Ophthalmology - Glaucoma

Question 1

Describe the normal production + secretion of aqueous fluid.

Answer 1

1. Produced by ciliary processes within ciliary body…
2. flows between ant. lens and iris, through pupil and into AC…
3. drains from AC via either:
   i. trabecular route (90%): through iridocorneal angle into trabecular meshwork, then into canal of Schlemm to episcleral vessels and venous circulation. Pressure-sensitive outflow.
   ii. uveosacral route (10%): through root of iris and/or ciliary muscle and into scleral vascular system. Pressure-independent outflow.

Question 2

What is the normal IOP and how is this measured?

Answer 2

Normal IOP = 11-21 mmHg.

Measured using tonometry: measures force required to flatten the corneal surface - the greater the force needed to flatten the cornea, the higher the pressure.

Question 3

Describe the autonomic control of IOP.

Answer 3

1. B2 Rs: stimulation increases IOP by increasing aqueous production
2. a2 Rs: stimulation decreases IOP by decreasing aqueous production (and may increase uveoscleral outflow)

Question 4

A 56 year old man is referred by his optician with probably chronic open-angle glaucoma.
Describe the 3 key features of this condition.

Answer 4

1. increased IOP (>21 mmHg)
2. optic disc changes e.g. cupping, high C:D ratio, disc haemorrhage, rim notching/thinning
3. VF defects

Question 5

A 56 year old man is referred by his optician with probable chronic open-angle glaucoma.
Suggest risk factors you would ask about in your history?

Answer 5

1. increased age
2. Afro-Caribbean ethnicity
3. FHx
4. steroid use
5. vascular disease e.g. DM
6. myopia

Question 6

A 56 year old man is referred by his optician with probable chronic open-angle glaucoma.
Name 3 examinations and 1 investigation you would want to perform in your assessment.

Answer 6

Examinations:

1. tonometry - measure IOP
2. gonioscopy - direct visualisation of AC and chamber angle to rule out angle-closure
3. fundoscopy - assess changes to optic disc

Investigation: visual field test

Question 7

A 56 year old man is referred by his optician with probable chronic open-angle glaucoma. He undergoes visual field tests. Suggest classical findings in chronic glaucoma.

Answer 7

Focal defects respecting horizontal meridian e.g.

• nasal step
• temporal wedge
• arcuate defects
• tunnel vision (severe)

Question 8

A 56 year old man displays features of chronic open-angle glaucoma. Describe possible pharmacological therapies. What are the MOA, and relavant s/e and c/i of each?

Answer 8

1st line:

i. prostaglandin analogues e.g. LATANOPROST
- MOA: increases uveoscleral drainage
- s/e: iris hyperpigmentation, lengthening of eyelashes
ii. B-blockers e.g. TIMOLOL
- MOA: decreases production of aqueous fluid
- c/i: asthma, heart block

2nd line:

i. a2 agonists e.g. APRACLONIDINE
- MOA: reduces production of aqueous + increases outflow
- s/e: hyperaemia
- c/i: avoid if taking MAOIs or tricyclic antidepressants
ii. carbonic anhydrase inhibitors e.g. DORZOLAMIDE
- MOA: reduce aqueous production
- s/e: systemic absorption can cause allergic reaction
iii. miotics e.g. PILOCARPINE
- MOA: increase uveoscleral outflow (by ciliary muscle contraction opening trabecular meshwork)
- s/e: constricted pupil, headache, blurred vision

Question 9

A 56 year old man displays features of chronic open-angle glaucoma. Pharmacological treatment has not been effective. Describe the next treatment options.

Answer 9

1. laser trabeculoplasty (IOP control fails with time, with 50% failure at 5 yrs, usually appropriate in frail pts)
2. surgical trabeculectomy (usually appropriate if drop-intolerant or at high risk of progression/advanced disease)