CRVO and PRP Laser

Central Retinal Vein Occlusion (CRVO) - Overview

CRVO is classified into three types based on severity:

Type	Features
Impending CRVO	Younger patients, mild venous dilatation/tortuosity, few scattered dot-blot haemorrhages, mild or no macular oedema. Usually good prognosis but can deteriorate.
Non-ischaemic CRVO	More common. Sudden painless monocular vision fall. Tortuosity and dilatation of all retinal vein branches, dot/blot/flame haemorrhages in all quadrants. Absent or mild RAPD. ~1/3 progress to ischaemic CRVO.
Ischaemic CRVO	Substantially reduced retinal perfusion with capillary closure. VA typically "counting fingers" or worse. RAPD present. High risk of rubeosis iridis (~50%) and neovascular glaucoma.

Key diagnostic pointer: VA <6/60 + RAPD = significant ischaemia + poor visual prognosis in CRVO.

Ischaemic CRVO - Fundus & Investigations

Fundus findings:

Severe tortuosity and engorgement of all retinal vein branches
Extensive deep blot and flame haemorrhages (peripheral and posterior)
Prominent cotton-wool spots
Optic disc swelling and hyperaemia

Fig. 13.34 Ischaemic CRVO - (A) cotton-wool spots, flame and deep blot haemorrhages; (B) venous distension with cotton-wool spots; (C) shunt vessels; (D) FA showing extensive hypofluorescence from capillary non-perfusion

FA findings: Marked delay in arteriovenous transit time, extensive capillary non-perfusion, vessel wall staining/leakage. More than 10 disc areas of capillary non-perfusion = substantially increased neovascularization risk.

NVI (Rubeosis iridis): Develops in ~50% of ischaemic CRVO, typically 2-4 months after occlusion ("hundred-day glaucoma"). Gonioscopy is mandatory before pupillary dilatation (angle NV can occur without visible rubeosis).

Rubeosis iridis at the pupillary border:

Rubeosis iridis - neovascularization at pupillary border

Treatment of Macular Oedema in CRVO

Treatment is indicated when VA is worse than 6/9 and/or central macular thickness >250 µm on OCT. It is unlikely to benefit if VA is 6/120 or worse.

1. Intravitreal anti-VEGF agents (current standard of care):

Ranibizumab (CRUISE study): monthly injections x6 months superior to placebo
Aflibercept (COPERNICUS study): effective even on "as-needed" protocol
Bevacizumab: effective in practice, commonly used

2. Intravitreal dexamethasone implant (Ozurdex 700 µg) - GENEVA trial:

Substantial visual and anatomical improvement in first 2 months
Declines to baseline by 6 months; can be repeated after 4-6 months
Administer within 90 days of CMO onset for best results
COMRADE study: ranibizumab shows better VA than dexamethasone at 6 months
Side effects: IOP elevation, cataract

3. Intravitreal triamcinolone (SCORE study):

25% improve by 3+ lines at 1 year (vs 7% controls), using 1 mg preservative-free preparation
Higher risk of IOP elevation with 4 mg vs 1 mg

4. Laser photocoagulation for macular oedema:

Although anatomically improves oedema, laser is not beneficial for visual outcome in CRVO (except possibly in some younger patients)

PRP (Pan-Retinal Photocoagulation) in CRVO

When NOT to do PRP:

There is NO benefit in performing PRP before the development of iris and angle neovascularization. Prophylactic PRP in ischaemic CRVO is not recommended.

Indication for PRP:

PRP is indicated when NVI or angle neovascularization develops. It should be performed without delay once these appear.

PRP Parameters:

Parameter	Value
Number of burns	1500-2000 initially
Duration	0.05-0.1 seconds
Spacing	One burn width apart
Energy	Sufficient for moderate reaction
Avoid	Areas of retinal haemorrhage
Approach	Treatment may be fractionated (split into sessions)
Further photocoagulation	Commonly required

Special situations:

Poor retinal view: Indirect ophthalmoscopic PRP, or performed in the operating room with iris hooks
Opaque media: Trans-scleral cryotherapy as alternative or adjunct

PRP + Anti-VEGF:

Adjunctive intravitreal anti-VEGF injections are commonly given every 6 weeks until stabilization:

Leads to faster regression of NV than PRP alone
Reduces macular oedema simultaneously
Onset of NVG may be delayed by up to 18 months
These patients need 3-monthly follow-up for at least 2-3 years

What PRP does and doesn't do:

Does: Induces regression of neovascularization; prevents progression to neovascular glaucoma if performed early
Does not: Reverse an established fibrovascular membrane

Management of Neovascular Glaucoma (NVG) in CRVO

If NVG develops despite PRP:

Medical IOP treatment (avoid miotics; use topical atropine 1% twice daily)
Cyclodiode (ciliary body ablation) if IOP uncontrolled
Filtration surgery (glaucoma drainage device or trabeculectomy with MMC) if VA is HM or better
Preoperative anti-VEGF to control active neovascularization before surgery

Review Schedule

Ischaemic CRVO: Monthly for 6 months, then every 3 months for 2-3 years
Non-ischaemic CRVO: Review at 3 months; discharge usually at 18-24 months
Once optic disc collaterals develop, neovascularization risk reduces

Prognosis

Main cause of poor vision after CRVO: chronic macular oedema
Ischaemic CRVO: generally very poor visual prognosis due to macular ischaemia
Non-ischaemic CRVO without progression: ~50% return to normal or near-normal VA

Sources: Kanski's Clinical Ophthalmology: A Systematic Approach, 10th edition

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