Functional Visual Symptoms: Diagnostic Technique Inventory

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Acuity comparisons · Field comparisons · Optokinetic response

Diagnostic techniques at a glance

Visual acuity at different distances

A specialist compares reading performance with the change expected when distance changes. A reproducible optical inconsistency may demonstrate better vision than the person experiences. This is a clinical demonstration with limited test-specific accuracy evidence, not a test of honesty. [1]

Tubular visual fields

A field retaining the same physical width at different viewing distances conflicts with the expected widening of a visual field. It can support functional visual loss, but careful technique, understanding and ocular assessment remain essential. [1]

Spiralling, crossing or stacked isopters

Formal field testing may produce contours that change or cross unexpectedly. These patterns can support a functional formulation, but fatigue, poor technique and eye disease can also produce unreliable fields. A cloverleaf pattern alone is insufficient. [1]

Binocular versus monocular fields

The specialist checks whether binocular vision compensates for a field deficit in the expected way. A reproducible inconsistency may demonstrate preserved function. Interpretation depends on the claimed deficit, fixation and complete eye examination. [2]

Optokinetic response

A moving visual target can elicit an automatic tracking response, demonstrating some preserved visual function. It does not establish normal conscious vision or explain every deficit. Avoid intolerable moving patterns; this is a specialist observation with limited standalone validation. [1]

Mirror tracking

Following a reflected image may demonstrate visual capacity during apparent severe loss. This is a described bedside observation rather than a broadly validated diagnostic-accuracy test. Preserved tracking must be interpreted with neurological and ophthalmic findings. [2]

Fogging

The clinician blurs the better-seeing eye with lenses and assesses what can still be read. Reading beyond that eye’s available vision can demonstrate function in the affected eye. Explain the finding openly; this is not a covert test of truthfulness. [1]

Prism dissociation

Prisms separate images so reported double vision or corresponding eye movements can demonstrate input from both eyes. Interpretation depends on alignment and the specific protocol. Clinical descriptions support its use, but universal sensitivity and specificity are not established. [1]

Prism fusion response

A prism-induced eye adjustment can demonstrate binocular visual function even when double vision is not reported. This requires specialist interpretation and differs from the subjective prism-dissociation comparison. It does not exclude coexisting ocular disease. [1]

Stereopsis

Depth-perception testing can establish a minimum level of binocular function. It may contradict a particular degree of reported loss, but estimates of each eye’s acuity have limits. It does not establish that all visual symptoms are functional. [1]

Bagolini lens testing

Striated lenses produce a binocular pattern that requires input from both eyes. Seeing the expected pattern can demonstrate preserved binocular function. This is a specialist clinical method, with limited standalone diagnostic-accuracy evidence for FND. [1]

Colour or polarizing dissociation

Selected targets visible separately to each eye can reveal visual capacity not accessible during ordinary testing. These are described ophthalmic comparisons, not interchangeable validated tests; optical setup and coexisting disease matter. [2]

OCT, retinal testing and visual evoked potentials

Retinal imaging and electrical-response tests address structural or physiological differential diagnoses. They are not positive FND tests; normal results alone do not establish functional visual loss, and coexisting eye disease is common. [1][3]

Research and Sources

The reviews describe clinical methods; these entries do not establish universal diagnostic accuracy. The coexistence study concerns a selected referral population.

Citation	Full citation
[1]	Ramsay N, McKee J, Al-Ani G, Stone J. How do I manage functional visual loss. Eye. 2024;38:2257–2266. FND-CIT-0024. https://doi.org/10.1038/s41433-024-03126-w
[2]	Raviskanthan S, Wendt S, Ugoh PM, et al. Functional vision disorders in adults: a paradigm and nomenclature shift for ophthalmology. Survey of ophthalmology. 2022;67(1):8-18. DOI. PMID: 33737039. FND-CIT-0179.
[3]	Scott JA, Egan RA. Prevalence of organic neuro-ophthalmologic disease in patients with functional visual loss. American journal of ophthalmology. 2003;135(5):670-675. DOI. PMID: 12719075. FND-CIT-0180.