Search PubMed⌕ Search

Biomedical subjects

Vaegan

Publications and source records attributed to Vaegan.

At least 37 records · Page 2Linked to original sources
PubMed1995

Amplitude scaling relationships of Burian-Allen, gold foil and Dawson, Trick and Litzkow electrodes.

The bipolar Burian-Allen electrode represents the International Society for Clinical Electrophysiology of Vision standard for recording the electroretinogram. With prolonged recording there is a high risk of corneal abrasion from the electrode, while alternatives such as gold foil electrodes or fibers represent less risk. The standards require that alternative electrodes be demonstrated to give equivalent waveform and amplitudes. Electroretinograms were recorded with the bipolar Burian-Allen electrode and four alternative electrode configurations: a unipolar Burian-Allen electrode, a bipolar and monopolar gold foil electrode and a Dawson, Trick and Litzkow fiber electrode with all other recording conditions identical. The results represent a guide for comparisons of electroretinograms between studies using these electrodes. Recordings were made from two subjects for all five electrode configurations and six additional subjects with unipolar gold foil and bipolar gold foil electrodes alone. Flash stimuli over a range of intensities from full intensity to -1.5 log units were used. Recordings were repeated in the one session and on a subsequent session to provide test-retest reliabilities. Significant (p < 0.0001) differences in b-wave amplitude resulting from electrode type and intensity were demonstrated. The unipolar Burian-Allen and unipolar gold foil electrodes produced the greatest amplitude responses. The alternatives to the bipolar Burian-Allen electrode were equally or more reliable. The Dawson, Trick and Litzkow electrode produced lower-amplitude response than the bipolar Burian-Allen electrode but was the only one with significantly greater between-session reliability.

Analysis of Variance↗
PubMed1995

Flash and pattern electroretinogram changes with optic atrophy and glaucoma.

We investigated recent reports that, contrary to common belief, glaucoma can affect flash as well as pattern electroretinograms. An extensive flash and pattern electroretinogram test protocol was used in a large sample of glaucoma patients and age-matched controls who were either visually normal or had other optic nerve diseases. All electroretinogram parameters were reduced and delayed in normal people > 55 years of age. The effect did not increase in later decades. In patients aged < or = 55 years, flash electroretinograms showed mild reductions and delays from optic atrophy alone. Glaucomatous ERG changes were larger and increased with disease severity. Pattern electroretinograms and oscillatory potentials were almost equally reduced in optic atrophy and all degrees of glaucoma. Mildly affected patients > 55 years of age had similar electroretinogram change to age-matched normals in most conditions. Advanced glaucoma patients showed similar differences from normal irrespective of age. This suggests that direct diagnostic application of these results to older patients will be difficult, that the ERG changes in glaucoma cannot be attributed simply to optic atrophy and that additional widespread outer retinal damage occurs in glaucoma.

Age Factors↗
PubMed1994

Effect of kainic acid and NMDA on the pattern electroretinogram, the scotopic threshold response, the oscillatory potentials and the electroretinogram in the urethane anaesthetized cat.

Kainic acid (KA, 12.5-100 nmol) or N-methyl-D-aspartate (NMDA 25-250 nmol) was injected into the vitreous of one eye of urethane anaesthetized cats. Pattern electroretinograms (PERGs) were recorded to transient contrast reversing bars. Scotopic luminance electroretinograms (ERGs) were recorded to blue flashes. All doses of KA reduced the oscillatory potentials (OPs), PERG and focal ERG (FERG). At 50 nmol KA, the b-wave and scoptic threshold response (STR) were normal. At 100 nmol KA, the STR was absent and the b-wave reduced by over 50%. OPs and STRs were reduced in all NMDA injected eyes. NMDA at 25 nmol enhanced the FERG, PERG, and b-wave and high doses (above 150 nmol) reduced them. Light microscopic examination of retinas showed 25 nmol KA only damaged dendrites of ganglion cells. NMDA damage was slight with < 200 nmol. These data show that the cat PERG has a proximal component which is very sensitive to low doses of KA; the PERG and FERG are very similar; the STR and PERG are generated by different structures and that the OPs and the FERG and PERG are all generated close to the ganglion cell layer, proximal to the STR.

