Correlation between ERG oscillatory potential and psychophysical contrast sensitivity in diabetes

Correlation between the electroretinographic oscillatory potential and psychophysical contrast sensitivity function was examined in patients with different stages of diabetic retinopathy. Contrast sensitivity function was evaluated by Arden's grating test. The amplitude of the oscillatory potential was significantly reduced in cases with low contrast sensitivity (P less than 0.01).     

Evoked responses to sinusoidal gratings in the pigeon optic tectum

Tectal evoked potentials (TEPs) in response to sinusoidal gratings of different contrast, spatial and temporal frequency have been recorded from the tectal surface of the pigeon. Responses have been digitally filtered in order to isolate transient oscillatory (fast) potentials (50-150 Hz), transient slow potentials (1-50 Hz), and the steady-state second-harmonic component (16.6 Hz). Transient slow potentials, as well as the steady-state second-harmonic component, are band-pass spatially tuned with a maximum at 0.5 cycles/deg and attenuation at higher and lower spatial frequencies. The high spatial frequency cutoff is 4-5 cycles/deg. Both transient slow potentials and the steady-state second-harmonic component increase in amplitude as a function of log contrast and saturate at about 20% contrast. The contrast sensitivity, as determined by extrapolating TEP amplitude to 0 V is 0.1-0.2%. These characteristics of spatial-frequency selectivity and contrast sensitivity are similar to those reported for single tectal cells. Unlike slow potentials, oscillatory potentials are not band-pass spatially tuned. In addition, their contrast response function does not saturate at moderate contrast. These differences suggest that tectal evoked slow and fast potentials reflect the activity of different neuronal mechanisms.     

Dose-dependent effects of 6-hydroxy dopamine on deprivation myopia, electroretinograms, and dopaminergic amacrine cells in chickens.

We found that a single intravitreal injection of 6-hydroxy dopamine (6-OHDA) is highly efficient in blocking the development of deprivation-induced myopia in young chickens. To investigate the effects of 6-OHDA on retinal function, we studied electroretinograms (ERGs) in chickens aged 15-25 days, 4 days subsequent to the injection. Both spectral sensitivity and oscillatory potentials were tested. In addition, a histological examination was performed of dopaminergic amacrine cells labeled by a monoclonal antibody against tyrosine hydroxylase. We found that, at doses of 6-OHDA sufficient to suppress deprivation myopia entirely, no effect could be detected on either the ERGs or on the density and appearance of dopaminergic amacrine cells. For higher doses, spectral sensitivity and the number of dopaminergic amacrine cells declined gradually. In contrast, as doses increased, oscillatory potentials 1 and 2 grew in amplitude only to decline at the highest doses. The results indicate that (1) development of deprivation myopia requires normal retinal function and that (2) slight changes in the gains of dopaminergic pathways are sufficient to block the development of deprivation myopia.     

The effect of spatial frequency and contrast on the latency in the visual evoked potential

The latency in the visual evoked potential was measured at spatial frequencies of 2–12 c/deg in 10 subjects. The contrast levels of the sinuosoidal grating patterns were set at 1.5, 1.75, 2.0, 2.25, 2.5, 2.75 and 3.0 log units above each subject's contrast sensitivity threshold. Two factors were shown to influence the latency: suprathreshold contrast and, to a lesser extent, spatial frequency. The visual evoked potential latencies at contrast sensitivity threshold were extrapolated. These threshold latencies showed considerable variation with spatial frequency and between subjects. Therefore, the visual evoked potential latency cannot be considered a useful tool for estimating the contrast sensitivity function.     

Aging effects on vernier hyperacuity: a function of oscillation rate but not target contrast.

