Biomedical subjects

B Falsini

Publications and source records attributed to B Falsini.

At least 55 records · Page 3Linked to original sources

PubMed1993

The second harmonic of the electroretinogram to sinusoidal flicker: spatiotemporal properties and clinical application.

The photopic, focal electroretinogram elicited by sinusoidal modulation (8 Hz) of the luminance of a uniform field (flicker electroretinogram) presented in the macular region contains two main components: the first harmonic at the stimulus frequency (1F) and the second harmonic at twice the stimulus frequency (2F). Physiologic and clinical studies have demonstrated that the 1F originates in the outer retina, whereas the 2F has multiple postreceptoral sources, with a contribution of the innermost retina. The 2F, unlike 1F, is selectively altered in amplitude and phase in the early stages of optic neuritis and glaucoma. Both 1F and 2F are altered in maculopathies. An additional property of the focal electroretinogram is that the 2F, unlike 1F, has a very limited summation area (i.e., the function relating 2F amplitude with stimulus area is saturated for central stimulus sizes of the order of the macular region). This overrepresentation of the macular activity suggests that the 2F component of the flicker electroretinogram may provide a specific macular test even for full-field stimuli presented through opacities of the optical media.

Cataract↗

PubMed1992

Macular electroretinograms to flicker and pattern stimulation in lamellar macular holes.

Steady-state macular (9 degrees x 9 degrees) electroretinograms in response to either sinusoidal flicker (focal electroretinogram) or counterphased sinusoidal gratings (pattern electroretinogram) were recorded in 14 patients with inner lamellar macular holes, in 4 patients with full-thickness macular holes and in 14 age-matched controls. Fourier analysis of focal and pattern electroretinograms yielded three main components: a first and a second harmonic to flicker, and a second harmonic to pattern. Recent evidence indicates that the first harmonic to flicker is of receptoral origin, whereas the flicker and pattern second harmonics represent, at least in part, the activity of different generators in the inner retina. When compared to controls, patients with inner lamellar holes showed significant amplitude reduction and phase delay for both flicker and pattern second harmonics, but not for the flicker first harmonic. Patients with full-thickness holes showed significant amplitude reduction also for the flicker first harmonic. These results indicate a prevalent functional involvement of the inner retina in lamellar macular holes, which can be clinically detected by evaluating focal and pattern electroretinogram second harmonics.

Adult↗

PubMed1992

Pattern electroretinogram as a function of spatial frequency after retrobulbar optic neuritis.

Steady-state (8-Hz) pattern electroretinograms in response to counterphased sinusoidal gratings of variable spatial frequency (0.6-4.8 c/deg) were recorded in 17 patients who had had retrobulbar optic neuritis in one or both eyes (23 eyes with a clinical history of optic neuritis) and in 21 age-matched normal subjects. Amplitude and phase of the Fourier-analyzed pattern electroretinogram second harmonic were measured. The mean pattern electroretinogram amplitude of patients was significantly reduced compared with that of controls. Amplitude reductions were more marked at intermediate (1-1.4 c/deg) than at lower or higher spatial frequencies. Therefore, the average amplitude versus spatial frequency response function differed significantly in patients compared with controls, displaying a lowpass instead of a band-pass shape. No significant differences in the mean pattern electroretinogram phase were observed between groups at any spatial frequency. These results indicate spatial frequency-dependent abnormalities in the pattern electroretinogram amplitude after optic neuritis, suggesting a specific loss of retinal neurons sensitive to stimuli of intermediate spatial frequencies.

Adult↗

PubMed1992

Macular dysfunction in multiple sclerosis revealed by steady-state flicker and pattern ERGs.

