Glaucoma Flashcards
Define glaucoma.
An optic neuropathy due to increased pressure inside the eye, resulting in visual field defects, with loss of sight .
What is normal intra-ocular pressure?
Normal intraocular pressure (IOP) is 10–21 mmHg. Some types of glaucoma can result in an IOP exceeding 70 mmHg
What is the epidemiology of glaucoma?
Second most common cause of blindness worldwide
Third most common cause of blind registration in the UK
What is primary open-angle glaucoma?
Most common form of glaucoma
IOP result from reduced outflow of aqueous humour through the trabecular meshwork.
What are the risk factors for primary open-angle glaucoma?
- Age (20% of 80yr olds affected)
- FH -first degree relatives of an open-angle glaucoma patient have a 16% chance of developing the disease
- Myopia
- Hypertension
- Afro Caribbeans (x5)
- Corticosteroids
- DM
What are the clinical features of POAG?
- Gradual, insidious, painless loss of…
- … Peripheral visual field causing loss of vision and ‘tunnel loss’ - central vision remains good until end-stage disease
- Decreased acuity
- Initially asymptomatic - identified in routine ophthalmic examination
O/E:
- Optic disc cupping - cup to disc ration >0.7 (normal 0.4-0.7)
- Optic disc pallor
- Bayonetting of vessels
- Cup notching and disc haemorrhages
What are the fundoscopy features of POAG?
1. Optic disc cupping - cup-to-disc ratio >0.7 (normal = 0.4-0.7), occurs as loss of disc substance makes optic cup widen and deepen
2. Optic disc pallor - indicating optic atrophy
3. Bayonetting of vessels - vessels have breaks as they disappear into the deep cup and re-appear at the base
4. Additional features - Cup notching (usually inferior where vessels enter disc), Disc haemorrhages
Treatment: prostaglandin analogue eye drops
How is POAG diagnosed?
Intra-ocular tonometry - IOP > 24 mmHg as measured by Goldmann-type applanation tonometry
Slit-lamp examination - done with pupil dilatation, retinal and optic disc visualisation
Visual field exam via automated perimetry test- peripheral field loss
Pachymetry - provides measurement of corneal thickness which is predictive of ocular pressure
Gonioscopy - assesses peripheral anterior chamber configuration and depth
NB: provisional diagnosis done by optometrist but GP needs to refer to ophthalmology.
What is the management of POAG?
Aim to lower intra-ocular pressure to prevent visual field loss
- Eye drops - prostaglandin analogue e.g. latanoprost OD
- 2nd line: beta-blocker (e.g. timolol, betaxolol), carbonic anhydrase inhibitor (e.g. dorzolamide), sympathomimetic eyedrop (e.g. brimonidine)
- Surgery - trabeculectomy in refractory cases
- Laser treatment
Reassess progression of visual field loss; reassess frequently if risk factors for this.
What is the MOA of POAG treatments?
Increase uveoscleral outflow = prostaglandin analogues, miotics (e.g. pilocarpine), sympathomimetics
Reduce aqueous production = beta-blockers (e.g. timolol, betaxolol), carbonic anhydrase inhibitors (e.g. dorzolamide), sympathomimetics
What is acute angle-closure glaucoma?
Ophthalmic emergency
Closure of the anterior-chamber angle causing raised IOP(>21mmHg but usually over 40mmHg), usually due to sudden blockage by the trabecular meshwork by the iris.
What are the risk factors for acute angle closure glaucoma?
- Shallow anterior chamber e.g. hypermetropes and women
- Female
- Hyperopia - anterior chamber depth and volume are smaller in long-sightedness
- Hx of angle closure in other eye
- Inuit and Asian
- Older age
- Reduced light conditions (when pupil is dilated) - attack is more likely to occur.
What are the clinical features of AACG?
- Sudden onset red, painful eye with blurred vision.
- Halos around lights
- Patients become unwell - N&V
- Headache
- Severe ocular pain
- Eye is injected and tender and feels hard
- Hazy cornea
- Pupil is semi-dilated
What investigations would you do for AACG? What would the results show?
Gonioscopy - exam of anterior chamber; DIAGNOSTIC. Trabercular meshwork is not visible in angle closure because peripheral iris is in contact with it.
Slit-lamp examination - shallow anterior chamber; signs of glaucoma: large optic cup, narrowing of neuroretinal rim, splinter haemorrhage, nerve fibre loss.
Automatic static perimerty - visual field defects- identifies presence and amount of visual field loss.
Other tests:
- US biomicroscopy
- anterior segment optical coherence tomography (of angle)
- evaluation of optic nerve head by fundocsopy - may show large optic cup and nerve fibre loss
- retinal optical coherence tomography
- Heidelberg’s retinal tomography
- GDx nerve fibre analyser
What investigations would you do for open-angle glaucome? What would the results show?
Tonometry - Goldmann tonometry is most accurate and expensive; small sterile cone makes contact with the cornea- IOP elevated if above normal range: 10 mmHg and 21 mmHg
Direct/indirect ophthalmoscopy - cup-to-disc ratio over 0.6 may be suspicious of glaucoma as is asymmetry of greater than 0.2 between the two eyes; visualisation of optic disc and retina quality; flame haemorrhages in late disease
Slit-lamp biomicroscopy - cornea should be clear, anterior chamber should be deep, and drainage angle should be open
Visual field testing - scotomas indicating loss of the nerve fibre layer. By the time of disease detection, 50% of the nerve fibre layer may be damaged
Other tests:
- Gonioscopy
- Photographs of the optic nerve head
- Pachymetry - measures corneal thickness which may be thin and predicts progression from high IOP to glaucoma
- Nerve fibre layer analysis
- Optical coherence tomography scanning
What are the differential diagnoses of acute red eye and how do you distinguish between them?
List 4 differences between open and closed angle glaucoma.
Open angle makes up 90%, and progresses more slowly
Acute, although less common, is important to be aware of because it can present as an acute, red and painful eye and if you don’t recognise and treat it the patient may lose their vision
How are glaucomas classified?
Based on whether the peripheral iris is covering the trabecular meshwork which is important in the drainage of aqueous humous from the anterior chamber in the eye
- Primary open-angle glaucoma = iris is clear of the meshwork but trabecular network offers resistance to aqueous flow causing raised IOP
- Acute angle-closure glaucoma = rise in IOP secondary to an impairment of aqueous outflow
What are these investigations called?
Fundoscopy may show disc cupping
Gonioscope in the top right – this device allows you to look at the angle of the iris to help determine if it is closed or open angle glaucoma
Slit lamp allows to examine the eye as a whole more closely
Tonometry in the bottom right measures intraocular pressure
