Common eye disorders Flashcards
Briefly describe trachoma
- Most common infective cause of blindness
- Is still occurring in some remote areas in Australia, but has declined from 14% (2009) to 4% (2014)
- Approx. 4% of blindness worldwide
- Chlamydia trachomatis (serotype A-C)
- Chronic conjunctivitis
- Transmitted by flies or close contact
- Poor socio-economic communities; hygiene
Describe the four key features of trachoma
I. Follicular conjunctivitis – active repeated episodes over years
II. Tarsal conjunctival scarring
III. Trichiasis
IV. Corneal opacity
Describe the condition of trachoma in Au
The bad news
Australia is the only developed country in the world to still have cases of trachoma.
(as per previous slide) rates in some Communities can be as high at 5% which is considered endemic levels.
Trachoma was eradicated from mainstream Australia 100 yrs ago.
In 1975 $1.4m was committed to the National Trachoma and Eye Health Program (under Fred Hollow’s Foundation).
The good news
Of 200 “at risk” Communities, 150 no longer have trachoma.
According to the National Indigenous Eye health Survey (NIEHS) and the National Eye Health Survey (NEHS) the level of blindness has decreased from 2.8% (2008) to 0.3% (2016).
2017 – Commonwealth Government committed $20.6m over 4yrs to support trachoma eradication targets.
Describe the management and prevention of trachoma
Surgery for trichiasis
Antibiotics - azithromycin p.o., even a single dose can last for 2 years; topically tetracycline or polymixin
Facial cleanliness and hygiene
Environmental improvements - water and sewage system
Describe the burden of eye disease in Australia
The health costs of treating eye disease are extremely large -»_space; $5 billion in 2009.
This is more than the combined cost of
- coronary heart disease
- stroke
- arthritis
- depression
More than the health spending on diabetes and asthma - two ‘National Health Priority Areas’ – combined
Define vision impairment
- Vision impairment is any diagnosed condition of the eye or visual system that cannot be corrected to within normal limits.
- Disease, damage or injury causing vision impairment can occur to any part of the visual system - the eye, the visual pathways, to the brain and/or visual cortex.
Severe vision impairment: 6/60 - 3/60 - otherwise known as legal blindness
Blindness fro 3/60 to 1/60
Blindness is 1/60 with light perception
Blindness with no light perception
List some causes of reading difficulties
- macular degeneration (10%)
- glaucoma (3%)
- diabetic eye disease (2%)
List some causes of blindness in all ages
- cataract (12%),
- glaucoma (14%)
- refractive error (4%)
- all other (11%)
Describe cataracts broadly
- cataract is the most common eye disease
- increasing prevalence with age
- 70% Australians > 80 yrs have cataracts, or have had cataract surgery
Describe the three types of cataracts
Cataract is loss of lens transparency
Nuclear Cataract
- hardening of the core of the lens (hence ‘nuclear’ as in ‘nucleus’) that expands through the layers
- associated with yellowing/ ‘brunessence’ of the lens (due to accumulation of glutathione-3-hydroxy kynurenine glycoside)
- causes reduced transmittance of light (especially blue), increased scatter, and increased fluorescence. Things appear more reddish, and ‘blurry’.
- Associated with aging.
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Cortical Cataract
- changes to lens proteins that start at the margin of the lens, and spread through the more superficial layers towards the optic axis
Capsular Cataract
- modification of the lens capsule, anteriorly or posteriorly
- often occur subsequent to eye surgery, or trauma
Discuss the prevalence of cataracts in Indigenous populations,causes of cataracts and potential barriers to accessing care
Aboriginal and Torres Strait Islander people are 3x more likely than non-Indigenous Australians to be affected by vision loss due to cataracts.
It is the second leading cause of blindness in Aboriginal and Torres Strait Islander peoples (2016).
Causes include high UV exposure.
Barriers to cataract surgery exist at health-service, community and individual levels:
- lack of access to optometrists and ophthalmologists,
- isolation, transport
- complexity of the system / clinical pathways
- infrastructure
- interpreters
- cost
- Community and individual factors include ignorance of cause, fear of surgery
In the ACT today it is difficult to access cataract surgery as a public patient… this affects all people on low income, and has a disproportionate impact on people of Aboriginal and Torres Strait Islander backgrounds.
Describe glaucoma
Second leading cause of blindness worldwide ~70 million people affected / impairs the vision of about 2% of persons over the age of 50 years and 12% over 85. ~50% of those affected are unaware (and 50% of these have been to an ophthalmologist)
‘Glaucoma’ is a spectrum of related disorders characterized by progressive death of ganglion cells (GC) and axon loss (optic nerve).
It is an ‘anterior segment’ disorder that has its impact in the posterior segment, causing death of ganglion cells.
Strongly associated with increased intraocular pressure (IOP). However, about 50% of diagnosed glaucoma occurs in the absence of increased IOP
Describe the pathophysiology of glaucoma
Pressure on the posterior aspect of the iris causes the iris to buckle, compressing the trabecular meshwork and restricting the drainage of aqueous. Alternatively, the trabecular meshwork and drainage network can become ‘clogged’ and restrict the passage of aqueous…this is open angle glaucoma
Increased IOP in the anterior segment is transferred posteriorly through the vitreous. Pressure distorts the sclera at the lamina cribrosa, compressing GC axons leading the GC death.
Mechanism of GC loss involves:
- Decline in the retrograde supply of neurotrophins to GC from their axon terminals
- Release of excitotoxic amino acids by damaged GC, 2-8 fold.
- Apoptotic cell death of GC
Note that it tends to affect peripheral vision so frequently not noticed until quite late
Describe glaucoma diagnosis
Initial finding, and raising suspicion is based on assessment of the optic disc (OD).
ODs are normally mirror images of each other. This underlies importance of comparison
Normal disc has a distinct, reddish neural margin, where the majority of axons are located. The centre is paler (‘pallid’)
In glaucoma
- the margin appears eroded, often inferiorly
- the disc appears enlarged, and the area of ‘pallor’ increases
- the normally shallow ‘cupping’ of the disc increases over time, with progression of the disease
Bundles of axons tend to be affected, resulting in loss of GC input to brain from specific sectors / regions of the retina
Changes seen at the disc and in the fundus are associated with progressive visual field loss, due to death of ganglion cells, resulting from compression of their axons
Typically losses are patchy, begin in peripheral visual field, and progress centrally < losses compensated for by eye movements and may not be registered
Describe advanced glaucoma course and management
Management of intraocular pressure is most efficacious strategy - but if IOP is not raised, options are limited.
Animal models show large diameter axons affected before smaller ones (ie., parasol system ahead of midget) ß hence effects in periphery rather than central retina
