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At least 19 recordsLinked to original sources
PubMed1989

Purkynĕ's description of pressure phosphenes and modern neurophysiological studies on the generation of phosphenes by eyeball deformation.

(a) When a subject indents one of his eyeballs in total darkness, he immediately perceives light extending slowly across the whole visual field of the indented eye. The appearance and the time course of these pressure or deformation phosphenes are described. (b) With simultaneous binocular indentation of the eyeballs a flickering patterned phosphene is observed. (c) A short history of the research on pressure phosphenes and its consequences for the theories of vision is presented. (d) Purkynĕ's observations of monocular deformation phosphenes are described. He repeatedly noted patterned light structures, which most observers only perceive with simultaneous binocular eyeball deformation. It is suggested that Purkynĕ's deviating observations were caused by amblyopia of one eye. (e) The neurophysiological basis of the monocular pressure phosphenes was investigated by means of microelectrode recordings from single optic tract fibers. The activity of single retinal ganglion cells (on-center, off-center neurons, latency class I [Y-neurons] or latency class II [X-neurons]), was recorded in anaesthetized cats. Eyeball deformation in total darkness led to an activation of the on-center ganglion cells, while the off-center ganglion cells were inhibited. The latency and strength of this activation or inhibition varied considerably between different neurons, but were fairly constant in the same neuron when the eyeball indentation was repeated after a pause of 1-3 min. The latency and strength of neuronal activation or inhibition seemed to be dependent mainly upon the neuron location relative to the point of eyeball indentation. Some on-center neurons also exhibited a short activation at "deformation off". (f) The antagonistic response type of on-center and off-center ganglion cells was also observed when the eyeball was deformed as a hydrostatic open system and the intraocular pressure was kept at 25 mm Hg basic pressure. (g) Dark adaptation up to 45 min affected the deformation responses of retinal neurons only to a small degree, if at all. This corresponds to the observation that deformation phosphenes in a human observer changed little during the course of dark adaptation. (h) We assume that the activation of on-center and inhibition of off-center ganglion cells by eyeball deformation are caused by retinal stretching, which also leads to horizontal cell stretch. Stretching the horizontal cell membrane probably generates an increase in membrane sodium conductivity and a depolarization of the membrane potential. This depolarization of the horizontal cell membrane potential is transmitted either directly or indirectly (via receptor synapses) from the horizontal to the bipolar cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1974

Phosphenes produced by electrical stimulation of human occipital cortex, and their application to the development of a prosthesis for the blind.

1. To explore the feasibility of a visual prosthesis for the blind, human visual cortex has been stimulated during a series of surgical procedures on conscious volunteers undergoing other occipital lobe surgery.2. Area no. 17 seems the most effective locus for such stimulation, at least in sighted or recently hemianopic patients.3. Changes in electrode size and configuration, or in stimulus parameters, have little effect on subjective sensation.4. Thresholds do vary depending on parameters, but not electrode size, and these effects have been studied.5. Painful effects are associated with stimulation of the dura, but not of the calcarine artery and associated vessels.6. Stimulation of a single electrode usually produces one phosphene, whose size ranges from tiny punctate sensations like ;a star in the sky' up to a large coin at arm's length. Very large elongated phosphenes, like those seen by Brindley's second patient, have not been reported despite the number of patients, electrodes, and combinations of stimulus parameters tested. These large phosphenes may be an effect of prolonged blindness.7. Stimulation substantially above threshold may produce a second conjugate phosphene, inverted about the horizontal meridian.8. Stimulation of a single electrode may also produce multiple phosphenes with no differential threshold.9. Chromatic effects and/or phosphene flicker may, or may not occur. This can vary from point to point on the same patient.10. Phosphenes fade after 10-15 sec of continuous stimulation.11. All phosphenes move proportionately with voluntary eye movements, within the accuracy of our mapping techniques.12. Brightness modulation can easily be achieved by changing pulse amplitude.13. 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. Patients can usually discriminate phosphenes produced by 1 mm(2) electrodes on 3 mm centres, although this seems to be close to the limit of resolution.15. Patterns of up to four phosphenes produced by four electrodes have been recognized. However, a variety of complex interactions have been reported.16. Multiple phosphenes are co-planar, although patients are unable to estimate their distance.17. Phosphenes appear immediately when stimulation is begun, and disappear immediately upon cessation of stimulation.18. Future work must concentrate on blind volunteers to explore possible differences in subjective sensation produced after prolonged blindness, and to explore more complex pattern presentation which requires substantial periods of time with any given patient.

