Non-physiological visual loss

Description

Non-physiological visual loss is a visual abnormality not associated with a structural (refractive) change or an organic disease process. It may be due to:

(a) Malingering: in this condition the patient claims visual disability but does not actually experience the symptoms. The claim is usually made for financial or other gain.

(b) Functional change. A subconscious (not willful) change, where the patient actually experiences the symptoms. This condition is most often seen as a pediatric functional bilateral amblyopia. Such patients often have multiple symptoms, as well as a reduced academic achievement.  It is linked to visual or emotional stress and the prognosis is usually good. The condition is not associated with a hysterical personality.

Symptoms

Symptoms are usually vague and the patient may be curiously unconcerned. There may be blurring of vision, diplopia, metamorphopsia, visual field restriction or other symptoms.

Signs

The apparent absence of macular or other pathology is insufficient to arrive at a diagnosis of non-physiological visual loss. The diagnosis can be positive when vision tests give a pattern of results inconsistent with organic pathology:

(1)  The visual acuity defect is variable.  Measurements are unreliable when different charts and test distances are used.  Pinhole may further reduce vision.  Clinical manipulations with low power lenses or suggestion may in some cases demonstrate normal visual acuity.

(2)  Visual field and colour vision defects are non-organic in nature.  Kinetic visual fields may spiral, or be tubular when tested at different distances. Confrontation testing may also demonstrate tubular fields, whereas static fields show isolated relative losses with no particular pattern.

(3)  There is an absence of pathology. Fundus appearance, pupil responses, refractive error with retinoscopy, keratometry and eye movements are normal.  There is no history of amblyopia.

(4)  A convergence or accommodative anomaly may be present, e.g. accommodative and/or convergence excess, accommodative and/or convergence insufficiency. Other abnormal signs may be present including eye movements or blepharospasm.

Prevalence

Common (approximately 1/100) in clinical pediatric populations

Significance

Whilst non-physiological visual loss is typically benign, the consequences of misdiagnosis can be significant if early signs of ocular disease are not detected.

Diff. Diagnosis

Stargardt’s disease, Retinoschisis – juvenile x-linked, Central serous retinopathy, optic neuritis, Best’s vitelliform dystrophy, retinal detachment, keratoconus, chiasmal compressive lesion. Organic amblyopia is typically unilateral, with intact peripheral visual fields and a prior history is present.

Management

Additional Investigations

If macular disease or dystrophy is suspected, then fluorescein angiography or electrophysiological testing may be indicated. In addition, photostress recovery time (PSRT) may be prolonged:  The time taken in PSRT to read any 3 letters on the pre-test acuity line, after the patient fixates the ophthalmoscope at 3 cm for 10 seconds, is greater than 50 seconds in macular disease.

Refractive correction or low vision aids

Non-physiological visual loss with a functional basis is treated using appropriate refractive correction, therapy for any accommodative /convergence disorder and reassurance for the visual loss. If the visual problem is only part of a complex clinical syndrome with somatic signs and symptoms then a psychiatric referral may be indicated.

Prognosis and review

Prognosis is excellent, although regular reviews are recommended both for monitoring vision and accommodative /convergence performance, as well as to ensure no other disorder is being masked.