Examination strategies in simulation and functional vision disorders

Abstract

The diagnosis of malingering and functional visual loss should be proven by specific tests-after the exclusion of differential diagnoses such as optical disturbances, amblyopia, early stages of macula and optic nerve disease and cortical lesions. Malingering and functional visual loss are based on different causes and pathogenetic mechanisms. However, they produce the same symptoms and can therefore be examined by the same methods. The strategy consists of three parts: 1) check the reproducibility of the results, 2) specific procedures: provocation of reflectory responses, deception, measurement of the same function with different methods and objective methods and 3) proof. In alleged bilateral blindness the provocation of reflexes and deceptive strategies are especially useful, in alleged bilateral reduction of visual acuity deceptive methods (related to the size of the optotype), the examination of central vision by other methods (equivalents to visual acuity) and objective methods are applied. In alleged monolateral blindness or reduction of visual acuity the binocular tests are valuable. Additionally, methods to provoke reflexes, especially pupil reaction, are used as well as the measure of equivalents to visual acuity. In alleged concentric constriction of the visual fields three strategies are mainly used: 1) check if visual field size is in accordance with the visual angle, 2) different methods to examine the isopters and 3) different perimetric methods. In case of an alleged hemianopic field defect the following methods are of special value: 1) binocular examination, 2) reading ability, 3) different perimetric methods and 4) half-field stimulation. After finishing the specific tests the diagnosis of malingering or functional visual loss should be unambiguous and the existing function should be determined. Strategies for further management are shown--dependent on the pathogenesis: the aim is to avoid repetition and to set the right course for the future. In case of malingering the reliable expert's report is helpful. In case of functional visual loss it is important to avoid unnecessary examinations and to offer specific aids.