PURPOSE: Most previous studies have shown static vernier acuity for high-contrast targets to be largely unaffected by aging; those examining adult age differences on oscillatory displacement thresholds have consistently reported marked age deficits. The goals of this study were to (1) measure the age deficit on oscillatory discrimination beyond that attributable to any change in spatial discrimination by using the same target configuration for both task types and (2) determine whether an age-related change in the contrast response of the visual system contributes to age differences on static or oscillatory discrimination. METHODS: The displacement thresholds of young and old observers for a vernier task configuration were determined at two target contrast levels (0.08 and 0.64) for static and oscillating targets (2 and 6 Hz) RESULTS: No age differences were seen on static displacement thresholds at either high or low contrast. A marked age deficit that emerged when oscillation was increased was unrelated to target contrast or observer contrast sensitivity. CONCLUSIONS: Age-related declines in oscillatory discrimination beyond those attributable to spatial discrimination do not appear to be attributable to optical factors nor to a decline in the contrast response of the senescent visual system. These findings are discussed in terms of a functional decline in the magnocellular pathway, or "neural entropy," possibly due to random cell loss.     

Diminished spatial summation contributes to the age deficit in the discrimination of low-contrast vernier oscillation.

PURPOSE: This study sought to determine whether a decline in spatial summation contributes to age-related deficits on oscillatory displacement thresholds (ODT's). A secondary goal was to evaluate the extent of spatial summation on a dynamic version of vernier hyperacuity. METHODS: The ODT's and contrast sensitivity functions (CSF's) of optimally corrected young and old observers were compared as a function of vernier target length (4, 8, or 32 min), contrast level (5 or 30%), and oscillation rate (2 or 8 Hz). RESULTS: Age deficits on ODT's were related directly to rate of oscillation, but not target contrast. No age difference was seen in ODT's for short low-contrast targets; as target length increased thresholds improved more rapidly for young than old observers; this pattern was reversed at high contrast. ODT's were related strongly and consistently to contrast sensitivity for old but not young observers. CONCLUSIONS: Diminished spatial summation appears to contribute to the aging visual system's loss of temporal discrimination for low contrast oscillating targets. Spatial summation contributes more importantly to the displacement discrimination of oscillating than to static vernier targets.     

Visual function in multiple sclerosis

126 patients with multiple sclerosis and normal visual acuity were submitted to a battery of tests of visual function. The investigation included visual evoked potential, contrast sensitivity by three methods, and a segment of the Farnsworth-Munsell 100 Hue test.22 of the patients gave a history of unilateral acute optic neuritis and in these the abnormalities were greater in degree.Contrast sensitivity emerged as the most useful test and was abnormal in 92.2% of eyes. Visual evoked potential was delayed in 35.6% and colour vision was abnormal in less than a third.In general, contrast sensitivity was depressed at all frequencies and most of the abnormalities could be identified by testing at a single frequency of 4 cycles/degree.Abbreviations CD clinically definite - CS contrast sensitivity - CP clinically probable - MS multiple sclerosis - VEP visual evoked potential     

Tolerability of levocabastine eye drops

We used an oscillatory potential power method (a measure of the summed oscillatory potential activity) based on fast-Fourier transform analysis to study the oscillatory potentials in early diabetic retinopathy. The method was used in 29 diabetic patients with no ophthalmoscopically visible diabetic retinopathy, 29 diabetic patients with early signs only and 27 control subjects. The reduction in oscillatory potential power was compared with the reduction in the second and third oscillatory potential amplitudes and increase in implicit time in the diabetic patients. The amplitude of the second oscillatory potential was slightly more resistant to diabetic retinopathy than was the amplitude of the third oscillatory potential. Because the oscillatory potentials were detected by means of a high-resolution technique, their implicit times seem to be as discriminating as the oscillatory potential power in the detection of early diabetic retinopathy.     

