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Sickle-cell disease (SCD) is a genetically determined haemoglobinopathy. Haemoglobin is a key protein of the erythrocyte, responsible for oxygen transport in the blood. SCD causes erythrocyte dysfunction with reduced blood flow, increased blood clots, tissue hypoxia and eventual pathology.

Erythrocytes have a shortened life, which in some conditions may cause haemolytic anaemia. All parts of the body, including the eye, may be affected by vascular complications. Proliferative retinopathy and sequelae are a risk in the eye.

Genetics

Inheritance of SCD is autosomal co-dominant, with each parent providing one gene for the abnormal haemoglobin. The genotypes are:

• Normal haemoglobin (AA globin genotype)
• Sickle-cell anaemia (SS) - this form has the most systemic symptoms and proliferative retinopathy may occur in up to 20 per cent of patients
• Sickle-cell disease (SC) - proliferative retinopathy may develop in up to 40 per cent of patients
• Sickle-cell thalassaemia (S Thal)
• Sickle-cell trait (AS) - this form has the fewest systemic complications.

Systemic signs and symptoms

Chronic anaemia, fatigue, jaundice, crisis (extended periods of skeletal and abdominal pain) and chest pain due to pulmonary infarction. Blurring of vision.

Signs

• Anterior signs include iris atrophy and neovascularisation, bulbar conjunctiva comma-shaped vessels
• Non-proliferative signs include:
  - Black sunbursts (RPE hyperplasia secondary to deep retinal vascular occlusions)
  - Salmon patch lesions (intraretinal haemorrhages)
  - Angioid streaks
  - Arterial or venous occlusions
  - Macular microvascular occlusions
• Proliferative retinopathy has a standardised classification:
  - Peripheral retinal arteriolar occlusions
  - Peripheral arteriovenous anastomoses
  - Neovascular proliferation: Neovascular fronds, known as sea fans are diagnostic of SCD
  - Vitreous haemorrhage from neovascular membranes
  - Retinal detachment from severe vitreous traction.

Prevalence

Common (approximately 1/100) in people with African descent, no gender bias.

Significance

Proliferative retinopathy is sight threatening, requiring prompt management.

Differential diagnosis

Diabetic retinopathy, Vascular occlusions, Ocular ischaemic syndrome, Sarcoidosis.

Management

Laboratory tests

Sickledex, sickle prep and plasma haemoglobin electrophoresis are useful in SCD.

Genetics

Genetic assessment and counselling should be undertaken (see above).

Additional Investigations

Fluorescein angiography is useful for assessment of proliferative disease or choroidal neovascularisation associated with angioid streaks and to guide pan-retinal photocoagulation.

Oral medications

SCD requires systemic management that may include blood transfusions, antiplatelet therapy, anticoagulationa and thrombolytic agents. Oral carbonic anhydrase inhibitors or IV mannitol are contraindicated for glaucoma therapy as they may precipitate a systemic crisis.

Laser surgery

Argon laser panretinal or sector photocoagulation may be indicated for proliferative disease.

Incisional surgery

Vitrectomy may be beneficial for persistent vitreous haemorrhage or retinal detachment. Scleral buckling may also be required for retinal detachment, although there is an increased risk of complications related to ocular ischaemia in SCD patients.

Advice

Physical activity or dehydration may precipitate systemic sickle-cell crisis.

Review

Patients at risk of proliferative retinopathy should be reviewed at six-month intervals.

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