ABSTRACT
This chapter provides electrophysiological information on non-organic visual loss as well as other ocular and systemic conditions not covered by other chapters. Awareness of the potential effects of common ocular conditions such as refractive error and cataract is important in the interpretation of electrophysiological tests. In addition, some systemic disorders such as muscular dystrophy and liver dysfunction do not typically cause significant visual symptoms but may nevertheless be associated with abnormal electrophysiological responses. The outline of the chapter is as follows:
Non-organic visual loss (functional visual loss): Ocular disorders: Hyperopia, myopia, and myopic retinal degeneration Cataract and media opacities Retinal detachment Pigment dispersion syndrome
Systemic disorders: Human immunodeficiency virus (HIV) infection
Thyroid dysfunction Adrenocortical hyperactivity and corticosteroid Liver dysfunction Duchenne and Becker muscular dystrophies Myotonic dystrophy Albinism
NON-ORGANIC VISUAL LOSS
Non-organic or functional visual loss occurs when the nature or the amount of visual impairment is incompatible with objective clinical findings. Non-organic visual loss has been classified into two categories. In the ‘‘malingering’’ type, willful pretension or exaggeration of symptoms is consciously made for personal gains. In the so-called ‘‘hysteria’’ type, non-organic symptoms are the result of subconscious process. Because differentiation between the two types depends on knowing the psychological origin of the symptoms, determining whether the non-organic visual loss is strictly due to ‘‘malingering’’ or ‘‘hysteria’’ is not always possible. Thompson (1) further categorized patients with non-organic visual loss into four groups. The ‘‘deliberate malingerer’’ purposely feigns visual loss. The ‘‘worried imposter’’ willingly exaggerates visual loss but worries that there may be serious disease. The ‘‘impressionable exaggerator’’ believes disease is present and is determined not to hide his disease. The ‘‘suggestible innocent’’ is convinced the symptoms are real but remains inappropriately complacent. The diagnosis of nonorganic visual loss is made on the basis of excluding organic diseases, which requires thorough clinical examination and appropriate work-up. Therefore, patients with occult or early organic disease may be erroneously diagnosed as having nonorganic visual loss. Further, non-organic visual loss may occur in the presence of concurrent unrelated organic ocular disease as well as in visually asymptomatic patients who have non-physiological test results such as tunneling of visual fields. On the other hand, patients with mild vague com-
be given a diagnosis of non-organic visual loss. The prognosis of non-organic visual loss is variable and unpredictable (2,3).