Adult↗
PubMed1990

On the history of deformation phosphenes and the idea of internal light generated in the eye for the purpose of vision.

Deformation phosphenes are light sensations evoked by deformation of the eyeball in total darkness. They were first reported in Western literature by Alcmaeon of Croton in the fifth century B.C. 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. In the theories of vision this cone of vision played an important role as a signal-transmitting structure and was also used by the Greek opticians as a geometrical construction to explain optical properties of vision. The impact of the deformation phosphene experiment on the ideas of visual sensation can be followed from Greek antiquity through the period of Roman dominance and Galen's medical teaching on to medieval times and up to the late Renaissance when, based on the anatomy of the eye as illustrated by Felix Platter, the image formation on the retina was correctly described for the first time by Johannes Kepler. In the generations following, deformation phosphenes were still employed as an important argument in defence of the theories of vision. However, the idea of physical light generated by eyeball deformation was rejected with increasing frequency during the 17th and 18th centuries. The literature on this topic is discussed, comprising the contributions of the Arabic philosophers and physicians of the 9th and 10th centuries A.D., the Franciscan and Dominican philosophers of the 13th century, Nicolaus Cusanus of the 15th century, several anatomists of the 16th and 17th centuries, Kepler, Plempius, Descartes, Boyle, Newton and others. After Kepler, the mechanical interpretation of the deformation phosphene being caused by direct action of the eyeball deformation onto the retina slowly became dominant, and the idea that physical light is generated in the eye disappeared. The experimentum crucis in this matter was performed by Giovanni Battista Morgagni (1682-1771) and repeated and extended by Georg August Langguth (1711-1782). On the basis of their results, the case for physical light being generated in the eye by deformation was refuted definitively and slowly vanished thereafter from scientific literature. Deformation phosphenes were used in the 19th and 20th centuries as an instructive example of the percepts evoked by inadequate stimulation of a sense organ. J.E. Pŭrkyne in particular contributed to the study of deformation phosphenes, and finally in 1978, F. Tyler devoted a careful study to the differences between monocular and binocular deformation phosphenes.(ABSTRACT TRUNCATED AT 400 WORDS)

History, 15th Century↗
PubMed1991

[Phosphenes elicited by subcortical stimulation in man].

Electrical stimulation of a point in the visual pathway can evoke a visual sensation which is called a phosphene. The phosphenes elicited by intracerebral stimulation were investigated in twenty-three subjects. One hundred and seven phosphenes were reported and all of them appeared in the visual field contralateral to the side of stimulation. The exception was a single case where a diffuse flashing sensation appeared in the whole visual field. Thirteen patients reported white phosphenes and nine patients reported coloured phosphenes. 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. In the lateral area (16-32 mm from the midline), however, stimuli above the level of the calcarine fissure tended to produce phosphenes in the upper quadrant. These findings appear to conflict with traditional concept of the physiological anatomy of the visual pathway in man. The possible mechanism of this phenomenon produced by intracerebral stimulation is discussed in relation to the phosphenes produced by cortical stimulation.

Adult↗
PubMed1990

The radiation phosphene.

A low flux of X-rays below the Cerenkov energy threshold generates a phosphene by direct action on the retina without a fluorescence in the ocular media. X-rays above the Cerenkov threshold can generate only a faint luminescence in the lens and cornea. 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. From calculations of the photon yield due to Cerenkov radiation in the eye from radium, one finds intensities of approximately 90% and approximately 10% for beta and gamma-rays, respectively, if only Cerenkov radiation is considered. Thus, one may conclude that the dominant mechanism of the radium phosphene is Cerenkov radiation, primarily from electrons and not fluorescence as previously speculated. The term "radium phosphene" is a misnomer and should be subsumed along with the X-ray phosphene and particle induced visual sensations under the name "radiation phosphene".

Dose-Response Relationship, Radiation↗
PubMed1994

Phosphenes induced by magnetic stimulation over the occipital brain: description and probable site of stimulation.

Phosphenes were elicited by brief, intense magnetic pulses directed to the occipital area of the brain with two different magnetic stimulators and various coils. The observed phosphenes were described or sketched by the subject. Phosphenes were usually wedge-shaped flashes of light in the midperiphery, although occasionally structured phosphenes were reported (stripes or grids). The depth of effective stimulation was measured by determining the phosphene threshold for two different size coils. Additional depth measurements were made at the cortical motor strip for threshold finger twitches. The visual stimulation site was clearly deeper (approximately 4 cm) than the site for motor stimulation (approximately 2 cm), and lay near the midline. Both foveal and peripheral phosphenes had identical stimulation depths, implying a subcortical stimulation site, possibly in the optic radiation fibers adjacent to the posterior tip of the lateral ventricles. Fibers closest to the ventricle, representing the horizontal meridian of the visual field, would be preferentially stimulated, in agreement with experimental results.

