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Biomedical subjects

M F Marmor

Publications and source records attributed to M F Marmor.

At least 91 records · Page 5Linked to original sources
PubMed1990

[The relationship between amplitude and extent of detachment indicated by the ERG c-wave of rabbit eyes with experimental retinal detachment].

We recorded ERG b- and c-waves from rabbit eyes with experimental retinal detachment and investigated the relationship between amplitude of the ERG and extent of the detachment. Three different extents of detachment (20, 60, 100% of the fundus) were made in three different groups of rabbits. In all 3 groups, the amplitude of both b- and c-waves remarkably decreased 1 hour after detachment and recovered at 6 hours to values corresponding to the extent of detachment. At 12 hours, the b-wave amplitude remained at almost the same values at 6 hours, whereas the c-wave amplitude showed further reduction. It was suggested that functional disorder in undetached retina occurred earlier in the retinal pigment epithelium than in the sensory retina of the eyes in the acute stage of the retinal detachment.

Animals↗
PubMed1989

Dextromethorphan protects retina against ischemic injury in vivo.

Retinal ischemia was induced in rabbits by increasing intraocular pressure above systolic blood pressure for 60 or 75 minutes, and retinal function was monitored by electroretinography. Pretreatment with intravenous dextromethorphan, a nonprescription antitussive and selective antagonist of N-methyl-D-aspartate receptors, enhanced greatly the post-ischemic recovery of b-wave amplitude. Dextromethorphan may prove to be useful clinically in the management of retinal ischemic disease.

Animals↗
PubMed1989

An international standard for electroretinography.

An international standard procedure for electroretinography (ERG) has finally been established. It represents a minimum protocol to record five basic signals (rod response, scotopic maximal response, oscillatory potentials, single-flash cone response, 30-Hz flicker response). Individual laboratories may continue to do additional or specialized procedures, but the hope is that all laboratories will include "standard" responses in their routine protocols so ERG data can be compared throughout the world for patient care and for research.

Electroretinography↗
PubMed1989

Large rod-like photopic signals in a possible new form of congenital night blindness.

A 10-year-old Persian girl has symptoms of congenital stationary night blindness and some drusen-like lesions in the region of the vascular arcades. Her electroretinogram shows no rod response to a weak stimulus, but a large (475 microV) slow scotopic response to a strong stimulus that is unchanged by photopic conditions (15 Fl background illumination). However, the response to flicker had the typical (smaller) amplitude of a cone signal. They may represent a new form of night blindness in which rod sensitivity is reduced so that there is no vision under dim conditions but rod function still persists under photopic conditions.

Child↗
PubMed1989

Photoaversion in retinitis pigmentosa.

Photoaversion, or light-induced interference with visual comfort and performance, has been a recognised but poorly documented symptom in retinitis pigmentosa (RP). We found that a majority of our RP patients complained of photoaversion even in the absence of significant cataract. RP patients had reduced contrast sensitivity relative to normal people, but the decrement in their visual performance as a result of glare or photostress was only slight. RP patients had raised short-term adaptation and increment threshold levels, but their rate of short-term or photopic adaptation was normal. Photoaversion in RP may result because a small interference with contrast sensitivity or adaptation can place patients in a range of functional disability, or it may derive from a combination of minor aberrations.

Adaptation, Ocular↗
PubMed1989

The enhancement of retinal adhesiveness by ouabain appears to involve cellular edema.

Our previous work showed that ouabain increases retinal adhesion to the retinal pigment epithelium, but the mechanism of this effect has been unclear. In this study, we have found that the ouabain-induced increase in retinal adhesiveness was blocked reversibly by removing sodium from the medium or by exposure to hyperosmotic solution. Hyposmotic solution slowed down the postmortem failure of adhesion. Tissue edema could not be documented histologically, but retinal tissue water content increased by 2.9% after exposure to ouabain. These data suggest that the ouabain effect involves cellular edema, which may enhance adhesion by tightening the interdigitation between photoreceptor outer segments and retinal pigment epithelial microvilli.

Adhesiveness↗
PubMed1989

Reversibility of retinal adhesion in the rabbit.