Animals↗
PubMed1994

Development of pattern ERG and pattern VEP spatial resolution in kittens with unilateral esotropia.

PURPOSE: To follow the development of strabismic amblyopia longitudinally by comparing mean amplitudes and the visual spatial resolving ability of retinal and cortical pattern responses at various stages of postnatal development in unilateral iatrogenic convergent strabismic kittens. METHODS: Surgery to produce iatrogenic convergent strabismus was performed on 20 kittens at 3 weeks of age; three kittens were used for controls. The monocular transient pattern electroretinogram (PERG) and pattern visual evoked potential (PVEP) were recorded simultaneously on the 23 kittens throughout development. RESULTS: The PVEPs of the strabismic eyes were very reduced at 4 to 5 postnatal weeks (P < 0.01). The reduction increased at 6 to 16 weeks but was even worse at 17 to 30 weeks. The PERG of the squinting eye showed only a slight reduction in the first 4 to 5 weeks of age (P > 0.05), the decrease of responses was significant (P < 0.01) at 6 to 16 weeks and 17 to 30 weeks. At 4 to 8 weeks of age, the PVEP evoked through the unoperated eye in kittens consisted mainly of two positive components of similar amplitude. During development, the slow component decreased in comparison to the fast one, and its peak shifted forward until it merged into the fast (P100) component. CONCLUSIONS: Esotropic amblyopia did affect the PERG and the PVEP in the amblyopic eye, but the effect on the PERG was less severe, had slower onset, and did not continue as long as for the PVEP.

Amblyopia↗
PubMed1991

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.

Action Potentials↗
PubMed1991

High correlation between absolute psychophysical threshold and the scotopic threshold response to the same stimulus.

The scotopic threshold response (STR) is a negative potential to low intensity light recorded from the dark-adapted retina. It reflects inner retinal function. The STR is now recorded routinely as part of our electroretinography protocol. The projected absolute threshold calculated from the amplitude versus intensity function for the STR has been found to correlate well (r = 0.59) with the absolute subjective threshold to the same stimulus. The correlation holds for about 1.5 log units above normal. With further elevation the STR is usually abnormal or absent as b wave threshold is approached. The correlation would have been much greater were it not for this truncated range over which both are recordable. This report includes our findings in 127 patients and examines several disease groups. When the STR had a reduced and abnormal intensity series or was absent, the subjective threshold was elevated in almost all cases (92.2%). The converse relationship also held. When there was a discrepancy, recording problems were usually identified. Since the STR requires difficult, time consuming signal averaging for reliable recording, it may be adequate to record the subjective threshold alone to provide a relatively easily recordable indicator of inner retinal function. Additional STR recording will seldom be warranted.

Dark Adaptation↗
PubMed1990

Fundamental differences between the nonlinearities of pattern and focal electroretinograms.

We directly compared nonlinear kernels of normal human pattern electroretinograms (PERGs) and corresponding localized flash ERGs (FERGs). The FERG was triphasic and resembled an adaptive process because it decayed slowly without changing shape over several kernel orders and interpulse intervals. The PERG was biphasic in the slice nearest the diagonal of the second-order kernel, similar to the FERG in slices farther from this diagonal, and without power in higher-order kernels. The unique PERG features were short-term effects that immediately followed a contrast transition. The appearance-disappearance PERG had a triphasic first-order kernel and a biphasic second-order kernel. The latter was similar to, but half the size of, that for the contrast-reversal PERG. When the first off-diagonal slices of the two PERG second-order kernels were analyzed in detail, we found in both that the first positive peak was larger than the FERG at intermediate spatial frequencies. Both PERG peaks in the slice had a low contrast threshold and were linear with contrast. The three FERG peaks of the corresponding FERG slice had a higher threshold and were saturated with increasing contrast. These observations show that the PERG contains substantial pattern specific nonlinear components and cannot be dismissed as merely the nonlinear subcomponents of the corresponding FERG.

