• Clinical science

Retinal vessel occlusion

Abstract

Retinal artery occlusion refers to occlusion of the central retinal artery and/or its branches, usually as a result of thromboembolic phenomena. Common risk factors include atherosclerosis, atrial fibrillation, and vasculitis (e.g., temporal arteritis). Central retinal artery occlusion (CRAO) is characterized by sudden, painless loss of vision and a relative afferent pupillary defect. Ophthalmoscopy reveals a pale, edematous retina and a cherry-red spot in the foveal region. Branch retinal artery occlusion (BRAO) presents with specific patterns of visual field defects depending on which branch is involved. Treatment is usually ineffective because of irreversible ischemic damage to the retina. The prognosis is especially poor if the macula is involved. Retinal vein occlusion is more common than retinal artery occlusion and follows a less fulminant course. Risk factors for central retinal vein occlusion include prothrombotic states and raised intraocular pressure. Retinal vein occlusion may involve the central retinal vein and/or one of its branches. Branched retinal vein occlusion (BRVO), which is more common than central retinal vein occlusion (CRVO), is usually asymptomatic unless the macula is involved. CRVO may be either non-ischemic or ischemic: Non-ischemic CRVO, which is more common than the ischemic variant, presents with minimal retinal hemorrhage on ophthalmoscopy and mild to moderate loss of vision. Ischemic CRVO presents with severe loss of vision, a relative afferent pupillary defect, and extensive retinal hemorrhage on ophthalmoscopy. Fluorescein angiography is required in order to differentiate between ischemic and non-ischemic retinal vein occlusion. The prognosis of ischemic CRVO is less favorable since it is associated with neovascular glaucoma and retinal detachment. While BRVO and non-ischemic CRVO usually do not require any treatment, ischemic CRVO requires laser therapy.

Definition

Retinal vessel occlusion causes retinal ischemia. Based on the site of occlusion, retinal vessel occlusion can be classified into the following entities:

Epidemiology

Retinal artery occlusion

  • Incidence in the general population:
    • CRAO: 5/1,000,000
    • BRAO: 3/1,000,000
  • Age of onset: > 60 years
  • Sex: >
  • Race: no specific racial predisposition

Retinal vein occlusion

  • Prevalence in the general population:
    • CRVO: 1/1,000
    • BRVO: 6/1,000
  • Age of onset: > 80 years
  • Sex: =
  • Race: slightly higher prevalence among Latinos and Asians

Retinal vein occlusion is much more common than retinal artery occlusion. Retinal vein occlusion is the second most common vascular disease of the retina (after diabetic retinopathy)!

References:[1][2][3][4][5]

Epidemiological data refers to the US, unless otherwise specified.

Etiology

Retinal artery occlusion

Retinal vein occlusion

The exact cause of thromboembolic retinal vein occlusion is unknown, but risk factors include:

References:[1][6][7]

Clinical features

Retinal artery occlusion

CRAO BRAO
Symptoms
  • Sudden, painless loss of vision in one eye (often described as a “descending curtain”)
  • A past history of amaurosis fugax may be present.
  • Sudden onset of visual field defects (scotomas) in the affected eye
  • A past history of amaurosis fugax may be present.
Relative afferent pupillary defect
  • Present
  • Absent
Ophthalmoscopic findings
  • Grayish-white discoloration of the entire retina
  • Cherry-red spot at the fovea centralis
  • Box-carring of all retinal vessels in the acute phase
  • Narrowing of all retinal vessels
  • Retinal emboli/plaques (∼ 20% of cases).
  • Grayish-white discoloration of the retinal quadrant supplied by the affected vessel
  • Box-carring of retinal vessels during the acute phase in the affected retinal quadrant
  • Narrow retinal vessels in the affected retinal quadrant
  • Retinal emboli/plaques (∼ 60–70% of cases)
General physical examination

Retinal vein occlusion

CRVO BRVO
Non-ischemic CRVO Ischemic CRVO
Symptoms
  • Subacute, mild to moderate loss of vision in the affected eye
  • Sudden, severe loss of vision in the affected eye
  • Usually asymptomatic
Relative afferent pupillary defect
  • Absent
  • Present
  • Absent
Ophthalmoscopic findings
  • Dot-and blot and/or flame-shaped hemorrhages in the retinal quadrant drained by the affected vein

References:[1][6][7]

Amaurosis fugax

Diagnostics

Retinal vessel occlusion is primarily a clinical diagnosis (based on the patient's history and fundus examination). Additional investigations are usually performed to identify underlying risk factors, to differentiate between subtypes (e.g., in the case of CRVO).

Retinal artery occlusion

  • One or both of the following tests are performed if fundus examination is normal but retinal artery occlusion is still suspected based on the patient's history:
    • Fluorescein angiography
    • Electroretinography: shows decreased b-wave amplitude
  • Evaluation for cardiovascular risk factors:
    • Carotid doppler (to look for atherosclerotic plaques)
    • Echocardiography (to look for potential sources of emboli)
  • Tests to rule out temporal arteritis:

Retinal vein occlusion

References:[6][1]

Treatment

Retinal artery occlusion

Retinal artery occlusion is an ophthalmologic emergency. The following measures should be taken to improve retinal perfusion:

Treatment should be initiated as soon as possible, as permanent retinal damage occurs within 1.5 hours of central retinal artery occlusion.

Retinal vein occlusion

At the onset of symptoms, hemodilution with the help of IV fluids (with the aim of decreasing hematocrit to 35%) might improve retinal blood flow. Further management depends on the type of retinal vein occlusion:

  • Ischemic CRVO must be treated with:
    • Laser therapy
      • Panretinal photocoagulation
      • If macular edema is present: grid photocoagulation
    • Intravitreal injection of VEGF inhibitors and/or steroids
  • BRVO and non-ischemic CRVO usually do not require treatment.

References:[6][8][9][10][1]

Complications

Release of vasoproliferative substances (e.g., VEGF) from the ischemic retina causes:

Of all types of retinal vessel occlusion, ischemic CRVO is most commonly associated with neovascularization!
References:[1][7]

We list the most important complications. The selection is not exhaustive.

Prognosis

Retinal artery occlusion

  • Central retinal artery occlusion: severe loss of vision
  • Branch retinal artery occlusion: loss of vision and/or visual field defects (depending on which branch of the retinal artery is affected)

Retinal vein occlusion

  • Rule of thirds: Visual acuity improves in one-third of cases, remains the same in another third, and worsens in the remaining third.
  • The prognosis is especially poor in the case of ischemic CRVO.

References:[6][7]