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Biomedical subjects

M F Marmor

Publications and source records attributed to M F Marmor.

At least 127 records · Page 7Linked to original sources
PubMed1984

Effects of subretinal and systemic osmolality on the rate of subretinal fluid resorption.

Small norhegmatogenous retinal detachments (blebs) were made in Dutch rabbit eyes by injecting solution into the subretinal space. There was no difference in resorption time between blebs made with isotonic, hypertonic or hypotonic sodium chloride. However, blebs made with sucrose solution took longer to resorb than those made with Hanks' solution, regardless of whether the sucrose was hypotonic or hypertonic. Intravenous injection of hyperosmotic solution (mannitol) accelerated the resorption of Hanks'-filled blebs but the injection of hypoosmotic solution (water) had no clear effect. The authors conclude that osmotic differences between the subretinal space, and the vitreous and/or choroid, are rapidly equilibrated by the surrounding tissues; but the rate of bleb resorption will be affected by the size and membrane permeability of the molecules within the subretinal space. The effects of increased serum osmolality may involve not only osmotic pressure but an opening of the tight junctions of the RPE.

Animals↗
PubMed1983

From sea lemons to c-waves.

This review of retinal pigment epithelial (RPE) physiology pays tribute to Anthony L. F. Gorman, who introduced the author to the giant neuron of Anisodoris nobilis (the sea lemon) and cellular neurobiology. The RPE is an epithelial monolayer with tight junctions, which controls the environment of the photoreceptor outer segments. The apical and basal membranes have different electrical properties and generate a standing potential across the eye. The RPE helps maintain adhesion between the retina and the wall of the eye. Adhesion is weakened by cyanide, low pH or low calcium, but enhanced by ouabain or acetazolamide. The RPE transports water from the subretinal space toward the choroid. This water movement is inhibited by hypoxia or cyanide but enhanced by ouabain or acetazolamide. The c-wave of the electroretinogram is a composite of a cornea-positive wave produced by hyperpolarization of the apical RPE membrane and a cornea-negative wave produced by the Muller cells, both in response to the fall in extracellular potassium that follows illumination of the photoreceptors. The "light response" of the standing potential is produced by depolarization of the basal membrane of the RPE. These examples illustrate how principles of cellular neurophysiology can be applied to questions of clinical relevance.

Animals↗
PubMed1983

An evaluation of night vision mobility aids.

Two night vision aids are commercially available to help individuals who have diseases that cause night blindness. The ITT Night Vision Aid (NVA) is a light amplification device; the Wide Angle Mobility Light (WAML) is a wide beam flashlight. The effectiveness of both instruments in helping night-blind, field-restricted subjects to walk a course of residential streets at night was tested. WAML users were also surveyed to determine the usage, applications, and reliability of the device. We found that the WAML significantly reduced error rates and was preferred by most subjects; it was reported to be used regularly by individuals who owned it. The NVA did not significantly improve error scores, and was not effective as an ambulatory night mobility aid for most patients.

Adult↗
PubMed1983

The resorption of subretinal fluid after diffuse damage to the retinal pigment epithelium.

We studied the role of the retinal pigment epithelium (RPE) in the resorption of different subretinal fluids from under small experimental retinal detachments (blebs) in the rabbit. Damaging the RPE with sodium iodate caused the resorption time, for blebs made with an ionic solution (Hanks'), to decrease from 2-6 hours to only about 30 minutes. Blebs made with sucrose also absorbed much more quickly after iodate. However, blebs made with autologous serum resorbed no faster after iodate. We conclude that iodate destroys the membrane barrier properties of the RPE, allowing subretinal fluid to cross freely according to oncotic pressure. We postulate that in the normal eye, where osmotic fluid movement is low because of the high resistance barrier, the RPE must transport fluid actively to keep the subretinal space dehydrated.

Absorption↗
PubMed1982

The relationship between the c-wave and light response of the rabbit eye.