Recent evidence indicates that the 2nd harmonics of steady-state (8 Hz) electroretinograms to either sinusoidal flicker (FERG) or to counterphased gratings (PERG) presented in the macular region (9 degrees) represent different subsets of generators in the inner retina. We evaluated the steady-state macular FERG and PERG 2nd harmonics (2F and 2P, respectively) in 19 normal subjects (19 eyes) and in 23 multiple sclerosis patients (44 eyes; 25 eyes with a history of clinical optic neuritis, and 19 eyes with no history of optic neuritis, subclinical eyes). The mean 2F and 2P amplitudes were significantly reduced, as compared to controls, in both subclinical and optic neuritis eyes. The 2P phase was significantly delayed, as compared to controls, in subclinical eyes, whereas 2F phase was delayed in eyes with optic neuritis. 2F was outside the 95% confidence limits (in amplitude or phase) in 11/19 subclinical eyes and in 25/25 optic neuritis eyes. 2P was outside the normal range in 12/19 subclinical eyes and in 24/25 optic neuritis eyes. These results show that FERG and PERG 2nd harmonics are significantly altered in multiple sclerosis eyes with or without a clinical history of optic neuritis. This finding suggests a dysfunction of inner macular layers which may result from direct retinal involvement or retrograde degeneration.

Adolescent↗

PubMed1992

Pattern electroretinograms and visual evoked potentials in idiopathic intracranial hypertension.

A subclinical visual dysfunction can be detected by psychophysical methods in early-stage papilledema associated with idiopathic intracranial hypertension (IIH). We recorded steady-state pattern electroretinograms (PERGs) and visual evoked potentials (VEPs) to sinusoidal gratings of variable spatial frequency [0.6, 1.0, 1.4, 2.2 and 4.8 cycles/degree (cpd)] in 18 patients with IIH and early papilledema and in 21 age-matched controls. Spatial frequency selective reductions in the mean PERG (at 1-4.8 cpd) and VEP (at 4.8 cpd) amplitudes were found in patients in comparison with controls. The response functions of amplitude versus spatial frequency of patients' PERG and VEP displayed a low-pass shape, whereas in normal subjects PERG and VEP functions showed a band-pass and a high-pass shape, respectively. PERG and VEP abnormalities were found in 14 (77.7%) and 10 (55.5%) out of 18 patients, respectively. Most of these abnormalities involved only selected spatial frequencies (1.4-4.8 cpd). These results indicate spatial-frequency-dependent functional losses on both PERG and VEP in early papilledema, and suggest a potential value of these responses for detecting subtle visual abnormalities in IIH.

Adult↗

PubMed1992

Nonselective loss of contrast sensitivity in visual system testing in early type I diabetes.

OBJECTIVE: Psychophysical methods in patients with diabetes mellitus reveal deficits of central or foveal vision. Our aim was to evaluate the contrast-sensitivity thresholds in 24 insulin-dependent (type I) diabetic patients with a short disease duration and without retinopathy, taking into account metabolic control. RESEARCH DESIGN AND METHODS: The control group consisted of age-matched nondiabetic subjects. None had visual or systemic symptoms. Contrast sensitivity measured at eight different spatial frequencies to sinusoidal bar patterns of 0.6-12.2 cycles/deg can detect functional defects in the spatially sensitive retinal ganglion cells or in higher visual pathways. We performed two different temporal types of contrast-sensitivity testing, dynamic (8 Hz) and static (0 Hz). RESULTS: Significant losses with dynamic contrast-sensitivity test at all but the highest spatial frequencies (i.e., 12.2 cycles/deg) were shown, whereas there was significant attenuation of contrast sensitivity at five spatial frequencies (1.0, 1.4, 2.2, 7.1, and 9.6 cycles/deg) in the static mode. Grating losses (less than 2SD of control means) of contrast sensitivity were found in 33.3% (dynamic) and in 72.9% (static) of eyes of diabetic patients. HbA1c values were positively correlated at variable spatial frequencies (1.0, 1.4, and 2.2 cycles/deg for dynamic test and 0.6, 1.0, 1.4, 2.2, 4.8, and 7.1 cycles/deg for static test). CONCLUSIONS: Our results suggest an early, generally nonselective neuronal damage of visual pathways that occurs before the onset of clinically detectable retinopathy. The visual deficit may be related directly to the effects of diabetes; repetitive minor hypoglycemic insults may contribute more than a marked hyperglycemic condition to the mechanisms underlying physiological changes along the optic nerve.

Adult↗

PubMed1991

Spatial-frequency-dependent changes in the human pattern electroretinogram after acute acetyl-L-carnitine administration.

