Functional Disorders

Non-organic/functional disorders

Two major types are malingering and conversion disorder.

Conversion disorder

A subconscious expression of symptoms without organic findings, also called hysteria or psychogenic disorder.

Malingering

Conscious willful misleading for the purpose of achieving a consciously desired end.

Key behavior of malingerers

They may exaggerate symptoms, are often irritable and combative, and may act 'blinder than the blind.'

Triggers for conversion disorder

Psychological stress or physical trauma.

Patient response in conversion disorder

Generally indifferent to the affliction and usually cooperative.

Total blindness

Rare; truly blind patients typically move cautiously.

Behavior of a malingerer supposedly blind

May go out of their way to bump into things.

Intact pupillary responses

Exclude anterior pathway disease.

Menace reflex

Blinking in response to a threat.

Reflex tearing stimulus

A strongly illuminated light presented suddenly.

Signature evaluation for functional blindness

A truly blind patient can make a signature without difficulty, whereas a functionally blind patient may produce exaggerated illegibility.

Index fingers task for blindness evaluation

This task relies on proprioception rather than vision.

Optokinetic nystagmus test

Useful in evaluating functional blindness as it's difficult for a malingerer to suppress.

Mirror tracking test

The patient's eyes should move in response to a large mirror rocked back and forth.

VECP check size

Additional test to evaluate total binocular blindness.

Functional monocular vision loss prevalence

More common than binocular loss.

Malingerers typically feigned vision loss

Monocular loss.

Binocular blindness testing for monocular blindness

The tests can be performed monocularly.

Diplopia test

Occlude the supposedly poor eye and induce monocular diplopia in the good eye; if diplopia is reported, malingering is suspected.

Prism used for version/vergence movement test

10Δ base-out.

Expected movements with 10Δ base-out in normal eye

Look for version and vergence movements.

Expected response with 10Δ in a blind eye

No movement in either eye.

Fixation test for monocular blindness

Present a target in front of both eyes and observe whether the patient shifts gaze to read in the supposedly blind field.

Response of a truly monocular patient during fixation test

They will shift gaze to read in the blind field.

Visual angle test

Vary test distance using Snellen, Landolt C, and Tumbling E.

Plano lenses purpose in vision testing

To supposedly 'increase magnification' by placing combinations of lenses that amount to plano.

Keratoconus

An ocular condition that can mimic functional vision loss.

Conditions to consider in amblyopia evaluation

Strabismus or anisometropia.

Macular diseases mimicking functional vision loss

Early Stargardt macular dystrophy, central serous chorioretinopathy, cystoid macular edema.

Evaluation for suspected macular disease

Careful macular examination and fluorescein angiography.

Useful test for suspected cone dystrophy

ERG.

Signs of hysterical visual field loss

Tunnel vision that does not expand with increasing test distance; inconsistent Humphrey visual fields.

Goldmann visual fields test

Useful for functional field loss.

Suspicious patterns in Goldmann visual fields

Spiraling isopters and crossing isopters.

Voluntary nystagmus

Irregular, brief bursts of rapid-frequency, low-amplitude horizontal pendular eye movements.

Voluntary blepharospasm

Voluntary eyelid closure resembling ptosis or true blepharospasm.

Treatment for accommodative spasm

Patching or cycloplegia.

Conditions causing monocular diplopia

Irregular astigmatism, keratoconus, tilted lens, cataracts, macular cysts.

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