(n.) A luminous impression produced through excitation of the retina by some cause other than the impingement upon it of rays of light, as by pressure upon the eyeball when the lids are closed. Cf. After-image.
Example Sentences:
(1) Excitatory (positive) phenomena are subjective photic sensations (phosphenes) which can be elicited by transcranial magnetic stimulation over occipital parts of the skull.
(2) Stimulation substantially above threshold may produce a second conjugate phosphene, inverted about the horizontal meridian.8.
(3) Phosphenes appear immediately when stimulation is begun, and disappear immediately upon cessation of stimulation.18.
(4) The position of phosphenes in the visual field corresponds only roughly with expectations based on classical maps showing the projection of the visual field onto the cortex.14.
(5) The configuration of the phosphene fields hints at an excitation of the primary visual cortex (Brodmann's area 17).
(6) A visual prosthesis based on electrical stimulation of the visual cortex with an array of penetrating electrodes is expected to produce pixelized visual images consisting of punctate spots of light (phosphenes).
(7) The findings of these examinations correlated best of all with the clinical picture when visual evoked potentials (latency increase, decrease of the amplitude with atrophy augmentation, interhemispheric asymmetry in chiasmal and retro-chiasmal involvement) or the critical frequency of phosphene disappearance (reliably reduced if a disease was developing) were recorded.
(8) The phenomenon of deformation phosphenes was instrumental in prompting some pre-Socratic philosophers and Plato to conceive the idea that efferent light is emitted from the eye for the purpose of vision and a 'cone of vision' is formed by interaction with the external light.
(9) Because of the variation in repeated observations of the same phosphene pair, some method is needed to provide the 'best' fitting map to the observations.
(10) The increment threshold for a small spot of light on the phosphene in the dark is some 0.5 log td higher than for the same spot on a patch of light matched in appearance to the phosphene under the same conditions.5.
(11) Our findings indicate that the psychological component of the perception of electric and magnetic phosphenes must not be underestimated.
(12) For cortical phosphenes there is no sharp flicker fusion frequency, and probably no flicker fusion frequency at all.7.
(13) From experimental work on humans in 1905 with unencapsulated radium, it is known that approximately 80% of the intensity of the radium phosphene is from the beta-ray component and approximately 20% from the gamma-ray.
(14) Experiments are described in which the phosphene produced by passing alternating current of frequency 100 Hz through the eye is matched with a patch of light having the same apparent size.2.
(15) The prosthesis would create a pixelized visual sense consisting of punctate spots of light (phosphenes).
(16) The phosphenes appear on the left or right side of the visual field depending upon the direction of the coil currents, which determines whether the visual cortex of the right or the left hemisphere is activated.
(17) Electrical stimulation of the occipital cortex resulted in discrete photic sensations or "phosphenes" in two volunteers who had been totally blind for 7 and 28 years, respectively.
(18) Patterns of up to four phosphenes produced by four electrodes have been recognized.
(19) The influence of coil position on the size of electromyographic responses and on the intensity and position of phosphenes in the binocular visual field was studied.
(20) In the medial area (10-15 mm from the midline) of the occipital lobe, stimuli above the calcarine fissure resulted in phosphenes in the lower quadrant of the visual field.
Retina
Definition:
(n.) The delicate membrane by which the back part of the globe of the eye is lined, and in which the fibers of the optic nerve terminate. See Eye.
Example Sentences:
(1) The distribution of gelsolin, a calcium-dependent actin-severing and capping protein, in the retina of the developing and adult rabbit was studied.
(2) At day 7 MD occupy about 14% area of posterior retina in transverse sections in Campbell rats versus 7% in normal animals.
(3) Chromatolysis and swelling of the cell bodies of cut axons are more prolonged than after optic nerve section and resolve in more central regions of retina first.
(4) Reverse transcription of retina mRNA followed by DNA amplification using D4-specific nucleotides demonstrates the presence of D4 mRNA in retina.
(5) Electroretinographic (ERG), morphometric and biochemical studies on retinas from monkeys or rats reveal that moderate level developmental lead (Pb) exposure produces long-term selective rod deficits and degeneration.
(6) Cultured cells from fourth to ninth passage showed positive labelling for S 100 protein, carbonic anydrase (CAA), glutamine synthetase (GS), alpha cristallin (alpha C) and polyclonal glial fibrillary acidic protein (GFAP) antibody, but were negative for both monoclonal GFAP antibody and also for Muller cells in the retina.
(7) This study examines the morphology of sporadic congenital microphthalmia in 1-day-old chicks, with particular emphasis on the neural retina.
(8) We based our approach on the anteroposterior location of the incarceration site and the amount of retina incarcerated into the wound.
(9) The posterior retina remained uninvolved, and no further treatment was needed.
(10) On histopathologic examination there were microabscesses in the inner choroid and subretinal space, disrupting the outer retina but sparing the inner retina.
(11) Although the Ca2+-independent mechanism accounts for about two thirds of the total acetylcholine release in the dark, the amount of acetylcholine released in this way is small compared with the release of acetylcholine triggered by stimulation of the retina with light.
(12) These results are consistent with the idea that RPE pigment dispersion is triggered by a substance that diffuses from the retina at light onset.
(13) A specific vitamin A-dependent fluorophore was isolated from these retinas using thin-layer chromatography (TLC).
(14) Premature infants possessed 35-50% higher levels of retinal vitamin C than those found in mature retinas.
(15) The relationship of these observations to the genesis of positional markers in the regenerating retina is discussed.
(16) One may speculate whether clinical conditions exist--apart from hereditary retinal dystrophies--in which the retina becomes more sensitive to light from strong artificial or natural sources, which are otherwise innoxious.
(17) We also used an optical device to stabilize images of the real world upon the retina.
(18) The three-dimensional view obtained with scanning electron microscopy provides another perspective on the pathogenetic changes of the RCS retina.
(19) Although the chicks were behaviorally and electrophysiologically blind at the time of hatching, their retinas appeared morphologically comparable to normal chicks at this stage.
(20) These observations suggest that IDDM patients have reduced fibrinolytic activity in their retinas, which might predispose them to thromboembolic disease.