

Usually good Risk of long term visual disability in: Elderly, contact lens wearer, fungal disease

Question 40

What happens in a cataract lens?

Answer 40

Disruption of lens fibres leading to protein aggregation and deposition in the lens Causes clouding, light scattering and vision obstruction

Question 41

What complications are associated with phacoemulsification?

Answer 41

``` Rupture of posterior capsule Infection Inadequate correction for refractive error Haemorrhage Posterior capsule opacification ```

Question 42

What is a congenital cataract?

Answer 42

Inherited cataract | Cataract secondary to intrauterine infection - rubella

Question 43

What can happen in congenital cataracts aren't removed?

Answer 43

Lead to nystagmus and amblyopia

Question 44

What are children who have surgery for a congenital cataract within their first year of life at risk of?

Answer 44

High risk of glaucoma

Question 45

What are the ADR's associated with latanoprost?

Answer 45

Iris turn brown Risk of uveitis and keratitis Longer eyelashes

Question 46

What are the CI for latanoprost?

Answer 46

Uveitis | Pregnancy

Question 47

What are the ADR's associated with Timolol?

Answer 47

Irritated, red, dry eye Bronchospams Bradycardia

Question 48

What are the CI's for timolol?

Answer 48

Asthmatics | Heart block

Question 49

What are the ADR's for Dorzolamide (carbonic anhydrase inhibitors)?

Answer 49

N&V Headache Dizzy

Question 50

What are the CI's for carbonic anhydrase inhibitors?

Answer 50

Renal impairment

Question 51

What are the ADR's associated with sympathomimetics (brimonidine)?

Answer 51

Dry eye | Postural hypotension

Question 52

What are the ADR's associated with parasympathomimetics (pilocarpine)?

Answer 52

Blurred vision Constricted pupil Sweating Bradycardia

Question 53

What the are CI's associated with sympathomimetics?

Answer 53

Angle closure glaucoma | On MAOI's

Question 54

What are the CI's associated with parasympathomimetics?

Answer 54

Uveitis