glaucoma

Question 1

what is glaucoma?

Answer 1

a group of eye diseases that cause progressive optic neuropathy and in which intraocular pressure is a key modifiable factor. It is commonly associated with raised intraocular pressure and is characterised by

• changes to the optic nerve head such as pathological cupping or pallor of the optic disc (late)
• visual field defects

Question 2

define ocular hypertension

Answer 2

elevated intraocular pressure greater than 21mmHg but with no signs of pathological optic disc cupping or visual field defects

Question 3

how is aqueous humour produced and drained?

Answer 3

production - active secretion by the epithelium of the ciliary process of the ciliary body requiring the enzyme carbonic anhydrase

drainage - occurs through 2 routes

• conventional route - 85-90% drains through trabecular meshwork into the canal of schlemm in the anterior chamber angle and into the circulation.
• uveoscleral route - 10-15% drains through ciliary body into ciliary circulation

Question 4

what is normal intraocular pressure and how is this maintained?

Answer 4

10-21mmHg
dynamic balance between production and drainage of aqueous humour maintains the pressure in this normal range (calculated as a normal distribution of the population)

it is important to remember that intraocular pressure varies throughout the day and night

Question 5

what are the different types of glaucoma?

Answer 5

primary open angle glaucoma - most common, develops gradually

acute angle closure glaucoma - uncommon caused by a sudden block in drainage and sudden onset

secondary glaucoma - caused by an underlying eye condition such as uveitis

childhood glaucoma - congenital abnormality

Question 6

outline the pathogenesis of primary open angle glaucoma

Answer 6

Primary open angle glaucoma is a syndrome

Raised intraocular pressure above 21mmHg - caused by possible degenerative change in the trabecular meshwork causing more resistance to aqueous outflow. This develops gradually overtime

This causes a Pathologically cupped optic disc and Glaucomatous visual field loss

There are 2 theories as to how the raised pressure causes neuropathy:
Direct mechanical theory - the raised pressure directly damages the nerve
Indirect ischaemic theory - the raised pressure interferes with microcirculation and the perfusion pressure is too low to compensate causing ischaemia to the nerve which causes damage

Question 7

what are the risk factors for primary open angle glaucoma?

Answer 7

raised intraocular pressure 
age 
family history 
ethnicity - x2 common in black people vs white 
corticosteroids - stiffens trabecular meshwork
myopia - mechanical factors 
type 2 diabetes 
hypertension and other CV disease

Question 8

what are the symptoms of primary open angle glaucoma?

Answer 8

initially asymptomatic
no pain
white eye
visual loss when it is advanced - people may not be aware of visual defects at first because the visual fields overlap and therefore one eye may compensate for another initially. Peripheral vision goes first, then central vision - blindness is possible

Question 9

what are the complications of primary open angle glaucoma?

Answer 9

• irreversible loss of vision (partial or compleate) due to damage to the optic nerve
• retinal vascular occlusion

Question 10

how do you assess someone with glaucoma?

Answer 10

• assess visual acuity (may be normal)
• assess central corneal thickness - eyes with thin corneas may have the pressure measured wrong
• use tonometer to assess intraocular pressure
• otoscopy - optic disk cupping, open drainage angle, optic disk pallor (late sign)
• Humphrey test - flashing lights in visual field

(useful images and diagrams in notes)

Question 11

how are people with glaucoma monitored?

Answer 11

• monitor intraocular pressure
• calculate cup disk ratio of the optic disk every 12 months
• yearly assessment of visual fields
• most patients are seen 4-6 monthly if stable

Question 12

what medical treatment is available for glaucoma?

Answer 12

medical treatment focuses on decreasing production of aqueous humour and increasing the aqueous outflow

topical medication (eyedrops which can be increased or added to if the glaucoma is not controlled):

• prostaglandin analogue/ prostamide - drops at night to increase uveoscleral outflow
• beta blockers - drops twice a day to decrease aqueous humour production
• carbonic anhydrase inhibitors - drops 2-3 times a day to decrease aqueous humour production
• alpha 2 agonist - drops twice a day decreases aqueous production and increased uveoscleral outflow

systemic medication (temporary or emergency treatment due to uncontrolled glaucoma/ systemic side effects):
- oral carbonic anhydrase inhibitor

Question 13

what surgical treatment is available for glaucoma?

Answer 13

surgical options focus on increasing the aqueous outflow

• selective laser trabeculoplasty
• trabeculectomy - surgical formation of a fistula connecting the anterior chamber to the subconjunctival space which provides alternative path for drainage
• drainage shunt or tube - small flexible silicone tube is inserted through the sclera into the anterior chamber which allows the aqueous humour to drain into an artificial reservoir.
• minimally invasive glaucoma surgery such as stents