Biomedical subjects

Bryan J Winn

Publications and source records attributed to Bryan J Winn.

4 recordsLinked to original sources

PubMed2004

Detecting early to mild glaucomatous damage: a comparison of the multifocal VEP and automated perimetry.

PURPOSE: To gain better understanding of the relationship between abnormalities detected by the multifocal VEP (mfVEP) compared with those detected by static achromatic, automated perimetry in patients with glaucoma. METHODS: Fifty patients were studied who had open-angle glaucoma that met the following criteria: (1) a mean deviation (MD) of better than -8 dB in both eyes on the 24-2 Humphrey visual field (HVF) test (Carl Zeiss Meditec, Dublin, CA); and (2) glaucomatous damage in at least one eye, as defined by a glaucomatous optic disc and an abnormal 24-2 HVF test result (pattern standard deviation [PSD] <5% and/or glaucoma hemifield test [GHT] results outside normal limits). Monocular mfVEPs were obtained from each eye by using a pattern-reversal dartboard array, 44.5 degrees in diameter, which contained 60 sectors. Recording electrodes were placed at the inion (I) and I+4 cm, and also at two lateral locations up 1 cm and over 4 cm from I. Monocular and interocular mfVEP probability plots were derived by comparing the results with those of normal control subjects. For both the HVF and mfVEP probability plots, a hemifield was classified as abnormal if three or more contiguous points were significant at less than 5%, with at least one at less than 1%. RESULTS: Of the 200 hemifields tested (50 patients x two eyes x two hemifields), 75 showed significant clusters on the HVF, and 74 (monocular probability plot) and 93 (monocular or interocular plot) showed significant clusters on the mfVEP. Overall, the HVF and mfVEP results agreed on 74% of the hemifields, and 90 hemifields were normal and 58 were abnormal on both the mfVEP (interocular and/or monocular abnormal) and HVF cluster tests. Of the 52 disagreements, 35 hemifields had a significant cluster on the mfVEP, but not on the HVF, whereas the reverse was true of 17 hemifields. A case-by-case analysis indicated that misses and false-positive results occurred on both the HVF and mfVEP tests. CONCLUSIONS: As predicted from a theoretical analysis, under these conditions (i.e., the signal-to-noise level) the HVF and monocular mfVEP tests showed a comparable number of defects, and, with the addition of the interocular test, the mfVEP showed more abnormalities than the HVF. However, although there were abnormalities detected by the mfVEP that were missed by the HVF, the reverse was true as well.

Adult↗

PubMed2003

The multifocal electroretinogram.

The multifocal electroretinogram (mfERG) technique allows local ERG responses to be recorded simultaneously from many regions of the retina. As in the case of the full-field ERG, the ganglion cells contribute relatively little to the response, which originates largely from the outer retina. The mfERG is particularly valuable in cases in which the fundus appears normal, and it is difficult to distinguish between diseases of the outer retina and diseases of the ganglion cells and/or optic nerve. The mfERG can also help to differentiate among outer retinal diseases, to follow the progression of retinal diseases, and, with the addition of the mfVEP, to differentiate between organic and nonorganic causes of visual loss. However, because the difficulties encountered in recording and analyzing mfERG responses are greater than those involved in full-field ERG testing, mfERG testing is best left to centers with an electrophysiologist familiar with the mfERG test. Although this technique is relatively new and standards are still being developed, centers capable of recording reliable mfERG responses can be found in hundreds of locations around the world.

Electroretinography↗

PubMed2003

The multifocal visual evoked potential.

With the multifocal technique, visual evoked potentials (VEPs) can be recorded simultaneously from many regions of the visual field. For the multifocal VEP (mfVEP), the patient views a display that typically contains 60 sectors, each with a checkerboard pattern. The display covers about the same retinal area as the 24-2 Humphrey visual field (HVF). However, due to the scaling of the sectors of the mfVEP display, the fields are sampled differently by the mfVEP and HVF. To assess local defects in the visual field, the mfVEP responses must be compared with normal controls. These comparisons require relatively sophisticated analyses and software. Whereas the mfVEP can be recorded relatively easily with the same equipment used to record multifocal electroretinograms (mfERGs), the software needed to perform the analysis is not yet widely available. The mfVEP is valuable for ruling out non-organic visual loss, diagnosing and following patients with optic neuritis/multiple sclerosis, evaluating patients with unreliable or questionable HVFs, and following disease progression. When combined with the mfERG, diseases of the outer retina (before the retinal ganglion cells) can be distinguished from diseases of the ganglion cells and/or optic nerve. The difficulties encountered in recording and analyzing mfVEP responses are greater than those involved in full-field VEP testing. Thus, in its current form, the mfVEP is best recorded and interpreted by ophthalmologists and electrophysiologists experienced with the technique. However, this technique is developing rapidly; advances in commercial hardware and software are expected in the near future.

Electroretinography↗

PubMed2003

Detecting glaucomatous damage with multifocal visual evoked potentials: how can a monocular test work?

PURPOSE: To understand and improve the detection of glaucomatous damage with multifocal visual evoked potentials (mfVEP) obtained from single eyes. PATIENTS AND METHODS: Monocular mfVEP recordings were obtained from both eyes of 30 individuals with no known visual abnormalities. The 44.5 degrees -diameter display contained 60 sectors. Probability plots, analogous to the total deviation probability plot of the Humphrey Visual Field Analyzer, were created based on tests that compared each eye (monocular test), or the ratio of the responses from the 2 eyes (interocular test), to group norms. RESULTS: For the monocular test, the number of points exceeding the 5% confidence level was not distributed randomly among individuals or among field locations within an individual. Individuals with small signals (i.e., low signal-to-noise ratios [SNR]) showed too many "abnormal" points, while those with relatively large SNR values showed too few. Reasonably good specificity was obtained by defining an abnormality in terms of a cluster of significant points in the mfVEP probability plot. For the interocular test, the results were close to those expected by chance. CONCLUSIONS: Both monocular and interocular tests will be of value when testing glaucoma patients with the mfVEP technique. The interocular test is a more sensitive indicator of glaucomatous damage when a region when healthy has a large signal (SNR) and damage is largely unilateral, whereas the monocular test will be a more sensitive test when a region when healthy has a small signal (SNR). However, the statistics underlying monocular comparisons of mfVEPs are not simple. To obtain high specificity, criteria based on clusters of points need to be used and norms obtained for every laboratory.

Adult↗