Biomedical subjects

Alexander I Klistorner

Publications and source records attributed to Alexander I Klistorner.

5 recordsLinked to original sources

PubMed2005

Clinical application of objective perimetry using multifocal visual evoked potentials in glaucoma practice.

OBJECTIVES: To evaluate the role of objective perimetry using multifocal visual evoked potentials (mVEPs) in glaucoma practice, and to assess its utility in patients with inconclusive standard automated perimetry findings. Method A retrospective case series of 436 consecutive subjects referred for glaucoma investigation who underwent testing with the AccuMap V1.3 mVEP system (ObjectiVision Pty, Ltd, Sydney, New South Wales, Australia) within a defined 12-month period. Sensitivity was determined by comparing this testing with that of standard automated perimetry and that used in a subgroup in whom masked stereoscopic optic disc photographs were used as an alternative reference standard. Overall clinical diagnostic outcomes were assessed. RESULTS: The mVEP changes were correlated with the stage of disease and Humphrey mean deviation (r = 0.78). The overall sensitivity for detecting glaucoma with established subjective field loss was 97.5% (early glaucoma, 95.0%), whereas 92.2% of low-risk suspects had normal mVEPs. When masked disc assessment alone was used for diagnosis of abnormality, sensitivity of mVEP (80.6%) and Humphrey visual field results (81.9%) were similar, but mVEP specificity was better (89.2% vs 79.5%). The mVEP was particularly useful in assessing excessive subjective field loss (45 eyes) by showing a much closer correlation with the clinical picture. CONCLUSIONS: Multifocal VEP is an effective method for detecting visual field loss in glaucoma. It provides a valuable aid to the clinician in categorizing patients with unreliable, variable, unconfirmed, or excessive subjective field loss.

Evoked Potentials, Visual↗

PubMed2003

Effect of stimulus check size on multifocal visual evoked potentials.

In this study we examined the effects of varying stimulus check size on multifocal visual evoked potential (VEP). We also evaluated the currently used cortical scaling of stimulus segments. The ObjectiVision multifocal objective perimeter stimulates the eye with random check patterns at 56 cortically scaled segments within the visual field extending to a radius of 26 degrees. All cortically scaled segments have equal number of checks, which gradually increase in size from the center to the periphery, proportional to the size of the segment. Stimuli with 9, 16, 25, 36 and 49 checks/segment were tested on 10 eyes belonging to 10 normal subjects. The check size varied inversely with number of checks per segment. VEP was recorded using bipolar occipital cross electrodes (7 min/eye), the amplitude and latency of responses obtained were compared with the check size at different eccentricities. Our findings suggest that the existing setting with 16 checks/segment subtending 26' to 140' from center to periphery, is the most effective amongst all the check sizes. Decreasing the check size prolongs the latency in the central field only. Cortical scaling of segments generates responses of the same order of magnitude throughout the field, but could be improved slightly to enhance the signal from the outer two rings.

Adult↗

PubMed2003

Effect of pupil size on multifocal pattern visual evoked potentials.

The purpose of this study was to investigate the influence of pupil diameter on the amplitude and latency of multifocal visual evoked potentials (mfVEP). The multifocal objective perimeter (Accumap; Objectivision) was used to stimulate the visual field at 56 sites extending to 32 degrees using a pseudo-random pattern stimulus. The mfVEP were recorded using bipolar occipital electrodes, 7 min/eye. Ten normal subjects were recruited from the community and one eye was randomly selected for testing. The mfVEP were recorded at four different pupil diameters (2 mm, 4 mm, 6 mm, 8 mm), obtained by applying tropicamide (0.5%) or pilocarpine (2%) in different dilutions. Appropriate refractive correction was provided to overcome cycloplegia and achieve a visual acuity of 6/7.5 or better. Analysis revealed that at most pupil diameters the normalized full field amplitude did not show significant variation, except at the most miotic pupil diameter (2 mm), where the amplitude became reduced, based on 2-way anova and Tukey's T method. There was, however, significant correlation between latency and pupil area (correlation coefficient: upper field -0.63, lower field -0.76). The results suggest that even in the presence of mydriatics or miotics, the mfVEP test can be used to assess diseases that affect amplitude, provided near correction is used. The interpretation of latency, however, must be made with caution, as a borderline conduction defect with a dilated pupil may appear normal.

