Glaucoma

Question 1

What are the different chambers and sections of the eye?

Answer 1

Question 2

What is normal intraocular pressure?

Answer 2

15-20 mmHg

Question 3

How is intraocular pressure maintained?

Answer 3

This pressure balance is maintained by the flow of aqueous humour. Fluid is secreted by the ciliary body into the posterior chamber, flows to the iris and through the pupil into the anterior chamber, and then leaves through the trabecular meshwork or uveoscleral outflow routes.

In glaucoma, this drainage system can become (partially) blocked.

Question 4

Glaucoma is a disorder that causes progressive optic neuropathy. It is characterised by damage to the optic disc and visual field deficits.

What is open-angle glaucoma?

Answer 4

• open-angle glaucoma is characterised by an anatomically open angle
• with an obstructed and slowed drainage system outflow
• the mechanism of blockage is unclear
• rise in increased intra-ocular pressure results
• characterised by retinal ganglion cell damage as well as their optic nerve axons

Narrow angle and angle closure glaucoma are less common but can be acute and result in permanent sight damage unless treated quickly. In addition, glaucoma can occur secondary to other ocular conditions that increase pressure in the eye.

Question 5

It is often asymptomatic, but what are the possible signs and symptoms of open-angle glaucoma?

Answer 5

• gradual onset
• peripheral vision loss + scotomas
• cup-to-dic ratio >0.4
• notching of optic nerve cup
• FHx, age >50yrs, black

Question 6

What are the possible complications of open-angle glaucoma?

Answer 6

• high risk of losing peripheral vision early + central vision later if untreated
• 20% pts present w/ significant field loss, and if left untreated at intraocular pressures of >30mmHg, blindness can occur within 3 yrs
• vision loss typically occurs within 1-3 months in uncontrolled disease

Question 7

How is open-angle glaucoma diagnosed?

Answer 7

• Goldmann tonometry → IO pressure above 10-21mmHg
• direct opthalmoscopy → cup-to-disc ratio >0.6 or asymmetry >0.2 between 2 eyes
• indirect opthalmoscopy
• slit-lamp biomicroscopy → cornea should be clear, anterior chamber deep, drainage angle should be open
• visual field testing → scotomas indicating loss of nerve fibre layer

Question 8

Treatments for glaucoma aim to prevent loss of vision by lowering IOP. Recent trials have confirmed that IOP lowering is effective in preventing the progression of glaucomatous damage. Lower IOP targets than previously used have been recommended.

What is the treatment for open-angle glaucoma?

Answer 8

• first-line → eye-drops (topical opthalmic):
  
  • prostaglandin analogues → eg latanoprost
  • beta-blockers → eg timolol
  • carbonic anyhdrase inhibitors → eg brinzolamide
• selective laser trabeculoplasty
• surgery → trabeculectomy or aqueous shunt (last-line)

Question 9

Acute glaucoma (angle-closure) is an ocular emergency and blindness can result if treatment is delayed.

Who gets this?

Answer 9

• middle-age/older patients
• higher in east asians
• sudden increase in intraocular pressure due to mechanical blockage of trabecular meshwork by iris
• often predisposing cataract and small eye (hypermetropia)

Question 10

What are the clinical features of acute glaucoma?

Answer 10

• severe eye pain
• watering
• loss of vision
• headache, nausea, vomiting
• halos around lights

O/E → hazy cornea + fixed mid-dilated pupil

Question 11

What is the treatment for acute glaucoma?

Answer 11

• systemic (PO or IV) acetazolomide → to turn off fluid production in ciliary body
• pilocarpine eye drops → pulls iris away from trabecular meshwork
• topical ocular antihypertensives + topical steroids

Definitive treatment is with bilateral YAG laser iridotomy (make hole in iris to allow fluid passage)