Adult↗
PubMed1991

Magnetic stimuli applied over motor and visual cortex: influence of coil position and field polarity on motor responses, phosphenes, and eye movements.

Transcranial magnetic stimulation was performed over the motor and visual cortex with the Novametrix 12-cm diameter stimulation coil. 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. Furthermore, it was investigated whether stimulation over the visual cortex or over the frontal eye field evoked or disturbed eye movements. Coil position was recorded by constructing grids on the skull surface using extracranial bony landmarks, and was then related individually to underlying cerebral sulci by analysis of magnetic resonance images of the brain. Motor responses. Excitatory effects were maximal when the coil windings in the middle of the coil ring lay over the particular motor representation field of area 4. The response size depended on the direction of the coil currents passing over the motor cortex. For example, coil currents passing over the lateral part of the precentral gyrus from the front and transversely to the central sulcus elicited maximal responses in hand muscles. With the currents passing over the same area in the opposite direction, response amplitudes were much smaller, suggesting activation of different inputs to cortical motoneurons. Phosphenes. Fields of fixed, white and unstructured phosphens occurred in the lower half of the visual field when the coil center was placed about 7 cm anterior to the inion on the inion-nasion line. Counterclockwise or clockwise coil currents elicited phosphenes within the left or right lower quadrant of the binocular visual field, respectively, which could be attributed to an activation of the right or left primary visual cortex (area 17). The 'cortical' phosphenes moved with voluntary eye movements, but not during caloric and optokinetic nystagmus. Phosphenes resulting from an excitation of the optic nerve rather than the retina could be evoked by stimulation over frontal parts of the skull. Eye movements. The application of single magnetic field pulses over the frontal eye field or over the visual cortex did not elicit eye movements except for small vertical eye movements as part of a magnetically elicited blink.

Adolescent↗
PubMed1978

A method for plotting the optimum positions of an array of cortical electrical phosphenes.

The cortical visual prosthesis provides one approach to the substitution of vision in blind people. Usable visual information is provided in the form of phosphenes, and in order to make use of the prosthesis the positions of the phosphenes in visual space must first be determined. Such phosphene maps have to be constructed from observations of the angle and distance between various pairs of phosphenes. 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. By formulating the problem as one involving the minimization of a function of many variables, an algorithm is constructed which determines a two-dimensional co-ordinate for each phosphene by minimizing one of two criteria indicating the fit of the map to the observations. The minimization algorithm employed is, essentially, a 'steepest descent' procedure, and initial co-ordinate values are provided by a triangulation method.

Blindness↗
PubMed1995

Migraine phosphenes and the retino-cortical magnification factor.

Quantitative observations on the shape and position of migraine phosphenes within the visual field were obtained by controlled "perimetric" drawings of the phosphenes performed every 1-2 min during the aura state. The visual field eccentricity of the "fortification" or zig-zag patterns scintillating at about 10 Hz was plotted as a function of observation time. It is well described by an exponential function of time. This exponential function is the product of a first-order linear differential equation determined by the distribution of the retino-cortical magnification factor across the visual field and a constant diffusion speed of the cortical pathophysiological process leading to the migraine phosphene patterns. The observed "particle" size of the phosphene pattern and the width of the scotoma trailing the scintillating phosphenes could also be easily predicted from these assumptions. A model in which the main components are an increase in extracellular potassium concentration, a decrease in extracellular calcium concentration and the constant speed diffusion of the ions along the extracellular space of the stripe of Gennari within the primary visual cortex explains the observations.

Calcium↗
PubMed1992

Simulation of a phosphene-based visual field: visual acuity in a pixelized vision system.

A visual prosthesis for the blind using electrical stimulation of the visual cortex will require the development of an array of electrodes. Passage of current through these electrodes is expected to create a visual image made up of a matrix of discrete phosphenes. The quality of the visual sense thus provided will be a function of many parameters, particularly the number of electrodes and their spacing. We are conducting a series of psychophysical experiments with a portable "phosphene" simulator to obtain estimates of suitable values for electrode number and spacing. The simulator consists of a small video camera and monitor worn by a normally sighted human subject. To simulate a discrete phosphene field, the monitor is masked by an opaque perforated film. The visual angle subtended by images from the masked monitor is 1.7 degrees or less, depending on the mask, and falls within the fovea of the subject. In the study presented here, we measured visual acuity as a function of the number of pixels and their spacing in the mask. Visual acuity was inversely proportional to pixel density, and trained subjects could achieve about 20/26 visual acuity with a 1024 pixel image. We conclude that 625 electrodes implanted in a 1 cm by 1 cm area near the foveal representation of the visual cortex should produce a phosphene image with a visual acuity of approximately 20/30. Such an acuity could provide useful restoration of functional vision for the profoundly blind.

