CRV bifurcates at laminar cribrosa and divides into 4 main veins (supertemporal/nasal and interotemporal/nasal)
20% of the time CRV bifurcates inside the nerve
CRVO
o Non-ischaemic 75%
o Ischaemic 25%
- Defined by evidence of neovasculaisation on the surface of the iris or ischaemia (defined by angiography) of area greater than 10x size of optic disc.
Hemi-CRVO
o Ischaemic
o Nonischaemic
BRVO
o Major branch
o Macular branch
Overall Prevalence 5.2/1000
BRVO 4.42/1000
CRVO 0.8/1000
M=F
Chance of second eye involvement within 4 years = 7%
Increases with age 50% of cases are >65yrs age
Pathogenesis
o CRVO
- Occlusion occurs in the region of the lamina cribrosa
- Vein and artery share a common adventitial sheath
- A thickened and rigid artery at this site may compress the thin walled vein
o BRVO
- Occlusion occurs at sites of AV crossing
- There is however often no clear evidence of ongoing venous compression at the site of an occlusion
- It is suggested the artery intermittently compressing the vein results in damage to the vessel wall with resultant turbulence and eventual thrombosis
Local risk factors:
o Elevated IOP
Systemic risk factors:
o
HTN
- CRVO OR (of having HTN) 3.8, BRVO OR 3.0
o
Hyperlipidaemia
- Both types OR 2.5
o
DM
- OR 1.5 (CRVO OR 2.0, BRVO OR 1.1)
o
Atherosclerotic vascular disease
Other
disease associations:
o Vasculitis SLE, sarcoid, syphilis
o Neoplasia leukaemia, myeloma
o Medications OCP, diuretics
Haematological disorders
o No trials large enough to elucidate link with thrombophilia
o Probably more likely in patients <65 and without cardiovascular risk factors
o Hyperhomocystinaemia significant risk elevation in some studies
o Thrombophilia
- Factor V leiden/APC resistance significance in some studies (OR 1.49)
- Protein C and S deficiency, PT gene mutation, ATIII Possible link but NS in trials to date
- Antiphospholipid syndrome significant
Sudden painless visual loss
Macular oedema is the most important cause of reduced vision
Retinal haemorrhages
o Flame shaped, dot or blot
o Dilated tortuous veins
o +/- optic disc oedema
o Hard exudates yellow lipid deposits at the junction of the normal and oedematous retina
o Cotton wool spots ischaemia of the nerve axons
BRVO distribution
o Superotemporal 66%
o Inferotemporal 43%
Diagnosis based on clinical appearance.
Determination of ischaemia is of importance in determining prognosis and need for treatment. Predictors of ischaemia are:
o Defined by fluorescein angiogram (however very arbitrary cutoff spectrum of risk)
o Very poor poor visual acuity (i.e. 6/120 ~ hand movements)
o Presence of RAPD
Flourescein angiography
o
Useful to
- Confirm
occlusion
- Extent
of retinal non-perfusion (to allow definition as ischaemic)
- To distinguish neovascularisation from venous collateral/shunt vessels
- Acutely
50-60% of patients may have non-diagnostic scan due to swelling
o
Indication for use in BRVO:
OCT
o
Used to measure macular oedema
o
Gauge treatment response
Causes of visual loss
o Macular oedema
o Retinal ischaemia
o Secondary complications
- Vitreous haemorrhage
- Retinal detachment
- Neovascular glaucoma
BRVO
o >50% of eyes achieve >6/12
CRVO
o Non-ischaemic
o Ischaemic
No evidence for aspirin or anticoagulation
If ischaemic/significant macula oedema
o Anti-VEGF
o Pan retinal laser