Acetyl-L-carnitine (LAC) is a neuroactive compound that is thought to be involved in cholinergic transmission. The effects of acute intravenous LAC administration (30 mg/kg) on pattern-evoked electroretinograms (P-ERGs) were evaluated in nine healthy volunteers ranging in age between 21 and 27 years. Nine age-matched, normal subjects treated with a placebo served as controls. Steady-state (8 Hz) P-ERGs recorded in response to counterphased sinusoidal gratings of variable spatial frequency (0.6-4.8 cycles/degree) were obtained before and at 20, 50 and 80 min after LAC or placebo administration. The amplitude and phase of the Fourier-analysed P-ERG second harmonic were measured. As compared with placebo-treated controls, LAC-treated subjects showed a selective P-ERG amplitude increase (Mann-Whitney rank test: P less than 0.05), which was found 80 min posttreatment at a spatial frequency of 4.8 cycles/degree. For the same stimulus a significant (P less than 0.05) P-ERG phase shortening (at 50 min after drug administration) was also found. The spatial frequencies of other stimuli did not show a significant difference between the LAC- and placebo-treated groups. These results indicate that acute LAC administration induces a spatial-frequency-dependent enhancement of the human P-ERG. This is compatible with a cholinergic excitatory effect and suggests a therapeutic role for this compound in retinal dysfunctions with selective vulnerability to medium-high spatial frequencies.

Acetylcarnitine↗

PubMed1991

Detection of inner retina dysfunction by steady-state focal electroretinogram pattern and flicker in early IDDM.

The effects of diabetes on the neural retina before the onset of clinically detectable retinopathy can be investigated with electrophysiological methods. Our aim was to detect early retinal dysfunctions in 60 patients with insulin-dependent diabetes mellitus (IDDM) and with a short duration of disease. We used the steady-state focal (9 degrees field size) electroretinogram (ERG) of the macula in response to luminance modulation of a uniform field (flicker ERG) or to counterphase-modulated sinusoidal gratings (pattern ERG). The harmonic analysis of flicker ERG and pattern ERG yielded three main components: a first and a second harmonic to flicker (1F and 2F, respectively) and a second harmonic to pattern (2P). The 1F is believed to be correlated to photoreceptor activity, whereas 2F and 2P represent different subsets of generators in the inner retina. Results of focal ERG in IDDM patients with no or early retinopathy were compared with age-matched control subjects. Mean 2F and 2P amplitudes were significantly reduced in IDDM patients compared with the control group (P = 0.0001 by analysis of variance). 2P but not 2F amplitude was significantly more reduced in patients with retinopathy than in those without retinopathy (P less than 0.05). 2F but not 2P phase abnormalities were observed in some patients. 2F and 2P alterations were slightly correlated with metabolic control (r = 0.22, P = 0.02) and disease duration (r = 0.28, P = 0.003). 1F was not significantly altered in IDDM patients. Our results suggest that early diabetes causes selective neurosensory deficits of inner retina layers, whereas the photoreceptors appear unaffected.

Adult↗

PubMed1990

The human focal electroretinogram as a function of stimulus area.

Focal electroretinograms to on-off luminance modulation (2.7 Hz) of uniform fields with a different area (144-2.25 deg2) centered on the fovea were recorded in two young normal subjects. The electroretinogram responses typically consisted of an a-wave, a b-wave, a PIII component and a d-wave. The concentric reduction of the test field size caused progressive amplitude decrement of all components, while their response density increased. The spatial summation properties of the b-wave differed from those of the a-wave, PIII component and d-wave so that the relative contribution of the b-wave to the electroretinogram waveform depended on the stimulus area. For a critically small field size, the electroretinogram was dominated by the PIII and d-wave components. Only these two electroretinogram components displayed a density profile that could be compared with that of cone distribution.

Adult↗

PubMed1990

Spatial frequency-selective losses with pattern electroretinogram in type 1 (insulin-dependent) diabetic patients without retinopathy.

