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Biomedical subjects

G W Weinstein

Publications and source records attributed to G W Weinstein.

At least 19 recordsLinked to original sources
PubMed1992

Comparison of preoperative 10-Hz visual evoked potentials to contrast sensitivity and visual acuity after cataract extraction.

Cataract patients whose surgical outcomes were in question were referred for testing by visual evoked potentials, elicited through closed eyelids by a luminance stimulus (flash) that appeared 10 times per second. Visual evoked potentials were rated as normal (predicted acuity of 20/50 or better) or abnormal (predicted acuity of 20/60 or worse). Postoperative Arden and Optronix contrast sensitivities and visual acuities were determined in 37 patients who had no intraoperative or early postoperative complications. Arden grating scores of less than 100 were rated as normal. The optimal and cutoff spatial frequency values were determined for the Optronix scores. Optimal and cutoff values of greater or equal to 1 c/deg and 12 c/deg, respectively, were rated as normal. Visual acuities were considered normal at 20/50 or better. Preoperative visual evoked potentials were quantitatively compared to the postoperative contrast sensitivities and visual acuities by 2 x 2 contingency tables. The accuracy of prediction was 79% for the visual acuities, 62% for the Optronix optimal values, 70% for the Optronix cutoff values and 62% for the Arden gratings.

Aged↗
PubMed1991

Visually evoked potentials and electroretinography in neurologic evaluation.

Electrophysiologic testing of the visual system requires primarily the ERG and the VEP. The flash electroretinogram provides information about the outer retina only. The pattern electroretinogram is derived from both the outer retina and the innermost retinal layers including the ganglion cell layer. The VEP is based on electrical information recorded from the visual cortex in response to stimulation of the retina. Thus, the integrity of the entire visual pathway can be tested. Localizing ability of the VEP is limited. Since the visual cortex is heavily weighted by representation of the central retina, peripheral lesions, including those producing peripheral visual field abnormalities that do not impinge upon central fixation, may produce relatively little disturbance of the VEP. As with most tests, electrophysiologic studies of the visual system must be placed in context of the entire examination, including the patient's history and neurologic and especially neuro-ophthalmologic evaluation. Electrophysiologic testing has three main uses in neurology. Pattern-reversal VEPs may be useful in detecting hidden visual loss in multiple sclerosis; VEPs and ERGs can distinguish function from organic visual loss; and VEPs and ERGs can be useful in the diagnosis of visual loss in nonverbal patients, especially in children.

Electroretinography↗
PubMed1990

Visual function deficits in glaucoma. Electroretinogram pattern and luminance nonlinearities.

The pattern electroretinogram is abnormal in glaucoma. Part of the pattern electroretinogram may be attributed to the summation of responses to luminance increases and decreases (nonlinear luminance responses). We conducted a study to investigate the effect of glaucoma on the pattern electroretinogram component waves and to determine if the flicker electroretinogram nonlinear components are abnormal in glaucoma. We tested 35 subjects in two replications of four conditions: 10- and 20-Hz flicker, and 4- and 10-Hz pattern reversal. Only the even harmonics were recorded. The patients with glaucoma had reduced electroretinogram amplitudes for all measures relative to the normal subjects. Electroretinogram amplitudes of those suspected of having glaucoma were intermediate. The greatest amplitude reductions were for the 10-Hz flicker electroretinogram and the 4-Hz pattern electroretinogram. These results confirm pattern electroretinogram abnormalities and reveal flicker electroretinogram abnormalities in glaucoma.

Adult↗
PubMed1989

Electrophysiological discrimination between retinal and optic nerve disorders.

In this study we show how the Pattern ERG (PERG) can be used to distinguish between optic nerve and retinal disease. Records from eyes with RBN and delayed visual evoked responses are compared with those recorded from the normal fellow eyes. In optic nerve disease there is a selective reduction of the later negative component of the response. PERG's were also recorded from patients with mild diabetic retinopathy. These were divided into three groups on the basis of the delay in their Visual Evoked Potential (VEP). The amplitude of both positive and negative components fall with increasing severity of the disease thus showing that the abnormally long delau in VEP found in some cases is due to retinal disease rather than optic nerve disease.

Adolescent↗
PubMed1988

The pattern electroretinogram (PERG) in ocular hypertension and glaucoma.

Studies of normal subjects and of patients with optic nerve disorders suggest that one of the components of the pattern electroretinogram (PERG), the second negative wave, is related to optic nerve function and appears to be diminished even when the condition is relatively mild, with little alteration of visual acuity. It is known that significant loss of nerve fibers may occur prior to the development of visual field loss. We have investigated the PERGs of a group of subjects with early glaucoma and ocular hypertension, comparing them with normal subjects, and have found a selective reduction in the second negative wave in patients with evidence of optic nerve dysfunction. The PERG may prove helpful in discriminating those patients with ocular hypertension who are destined to develop visual field loss unless medical or surgical therapy were to be employed.

