Objective detection of hemifield and quadrantic field defects by visual evoked cortical potentials.

Abstract

Aims/Background-An objective method for detecting hemifield and quadrantic visual field defects has been developed using steady state visual evoked cortical potentials (VECPs), an adaptive noise cancelier (ANC), and Hotelling's t2 statistic. The purpose ofthis study was to determine the sensitivity and specificity of the technique. Methods-Nine subjects (mean age 44 years) were investigated with field loss due to a variety of causes including both anterior and posterior visual pathway lesions. Dynamic perimetry was performed by means of a Goldmann or Tubingen perimeter. VECP recordings were made from each visual field quadrant (230x230) by means of a steady state reversing checkerboard (7.7 rev/s). The central 5°of the visual field and the vertical and horizontal meridians were masked during these measurements. Recordings were made from three electrode sites, positioned over the visual cortex, relative to a mid frontal electrode. Each recording lasted 2 minutes, during which time fixation was monitored. The data from each recording were divided into 4 second segments, and the amplitude and phase of the VECP signal measured using the ANC. Hotelling's t2 statistic was applied to determine the probability of signal detection. Receiver operating characteristic curves were used to find the optimum signal detection threshold for identification of the visual field defects.Results-The results of the study confirmed patterns of subjective visual field loss. The technique had a sensitivity and a specificity of 81% and 85%, respectively, for detecting 'non-seeing' areas in the inferior visual field, and 82% and 89%, respectively, for detecting 'non-seeing' areas in the superior visual field.Conclusion-These results demonstrate that the technique is of potential clinical value to ophthalmologists and neurologists when subjective perimetry is not possible. (BrJ Ophthalmol 1996; 80: 297-303) Many workers have attempted to use measurement of visual evoked cortical potentials (VECPs) (Fig 1).18 19 Yanashima1I took advantage of this property in his study, using the Fourier transform for signal measurement. Quadrant field studies could be further improved by using objective statistical methods to detect the VECP signal. Such a method has been developed using frequency domain analysis and Hotelling's t2 statistic.20 21 The purpose of the current study was to determine the sensitivity and specificity of the technique for the detection of hemifield and quadrantic visual field defects in a range of subjects with pathology affecting different parts of the visual pathway. Materials and methodsNine subjects, two males and seven females, ranging in age from 17 to 69 years (mean 44 years) were investigated. All subjects gave informed consent for their participation in the study. The referring criteria were that the subjects had hemifield or quadrantic visual field defects and an acuity of 6/18 or better. A good visual acuity was necessary to enable accurate fixation. Most subjects were referred from the neuro-ophthalmology c...

Effect of different stimulus configurations on the visual evoked potential (VEP)

“…This finding may be due to the lower signal-to-noise ratio when the aggregate cone stimulation was minimal with those very peripheral-only stimuli. The notion of high repeatability, in conjunction with the aforementioned finding of relatively good linearity, support the concept of using the VEP as an objective indicator of visual-field dysfunction, as has been suggested and tested to some degree in earlier studies [9,[23][24][25][26][27][28][29]. 14 Relationship between total cumulative increase in cone number (X 1,000/mm 2 ) and mean VEP amplitude (microvolts) with increase in stimulus diameter Fig.…”

“…Furthermore, it provides global real-time information as to the patient's performance (i.e., assessing VEP amplitude and latency as the averaged responses dynamically summate over time) for the specific stimulus pattern. Moreover, the objective VEP information can be used to correlate with, and corroborate, the conventional subjective psychophysical results of a clinical visualfield assessment [9].…”

Steady-state multifocal visual evoked potential (ssmfVEP) using dartboard stimulation as a possible tool for objective visual field assessment

“…Similarly, the present data showed that maximal SNRs can be found in any one of the six channels. For improvement of the SNR, in future studies with the steady-state technique, the benefit of additional (e.g., forehead) electrodes [28,35] [12] should be investigated. Using such electrode setups, the combined evaluation of orthogonal signals (Euclidian sum) might reveal larger SNRs than any single channel [29].…”

Neural and Vascular Responses to Fused Binocular Stimuli: A VEP and fNIRS Study

“…A strong correlation between O z , and the average of O 1 and O 2 is a good indication of the overall associations between neural and vascular activation. 69,70 In summary, specific changes were observed across both VEPs and hemoglobin concentration levels in response to onset and static stimulation. In agreement with previous studies, we suggested that the N1-P2 complex could be a marker of stereopsis in V1.…”