Adult↗

PubMed2002

Multifocal objective perimetry in the detection of glaucomatous field loss.

PURPOSE: To test the ability of a new type of multifocal objective perimetry to identify glaucomatous visual field defects. METHODS: A multichannel visual evoked potential was recorded using the ObjectiVision Accumap perimeter. One hundred patients (age, 62.2 +/- 9.8 years, mean MD -6.5 +/- 4.17 dB) with open-angle glaucoma and confirmed glaucomatous visual field defects were tested and compared with the normal database of 100 normal subjects (age, 58.9 +/- 10.7 years). Both eyes were tested, but for determining sensitivity the eye with the lesser field defect was chosen if both qualified. The amplitude and intereye asymmetry coefficient for each zone of the field were calculated. A mean amplitude and multifocal objective perimetry severity index was calculated for each subject. RESULTS: In 95 of 100 (95%) patients with glaucoma Humphrey field defects were correlated with visual evoked potential amplitude reductions identifying a cluster of three or more abnormal zones. In two of five remaining patients with glaucoma the defect was detected on the intereye asymmetry analysis. Topographic location was well correlated with Humphrey fields. Mean amplitude was significantly reduced in 86 of the glaucoma cases (86%). The glaucoma severity index was abnormal in 93 glaucoma cases and showed a correlation with Humphrey MD (r = 0.67 right eyes, 0.69 left eyes). In 37 glaucoma cases with no scotoma by definition in the fellow eye, 22 (59.4%) had an abnormal multifocal objective perimetry, whereas only eight had some other aspect of their Humphrey visual field flagged as abnormal. CONCLUSIONS: Multifocal objective perimetry can assess the visual field and identify glaucomatous visual field defects. It may have the potential for identifying defects earlier than conventional perimetry.

Adult↗

PubMedDate not supplied

Effect of eccentricity on pattern-pulse multifocal VEP.

PURPOSE: The sparse pattern-pulse stimulation has been suggested to produce better cortical evoked responses compared to pattern reversal stimulation. This study examines varying pattern-pulse states and the effect of eccentricity of the stimulated visual field on the response amplitude and latency. METHOD: The multifocal visual evoked potential (mfVEP) was recorded using Accumap. 58 close-packed checkerboard segments in a dartboard configuration were used. The best configuration for pattern-pulse stimulation was determined. This optimal stimulus condition was then compared to pattern-reversal stimulation at different eccentricities of visual field.in terms of latency and signal/noise ratio (SNR) of mfVEP amplitude. RESULTS: The maximal response was seen when each element "1" of the binary sequence was represented by two "pattern on" frames followed by two "pattern off" frames while each element "0" of the binary sequence is represented by four "pattern off" frames. There was a significant overall increase of SNR using this pattern-pulse stimulating mode (SNR=15.5+/-3.8) compared with pattern-reversal stimulation (SNR=12.4+/-2.6). However, this was strongly dependant on eccentricity. In rings 1, 2 and 3 SNR improved by 48%, 43% and 26% respectively with ring 4 the effect was marginal and ring 5 was not significantly different. There was also a significant delay (10.1+/-5.3 msec) of the mfVEP response in pattern-pulse stimulation compared to pattern-reversal. CONCLUSIONS: The pattern-pulse method offers some advantages for achieving larger mfVEP signals from the central visual field. However, the more peripheral field where it is the most difficult to obtain signals, does not show any benefit.

Evoked Potentials, Visual↗