functional visual loss

[rubensan]

what tricks do you use?

[ronk]

i have been taught by my neuro-oph attending to first find out what kind of functional visual loss there is. there is a great article by thompson (Thompson HS. Functional visual loss. American Journal of Ophthalmology. 100(1):209-13, 1985 Jul 15.) which describes 4 categories of functional visual loss ranging from the "suggestible innocent" to a "deliberate malingerer." these categories are pretty readily identifiable and are important in finding out how to approach these patients.
many patients who are not deliberately malingering can be well managed by reassuring them that they will improve and seeing them back often. this can help establish your rapport with them and prevent them from going from doctor to doctor finding someone who will no accuse them of "faking." although this can be trying for the physician in terms of frustration at the situation and time commitment, it is probably in the best interest of the patient and the health care system to do so.
if they are truly malingering...that get's harder. haven't had to deal with it yet.
any other suggestions?

[Wolverine98]

It depends on the level of vision and whether it's unilateral or bilateral.

If you're talking about the profound level of vision loss, I do the simple tricks, like a mirror that you rotate from side to side, the OKN drum, or, if I'm in the ER or something without convenient equipment, I do the old trick of suddenly tossing something like a wadded up peice of paper right at them. You'd be surprised how hard it is to stop the reflex of reaching up to catch or block something in that situation. If they're at this level, and they flinch as the applanation tip is coming close, that's a nice giveaway too.

If it's more subtle than that, like in the 20/30-20/50 range, it can be more difficult, then I try HVF first (just because I can usually get those faster). If it's still not definite (like a complete blackout for someone with 20/40 vision), then I get a GVF; there's debate over whether or not to let the perimetrist know that this is what you're looking for. I usually do, and I've gotten several spiral isopters.

Sometimes you just have to run them through the full spectrum, FA, ERG (multifocal if it's mild vision loss), maybe VEP. You also might have to look at getting an MRI.

Sometimes it's very hard to tell. I had one patient in my first year who we were sure was malingering. She was inconsistent in her exam, everything looked completely normal, her VF were useless. She was blaming her previous doctors for everything wrong with her. A CT of her head showed some abnormalities in the occipital lobe. We got an MRI which showed that she had some occipital lobe T2 hyperintensity. It ended up that she had posterior reversible encephalopathy syndrome, which had been brought on by the combination of pre-eclampsia and crack. (I just throw this in there to emphasize that you still have to rule everything else out before you can call them "functional").

One of our pediatric staff had a 12 year-old who, for two years, was able to get reliable humphrey visual fields with very consistent defects; that's pretty amazing. They caught her when they tried a GVF. This girl had been through the works before this (CT, MRI/MRA, LP, mERG, ERG, VEP).

IME the toughest patients are those who do have an organic cause of visual loss with functional overlay. That can be extremely hard to deal with.

Now that I'm in my glaucoma fellowship, I just send them all to the neuro-oph clinic.

Dave

[TropicalFish]

once we had a teenage female who claimed vision loss in one eye. Our neuro-ophth place a phoropter in front of the patient and progressively fogged the good eye until the plus 10 lens was reached while the patient kept on reading the eye chart. She read down to 20/25! (MRx was plano of the good eye)

[neurodoc]

Of the "trick" tests to detect "functional" visual loss, the most reliable is the finding of "tunnel vision" that is fixed regardless of the patient distance from the tangent screen. No way can this finding reflect "organic" disease of the visual system. A sophisticated faker, of course, won't be fooled. There is still the possibility of hysteria (technically these are not "fakers").

Deflecting the light path with phoropter/prismatic occlusion/fogging can better trick fakers as well as hysterics.

It is important to remember that "functional" visual loss is a diagnosis of exclusion, and you must be sure that you have excluded an organic lesion of the visual system. Lesions to the primary and associational visual cortex can present apparently bizarre symptoms, including polyopia (and don't forget to look for something as simple as a dislocated lens in monocular diplopia).

Also remember that the visual system has two pathways: one (cortical visual) bypasses the brainstem and the other (the phylogenetically older reflexive pathway) can function independent of the cortex. This older system controls the pupillary and VOR responses. A patient can be "cortically" blind and show intact pupillary refleses and OKN's.

Nick