Abstract
BackgroundVisual evoked potentials (VEPs) are electrical potentials generated by neurons in the central nervous system in response to visual stimuli. A series of positive and negative wavelets in response to flash-stimuli (flash-VEP; FVEP) or reversing, iso-luminant patterns (pattern-VEP; PVEP) are recorded. Pathological conditions affecting the post-retinal pathways can alter overall waveform morphology, and also affect wavelet peak times and amplitudes. FVEPs have recently been described in horses, but more data on the variability within and between subjects is required, to adequately interpret results from clinical equine patients. Therefore, the purpose of this study was to describe the variability, repeatability and test-retest reliability of equine FVEPs in normal, adult horses.ResultsEquine FVEPs were recorded from one randomly selected eye in 17 horses, from both eyes in eight of these horses, and also at two separate recording sessions in six horses. N1, P2, N2 and P4 wavelets were present in 100% of the recordings in all horses, while P1, N2a, P3 and P5 were only present in some recordings. Coefficients of variation (CVs) were low for P2, N2 and P4 peak times, but higher for all amplitudes. There were no statistically significant differences comparing peak times and amplitudes between eyes or between sessions. Coefficients of repeatability (CRs) are reported for P2, N2 and P4 peak times between eyes (P2; 5 ms, N2; 18 ms, P4; 18 ms) and also between sessions (P2; 5 ms, N2; 16 ms, P4; 39 ms). Intraclass correlation coefficients (ICCs), as an estimate of test-retest reliability, was assessed to be fair to excellent for most parameters.ConclusionsThis study provides important data on variability, repeatability and test-retest reliability of FVEPs in normal, adult horses. We conclude that P2, N2 and P4 peak times should be included in the evaluation of equine FVEPs. The large inherent variability of FVEP amplitudes is likely to make them less suitable and useful for establishing a diagnosis on their own in most clinical patients, but they may occasionally provide support to a clinical diagnosis.
Highlights
Visual evoked potentials (VEPs) are electrical potentials generated by neurons in the central nervous system in response to visual stimuli
We have examined the variability, repeatability and testretest reliability of Flash visual evoked potential (FVEP) in normal, adult horses to evaluate if this method may be a suitable, additional diagnostic tool to use in the clinical work-up of equine patients with ophthalmological and/or neurological disease
Coefficients of variation (CV), coefficients of repeatability (CR) and intraclass correlation coefficients (ICC) are reported narrower for P2 and N2 peak times in the equine FVEP (Table 2), compared to more than 50-ms-intervals considered to represent the normal ranges for N2 and P2 in the human study
Summary
Pathological conditions affecting the post-retinal pathways can alter overall waveform morphology, and affect wavelet peak times and amplitudes. Visual evoked potentials (VEPs) are electrical potentials generated by neurons in the central nervous system in response to visual stimuli These potentials in response to flash-stimuli (flash-VEP;FVEP) or reversing, iso-luminant patterns (pattern-VEP;PVEP), are recorded by electrodes placed on the scalp over the visual cortex. Several pathological conditions affecting the post-retinal pathways can alter overall morphology of the recorded waveform and affect wavelet peak times and amplitudes [1]. In human medicine, recording of VEPs has many clinical indications including evaluation of patients with optic neuropathies, lesions compressing post-retinal pathways, Alzheimer’s disease, glaucoma and central visual impairment (CVI) of different etiologies [2,3,4,5,6,7]. Recording of PVEPs require cooperation by the patient (fixation and focus on the pattern) and FVEPs are usually still the test of choice in infants, as well as in uncooperative, sedated and comatose patients [1]
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