We have studied retinal adhesion in the rabbit using a new technique for quantifying adhesiveness by the observation of how much pigment remains adherent to the photoreceptors after separation. Previous in vitro work has shown that retinal adhesiveness falls within 3 min after enucleation, is weakened by low pH or the removal of calcium and magnesium, and is increased by cold temperature. This report shows that the effects of low pH, low calcium/magnesium and temperature are all rapidly reversible. Thus, restoring normal pH or normal calcium/magnesium will restore adhesiveness to control levels, and adhesion may be repeatedly weakened or strengthened by the adjustment of temperature or the ionic environment. The actions of pH and calcium/magnesium are in part additive, while cold temperature can maintain adhesion even in low pH or low calcium/magnesium. These findings suggest that irreversible processes such as metabolic or enzymatic decay are not primarily responsible for the loss of retinal adhesion which occurs so rapidly after enucleation or death. They also suggest that retinal adhesion is a multifactorial process.

Adhesiveness↗
PubMed1988

Retinal folds in the shaken baby syndrome.

We examined two children with presumed shaken baby syndrome. Both children suffered severe, indirect closed head trauma with intracranial hemorrhage, sharply increased intracranial pressure, and extensive neurologic damage. In addition to extensive retinal and preretinal hemorrhages, bilateral symmetric white ring-shaped retinal folds were seen encircling the macula outside the vascular arcades. These retinal folds may be a hallmark of shaking injuries in child abuse victims.

Child Abuse↗
PubMed1988

The effect of choroidal congestion in retinal pigment epithelium function and the electroretinogram.

Increased choroidal pressure and choroidal stasis were induced in Dutch rabbit eyes by tying off vortex veins. Ligating one to three vortex veins caused a progressive diminution in the b- and c-waves of the electroretinogram so that the amplitudes were approximately half of control values when three vortices had been ligated. After ligation of four vortex veins, the responses rapidly disappeared. Release of the occlusion twenty minutes later caused the b-wave to return to normal over a few hours' time, but the c-wave showed variable recovery and was replaced by a large slow pIII response in half of the experiments. These observations may reflect a combination of hypoxia and alterations in fluid movement that affect the status of the subretinal space.

Animals↗
PubMed1988

Oscillatory potentials as a marker for dopaminergic disease.

In an effort to find electrophysiologic correlates of dopaminergic disease in man, we measured oscillatory potentials of the electroretinogram in normal and unmedicated schizophrenic subjects, and in rabbits given D1 agonist or antagonist drugs. We found highly reproducible oscillatory potentials in twelve male schizophrenics that were indistinguishable from those in nine male normal volunteers. We also found little electroretinographic difference among four rabbits given intramuscular injections of SKF 38393 (a D1 agonist) and four control animals injected with saline. However, four animals given SCH 23390 (a D1 antagonist) showed diminution of the b-wave and selective suppression of the second oscillatory potential. This effect was more prominent in oscillatory potentials generated by 5-Hz flicker than by a single flash. These rabbit data suggest that further efforts at finding clinical correlations may be worthwhile, possibly with trial of flicker oscillatory potentials, and they support the concept that different oscillatory potentials have different generators.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1988

New hypotheses on the pathogenesis and treatment of serous retinal detachment.

Recent experimental work has shown that, under normal conditions, most subretinal fluid is absorbed rapidly by active transport across the retinal pigment epithelium (RPE). However, in the presence of damage to the RPE blood-retinal barrier, subretinal fluid is rapidly cleared by passive forces. Thus, it is apparent that RPE defects do not by themselves cause serous retinal detachment. A hypothesis is presented that some serous detachments occur because normal metabolic transport systems of the RPE have been damaged, while the blood-retinal barrier remains intact to prevent passive drainage of the subretinal space. Under these conditions, a focal RPE "leak" can overload the system so that the serous fluid accumulates and persists. Photocoagulation of a leaking point can facilitate resolution of the fluid, but as long as the underlying metabolic dysfunction of the RPE persists, recurrence is possible. Some forms of serous detachment may thus be viewed as diffuse rather than focal ocular disorders in which the transport capability of the RPE has been damaged; such damage can result from systemic pathology such as adrenergic stress (e.g., central serous chorioretinopathy) or vascular disease (e.g., hypertension).

Animals↗
PubMed1988

Rapid enhancement of retinal adhesion by laser photocoagulation.

To determine how quickly laser photocoagulation produces a bond between retina and pigment epithelium, the authors measured the strength of retinal adhesion after making laser burns through intact and recently reattached rabbit retina. After photocoagulation of intact retina, the adhesive force was reduced 50% at 8 hours but increased beyond normal (to approximately 140%) by 24 hours and remained twice normal between 3 days and 4 weeks. Photocoagulation of retina that had just settled after experimental detachment produced similar results, except that the maximum strength of adhesion (reached at 2 weeks) was three times normal. In contrast, retina that reattached spontaneously, without photocoagulation, showed only 10% of normal adhesiveness at 24 hours, and still was only 75% of normal after 4 weeks. These data suggest that laser photocoagulation may be acutely beneficial in the prevention or management of retinal tears and detachments.