OSCILLATORY MOVEMENT DISPLACEMENT THRESHOLDS: RESISTANCE TO OPTICAL IMAGE DEGRADATION

Vernier acuity, under optimal conditions, appears remarkably resistant to image degradation. This characteristic has been used to assess neural function in cataract patients who exhibit poor spatial resolution. Conventional resolution tests fail to differentiate between neural and optical causes of visual loss. The oscillatory movement displacement threshold--the smallest amplitude of oscillation which gives rise to the perception of movement--provides an alternative hyperacuity test. This may offer advantages over vernier acuity. The effect of image defocus upon displacement thresholds for a sinusoidal contrast grating of spatial frequency 2 c deg-1 was investigated for high (15 Hz) and low (2 Hz) oscillation frequencies. With visible stationary references, subjects were more sensitive to oscillation frequencies of 2 Hz than to 15 Hz (F 1,9 = 33.34, p less than 0.005) whilst blur of up to 2 dioptres had no significant effect (F3,27 = 1.73, p greater than 0.1). Simulating media opacities by spatial degradation affected both grating acuity and contrast sensitivity functions, whilst displacement thresholds remained largely unaffected. Results suggest that oscillatory movement displacement thresholds may be of value in assessing ocular neural dysfunction in the presence of media opacities.     

Selective reduction of oscillatory potentials and pattern electroretinograms after retinal ganglion cell damage by disease in humans or by kainic acid toxicity in cats

We recorded pattern electroretinograms, scotopic threshold responses, oscillatory potentials and ganzfeld flash electroretinograms in patients with glaucoma or other optic nerve diseases and in cats with inner retinal damage caused by intravitreal injections of kainic acid. In both studies, the scotopic b-wave and the scotopic threshold responses were normal but the oscillatory potentials and pattern electroretinograms were not. The photopic b-wave was also often reduced in patients with scotopic oscillatory potential reduction, and the reduction was proportionate to the oscillatory potential change. Oscillatory potentials were as frequently reduced as pattern electroretinograms in both patient groups, and in the few cases where only one response was reduced, there was no bias toward either measure. In cats, the effects of intravitreal injection of various doses of kainic acid on the retina were evaluated electrophysiologically, and structural damage was assessed histologically. After 25 nmol of kainic acid, the pattern electroretinograms and oscillatory potentials were reduced but neither the b-waves nor the scotopic threshold responses, were affected. Histologic studies of retinas after this dose showed swollen dendrites that were restricted to the outer part (off-sublamina) of the inner plexiform layer. Serial semithin sections indicated that most, if not all, of the swelling was confined to dendrites of large ganglion cells. Our results indicate that the size and sensitivity of the oscillatory potential response may have a role in the diagnosis and management of early glaucoma and optic nerve disease, and that the photopic electroretinogram may give similar information.     

老年性白内障术后早期的对比敏感度变化

目的：探讨老年性白内障术后早期的对比敏感度（CSF）变化。方法：对行超声乳化白内障吸附联合折叠型IOL植入手术的老年性白内障术后患者87例（95眼），早期应用对比敏感度测试卡（FACT）进行CSF测定。结果：以术后矫正视力为标准，分成A（0．8－），B（0．4－0．6），C（0．2－0．3）三组。A（0．8－）组患者CSF曲线大多在正常范围区域；B（0．4－0．6）组患者CSF曲线主要为中，高空间频率异常，尤其在高频区，如：D和E排； C（0．2－0．3）组患者CSF曲线随着视力下降，中、高、低空间频率异常，以致个人的对比值曲线落在正常范围之下，结论：老年性白内障术后早期的CSF变化与视力因素明显相关，与植入的折叠型IOL无关。     

High visual contrast sensitivity in the young human infant

The visual evoked potential (VEP) was used to estimate photopic contrast sensitivity of 10-week-old infants over a wide range of spatial frequencies including the acuity limit. Adult and infant VEP contrast sensitivity was compared for sinusoidal luminance gratings reversed in contrast at 6 Hz. Space-average luminance was 220 cd/m2. Grating contrast was swept from well below the measured thresholds to well above them in 10 sec trials. Contrast thresholds were defined as the zero voltage intercept of the initial rising portion of the VEP amplitude versus contrast function. The VEP contrast sensitivity of 10-week-old infants was close to that of the adults for spatial frequencies below about 1 cycle (c)/deg.     