Contrast Sensitivity↗
PubMed1990

The effect of various anaesthetics on the spatial tuning of two major wave peaks in the transient pattern electroretinogram of the cat: evidence for pattern and luminance components.

The main PERG component of the transient contrast reversal pattern electroretinogram (PERG) in cats was a negative wave (3.5 microV average, SD 1.7 microV) peaking at about 130 msec (N130) with a spatial resolution above 5.5 c/deg, close to behavioural estimates. The early positivity (P35) was more variable, smaller and had lower spatial resolution. Different anaesthetic protocols affected both the waveform and the amplitude by spatial frequency functions. Responses of urethane anaesthetised cats were like those reported previously for decerebrate cats or cats paralysed and ventilated with N2O/O2/CO2 (75%/24%/1%). P35 was evoked only by coarse stimuli and N130 amplitude decreased linearly as spatial frequency increased. When the luminance response amplitude, predicted from the optical transfer function of the eye, was subtracted, spatial tuning appeared. An anaesthetic mixture of ketamine hydrochloride and xylazine depressed both P35 and N130 at low spatial frequencies while enhancing them at high frequencies. In paralysed animals ventilated with N2O/O2 (67%/33%) P35 was larger and recordable to 1.6 c/deg. Peak times were reduced and the inter-peak time halved. Other anaesthetics depressed the ERGs. These effects suggest that cats are a good model for studying N130 in isolation or its interaction with P35 and that both PERG peaks include luminance and pattern components.

Anesthetics↗
PubMed1990

Lateral interaction component and local luminance nonlinearities in the human pattern reversal ERG.

Two different mechanisms are presumed to contribute to pattern electroretinograms: non linearities of the local luminance response and nonlinear effects of lateral interactions. Previous attempts to discriminate the two components relied on the theoretical MTF of the optics. In this study, techniques of nonlinear systems analysis are used to extract the two components from the response to pattern reversal of different check sizes. The decomposition is based on the structure of the second order pattern reversal kernels alone. Detailed information about the two mechanisms can be gleaned from the kernel structure. The component properties are compared and discussed.

Contrast Sensitivity↗
PubMed1989

Urethane as a sole general anaesthetic in cats used for electroretinogram studies.

Cats are very sensitive to induction of anaesthesia by urethane. To anaesthetize cats with urethane, 1.0-1.3 g/kg, of freshly prepared urethane is administered intravenously at a rate of 1.92 g/h, while anaesthesia is maintained with 0.5% halothane in a 66%/33% nitrous oxide/carbogen gas mixture. Cats can then be maintained for up to 3 days by intravenous infusion at a rate of 4 ml/h of a 100 ml solution containing 50 IU heparin, 2.4 mg atropine, 4.7 g anhydrous D-glucose, and 240 mg urethane/kg. Using this anaesthetic, excellent electroretinograms can be recorded with no interfering eye movements.

Anesthesia↗
PubMed1987

Normal strobe electroretinograms without pattern electroretinograms in albino rats.

Electroretinograms (ERGs) were obtained from pigmented and albino rats to step luminance changes of an unpatterned TV screen. Surround luminance was increased until the ERG became small and focal. In pigmented rats the ERG at on was positive, earlier, and about twice the amplitude of the negative ERG at off. All pigmented rats had pattern ERGs-0.5 cycles/deg in dark agouti rats and an octave less in hooded rats. Implicit peak times were similar to that of the sum of on plus off focal ERGs from the same animals (85 ms). In albino rats off responses were more like on. The resultant sum was consequently small. Both peak times were similar and did not move earlier than 120 ms as surround luminance increased. Pattern ERGs could not be recorded from albinos at any spatial frequency or surround luminance. These pigmented rat ERGs seem to have two major components. One follows luminance linearly; the other is a fully rectified nonlinearity with about one-third the amplitude. The albino rat retina apparently lacks the latter component. These deficiencies may occur in albinos of other species and be associated with their visual system abnormalities.

