My preferred definition is:
‘Any disturbance of the afferent visual system which cannot be attributed to demonstrable pathology, in patients whose symptoms can be circumvented using standard clinical tests’.
This means that people are pretending not to see well when really they can.
The apparent decrease in visual acuity may involve one or both eyes and vary from mild blurriness to complete blindness. The visual field defects may affect one or both eyes and include constricted or tunnel visual fields, and hemianopias.
There are many different reasons for this. There is a spectrum from the malingerer (to feign for secondary gain-in my experience adults trying to gain money) to subconscious visual loss caused by underlying psychological disorders in the patient (in my experience-worried children). The eye specialist’s role is to prove that the vision and/or visual field is in the normal range.
Bear in mind that one study has shown 16-53% of patients presenting with non-organic vision loss may have co-existing organic disease.
My experience is with 10 to 11-year-olds where social conflicts such as problems with school work, peer pressure, and new child in the family, are the cause. It is interesting that patients are usually relaxed despite suggesting severe visual complaints. They are also usually cooperative with testing.
There are several ways to prove that visual function is better than the patient wants the practitioner to believe. Two that I find work in most cases are:
Neutralising trial lenses combined with suggestion. This involves placing a high plus lens such as +10DS over any refractive correction and then adding in a -10DS, at the same time suggesting that the visual acuity will get better with this ‘extra strong lens’. It often improves to 6/6 in each eye using this technique.
Reduced test distance for vision measurement. For example, if the child presents with 6/18 in one eye at 6 m, and the vision loss is organic then at a 3 m testing distance the vision will be 3/9. The size of the letters seen at 3 m is half that seen at 6 m. If the vision loss is non-organic then at a 3 m testing distance the vision will often be 3/18. This is known as size constancy. Organic vision loss cannot cause size constancy.
To manage non-organic vision loss in children of this age give praise for doing well, offer reassurance, and privately explain your findings to the accompanying adult. This often results in the accompanying adult offering a cause for the behaviour.
Follow-up appointments are important to further document improvement as well as to be vigilant for co-existent organic disease. If the patient or accompanying adult desires, psychological treatment could be arranged.