Non-simulator-based techniques in teaching direct ophthalmoscopy for medical students: a systematic review

Non-simulator-based examination methods of the fundal examination have shown to be cost-effective.We reviewed different non-simulator-based direct fundoscopy examination methods used in undergraduate curricula and their outcomes.PubMed(MEDLINE) and Cochrane Database of Systematic Reviews were searched using standard Medical Subject Heading(MeSH) terms ophthalmoscopy,medical education,undergraduate medical education,medical student,educational assessment and learning.The search included publications until 28^thFebruary 2019.We obtained 34 articles after screening abstracts;of them,12 articles were included in the qualitative synthesis.The studies were comprised of diverse teaching methods which included fundal photograph matching with corresponding eye,continuous education using community-based eye clinics,formal instructions and demonstrations prior to skills training,ophthalmoscopy skills practice using eye pathologies,teaching versus conventional ophthalmoscopy and group-based teaching.We concluded that non-simulator-based techniques such as use of fundal photograph matching of an eye of a volunteer,introduction to eye pathologies,smaller student groups and formal instructions with video demonstrations prior to skills training were highly effective in teaching direct ophthalmoscopy for undergraduate medical students.     

Assessment of contrast sensitivity. Part II: The relationship between objective lens opacity and laser interferometric contrast sensitivity in the cataract patient

The laser interferometer can effectively bypass the optics of the eye and measure retinal function in patients with immature cataracts. However, it is not known how much laser interferometric measurements are impaired by cataract density. In this study we compared objective lens opacity using the IntraOptics opacity lensmeter with contrast sensitivity (CS) measured by a Randwal He-Ne laser interferometer. Comparison of lens opacity with CS in the cataract population revealed an inverse linear relationship between objective lens opacity and retinal contrast sensitivity. Separation by cataract type showed correlation coefficients as high as -0.91 for nuclear sclerotic predominant cataracts and as low as no significant correlation for posterior subcapsular predominant cataracts. Comparisons of before and after implantation surgery contrast sensitivities (as measured by the laser interferometer) with preoperative lens opacities (as measured by the IntraOptics opacity lensmeter) quantified the extent to which laser interferometric measurements underestimated potential retinal function. We found that for all cataracts, other than posterior subcapsular predominant cataracts, potential contrast sensitivity (in decibels) was underestimated by about 0.2 to 0.3 times the opacity measured by this technique.     

Oscillatory potentials of the electroretinogram in patients with unilateral optic atrophy

The oscillatory potentials (OP) of the electroretinogram (ERG) of 26 patients with unilateral optic atrophy were studied. The severity of optic atrophy was graded according to clinical findings. Three groups of increasing interocular difference in contrast sensitivity and changes of the visual evoked cortical potentials were obtained. No significant difference between the amplitudes or peak latencies of the individual oscillatory peaks or summed amplitudes of the OPs between the affected and control fellows eyes in any group was found. Neither was there any significant interocular differences regarding the a- and b-waves. These findings show that there does not seem to be any major contribution of ganglion cell activity in the generation of the OPs. Secondly, the results do not support the existence of centrifugal optic nerve innervation of the human retina.     

Abnormal waveform of the human pattern VEP: contribution from gamma oscillatory components

PURPOSE: Stimulus-related oscillatory activity above approximately 20 Hz (gamma band) is observed in the firing rate and membrane or field potentials of neurons in the visual cortex of cat and monkey. Cortical mass responses in the same frequency range are evoked in humans by contrast stimulation and proved (partly) independent of conventional VEPs. Visual evoked responses (pattern VEPs) with abnormal waveform (quasi-sinusoidal or with bifid wave P100) are reportedly common in diseases affecting the visual pathways (e.g., multiple sclerosis). Contributions of gamma activity to the distorted VEP waveform are possible if the mechanisms of generation are differentially affected by brain disorders. This hypothesis was investigated in patients with documented impairment of the visual system. METHODS: VEPs and oscillatory responses to contrast stimulation (central 9 degrees of visual field; 1.3 to 5.0 cyc/deg; 80% contrast; reversal at 2.13 Hz) were recorded in 765 patients referred for standard visual testing and frequency analyzed. Controls were 40 healthy volunteers. The stimulus conditions and recording procedures replicated previous normative studies on the human oscillatory response. RESULTS: Conventional VEPs were replaced by oscillatory responses comparable to those of controls in the unfiltered recordings of 9.8% of examined patients (with postchiasmatic disorders in 59.9% of cases). Signal amplitude in the frequency interval of the VEPs (below approximately 19 Hz) was significantly lower in the frequency spectra of patients than of controls but did not differ in the frequency range above 20 Hz, reflecting the oscillatory response. CONCLUSIONS: The human gamma oscillatory response mediating in cortical visual information processing further proved independent of the VEPs. It can contribute to VEP waveform distortion, and its observation in substitution of VEPs should be regarded as an indication of impaired visual pathway function.     

