functional vision loss table 2

Functional Vision Loss

Functional vision loss - the symptomatic and measured loss of vision that is unassociated with an identifiable lesion of the visual pathwaysOther associated terms- hysteria, hysterical visual loss, malingering, nonphysiologic visual loss, factitious visual loss, nonorganic visual loss, psychogenic visual loss, Münchausen syndrome, and conversion disorder of vision

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First consider the following ocular pathologies with subtle clinical signs:-keratoconus-cone dystrophies-early Stargardt’s disease-amblyopia -retrobulbar optic neuritis-optic nerve compressionManagement: Ocular/Medical/Further testing Management: Reassurance, report suspected Child

abuse

1 2 3 4 Differentiating Sources of Symptoms (though it may not be possible to do so)

1 – purely organic

2—mostly organic, with small functional component/overlay

3—mostly functional (overlay) with small organic component

4—purely functional

Overview of Tests of Functional Vision Loss

Tests mostly based on the behavior of truly blind individualsTests that masquerade as tests of acuity and fields

-tests of proprioceptionIndirect tests of acuity and fields

-observationDirect tests of vision (mostly acuity)

-objective tests of vision -pupil testing -involuntary reflex, requires cooperative pt-(electrodiagnostics and other mostly objective testing, may still require a cooperative pt)

-nontraditional tests of vision -surprise, could be involuntary if involves menace reflex

-subjective tests of -binocular

-test a binocular-only function, like stereopsis-reading bar

-binocular and monocular-get better eye to read first then trick the other eye into reading-monocular targets in a binocular field using filters

-monocular-interferometry-varying testing method-varying testing distance-suggestive tests

-magic drop-lenses

-subjective tests of visual fields-motility testing, especially saccadic testing-confrontation, including pantomime-automated-Goldmann-Tangent Screen

-electrodiagnostics and mostly objective testing, may still require a cooperative pt

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Functional Vision (mostly acuity) Loss Table-Generally the following test items are used once a baseline of vision has been established, and the goal is to demonstrate and document vision better than baseline.-Items are organized by how the information about vision is obtained-Generally the worse the vision the items higher up in the following list are more useful, the better the vision the items lower on the list are more useful

Tests Reduced acuity: good in one, moderately reduced the other; ie. 20/20 and 20/40-20/60

Reduced acuity: good in one, severely reduced the other; ie. 20/20 and 20/400-NLP

Reduced acuity: moderate loss both; ie. 20/40-20/60 both

Reduced acuity: moderate loss one, severe loss the other; ie. 20/40-20/60 and 20/400-NLP

Reduced acuity: severe loss both:Ie. Total blindness

Tests mostly based on the behavior of truly blind individuals

Tests that masquerade as tests of acuity and fields

Tests of proprioception (can be done binocularly in total blindness pt)

signing name on paper; making index finger of two hands touch

Patch better seeing eye then: Very UsefulFunctional: difficultyOrganic:No difficulty

Patch better seeing eye then: Very UsefulFunctional: difficultyOrganic:No difficulty

Very UsefulFunctional: difficultyOrganic:No difficulty

Indirect tests of vision (acuity and fields)

Observation (can be done binocularly in total blindness pt)

blind pt wearing sunglasses into clinic, walking into and around obstacles in exam room, avoiding looking at examiner or other object of interest (like when pt directed to look at their own hand)

Patch better seeing eye then: Very UsefulFunctional:quicker purposeful movements, avoid looking at examinerOrganic:Cautious slower movements, feeling their way with hands and feet

Patch better seeing eye then: Very UsefulFunctional:quicker purposeful movements, avoid looking at examinerOrganic:Cautious slower movements, feeling their way with hands and feet

Very UsefulFunctional:quicker purposeful movements, avoid looking at examinerOrganic:Cautious slower movements, feeling their way with hands and feet, look in direction of examiner’s voice

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Functional Vision (mostly acuity) Loss Table continued

Direct tests of vision






objective tests of vision (mostly of acuity, but also fields) involving involuntary reflexes

pupil testing (stimulus is light)-can be confounded by pharmacological manipulation-only cortical blindness associated with normal pupils-photophobia with orbicularis contraction and reflex tearing during pupil testing

Most important testFunctional: no APDOrganic: small to large APD

Most Important When worst eye is NLPFunctional:possible symmetrically strong reaction to light in 20/400 eye; any reaction to light in NLP eyeOrganic:any (previously undocumented) APD in worst eye