Adolescent↗
PubMed1988

Color vision defects in ocular hypertension and glaucoma. Quantification with a computer-driven color television system.

In order to detect early defects of color vision caused by increased intraocular pressure, a computer graphics device and color monitor system were used to measure color contrast sensitivity. The system determines the threshold chrominance of a colored grating in which there is no change in luminance. The study included 13 control subjects aged 10 to 57 years and 19 patients with ocular hypertension or glaucoma aged 20 to 58 years. In the 13 eyes with visual field loss, color contrast sensitivity was profoundly reduced when the grating colors fell on a tritan color confusion line. In the eyes without visual field loss, tritan color contrast sensitivity was reduced to an average level considerably below the extreme limits of the control group. These results were compared with those of other color vision tests and diagnostic criteria for glaucoma. The findings suggest that among the tests used, color contrast sensitivity testing was able to discriminate most effectively between patients who had retinal damage and the normal population.

Color Perception Tests↗
PubMed1988

Preoperative prediction of postoperative visual acuity in patients with cataracts: a quantitative review.

Many tests of visual function have been proposed as means of preoperatively evaluating cataract patients' surgical outcomes. It is impractical to compare all of these tests simultaneously on the same group of patients. Quantitative reviews apply quantitative methods to comparisons across studies. We compared the results of 52 reports in which cataract patients' postoperative acuity was predicted by means of visually evoked potential, laser interferometry, or projection tests (potential acuity meters-pinhole). The results of each study were summarized in a 2 x 2 contingency table. Summary statistics were compared by means of analysis of variance and post hoc tests. Despite difficulties in metaanalysis, we found the visually evoked potential a better predictor with dense opacities. We recommend standardization in a quest for more precise predictions of postoperative visual acuity.

Cataract Extraction↗
PubMed1988

Prediction of post cataract extraction visual acuity: 10 Hz visually evoked potentials.

Cataract patients suspected of having disease that might interfere with good postoperative visual function were evaluated by eliciting monocular steady-state luminance visual evoked potentials (VEPs) with closed eyes at a stimulus rate of 10 flashes/sec. VEPs were rated as either normal or abnormal. Patients with normal VEPs were predicted to have visual acuity of 6/15 (20/50) or better. Patients with abnormal VEPs were predicted to have acuities of 6/18 (20/60) or worse. Postoperative acuities were determined for all patients who underwent surgery and who had no intraoperative or early postoperative complications. The predicted and observed postoperative acuities were quantitatively compared for the 59 patients who met these criteria, using a 2 X 2 contingency table. The chi-square was significant (p less than .001). The overall accuracy of prediction was 80%. Accuracy of the predictions for patients with preoperative acuities of 6/60 (20/200) or better was compared with the accuracy of the predictions for those with preoperative acuities of 60/120 (20/400) or worse. There was no significant difference (p greater than 0.10).

Cataract Extraction↗
PubMed1987

10-Hz flash visual evoked potentials predict post-cataract extraction visual acuity.

Cataract patients suspected of having disease which might interfere with good postoperative visual function were referred for evaluation. Monocular steady-state luminance visual evoked potentials (VEPs) were elicited with closed eyes at a stimulus rate of 10 flashes/sec. VEPs were rated as either normal or abnormal. Patients with normal VEPs were predicted to have an acuity of 6/15 (20/50) or better. Patients with abnormal VEPs were predicted to have acuities of 6/18 (20/60) or worse. Postoperative acuities were determined for all patients who underwent surgery and who had no intraoperative or early postoperative complications. The association of preoperative VEPs and observed postoperative acuities were quantitatively compared by a 2 x 2 contingency table for the 59 eyes which met these criteria. The chi-square was significant (p less than 0.001). The overall accuracy of prediction was 76%. Accuracy was 80% for patients with a preoperative acuity of 6/60 (20/200) or better and 75% for those whose postoperative acuity was 6/120 (20/400) or worse. This difference was not statistically significant.

Cataract Extraction↗
PubMed1987

A new surgical technique for managing sunset syndrome.

Although inferior subluxation of a posterior chamber intraocular lens following extracapsular cataract extraction (sunset syndrome) occurs infrequently, it is difficult to manage. We describe a new, relatively simple technique for managing subluxated posterior chamber intraocular lenses, in which the lens implant is "dialed" forward into the anterior chamber, bringing its haptics to rest in the chamber angle.

Adult↗