The rabbit c-wave and light response (LR) of the standing potential were recorded simultaneously while presenting the eye with light flashes at 15 sec intervals. The LR peaked about 15 min after the onset of flashes, but the c-wave amplitude remained constant after the first min of stimulation. Elimination of pigment epithelial activity with intravenous sodium iodate blocked both the c-wave and LR. Elimination of inner retinal activity with intravitreal aspartic acid blocked neither. These results are consistent with those from other mammals insofar as the pigment epithelium is required for both c-wave and LR, but differ from other species in two respects: (1) the rabbit LR is not sensitive to aspartate; (2) the rabbit c-wave does not vary in amplitude with the LR.

Animals↗
PubMed1982

The rate and route of fluid resorption from the subretinal space of the rabbit.

Small nonrhegmatogenous detachments were formed in living rabbit eyes by injecting a few microliters of fluid into the subretinal space. The change in volume of these detachments was followed by sequential photogrammetric measurements. Detachments of 1 to 3 mm diameter filled with a balanced salt and glucose solution (Ames' solution) resorbed at a constant rate over approximately 80 min of observation and appeared to be totally resorbed within 2 to 6 hr. The rate at which fluid resorbed per unit area of pigment epithelium was consistent with the rate of resorption in other transporting epithelia as well as with clinical observations in humans. Detachments filled with isotonic sucrose resorbed much more slowly than those filled with saline solutions, suggesting that fluid resorption requires the passage of ions through cell membranes. Hypoxia markedly and reversibly reduced the rate of resorption, suggesting that active transport is involved in the removal of the saline solutions from the subretinal space Anatomical and physiological evidence indicate that the site of active transport is the pigment epithelium. Active resorption of subretinal fluid is probably a factor in the maintenance of normal retinal adhesion.

Absorption↗
PubMed1981

The C-wave of the rabbit electroretinogram during dark-adaptation and the steady-state.

C-waves of the rabbit ERF under urethane anesthesia were elicited by a Grass photostimulator during dark adaptation and under steady-state conditions. After strong pre-adaptation with light, the amplitude and time-to-peak of the c-wave increased in parallel with the a- and b-waves, reaching a maximum of 90-130 min. In the dark-adapted steady-state, repetitive stimuli at intervals ranging from 15 sec to 5 min elicited a stable c-wave response except for a small dip in amplitude that occurred 2-6 min after initiating the shortest interval (15 sec) flashes. Although the changes in light and dark used in these experiments should have elicited shifts in the standing potential, no fluctuations of the c-wave amplitude were evident with a time course corresponding to a light response of the standing potential.

Animals↗
PubMed1981

Contrast sensitivity and retinal disease.

A new and practical test for contrast sensitivity (Arden gratings) was evaluated in retinal diseases and found to be a more sensitive indicator of dysfunction than Snellen acuity. Most patients with acuity of 20/30 or better (e.g., with retinitis pigmentosa or toxic retinopathy) showed diminished sensitivity to finely spaced gratings, while patients with poor acuity (e.g., with cone dystrophy) showed normal sensitivity to coarsely spaced gratings. Grating tests may allow earlier diagnosis and more precise follow-up of retinal disease, but their specificity for particular disorders remains to be established.

Adult↗
PubMed1980

Visual loss in retinitis pigmentosa.

I investigated the visual histories of 91 consecutive patients with retinitis pigmentosa to determine when, and how fast, visual acuity was affected by the disease. The results from recessive cases showed that visual loss may occur at any age in retinitis pigmentosa, and typically progresses from 6/12 (20/40) to 6/60 (20/200) in about six years. At any given time, most of the patients had either good or poor visual acuity; intermediate levels of visual acuity appeared to be unstable. Before age 20 years, 60 to 90% of the patients had a visual acuity of 6/12 (20/40) or better, and few had a visual acuity of 6/60 (20/200) or worse. By age 50 years, 25% of the patients still retained good visual acuity, but more than 50% had visual acuity of 6/60 (20/200) or worse.

Adolescent↗
PubMed1980

Wide-field high-intensity lantern. An affordable night mobility aid.