Functional:Any reaction to light eitherOrganic:No reaction to light either

OKN Drum or Sheet(stimulus is blur)

Useful if vision is worse than 20/400 in worst eyeFunctional: jerk nystagmus presentOrganic: jerk nystagmus only if vision 20/400 otherwise no nystagmus if vision worse than 20/400

Useful if vision is worse than 20/400 in worst eyeFunctional: jerk nystagmus presentOrganic: jerk nystagmus only if vision 20/400 otherwise no nystagmus if vision worse than 20/400

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objective tests of vision (mostly of acuity, but also fields) involving involuntary reflexes






Mirror test (stimulus is pt’s own face) elicits nystagmoid movement means hand motion vision or better, requires a cooperative pt

Very UsefulFunctional: nystagmoid movementOrganic:No movement

Horizontal prism shift (stimulus is diplopia) test with prism over affected eye and single letter distant target of smaller size than affected eye’s acuity and larger than better eye’s acuity.

Very useful, this is the only objective test for moderate unilateral vision lossFunctional:Compensatory eye movements of saccade towards apex of prism and then convergence Organic:No eye movement because no diplopia created

Functional:Compensatory eye movements of saccade towards apex of prism and then convergence Organic:Absolutely No eye movement because no diplopia created

Functional:Compensatory eye movements of saccade towards apex of prism and then vergence movement Organic:Absolutely No eye movement because no diplopia created

nontraditional tests of vision (acuity and fields)

surprise, could be involuntary if involves menace reflex (can be done binocularly in total blindness pt)stimulus is perceived threat-Bell’s phenomenon-could be humor or any other stimulus that evokes a noticeable response demonstrating purely visual recognition(-loud sounds)

Patch better seeing eye then: Very UsefulFunctional: any reactionOrganic:No reaction because there is no perceived threat

Patch better seeing eye then: Very UsefulFunctional: any reactionOrganic:No reaction because there is no perceived threat

Very UsefulFunctional: any reactionOrganic:No reaction because there is no perceived threat

6

subjective tests of acuity mostly

Binocular Tests Reduced acuity: good in one, moderately reduced the other; ie. 20/20 and 20/40-20/60





Stereopsis (a binocular only function) (see graph of acuity corresponding to local stereopsis values achieved using stereocircle test part of Stereo Fly Test)Very useful because can get an acuity; inconclusive if no stereopsis present

Functional: 7th-9th dots seenOrganic:1st-6th dots seen

Functional: 3rd-9th dots seenOrganic:No dots seen

Functional: 7th-9th dots seenOrganic:1st-6th dots seen

Functional: 3rd-9th dots seenOrganic:No dots seen

Reading barCan test for moderate unilateral vision lossMay be harder if affected eye is the left eye and that target’s print is left to right

Choose smaller printFunctional:Read smoothly across the line of printOrganic:Difficulty reading on same side of page as affected eye

Option of choosing larger printFunctional:Read smoothly across the line of printOrganic:Difficulty reading on same side of page as affected eye

Possible with 20/80-20/200 print:Functional:Read smoothly across the line of printOrganic:Difficulty reading on same side of page as affected eye

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Binocular and monocular

Get better eye to read first then trick the other eye into reading






Gradually fogging good eye with plus (is the better test b/c can start with DSRx on good eye) or cyl or polarized lenses and using distance manifest over affected eye

Functional:Reads 20/25-20/30 with affected eyeOrganic:Does not read better than 20/40 with affected eye

Functional:Reads 20/200 or better with affected eyeOrganic:Does not read better than 20/400 with affected eye

Functional:Reads 20/200 or better with affected eyeOrganic:Does not read better than 20/400 with affected eye

Vertical prism dissociationThe letterwas 2 lines larger than the best corrected visual acuity of thebetter eye. The patient was asked to identify theletter with both eyes open. A 4 prism diopters prism was thenheld base down in front of the better eye with best correctionin place and

Functional:two letters seen(the patient was asked what letters, how they are oriented, and ifone was clearer than the other)Organic:One letter seen(test is over)

Functional:two letters seen(the patient was asked what letters, how they are oriented, and ifone was clearer than the other)Organic:One letter seen (test is over)

Functional:two letters seen(the patient was asked what letters, how they are oriented, and ifone was clearer than the other)Organic:One letter seen (test is over)

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Binocular and monocular

both eyes open. The patient was asked what heor she saw on the Snellen chart.

