RETINAL VEIN OCCLUSION

It is more common than the artery occlusion. It
typically affects elderly patients in sixth or seventh
decade of life.
Etiology
1. Pressure on the vein by a sclerotic retinal artery
where the two share a common adventitia (e.g.,
just behind the lamina cribrosa and at
arteriovenous crossings).
2. Hyperviscosity of blood as in polycythemia,
hyperlipidemia and macroglobulinemia.
3. Periphlebitis retinae which can be central or
peripheral.
4. Raised introcular pressure. Central retinal vein
occlusion is more common in patients with primary
open-angle glaucoma.
5. Local causes are orbital cellulitis, facial erysipelas
and cavernous sinus thrombosis.
Classification
1. Central retinal vein occlusion (CRVO) It may be
non-ischaemic CRVO (venous stasis retinopathy)
or ischaemic CRVO (haemorrhagic retinopathy).
2. Branch retinal vein occlusion (BRVO)
Non-ischaemic CRVO
Non-ischaemic CRVO (venous stasis retinopathy)
is the most common clinical variety (75%). It is
characterised by mild to moderate visual loss. Fundus
examination in early cases (Fig. 11.9) reveals mild
venous congestion and tortuosity, a few superficial
flame-shaped haemorrhages more in the peripheral
than the posterior retina, mild papilloedema and mild
or no macular oedema. In late stages (after 6-9
months), there appears sheathing around the main
veins, and a few cilioretinal collaterals around the
disc. Retinal haemorrhages are partly absorbed.
Macula may show chronic cystoid oedema in
moderate cases or may be normal in mild cases.
Treatment is usually not required. The condition
resolves with almost normal vision in about 50 percent
cases. Visual loss in rest of the cases is due to chronic
cystoid macular oedema, for which no treatment is
effective. However, a course of oral steroids for 8-12
weeks may be effective.Ischaemic CRVO
Ischaemic CRVO (Haemorrhagic retinopathy) refers
to acute (sudden) complete occlusion of central retinal
vein. It is characterised by marked sudden visual loss.
Fundus examination in early cases (Fig. 11.10) reveals
massive engorgement, congestion and tortuousity
of retinal veins, massive retinal haemorrhages (almost whole fundus is full of haemorrhages giving a
‘splashed-tomato’ appearance), numerous soft
exudates, and papilloedema. Macular area is full of
haemorrhages and is severely oedematous. In late
stages, marked sheathing around veins and
collaterals is seen around the disc.
Neovascularisation may be seen at the disc (NVD) or
in the periphery (NVE). Macula shows marked
pigmentary changes and chronic cystoid oedema.
The pathognomic features for differentiating
ischaemic CRVO from non-ischaemic CRVO are
presence of relative afferent pupillary defect (RAPD),
visual field defects and reduced amplitude of b-wave
of electroretinogram (ERG).
Complications. Rubeosis iridis and neovascular
glaucoma (NVG) occur in more than 50 percent cases
within 3 months (so also called as 90 days glaucoma),
A few cases develop vitreous haemorrhage and
proliferative retinopathy.
Treatment. Panretinal photocoagulation (PRP) or
cryo-application, if the media is hazy, may be required
to prevent neovascular glaucoma in patients with
widespread capillary occlusion. Photocoagulation
should be carried out when most of the intraretinal
blood is absorbed, which usually takes about 3-4
months.
Branch retinal vein occlusion (BRVO)
It is more common than the central retinal vein
occlusion. It may occur at the following sites: main
branch at the disc margin causing hemispheric
occlusion, major branch vein away from the disc, at
A-V crossing causing quadrantic occlusion and
small macular or peripheral branch occlusion. In
branch vein occlusion oedema and haemorrhages are
limited to the area drained by the affected vein (Fig.
11.11). Vision is affected only when the macular area
is involved. Secondary glaucoma occurs rarely in
these cases. Chronic macular oedema and
neovasculari-sation may occur as complications of
BRVO in about one third cases.
Treatment. Grid photocoagulation may be required
in patients with chronic macular oedema. In patients
with neovascularisation, scatter photocoagulation
should be carried out.