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Cotton–Wool Spot

ROUTINE — Signs

Symptoms

Usually asymptomatic (incidental finding on dilated exam).

Visual acuity is typically normal.

Rarely presents as a paracentral scotoma if located immediately adjacent to the fovea.

Clinical Findings

Appearance

  • Small, fluffy, white superficial retinal lesion.
  • Feathery or indistinct margins.
  • Typically ≤1 optic disc diameter in size.
  • Located in the posterior pole (within 3 disc diameters of the optic nerve).

Pathophysiology

  • Focal microinfarct of the retinal nerve fiber layer (RNFL).
  • Caused by occlusion of a terminal precapillary arteriole.
  • Ischemia halts axoplasmic flow, leading to accumulation of "cytoid bodies."
  • Note: This is swollen axoplasm, NOT an extracellular exudate (unlike yellow/waxy hard exudates).

Clinical pattern-matching

  • Single CWS (No known DM/HTN): Red flag for HIV, SLE, carotid disease, or GCA.
  • Multiple CWS (≥6): Suggests diffuse ischemia (e.g., ischemic RVO, malignant HTN, severe DR).
  • Diabetes: Accompanied by microaneurysms, dot-blot hemorrhages, and hard exudates.
  • Hypertension: Accompanied by flame hemorrhages, AV nicking, and arteriolar narrowing.
  • Endocarditis/Leukemia: Often presents with Roth spots.

Imaging

  • Acute OCT: Hyper-reflective band in the RNFL/GCL with underlying shadowing.
  • Chronic OCT: Permanent focal RNFL thinning/atrophy.
  • OCT-Angiography: Triangular zone of capillary dropout with apex toward the disc.

Etiology

Common systemic causes

  • Diabetes Mellitus: Most common etiology.
  • Hypertension: Acute (malignant) or chronic.
  • Retinal Vein Occlusion: Significant CWS count (≥6) indicates ischemic variety.

Vasculitic & autoimmune

  • Systemic Lupus Erythematosus (most common collagen vascular cause).
  • Giant Cell Arteritis (if age ≥55 with disc pallor/jaw claudication).
  • Granulomatosis with polyangiitis (Wegener).

Infectious

  • HIV Retinopathy: Early ocular manifestation; presents as posterior pole CWS.
  • Others: Subacute bacterial endocarditis, Toxoplasmosis, Lyme disease.

Hematologic & other

  • Anemia, Leukemia, or Hypercoagulable states.
  • Purtscher / Pseudo-Purtscher retinopathy (bilateral peripapillary CWS).
  • Radiation Retinopathy: Resembles diabetic retinopathy; threshold ~1500–3000 cGy.
  • Interferon therapy.

Red Flags

Multiple CWS in a young patient → warrants urgent workup for HIV, lupus, or leukemia.

CWS combined with optic disc edema → consider hypertensive emergency or GCA.

CWS combined with Roth spots → suspect subacute bacterial endocarditis.

Isolated CWS in a healthy patient → warrants carotid Doppler or cardiac evaluation for emboli.

Investigations

Ocular exam

  • Dilated fundus exam (DFE) with 60/90D lens and indirect ophthalmoscopy.
  • Evaluate for concurrent hemorrhages, vasculitis, or vascular occlusions.

Systemic screening

  • Mandatory: Blood pressure, Fasting Glucose/HbA1c, and CBC.

Targeted workup

  • Infectious: HIV testing.
  • GCA (if ≥55): ESR, CRP, and platelet count.
  • Embolic: Carotid Doppler and Echocardiogram.
  • Rheum: ANA and ANCA (especially in young patients or multiple CWS).

Treatment

Systemic management

  • Treat the underlying condition; CWS is a clinical sign, not a primary ocular disease.
  • Optimize blood pressure, glucose, and lipid profiles.
  • Adjust HAART for HIV retinopathy or manage rheumatologic triggers.

Ocular management

  • No specific ocular treatment is required for the CWS itself.
  • Individual lesions typically fade over 4–12 weeks.

Clinical Pearl

A cotton-wool spot is a microinfarct of the nerve fiber layer. While often benign in diabetics, multiple CWS in a non-diabetic patient demand a workup for HIV, vasculitis, or embolic disease.

Differential Diagnosis

  • Myelinated nerve fibers (stable, feathery striations radiating from disc)
  • Commotio retinae (post-traumatic, deep retinal whitening)
  • BRAO (territorial inner-retinal whitening)
  • Hard exudates (yellow, waxy, sharply defined)

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