Individuals with disorders such as retinitis pigmentosa or severe glaucoma often have difficulty ambulating at night, not only because they have lost rod vision, but because flashlights do not help. The problem is that ordinary flashlights produce a very narrow beam of light (only about 3 degrees) which is hard to follow with tunnel vision. To eliminate this problem, we have designed a relatively inexpensive lantern which produces a bright wide beam of light. It can greatly enhance the night mobility of patients with severe field constriction or night blindness.

Eye Diseases↗
PubMed1980

The effect of metabolic inhibitors on retinal adhesion and subretinal fluid resorption.

Retinal adhesion and the resorption of subretinal fluid were studied in Dutch rabbits, with two experimental techniques. In the first, small local detachments were made in vivo by injecting a small amount of fluid under the retina with a micropipette, and the time for resorption of the detachment was monitored. In the second, strips of eyecup were maintained in a physiologic bathing medium, and the force required to peel retina from the pigment epithelium was measured. Using these techniques, we have found that both the mechanisms for removing subretinal fluid and for maintaining retinal adhesion in vitro are enhanced by exposure to ouabain, are inhibited by exposure to cyanide, and are inhibited by the replacement of the physiologic medium with normal saline. These data suggest that metabolic systems may simultaneously hydrate and dehydrate the subretinal space and that some factors which are important to the maintenance of normal adhesion are missing from normal saline.

Animals↗
PubMed1980

Osmotically induced retinal detachment in the rabbit and primate. Electron miscoscopy of the pigment epithelium.

Previous work has shown that the injection of a hyperosmotic solution into the rabbit vitreous will cause rapid detachment of the retina. The present experiments show that osmotic detachment also occurs in the monkey eye. No anatomic changes were found to account for the early separation of the retina, but within a few minutes of detachment in the rabbit or several hours in the monkey, the retinal pigment epithelium microvilli lose their normal organization. This may be a nonspecific response to separation from the outer segments. After longer periods of osmotic detachment in the rabbit, the RPE cells became edematous and the microvilli shrank and disappeared. Although some cells ruptured at the apical membrane and large cysts were often observed above the cell junctions, the intercellular tight junctions always appeared intact. Osmolarity should be accounted for in the evaluation of intravitreal injections for man, and care should be used to avoid injection of concentrated solutes near the retina.

Animals↗
PubMed1980

Similarities between the c-wave and slow PIII in the rabbit eye.

The c-wave of the electroretinogram was recorded from the eyes of Dutch rabbits and compared with the slow PIII response isolated by intravenous infection of sodium iodate and intravitreal injection of sodium aspartate. Although opposite in polarity, the waveforms of the two responses were remarkably similar over a wide range of stimulus intensities and durations. Plots of time-to-peak vs. log stimulus energy show that both responses follow the Bunsen-Roscoe law. Curves plotting the locus of all points for which the Bunsen-Roscoe law held were approximately parallel for the two responses, and the critical durations for each stimulus intensity were equivalent. The slow PIII peaked earlier than the c-wave, consistent with published observations that the time-to-peak of light-induced K+ changes is shorter near the photoreceptor inner segments than near the pigment epithelium. These data support the hypothesis that there is a common generator for the c-wave and slow PIII.

Animals↗
PubMed1979

The electroretinogram in retinitis pigmentosa.

Examination of electroretinographic (ERG) reports from 70 consecutive patients with retinitis pigmentosa (RP) showed that photopic and scotopic B-wave amplitudes correlated with age and visual acuity, but not with dark adaptation threshold. No appreciable differences in ERG characteristics (including B-wave implicit time) were observed between recessive, dominant, and X-linked cases. However, the ERG findings from one group of patients stood out clearly from the rest, because of normal flicker B-wave implicit times (less than or equal to 32 ms) and large B-wave amplitudes (less than or equal to 100 muV under scotopic conditions). These patients constitute a recognizable subgroup of RP, independent of the mode of inheritance, which is characterized by delimited disease, mild functional symptoms, and a good visual prognosis.

Adolescent↗