Adhesiveness↗
PubMed1988

Effect of visual blur on contrast sensitivity. Clinical implications.

Contrast sensitivity of normal subjects was measured under conditions of refractive blur that produced specific levels of visual acuity. Measurements were made at distance (with Vistech charts), at near (with Arden gratings), and with a pinhole to control pupil size. Under all conditions, when visual acuity was reduced by spherical lenses, there was a loss of contrast sensitivity over a broad range of spatial frequencies (i.e., not just at the higher frequencies that correlate with target letter size). By inference, it may be clinically hazardous to interpret contrast sensitivity results in patients with reduced acuity (from any cause) relative only to standard contrast sensitivity values based on subjects with normal visual acuity. If the potential effects of acuity are taken into account, contrast sensitivity testing can distinguish between deficits that are roughly equivalent to the loss of acuity and those which indicate more distinctive pathology of the media, retina, or optic nerve.

Humans↗
PubMed1988

Effects of retinal adhesion of temperature, cyclic AMP, cytochalasin, and enzymes.

We have studied factors that contribute to retinal adhesion, by measuring directly the force required to peel rabbit retina from the retinal pigment epithelium (RPE). Exposing the tissue to either testicular hyaluronidase or neuraminidase, or acidifying the medium to pH 6.0, reduced the peeling force within 2 min. Cooling the tissue to 25 degrees C or 4 degrees C increased the peeling force to such a degree that retinal separation occurred by rupture of the RPE cells rather than widening of the subretinal space. Inhibition of the cytoplasmic contractile system with cytochalasin had no significant effect on peeling force, but dibutyryl cAMP (which decreases fluid absorption by the RPE) weakened adhesion. These results suggest that retinal adhesion involves a number of interrelated physical and metabolic factors.

Adhesiveness↗
PubMed1988

Electrical responses from detached retina inside the intact rabbit eye.

The local ERG (LERG) from detached retina within the intact rabbit eye has been recorded. Retinal detachments were made in Dutch rabbit eyes by injecting Hanks' balanced salt solution into the subretinal space through a glass micropipette. Electrical responses were recorded with a double-barrelled microelectrode that was advanced through the vitreous until the tip penetrated the retina to enter the subretinal space while the other tip remained in the vitreous. Recordings from detached retina showed an initial fast positive, fast negative and late slow positive wave. The waveform and stimulus response characteristics of these waves (inverted) corresponded to the a-, b-wave and slow PIII respectively. None of the LERG waves was affected by intravenous sodium iodate and only the slow positive wave was extinguished by intravitreal barium chloride. This system for recording the LERG may be useful in investigating physiological changes in detached retina in vivo.

Animals↗
PubMed1988

Metabolic influences on the absorption of serous subretinal fluid.

Experimental detachments were made in Dutch rabbit eyes by injecting autologous serum or Hanks' solution into the subretinal space through a glass micropipette. The serum was resorbed at a rate of 0.064 +/- 0.023 microliter/mm2/hr, which is approximately half as fast as Hanks' solution. Both cyclic GMP and dibutyryl cyclic GMP accelerated serum resorption by 23%, whereas cyclic AMP and dibutyryl cyclic AMP (both used with IBMX) decreased the absorption rate by 46%. The absorption rate for Hanks' solution did not differ significantly between light and dark. Intravenous administration of acetazolamide (50 mg/Kg) and mannitol (2.5 g/kg) failed to alter the serum resorption rate significantly. Thus, cyclic nucleotides (and presumably metabolic transport) are important to absorption of serous fluid, but acetazolamide and hyperosmotic agents have less effect than on nonproteinaceous subretinal fluid.

Absorption↗
PubMed1988

Pigment adherence as a measure of retinal adhesion: dependence on temperature.

Retinal adhesion deteriorates rapidly after enucleation. We have developed a new in vitro method for measuring retinal adhesiveness in the rabbit that is faster than previous models, and can monitor changes sooner after enucleation. We used the percentage of retina which retained pigment after peeling from the RPE as a quantitative measure of retinal adhesiveness. We found that the failure of adhesion after death is more rapid and severe than previously reported, but can be inhibited by cold temperature. Pigment adherence was also modified by ionic and metabolic factors that have been found to affect other indices of adhesion. These results emphasize the limitations of in vitro data relative to the physiologic forces that maintain retinal adhesion in vivo.

Acetazolamide↗