The contrast sensitivity function and childhood amblyopia

We measured contrast sensitivity function and visual acuity in both eyes of strabismic and anisometropic amblyopic patients. There was a linear relationship between contrast sensitivity function and visual acuity in the amblyopic eye. As visual acuity decreased, the contrast sensitivity function decreased along the contrast sensitivity axis, and peak sensitivity shifted to lower spatial frequencies. After patching therapy, when visual acuity reached 20/20 in each eye, suggesting that the amblyopia was cured, there continued to be statistically significant difference in the contrast sensitivity functions between the eyes. The contrast sensitivity function from the previously amblyopic eye was depressed compared to the nonamblyopic eye. A comparison between patients with strabismic and anisometropic amblyopia showed that, when matched for visual acuity, the contrast sensitivity functions were similar for both the nonamblyopic and amblyopic eyes. However, a large difference was found between the amblyopic and nonamblyopic eyes of each group.     

Microelectrode depth study of the electroretinographic oscillatory potentials in the frog retina

The depth profile of the electroretinographic oscillatory potentials was studied in the isolated frog retina. The intraretinal electrode was introduced from the receptor side, and the reference electrode was placed on the vitreal side. The electroretinogram, recorded either transretinally or with the electrode tip in the receptor layer, showed 4 to 10 oscillatory potential wavelets. As the electrode was advanced proximally, the wavelets disappeared as a function of retinal depth. The wavelets with longer peak latencies disappeared earlier, and only the first one or two wavelets could be identified when the electrode was in the inner plexiform layer. These findings indicate that the oscillatory potentials are generated between the inner and outer plexiform layers and that the earlier wavelets originate in the more proximal retina. The results are consistent with the notion that the oscillatory potentials are generated by synaptic feedback circuits.     

非球面晶状体与传统球面晶状体植入术后对比敏感度的研究

目的:比较白内障术后早期非球面晶状体与传统球面晶状体植入术后功能视力.方法:白内障患者共50例,随机分成两组,一组患者植入以Acrysof IQ(Alcon)为代表的非球面晶状体,共23例 23眼;一组植入以AR40e(AMO)为代表的传统球面晶状体,共27例27眼.于术后1mo用CSV-1000E对比敏感度测试仪(由VECTOR VISION 公司提供)进行对比敏感度测定.结果:以Acrysof IQ (Alcon)为代表的非球面晶状体在6.12.18cpd时较以AR40e(AMO)为代表的传统球面晶状体能显著的提高患者对比敏感度.结论:以Acrysof IQ(Alcon)为代表的非球面晶状体可提高患者的功能视力     

Recording the oscillatory potentials of the electroretinogram with the DTL electrode

Suprathreshold photopic oscillatory potentials recorded with a DTL electrode were compared to those obtained with a Lovac corneal electrode. The overall oscillatory potential response (sum of oscillatory potentials) recorded with the DTL electrode was half of that obtained with the Lovac electrode. However, there was no evidence of a selective attenuation (or amplification) of any given oscillatory potential with the DTL electrode. Similarly, the oscillatory potential relative amplitude ratios and the peak times of the oscillatory potentials were identical for both electrodes. Our findings clearly indicate that the DTL electrode is adequate to record the high-frequency oscillatory potentials. Given the low cost and ease of use, as well as the disposable nature of the DTL electrode, we believe that electroretinographic specialists should seriously consider a wider utilization.