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Cortical Blindness

URGENT — Neuro

Symptoms

Bilateral complete or severe loss of vision.

Anton syndrome: patient may deny blindness (visual anosognosia).

Riddoch phenomenon: ability to perceive moving targets but not stationary ones.

Clinical Findings

Diagnostic triad

Severely reduced visual acuity bilaterally (may reach NLP).
Normal-appearing fundus and optic discs (initially and long-term).
Intact pupillary light reflexes (signals post-geniculate lesion; midbrain reflex arc is preserved).

Clinical phenomena

Riddoch phenomenon: statokinetic dissociation (moving targets perceived, stationary targets not).
Blindsight: involuntary forced-choice discrimination despite lack of conscious vision.
Incomplete cortical blindness: distance acuity may be better than near acuity due to small surviving macular islands.

Anton syndrome

Visual anosognosia (denial of blindness).
Confabulation of visual descriptions (e.g., describing absent relatives).
Results from bilateral occipital infarcts extending into visual association cortex.

Balint syndrome

Simultanagnosia: perceives only one object at a time.
Optic ataxia: misreaching under visual guidance.
Oculomotor apraxia: inability to voluntarily direct gaze to a target.

Differential etiologies

Vascular: embolic bilateral PCA infarct ("top of the basilar"), cardioembolic, or hypotensive watershed infarct.
PRES: associated with hypertension, eclampsia, or immunosuppressant toxicity.
Neurodegenerative: Posterior Cortical Atrophy (Benson syndrome) showing progressive visuospatial dysfunction.
Rare: Heidenhain variant of CJD (blindness + dementia + myoclonus), MELAS, or trauma contusions.

Imaging characteristics

MRI with DWI: test of choice; detects acute infarct within minutes.
FLAIR: identifies white-matter edema in PRES.
Gadolinium: reveals tumors, metastases, or demyelination.
Note: non-contrast CT may miss acute lesions; a normal CT does not exclude the diagnosis.

Etiology

Vascular (most common)

Bilateral occipital lobe infarctions (e.g., top-of-the-basilar embolic or cardioembolic events).

Inflammatory & toxic

Posterior reversible encephalopathy syndrome (PRES).
Toxic exposures or amniotic fluid embolus (postpartum).

Neoplastic & degenerative

Occipital tumors or metastases.
Neurodegenerative atrophy (Alzheimer variant).

Red Flags

Acute bilateral vision loss with intact pupils → suggests bilateral PCA infarct; emergent stroke workup required.

Anton syndrome → high risk of injury due to denial; mandates supervised ambulation.

Progressive cortical visual dysfunction → consider tumor or neurodegenerative disease (Benson syndrome).

PRES with hypertension → emergent blood pressure control required.

Investigations

Ocular assessment

Comprehensive exam to document intact pupils and normal fundus.
Visual acuity testing at distance (may reveal preserved macular islands).
Rule out nonphysiologic (functional) visual loss.

Systemic workup

Urgent neuroimaging: MRI with DWI/FLAIR/contrast (preferred over CT).
Cardiovascular: ECG, telemetry (rule out Afib), and echocardiogram.
Vascular: Carotid and vertebral artery imaging.
Clinical: Blood pressure and glycemic control.

Treatment

Acute management

Hospitalization for neurologic observation and evaluation of stroke etiologies.
Management of systemic triggers (BP control, eclampsia management).

Rehabilitation

Low-vision occupational therapy and rehabilitation.
Orientation and mobility training.
Family counseling regarding visual anosognosia (Anton syndrome).

Clinical Pearl

Normal pupils and a normal fundus in a blind patient point directly to the occipital cortex—MRI is the diagnostic test, not the dilated exam.

Differential Diagnosis

Bilateral optic neuropathy
Severe bilateral retinal disease
Nonorganic (functional) visual loss
Bilateral occipital tumor