Albinism↗
PubMed1987

Effect of pattern luminance profile on the pattern ERG in man and pigeon.

Pattern electroretinograms (PERGs) have been recorded in man and pigeon using phase reversing patterns. Studies were made in both species of the effect of grating spatial frequency, grating profile (sine or square) or the size of the squares of a checkerboard on the amplitude of the responses. The results obtained in the two species were similar. In general, the ratio of the amplitudes of the sine wave:square wave responses is that predicted by the Fourier fundamentals of the pattern, and is thus not determined by changes in local luminance or contrast as it is normally defined. Checks however gave larger responses than sine or square wave profile bars matched to the Fourier fundamental on the diagonal. The results are not explicable in terms of any single stimulus parameter and suggest that the PERG generator has a degree of center/surround organisation similar to retinal ganglion cells. It is however argued that, because of the known physiological properties, generators cannot be unequivocally localised by varying the stimulus or comparing retinal, cortical and perceptual response dynamics.

Animals↗
PubMed1986

Macular electroretinograms and contrast sensitivity as sensitive detectors of early maculopathy.

Eighteen patients with early maculopathies of various etiologies were tested with pattern and focal electroretinograms (macular ERGs), with high (400 cd/M2) and moderate (40 cd/M2) stimulus intensities and a four-alternative forced choice (4AFC) contrast sensitivity test in addition to intensive clinical examinations. High spatial frequency contrast sensitivity loss on the 4AFC test was the most striking and consistent feature of all cases. The only eyes not outside normal contrast sensitivity limits were three in which diagnosis was uncertain and the patients had not recognized any problem, including two marginal solar burns. Maculopathy also substantially reduced macular ERG amplitudes. Criterion scores on these tests separated patients from normals more effectively than other noninvasive procedures and only missed one eye detected by contrast sensitivity. Latencies were affected but the delays were of no clinical significance in the individual case. Stimulus intensity was not critical. The results indicate that contrast sensitivity testing and macular ERGs are very reliable indices of central visual dysfunction at a stage when visible macular changes are too subtle for confident diagnosis. Contrast sensitivity has appeal because of its reliability, objectivity, simplicity, and noninvasive nature. It is equally applicable to children and adults. Pattern and focal ERGs can establish that the visual deficit has a retinal origin and can provide the most reliable objective confirmation.

Electroretinography↗
PubMed1984

Macular electroretinograms: their accuracy, specificity and implementation for clinical use.

The pattern and the focal electroretinogram (ERG) are both non-invasive, electrophysiological responses recorded from circumscribed retinal areas and are most easily recorded from the macula. This paper describes how our department has incorporated these tests into our clinical protocol, shows how the recording technique and the method of electrode construction may be improved, and describes the normal limits of the macular responses we obtain. The ERG signal-noise ratio we obtained was better than that of the binocular visual evoked potentials (VEPs) recorded simultaneously. Pattern and focal ERGs, using improved methods of recording, show promise of being a valuable addition to the clinical investigation of subtle maculopathies and some forms of optic nerve dysfunction. Three illustrative cases are described. The first demonstrates normal macular ERG responses with abnormal Ganzfeld ERGs due to peripheral retinal damage. The second reveals differential pattern ERG reduction with normal focal ERG in recent optic neuritis. The third case demonstrates reversible simultaneous loss of Ganzfeld ERGs and macular ERGs in vitamin A deficiency.

Adult↗
PubMed1983

Vitreal and intraretinal responses to contrast reversing patterns in the pigeon eye.

