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Biomedical subjects

M L Wolbarsht

Publications and source records attributed to M L Wolbarsht.

71 records · Page 4Linked to original sources
PubMed1970

Responses to directional stimuli in retinal preganglionic units.

1. Extracellular recordings were made from directionally selective ganglion cell units in the isolated frog retina and decapitated Necturus preparation.2. Intracellular recordings were made from individual photoreceptor cells in the frog and Necturus retinae while stimuli which had evoked directionally selective responses at the ganglion cell level were presented. No evidence for inhibition of photoreceptors for any direction of movement of the light stimulus was found. This appeared to rule out a mechanism for directional selectivity involving inhibition of photoreceptor potentials.3. Intracellular recordings were made from the nuclear layer between photoreceptors and ganglion cells in Necturus. The responses were of two types: either transitory or sustained.4. The sustained type responses could be divided into two classes depending on their receptive field organization. One type of sustained potential had a large receptive field without any evidence for a centre-surround antagonism and corresponded to the luminosity type S-potential recorded in fish. The other type had a smaller receptive field and showed a difference in sign of response between centre and surround if the centre was flooded with a steady light. This is very similar to what has been described for a type of on-centre, off-surround ganglion cell.5. The transitory type of responses showed some centre-surround antagonistic organization. Some of these transitory units also appeared to show some discrimination in response as a function of the distribution of light on the retina.6. No specific directional selectivity was found from units at the inner nuclear layer. This further excluded any mechanism of directional sensitivity which involves selectivity at the photoreceptor level.7. It was concluded that although inner nuclear layer units may play a role in the mechanism of directional selectivity, no specific directionality was found at the first synaptic level of the retina.

Animals↗
PubMed1968

Receptive field organization of the S-potential.

The receptive fields of S-potentials have been studied in carp retinas. The relationship between the stimulus intensity and area of stimulation was examined for each component of three different types of S-potential. It appears that for each component there is full summation over a large portion of the retina, a type of organization different from that found in the ganglion cell.

Animals↗
PubMed1966

Visual acuity in a stumptail macaque.

Visual acuity in a normal stumptail macaque is 1.4 minutes of arc-similar to man's. Destruction of the fovea by photocoagulation decreased acuity to 9 minutes of arc. These facts suggest that the fovea in the macaque has the same physiological role in visual acuity as in man.

Animals↗
PubMed1965

Retina: pathology of neodymium and ruby laser burns.

Chorioretinal lesions hiave been prodluced in monkeys during experitments with ruby and neodlymium lasers. Most of the energy from the ruby laser (wavelength 6943 angstroms) is absorbed by the pigment epithelium, where the greatest damage appears. With the neodymium laser (10,600 angstroms) the neural portions of the retina absorb more of damage than the pigment epithelium and adjacent tissues.

Animals↗
PubMedDate not supplied

Contact lens filter for macular photocoagulation with monochromatic green argon laser.

Safer and more effective macular photocoagulation can be performed with monochromatic green light, thereby avoiding the energy absorption by the xanthophyll pigment in the inner retina in the blue portion (488 nm line) of the argon laser radiation. While an appropriate laser filter has been built into commercially available laser systems to provide a "green-only option," a contact lens filter which provides monochromatic green energy with a standard argon laser delivery system has been evaluated. The filter requires twice as much laser energy output from the laser, and may allow higher levels of energy to reflect off the filter towards observers.

Choroid↗
PubMedDate not supplied

Erbium:YAG (2.94 mum) laser effects on dental tissues.

Past trials with soft and calcified tissues have demonstrated that long pulse train (2.5 mus) Er:YAG (2.94 mum) laser may be used to ablate tooth structure of human teeth. Determination of physical and thermal damage to surrounding tissue during removal of enamel and dentin is a primary objective of this study. Extracted human teeth with thermal probes imbedded in the pulp chambers were submitted to cavity preparation using an Erbium YAG laser with water mist. Wavelength selection as well as use of a water mist during the procedure resulted in efficient tissue removal without significant surrounding damage. Ground sections and SEM sections of teeth showed little or no melting or ash formation in adjacent dentin and enamel and no visible change in the pulp chamber. The surfaces produced by laser ablation were rough and irregular with craters and grooves. Average temperature change in the pulp chamber monitored during tooth preparation was 2.2 degrees Centigrade. These findings suggest that constantly available water aids vaporization and microexplosions, increasing the efficiency of tooth structure removal, and aids in cooling of the tooth structures. The long pulse Er:YAG (2.94 mum) laser may be an effective method for tooth reduction applications when used with a water mist.

Animals↗
PubMedDate not supplied

Arthroscopic surgery: simple devices to facilitate multiple entries and manipulations of the knee.

A system has been especially designed and fabricated for use with an arthroscope and other instruments so that an open passage is maintained through the skin, retinaculum, and joint capsule to allow the insertion and withdrawal of instruments at will. This system is designed to minimize loss of irrigating fluid from the joint during use, including instrument exchanges. A companion stabilization device has been constructed to allow the unassisted application of valgus or varus stress to the knee while leaving the surgeon's hands free.

Humans↗