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Cotton wool spots are fluffy white lesions in the retinal nerve fibre layer that represent areas of focal ischaemia and oedema. The retina has a high metabolic rate, and is highly susceptible to any disease process that restricts its arterial oxygen supply. There are many possible diseases that may manifest cotton wool spots, as shown in the table.
Consequences of retinal hypoxia include tissue oedema, occlusion of precapillary arterioles, the local accumulation of fluid and metabolic products and interruption of axoplasmic flow within the nerve fibre layer, resulting in the characteristic appearance of cotton wool spots. Eventually, the swelling may subside and nerve fibre layer micro-infarction may result.
Symptoms
Cotton wool spots are asymptomatic. Symptoms may exist relating to the underlying cause, or to any ocular complications of this underlying cause.
Signs
Cotton wool spots appear on fundoscopy as white, fluffy lesions with hazy or feathered edges in the superficial retina. Underlying retinal vessels may be obscured.
Significance
Cotton wool spots indicate significant retinal ischaemia or other disorder. The underling cause requires identification and management.
Differential diagnosis
See the table below.
See also
Choroidal neovascularisation, Diabetic retinopathy, Hypertensive retinopathy, Central retinal artery occlusion, Central retinal vein occlusion, Ocular ischaemic syndrome (Ophthalmic artery hypoperfusion, Carotid occlusive disease), Lymphoma, Systemic lupus erythematosis, Acquired immunodeficiency syndrome (AIDS) Retinopathy, Cytomegalovirus retinitis, Radiation retinopathy.
Management
The principal objective is identification and management of the underlying condition.
Ocular tests, imaging investigations
When the cause is unknown, or when management decisions will be influenced by the results of ocular investigations (eg diabetic retinopathy), fluorescein angiography may be indicated. Cotton wool spots minimally block background choroidal fluorescence, appearing as dark areas on fluorescein angiography. Despite appropriate investigations, cotton wool spots may remain idiopathic in up to 5 percent of cases.
Review
After successful treatment of the underlying cause, cotton wool spots typically resolve over several weeks. Confluent areas of ischaemia may lead to neovascularisation review should be conducted initially at routine intervals of no less than three months following cotton wool spot resolution.