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Biomedical subjects

M F Marmor

Publications and source records attributed to M F Marmor.

At least 145 records · Page 8Linked to original sources
PubMed1979

Chalcosis: a study of natural history.

Ten patients harboring a small, intra-vitreal, copper foreign body in one eye for 4 months to 29 years have been studied clinically and electrophysiologically. Nine of the ten affected eyes had a visual acuity of 20/60 or better. Some asymmetry existed in the electrophysiologic responses of seven affected eyes as compared to the controls, but all of these responses were within the normal range. The electroretinogram was reduced in one eye but was consistent with vitreous opacification. Vitreous opacification and copper deposition in the macula were potentially serious sequelae observed in four eyes. Small, intraocular copper foreign bodies can be tolerated for long periods of time without retinal toxicity, but vitreous changes of maculopathy may necessitate intervention.

Adolescent↗
PubMed1979

Retinal detachment from hyperosmotic intravitreal injection.

Hyperosmotic solutions were injected into the rabbit vitreous to study their effects upon the retina. Injection of 0.05 ml of a 1000 mOsm solution caused rapid whitening of the posterior retina followed by the development of a large detachment and permanent retinal degeneration. The weakest solutions which produced ophthalmoscopically visible changes in the retina (after an injection of 0.05 ml) were near 500 mOsm. Sodium chloride, sodium aspartate, EDTA, mannitol, sucrose, and penicillin were effective at similar osmolarities. An osmotic load in the vitreous caused immediate loss of the c-wave of the electroretinogram (ERG), and a slower decline of the a- and b-waves. The reported intravitreal toxicity of some drugs may relate to osmotic rather than pharmacologic effects. Osmolarity should be accounted for in planning the amount and location of any vitreous injection.

Animals↗
PubMed1979

"Vitelliform" lesions in adults.

Symmetric yellow ("vitelliform") foveal lesions are occasionally seen in adults. These patients should not be diagnosed as having Best's vitelliform dystrophy unless the EOG light/dark ratio is severely depressed and the family history reveals a dominantly-inherited maculopathy. Adult vitelliform lesions may vary in size from one third to several disc diameters, and may be present with or without drusen. More than one etiology may be involved, but many of these lesions seem to be degenerative changes related to drusen or pigment epithelial detachment.

Adult↗
PubMed1978

Optic nerve head involvement with cytomegalovirus in an adult with lymphoma.

An optic nerve swelling that was thought clinically to represent a lymphomatous infiltrate of the nerve head developed in a 51-year-old man with histiocytic lymphoma. Histologic examination of the eyes showed the presence of cytomegalovirus (CMV) in the nerve head, but no lymphoma cells. Tru lymphomatous invasion of the nerve head in systemic lymphoma is probably very rare. This case points out an unusual manifestation of adult CMV infection, and a new concern in patients with compromised immune systems.

Adult↗
PubMed1978

Copper metabolism in American retinitis pigmentosa patients.

Serum copper, serum caeruloplasmin, and urinary copper excretion were measured in 38 American patients (and 15 family members) with recessive, dominant, and X-linked forms of retinitis pigmentosa. No abnormalities were found, in contrast to the findings of a recent study on Indian patients. Our data argue against a role for copper metabolism in ordinary retinitis pigmentosa.

Adolescent↗
PubMed1977

Pattern dystrophy of the pigment epithelium.

Three generations of a family showed alterations in the retinal pigment epithelium along with mild visual disturbance. Younger members had granular pigment dispersed beneath the fovea while older members showed a reticular pigment pattern. The electro-oculogram was subnormal in most affected individuals, but visual fields, color vision, dark adaptation, and the electroretinogram were normal. The pigmentary changes in these patients are similar to those seen in other pigment epithelial dystrophies such as reticular dystrophy and butterfly-shaped dystrophy. Until these disorders can be separated pathophysiologically, we suggest the definition of a more inclusive clinical term, "pattern dystrophies of the pigment epithelium.

Adolescent↗
PubMed1977

Acoustic microscopy of the human retina and pigment epithelium.

An acoustic microscope uses sound waves rather than light to image a sample, and displays viscoelastic rather than optical properties. The Stanford instrument, operating at frequencies near 1,000 MHz, achieves resolution and magnification that is comparable to a light microscope. Using this instrument, we examined sections of normal human retina and pigment epithelium and found that characteristic degrees of acoustic attenuation or phase shift were produced by structures such as cell nuclei, rod and cone outer segments, Bruch's membrane, red blood cells, and ocular pigment. Resolution was better with thin than thick sections, and fixation did not significantly alter the acoustic properties of the tissues studied. A comparison of iris tissue from albino and pigmented rabbits showed that melanin was a particularly strong acoustic attenuator. Acoustic microscopy may provide a new and direct means of probing the physical structure of tissues and cells.

Acoustics↗
PubMed1976

Corneal electroretinograms in children without sedation.

Many physicians assume that general anesthesia or sedation is necessary to perform electroretinograms (ERGs) on children and for this reason are reluctant to request the test. To challenge this assumption, routine contact lens ERGs, using topical anesthesia only, were attempted on 30 consecutively referred children (aged five months to six years). Mild restraint was sometimes needed, but successful oscilloscopic ERGs were obtained from all 30 children. The records were less stable than those from adults, but the response amplitude, wave-form and timing could always be evaluated and the cone and rod systems could be clearly differentiated.

