Cotton wool spots are fluffy white lesions in the retinal nerve fibre layer that represent areas of focal ischemia and edema. 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 edema, 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.
Cotton wool spots are asymptomatic. Symptoms may exist relating to the underlying cause, or to any ocular complications of this underlying cause.
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.
Cotton wool spots indicate significant retinal ischaemia or other disorder. The underling cause requires identification and management.
Choroidal Neovascularization, Diabetic Retinopathy, Hypertensive Retinopathy, Central Retinal Artery Occlusion, Central Retinal Vein Occlusion, Ocular Ischemic Syndrome (Ophthalmic artery hypoperfusion, Carotid occlusive disease), Lymphoma, Systemic Lupus Erythematosis, Acquired Immunodeficiency Syndrome (AIDS) Retinopathy, Cytomegalovirus retinitis, Radiation Retinopathy.
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 (e.g., 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.
After successful treatment of the underlying cause, cotton wool spots typically resolve over several weeks. Confluent areas of ischemia may lead to neovascularization; review should be conducted initially at routine intervals of no less than 3 months following cotton wool spot resolution.
|Table:Common causes of retinal ischemia|
|Microvascular disease||Diabetic retinopathy, hypertensive retinopathy|
|Occlusive vascular disease||Retinal artery & vein occlusions, ophthalmic artery hypoperfusion|
|Hematological disease||Anaemia, leukaemia, lymphoma|
|Collagen vascular disease||Systemic lupus erythematosis|
|Thrombo-embolic disease||Cardiac valvular disease, severe trauma|
|Infections||Human immunodeficiency virus, cytomegalovirus|
|Iatrogenic retinal damage||Radiation retinopathy|
Cotton wool spots. The lesions affect the retinal nerve fibre layer, obscuring the underlying retinal blood vessels.