Neurosensory abnormalities have been implicated in the first stages of diabetic retinopathy. The activity of retinal ganglion cells in 24 Type 1 (insulin-dependent) diabetic patients with short disease duration without retinopathy on fluorescein angiography was investigated by using a pattern electroretinogram in response to sinusoidal gratings of different spatial frequencies (0.6, 1.0, 1.4, 2.2 4.8 cycles/deg), counterphase modulated at 8 Hz. The pattern electroretinogram reflects, at least in part, the activity of subsets of generators (i.e. ganglion cells) which show spatial selectivity. Mean pattern electroretinogram amplitude was significantly reduced in patients at lower and intermediate, but not at higher spatial frequencies compared with 40 age-matched control subjects. At 1.4 cycles/deg the pattern electroretinogram amplitude was significantly correlated (r = 0.59) with age at onset (p = 0.002) and duration of disease (p = 0.002). Our results suggest that in Type 1 diabetic patients without retinopathy, there is an early sensory deficit of specific inner retina neurons which respond preferentially to gratings of medium and large size.

Diabetes Mellitus, Type 1↗

PubMed1990

Evidence for early impairment of macular function with pattern ERG in type I diabetic patients.

The electroretinogram (ERG) elicited by alternating gratings at constant mean luminance (pattern ERG) is a focal response reflecting the activity of the directly stimulated retinal area. In addition, pattern ERG is related, unlike the flash ERG, to ganglion cell activity. Therefore, this technique may be used to evaluate the integrity of inner retinal layers in the macular region. In this study, the steady-state pattern ERG, in response to alternating gratings (1.7 cycles/deg spatial frequency; 9 degrees field size) temporally modulated at 8 Hz, was recorded in 42 type I (insulin-dependent) diabetic patients with zero to four microaneurysms on fluorescein angiography and a duration of disease less than 11 yr. No patient had concomitant ocular or systemic complications. Mean pattern-ERG amplitude was significantly reduced in patients compared with age-matched control subjects (analysis of variance, F = 25.6, P less than 0.0001). Significant differences were observed between control and diabetic subjects without retinopathy (Scheffé F test, P less than 0.0001), between control and retinopathic subjects (Scheffé F test, P less than 0.0001), and between diabetic patients without retinopathy and those with early retinopathy (Scheffé F test, P less than 0.02). Pattern-ERG amplitude was inversely correlated with duration of diabetes (r = 0.22, P less than 0.05). Our results suggest a macular dysfunction in early diabetes resulting from metabolic and/or vascular injuries in the neurosensory retina.

Adolescent↗

PubMed1990

[Wilson's disease. Presentation of a case with special reference to the study of evoked visual potentials].

In the present work the Authors report one case of Wilson's disease showing peculiar characteristics diagnosed in pediatric-age patients. In this case, a deep electrophysiological visual analysis was carried out six years after diagnosis. The evoked visual potential alterations might be connected to a retina dysfunction. Further studies should be carried out in order to support such hypothesis.

Child↗

PubMed1989

Simultaneous foveal and parafoveal electroretinograms in hereditary degeneration of the central retina.

Simultaneous foveal and parafoveal electroretinograms (ERG) in response to two identical checks (6 degrees per side) alternating at constant mean luminance were recorded in 26 patients (52 eyes) affected by central hereditary chorioretinal diseases and in 14 age-matched normal subjects (14 eyes). Patients were divided into four groups according to clinical diagnoses: 1. Stargardt's disease; 2. cone dystrophy; 3. vitelliform degeneration; 4. pattern dystrophy. The amplitude and latency of the foveal ERG and the amplitude ratio between foveal and parafoveal ERG (F:PF ratio) were measured. The mean foveal ERG amplitude was significantly lower than the control mean in all patient groups. The foveal ERG latency showed a trend to a increase in all pathological groups. However, this difference was not statistically significant. The mean value of F:PF ratio was significantly reduced as compared with the control mean in Stargardt's disease and cone dystrophy only. In 46 of 52 affected eyes (88.5%) at least one of the electrophysiological parameters was abnormal. Our results suggest that the simultaneous foveal and parafoveal ERG recording may be a sensitive technique in hereditary degenerations of the central retina. This method may also contribute to a better understanding of cone degeneration pathophysiology.

Adolescent↗

PubMed1989

Steady-state pattern electroretinogram in insulin-dependent diabetics with no or minimal retinopathy.