The pattern electroretinogram (PERG) has been recorded vitreally and intraretinally in the pigeon eye. The amplitude of the PERG increases monotonically as pattern contrast is increased, with saturation at high levels. The PERG of the central yellow field has band-pass spatial tuning, with a high frequency cut-off at 8 c/deg. Time-to-peak is shortest at low spatial frequencies. Both PERG and local b-wave are small and positive-going close to the retinal surface, and large and negative-going in the inner nuclear layer. The PERG and b-wave show qualitatively similar depth profiles.

Animals↗
PubMed1983

Electroretinograms evoked in man by local uniform or patterned stimulation.

1. We have recorded electroretinograms (e.r.g.s) in normal subjects. Television monitors were used as stimulators. The screens were surrounded by brightly lit white reflecting surfaces to ensure that the responses were developed by defined retinal areas.2. Various types of stimuli were employed. Either (i) a pattern of dark and bright squares was reversed, to evoke a pattern e.r.g. (p.e.r.g.), (ii) the luminance of the uniform screen was abruptly increased and decreased to evoke a focal on-off e.r.g. or (iii) a pattern was made to appear and disappear from a uniform background. In each of these cases, the sequence of changes of luminance at any one point could be made identical. The aim of the experiments was to determine whether the e.r.g. was modified by the spatial organization of the stimulus.3. In other experiments a colour monitor was used so that (i) a red-green flicker, (ii) red-green pattern reversal or (iii) the appearance of a red-green pattern from a yellow background could be used as a stimulus. The responses were caused by the changes in hue, since all the colours were equiluminant.4. With black and white patterns the p.e.r.g. peaks 5 msec later than the focal on-off e.r.g. The largest response is produced by squares of 0.5-1 degrees subtense.5. The ratio of the amplitudes of the p.e.r.g. to the focal on-off response is largest for stimuli confined to the macula and smallest for those projected onto peripheral retina.6. The amplitude of responses to chequerboard reversing patterns increases nearly linearly with contrast up to the maximum contrast available.7. When patterns appear or disappear from a uniform screen, and there is an associated change in the quantity of light entering the eye, recognizable b-waves occur when the average screen luminance increases, independently of whether pattern contrast increases (appearance) or decreases (disappearance).8. When a pattern appears or disappears with no change in luminance, e.r.g.s are evoked at both ;on' and ;off'. The disappearance of the dark parts of the pattern causes the largest logarithmic increase in local retinal illumination. For patterns of square size > 4 degrees the pattern disappearance response is larger than for pattern appearance. As the square size is reduced, the appearance response grows and the disappearance response decreases. The e.r.g.s evoked by the appropriate changes in luminance of a uniform screen are no longer the same as those caused by the appearance and disappearance of the pattern.9. The responses to change of hue are 70% as large as those produced by black and white patterns. The same ratio occurs for pattern and focal on-off e.r.g.s.10. When coloured patterns appear from and disappear to a uniform field, the e.r.g.s. evoked are very similar to those recorded when the appropriate changes of hue occur in a uniform field. This result is quite different to the findings for black and white patterns (see 8 above).11. The results suggest that it is the change in local adaptation caused by the black and white patterns which modifies the e.r.g. and not the presence of contrasting borders.

Color Perception↗
PubMed1983

Comparison of the focal electroretinogram and the pattern electroretinogram in the pigeon.

A comparison has been made, under focal conditions, of the electroretinogram (e.r.g.) and the pattern electroretinogram (p.e.r.g.) of the central yellow field of the pigeon retina, using vitreal and intraretinal recordings. The sum of the on and off e.r.g. is of shorter time-to-peak and of smaller amplitude than the p.e.r.g. elicited by a grating of 1 cycle/degree, as predicted by the spatial tuning of the p.e.r.g. Depth profiles were made to compare with p.e.r.g. and the sum of the on and off e.r.g. The two responses co-vary in terms of amplitude, time-to-peak and form. This suggests that the p.e.r.g. has a conventional electroretinographic location.

Animals↗