Effect of recording duration on the diagnostic performance of multifocal visual-evoked potentials in high-risk ocular hypertension and early glaucoma

Tests for malingering in ophthalmology

Simulation can be defined as malingering, or sometimes functional visual loss (FVL). It manifests as either simulating an ophthalmic disease (positive simulation), or denial of ophthalmic disease (negative simulation). Conscious behavior and compensation or indemnity claims are prominent features of simulation. Since some authors suggest that this is a manifestation of underlying psychopathology, even conversion is included in this context. In today's world, every ophthalmologist can face with simulation of ophthalmic disease or disorder. In case of simulation suspect, the physician's responsibility is to prove the simulation considering the disease/disorder first, and simulation as an exclusion. In simulation examinations, the physician should be firm and smart to select appropriate test(s) to convince not only the subject, but also the judge in case of indemnity or compensation trials. Almost all ophthalmic sensory and motor functions including visual acuity, visual field, color vision and night vision can be the subject of simulation. Examiner must be skillful in selecting the most appropriate test. Apart from those in the literature, we included all kinds of simulation in ophthalmology. In addition, simulation examination techniques, such as, use of optical coherence tomography, frequency doubling perimetry (FDP), and modified polarization tests were also included. In this review, we made a thorough literature search, and added our experiences to give the readers up-to-date information on malingering or simulation in ophthalmology.

Multifocal visual evoked potential responses to pattern-reversal, pattern-onset, pattern-offset, and sparse pulse stimuli

The purpose of the present study was to compare standard multifocal visual evoked potential (mfVEP) pattern-reversal responses with those produced by pattern-onset, pattern-offset, and pulsed pattern stimuli. mfVEP recordings were obtained from five normal subjects using VERIS and a 4-electrode array. The standard reversal stimulus had 2(15) m-sequence steps (7.5-min duration). Pattern-onset and -offset responses were evaluated using sequences that all had 32 frames per m-step and 2(10) total steps (7.5 min); but the duration of the contrast step varied so that it was 1, 2, 4, 8, 12, or 16 of the 32 frames. The same series was also inverted so that adapting contrast was high and the stimulus step began with a contrast decrement. The effect of temporal sparseness was studied with positive contrast pulses (two-frame duration) within 16, 20, 24, 28, or 32 frames per m-step (all had 2(11) total steps). Four stimulus locations were isolated to study the effect of spatial sparseness. Standard mfVEP reversal responses were virtually identical to onset responses throughout the field, but ~3.5 times smaller. Responses to pattern onset were about twice as large as those for offset, especially in the lower hemifield, irrespective of adapting contrast level. Offset responses exhibited a different waveform compared with reversal, onset, or brief pulse responses. Though temporally sparse pattern-pulse responses were ~3.5 times larger than standard reversal responses, there was no improvement in signal-to-noise ratio (SNR). However, spatial isolation increased SNR by 22% for reversal responses and by 62% for temporally sparse pulses. Temporally sparse pattern-pulse stimuli do not improve mfVEP SNR unless they are also spatially sparse, suggesting that lateral inhibitory mechanisms have a greater impact than temporal contrast gain control mechanisms. The mfVEP response depends on the polarity of a contrast step, irrespective of the state of contrast adaptation.