Steady-state pattern electroretinogram (PERG) in response to sinusoidal gratings (1.7 c/deg spatial frequency; 9 x 9 deg field size) temporally modulated (sinusoidally) at 8 Hz were recorded in 40 insulin-dependent diabetics and 28 age-matched normal subjects. Visual acuity was greater than or equal to 20/20 in all 40 patients; 31 (62 eyes) showed no sign of retinopathy and nine (18 eyes) showed a few microaneurysms on fluorescein angiography. Insulin-dependent diabetics showed a significant reduction in the PERG mean amplitude as compared with age-matched control subjects (one-way analysis of variance: p less than 0.0001). Significant differences were observed between normals and diabetics without retinopathy (Scheffé test: p less than 0.0001), normals and diabetics with early retinopathy (Scheffé test: p less than 0.0001), no retinopathy and early retinopathy patients (Scheffé test: p less than 0.05). In diabetics without retinopathy multifactorial analysis of variance revealed a significant effect of age of onset of the disease (p less than 0.01) and an interaction effect between age of onset and duration (p less than 0.001) on PERG amplitude. These results suggest a possible use of the steady-state PERG to detect early macular dysfunction in insulin-dependent diabetics.

Adult↗

PubMed1989

Development of personal computer software for a visual electrophysiology laboratory.

This paper describes the software developed by the authors in order to introduce the flexibility and computing power of a modern personal computer in an existing visual electrophysiology laboratory. The basic problems that a programmer must solve in order to implement the main tasks requested are discussed. Such problems include signal acquisition, signal averaging, artifact rejection, time domain analysis, frequency domain analysis and data management. The software developed following our guidelines makes it possible for a personal computer equipped with a commercial analog-to-digital converter to interface directly with the physiologic amplifiers and visual stimulators commonly used either for classical electroretinography or for pattern and focal electroretinography.

Electroretinography↗

PubMed1989

Changes in spatial tuning of the pattern electroretinogram with age.

Experimental and clinical studies have demonstrated that the electroretinogram in response to periodical patterns alternating in contrast at constant mean luminance (pattern reversal ERG, P-ERG), is correlated with ganglion cell activity. Senile functional changes of these neurons might be therefore investigated by the P-ERG technique. Steady-state P-ERGs (8 Hz) in response to sinusoidal gratings of different spatial frequencies (0.6-6.8 c/d) were recorded in normal subjects ranging over 50 year age span. The P-ERG amplitude as a function of stimulus spatial frequency shows a maximum between 1.2-1.7 c/d and attenuation at higher and lower spatial frequencies (spatial tuning). The P-ERGs of the older subjects are reduced in amplitute, as compared to those of the younger ones, over the whole range of spatial frequency. This reduction is more marked at intermediate spatial frequencies resulting in a shallower tuning.

Adult↗

PubMed1988

Macular electroretinogram as a function of age of subjects.

Macular and paramacular electroretinograms in response to two adjacent checks (6 deg/side), alternating at constant mean luminance, were recorded in 34 normal subjects ranging in age from 16 to 74 years. The macular electroretinogram declines progressively in amplitude with age (R = -0.42; P = 0.013). The amplitude ratio between macular and paramacular responses tends to be independent of age (R = -0.21; P = 0.22). Age-related changes in the macular electroretinogram shown in our study are consistent with previous anatomical and functional studies, which indicate a deterioration of photoreceptors beyond 20 years of age. These results suggest a possible use of this technique for future studies on macular degeneration.

Adolescent↗

PubMed1988

The pattern electroretinogram by skin electrodes: effect of spatial frequency and age.

Steady-state (8 Hz) pattern electroretinograms in response to sinusoidal gratings were recorded from 18 elder subjects (mean age 62.7 years) and 22 young subjects (mean age 27 years) by means of skin electrodes. All subjects were free from ocular pathology and their corrected visual acuity was 1.0 or better. In young subjects the second harmonic amplitude as a function of spatial frequency is spatially tuned, with a maximum at around 1.7 c/deg. The response of elder subjects is significantly (P less than 0.05) reduced over the whole range of spatial frequency as compared with that of younger ones. This decrease is more marked (P less than 0.01) at intermediate spatial frequencies, resulting in a shallower tuning. The response phase is not significantly different between young and elder subjects.

Adult↗