Mono-cular targets in a bino-cular field using filters






red green glasses and red green phoropter filter -------------------An alternative test uses apink pen on white paper (ie. objectionable words). In this case the pink pen is seen by the green filtered “bad” eye. Could also try green pen with red filter on “bad” eye

Functional:Green good eye sees all letters on green sideRed affected eye sees 20/20-20/30 letters on red side Organic:Green good eye sees all letters on green sideRed affected eye sees no better than 20/40

Functional:Green good eye sees all letters on green sideRed affected eye sees 20/200 (20/100 on projector) or smaller letters on red side Organic:Green good eye sees all letters on green sideRed affected eye sees no better than 20/400

Functional:Green better eye sees 20/30 or better and/orRed worse eye sees 20/200 (20/100 on projector) or smaller letters on red sideOrganic:Green better eye sees 20/40-20/60Red worse eye sees no better than 20/400 (and no reaction is noted to what is written)

Monocular Interferometry Very usefulFunctional:sees 20/25-20/30Organic:Does not see better than 20/40

Very usefulFunctional:sees 20/150 or betterOrganic:Does not see lines

An important test because one of the few for binocular moderate loss of acuityFunctional:sees 20/25-20/30Organic:

Very usefulFunctional:sees betterOrganic:Does not see better

Very usefulFunctional:sees betterOrganic:Does not see better

9


Monocular

Does not see better than 20/40






Varying the VA test method: starting at 20/10 or counting the number of letters

Functional:Reads 20/25-20/30Counts 20/10 letters;Organic:Does not read better than 20/40 or count 20/10 letters

Functional:Reads 20/200 or betterCounts 20/60 or smaller letters;Organic:Does not read better than 20/400 or count 20/60 or smaller letters

Functional:Reads better bothCounts 20/60 or smaller letters in worse eye;Organic:Does not read better both or count 20/60 or smaller letters in worse eye

Varying the VA test distance (ie. Low Vision chart)

Could be difficult since only smallest low vision chart characters useful hereFunctional:Reads 20/10 characters at 10 feet Organic: Does not read better than 20/20 letters at 10 feet

Functional:Reads 20/200 or better characters at 10 feet Organic:Does not read better than 20/80 characters at 10 feet

Functional:Reads smaller equivalent characters at 10 feet Organic:Does not smaller equivalent characters at 10 feet

Suggestive tests, like magic drop or very low power lenses or lenses which neutralize each other

Functional:Reads 20/25-20/30Organic:Does not read better than 20/40

Functional:Reads 20/200 or betterOrganic:Does not read

Functional:Reads better in either eyeOrganic:Does not read

10

(magic drop test uses topical anesthetic with distanceRx and pinhole)

better than 20/400

better in either eye

-subjective tests of visual fields

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-motility testing, especially saccadic testing (Functional: an accurate saccade to a location beyond their baseline field; organic: no accurate saccade to location beyond baseline field)-confrontation (functional: tubular fields), including pantomime (functional: copies peripherally located purely visual hand movement)

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-automated

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Functional: cloverleaf pattern

Organic: fits pattern of known retinal/visual pathway disease; corresponds with detected disease

Functional: spontaneous improvement, no detected disease

Organic: persistence with corresponding disease

-Goldmann

Options for the stimulus Size: 0, I, II, III, IV, V : 0 is the smallest, V is the largest Intensity: 1, 2, 3, 4 : 1 is the dimmest, 4 is the brightest Intensity: a, b, c, d, e : a is the dimmest, e is the brightest

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-Tangent Screen

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-electrodiagnositics (recommended in all cases (S Beatty 1999)) and other mostly objective testing

-evoked potential- change in electrical activity of neurons/neuron system when stimulated; compare one eye’s activity to the other

-Cone or rod dystrophies can have ERG abnormalities-cone dystrophies can also have reduced color vision -----------------------------------------------------------complaints of night blindness in some hereditary retinal conditions can be investigated with dark adaptometry ----------------------------------------------------------- neuro-imaging indicated for: reproducible field defects, suspected cortical blindness, normal vision cannot be restored during the course of the examination (S Beatty 1999)

functional vision loss table 2

Health & Medicine

measured loss of vision

anddocument vision

nonorganicvisual loss

overview of tests

functional vision losstests

nonphysiologic visual

psychogenic visual loss

factitious visual loss