Peter H Derr

Extraction and modeling of the Oscillatory Potential: signal conditioning to obtain minimally corrupted Oscillatory Potentials

A method of extracting a temporally bounded component of a composite signal has been developed which minimizes data corruption in signal processing. The composite signal is windowed in the time domain, padding signals are attached, and finally, the conditioned signal is filtered to extract the component of interest. The method has been utilized to extract the Oscillatory Potential (OP) from the Electroretinogram (ERG). ERGs can contain impulse like transients, including flash artifacts and a-b wave transition, which may not be related to the Oscillatory Potential. Such transients will stimulate a filter, yielding its natural (filter) response and thus distort the actual OP signal. To avoid this effect, time-domain windowing and signal conditioning is used to extract the OP from the ERG. The extraction and modeling approach is applied to ERGs obtained from patients with recent monocular central retinal vein occlusion (CRVO). Model parameters clearly differentiate affected from fellow eyes and show subtle differences between eyes with benign and complicated outcomes.

Sensitivity and Specificity of Short-Duration Transient Visual Evoked Potentials (SD-tVEP) in Discriminating Normal From Glaucomatous Eyes

PURPOSE To evaluate the ability of the short-duration transient visual evoked potential (SD-tVEP) to discriminate between healthy eyes and eyes with early to advanced glaucomatous visual field loss. METHODS We tested 30 eyes of 30 healthy controls and 45 eyes of 35 glaucoma patients. Normal eyes had 20/30 or better visual acuity and normal 24-2 Swedish interactive thresholding algorithm (SITA) Standard visual fields. Glaucoma was staged as mild (mean deviation, MD > -6.0 dB), moderate (MD between -6.0 and -12.0 dB), and severe (MD < -12.0 dB). There were 15 eyes in each group. SD-tVEPs were recorded using the Diopsys NOVA-LX System. Each eye was stimulated with a low (Lc) and a high (Hc) Michelson contrast checkerboard pattern. Each test resulted in an Lc and an Hc SD-tVEP response. Each response was evaluated for overall waveform quality, P100 latency, and P100 amplitude referenced to the N75. The sensitivity, specificity, negative predictor value (NPV), and positive predictor value (PPV) were calculated. RESULTS Lc latency showed the highest accuracy for discrimination using receiver operating characteristic curves for high and low contrast parameters. The analysis for all subjects resulted in a 91.1% sensitivity, 93.3% specificity, 95.3% PPV, and an 87.5% NPV. Evaluating the mean Lc latency of the mild, moderate, and severe glaucoma patients against controls showed discrimination consistent with the glaucoma severity. CONCLUSIONS Short-duration transient VEP objectively identified decreased visual function and discriminated between healthy and glaucomatous eyes, and also showed good differentiation between healthy eyes and those with early visual field loss. VEP may be useful for early diagnosis of glaucoma.

Short duration transient visual evoked potentials in glaucomatous eyes.

PurposeTo investigate the correlation between structural and functional damage in patients with asymmetric glaucoma using a newly developed short duration transient visual evoked potential (SD-tVEP) device. MethodsTwenty-five patients with visual acuity ≥20/30 and asymmetric visual field (VF) loss [inter-eye difference in mean deviation index (MD) of at least 3 dB] were enrolled. Patients underwent optical coherence tomography (OCT) for macular thickness measurement, scanning laser polarimetry with variable corneal compensation for retinal nerve fiber layer measurement, and SD-tVEP (10% and 85% Michelson contrast, acquisition time of 20 s) in both eyes within 2 months. We correlated VF MD and structural test results with SD-tVEP P100 latency and Delta Amplitude (N75-P100). ResultsUsing 10% contrast, there was a significant difference in SD-tVEP latency and amplitude between eyes with better and worse VF MD (P<0.001). MD correlated significantly with both SD-tVEP parameters (r>0.33, P⩽0.01). When using 85% contrast, SD-tVEP amplitude differed between eyes (P=0.01) and MD values correlated significantly with amplitude results (r=0.32, P=0.01), but not with latency (P=0.46). In eyes with more advanced VF loss, there was a positive and significant correlation between SD-tVEP amplitude (85% contrast) and macular thickness on OCT (r=0.47, P=0.01), but not with retinal nerve fiber layer measured with polarimetry (P=0.26). ConclusionsIn cases of asymmetric glaucoma, SD-tVEP results correlate significantly with the level of VF damage as measured by MD. In the eyes with more advanced VF loss, reduced SD-tVEP amplitude was associated with decreased macular thickness on OCT. These findings suggest that SD-tVEP may be a fast and objective method to assess or screen for functional damage in glaucomatous eyes.