Blindness↗
PubMed1976

Movement phosphenes in optic neuritis: a new clinical sign.

Positive visual phenomena (phosphenes) elicited by eye movements have been described in normal individuals and in myopes with vitreous opacities. In the present paper we describe eye movement-induced phosphenes that appear to be related to optic nerve involvement in patients with optic neuritis and multiple sclerosis. This phenomenon is not associated with vitreous or retinal defects, nor is it similar to phosphenes observed in normal individuals. Instead, it shares many characteristics with the well-known Lhermitte sign and is believed to represent a similar phenomenon.

Adult↗
PubMed1996

Increase of posterior cerebral artery blood flow velocity during threshold repetitive magnetic stimulation of the human visual cortex: hints for neuronal activation without cortical phosphenes.

To analyze the effects of low intensity repetitive transcranial magnetic stimulation over the occipital cortex on regional cerebral perfusion, bilateral simultaneous monitoring of posterior cerebral artery blood flow velocity was performed using transcranial Doppler ultrasonography in 14 healthy subjects. During 20 s of unilateral magnetic stimulation with 3 Hz and 6 Hz a significant increase of ipsilateral flow velocity was observed during both stimulus conditions (3 Hz, 10.2 +/- 3.7%; 6 Hz, 12.8 +/- 4.7%). A significantly smaller flow velocity increase occurred also in the contralateral posterior cerebral artery (3 Hz, 8.6 +/- 4.0%; 6 Hz, 10.6 +/- 4.1%). Flow velocity increases were similar to values reported in the literature for physiological activation paradigms so that excessive excitation of the visual cortex does not seem to occur during repetitive magnetic stimulation. The largest increase of flow velocity was observed in the ipsilateral posterior cerebral artery of 5 subjects who experienced phosphenes in the contralateral visual half-field during stimulation (14.3 +/- 4.1%: mean of 3 and 6 Hz stimulation). In the other 9 subjects significant velocity increases indicated cortex activation in the absence of cortical phosphenes. The occurrence of maximum velocity responses within 2-3 heart beats following the first cortex stimulus points to a fast adjustment of cerebral perfusion in response to transcranial brain stimulation.

Blood Flow Velocity↗
PubMed1982

Auditory evoked phosphenes in optic nerve disease.

Five patients with optic neuropathy, four vascular and one demyelinating, are described who each complained of an unusual symptom. Bright flashes of light (phosphenes) occurred in the affected eyes and were evoked by sudden unexpected sounds. Movement of the eye alone did not reproduce the symptom. In all patients the phenomenon was sufficiently prominent to interfere with sleep and was the main complaint of one patient. An anticonvulsant (phenytoin) greatly reduced the frequency and intensity of the phosphene in one patient.

Acoustic Stimulation↗
PubMed1979

Phosphenes induced by sound.

Three adults with acquired unilateral visual impairment noticed phosphenes when they heard noises. They witnessed them only when resting in a dark or dimly illuminated room. The hallucinations persisted for days in a postkeratoplasty patient, for weeks in a patient with optic neuritis, and for months in a patient with compression of the optic nerve. The sound-induced phosphenes in these cases seemed to be a pathologic variety of hypnagogic hallucination. We theorize that under conditions of altered excitability and visual deafferentation of the brain, cells capable of responding to both visual and auditory stimuli become hyperresponsive to sounds.

Acoustic Stimulation↗
PubMed1973

Contour-like phosphenes from electrical stimulation of the human eye: some new observations.

1. The contour-like phosphenes that may be seen with electrical stimulation of the human eye are described.2. It is found that a moving edge is particularly effective in generating these patterns.3. The relation between the velocity of the edge, the frequency of the current and the resultant spatial frequency of the lines is as if one line were generated at the edge for every cycle of the current.4. The frequency-dependence of the phase-shift between phosphene and current is such as would be expected if the light was delayed by some 30 msec relative to the current at the site of interaction.5. Evidence is brought forward suggesting that this phenomenon is the result not of interference-like processes, but of coupling interactions of the retinal neurones, dividing the population into domains responding in opposite phase to the electrical stimulation.

Accommodation, Ocular↗