Age Factors↗
PubMed1975

The membrane of giant molluscan neurons: electrophysiologic properties and the origin of the resting potential.

The molluscan neuron, because of its large size and accessibility, has been an important model for studying the electrophysiology of nerve cells. This review catalogs data about specific molluscan neurons, but the greater importance of this material is in the broad picture of how a neuronal membrane maintains internal potential and is responsive to changes in the environment. Electrical properties of the membrane. The mechanisms which contribute to the resting potential in molluscan neurons can be separated into ionic and metabolic components. When the electrogenic sodium pump is eliminated experimentally, the ionic component of the potential follows the constant field equation quite closely. Many of the "constants" and "parameters" which characterize the membrane of molluscan neurons are actually variables which depend upon temperature, ionic environment, and membrane potential. The evaluation of the electrical parameters is complicated by extensive infoldings of the somatic membrane, and by large axons which drain current from the soma. Most molluscan neurons have a very high specific membrane resistance and a correspondingly low potassium permeability. Membrane capacitance is close to the 1 microF/cm2 value which characterizes biological membranes. The current-voltage relation of molluscan neurons may be complicated by inward-going rectification, but if that is inhibited the I-V curve follows the prediction of either the constant field equation or a simple electrical model. Factors which modify membrane behavior. The resting potential of molluscan neurons is very sensitive to changes in temperature and Ko, through a combination of effects upon the electrogenic sodium pump, inward-going rectification, and the membrane "parameters". Inward-going rectification depends upon a rectifying K conductance, and can be eliminated by cold or the removal of Ko. Strong or prolonged currents have time-dependent effects upon the membrane, and excessive polarization leads to a "high conductance state". The underlying (non-rectifying) K permeability of the membrane is relatively insensitive to temperature and ionic changes, whereas the Na permeability increases with warming. Membrane resistance varies with both temperature and ions (because the I-V curve is sensitive to these conditions) but membrane capacitance is relatively insensitive to external factors. Electrogenic sodium transport. Sodium transport is electrogenic in molluscan neurons. It can be stimulated by warm temperatures and an excess of substrate (e.g. high Nai); it can be inhibited by cold, by an absence of substrate (e.g. low Ko), or by pharmacologic agents such as cyanide or ouabain.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1974

Steady-state contribution of the sodium pump to the resting potential of a molluscan neurone.

1. The electrogenic contribution of the Na(+)-K(+) exchange pump to the membrane potential of the Anisodoris giant neurone (G cell) was examined under steady-state and Na(+) loaded conditions.2. The membrane potential was variable for the first 1-4 hr after impalement, but, in the absence of experimental manipulation, remained constant thereafter. The average membrane potential for ten cells maintained at 11-13 degrees C and measured 5-36 hr after impalement was 55.8 +/- 1.0 mV (S.E. of mean).3. Low concentrations of external ACh caused a reversible increase in membrane Na(+) conductance. Brief exposure to ACh proved a fast and reversible technique to load the cell with Na(+) ions, and transiently stimulate the electrogenic Na(+) pump.4. In ten cells maintained from 5 to 36 hr at 11-13 degrees C the reduction in membrane potential produced by inhibition of the Na(+) pump with ouabain was remarkably constant between cells and averaged + 9.7 mV.5. Cells maintained under steady-state conditions (at 11-13 degrees C) for extended periods of time were shown to be relatively insensitive to changes in temperature and to small changes in external K(+).6. It is estimated that the Na(+)-K(+) exchange pump contributes approximately - 10 mV to the steady-state resting potential of the G cell, and that two Na(+) ions are extruded for every K(+) ion transported into the cell per pump cycle.

Acetylcholine↗
PubMed1974

Long-term effect of ouabain and sodium pump inhibition on a neuronal membrane.

1. The long-term effects of ouabain on the membrane potential of the Anisodoris giant neurone (G cell) were examined in cells maintained for periods of up to 15 hr at 11-13 degrees C.2. In the presence of ouabain (5 x 10(-4)M), the membrane potential depolarized to a constant level for 1-4 hr, then hyperpolarized for 5-7 hr after which it gradually depolarized again.3. During the hyperpolarizing phase, after 6-8 hr in ouabain, [K](1) fell approximately 50%, [Na](1) increased 50-100% and the P(Na)/P(K) ratio decreased to 25% of its initial value.4. After 8 hr in ouabain the membrane conductance increased two- to fourfold. This increase was independent of temperature and membrane rectification.5. The K permeability (P(K)) was calculated from the constant field equation, and showed a fourfold increase after long-term treatment with ouabain. This rise in P(K) probably underlies the membrane hyperpolarization and the decrease in the P(Na)/P(K) ratio.6. It is suggested that inhibition of the Na(+) pump with ouabain causes a gradual rise in [Na](1) which secondarily leads to Ca(2+) uptake, an increase in [Ca](1), and thereby an increase in P(K).

Action Potentials↗