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1.
Electroencephalogr Clin Neurophysiol ; 92(5): 469-72, 1994 Sep.
Article in English | MEDLINE | ID: mdl-7523092

ABSTRACT

The few studies that have been done on short-latency, subcortical visual evoked potentials (SVEPs) have all used stroboscopic flashes as the evoking stimulus. The dimensions of the stimulator, the acoustical artifacts and the photic spread to the examination room limited the use of SVEPs to research laboratories. With the advent of high-efficiency light-emitting diodes (LEDs), high-intensity flashes can now be generated from goggle-mounted LEDs. In this study, a goggle-mounted high-intensity stimulator was constructed and its flashes used to evoke SVEPs. The reproducibility of SVEPs across subjects and the ease of using the high-intensity LED flash stimulator make them a promising candidate for testing subcortical visual pathway function in the operating room.


Subject(s)
Electroencephalography , Evoked Potentials, Visual , Photic Stimulation/instrumentation , Cerebral Cortex/physiology , Humans
2.
Isr J Med Sci ; 29(1): 17-22, 1993 Jan.
Article in English | MEDLINE | ID: mdl-8454439

ABSTRACT

Steady-state visual evoked potentials (SSVEP) were recorded in response to flashes from eyepatch-mounted light-emitting diodes during neurological surgery and in the intensive care unit. SSVEP were detected and measured with a microprocessor-based waveform correlator. The system enabled a continuous display, in real time, of SSVEP amplitude and latency. SSVEP amplitude and latency changes were monitored throughout a variety of surgical procedures. Some of these procedures directly affect the central visual pathway, some affect the central nervous system as a whole, while others do not affect central nervous system function. In addition, intensive care unit patients with a variety of intracranial pressures were monitored. The results of this study indicate that SSVEP recorded with this method showed changes in SSVEP within seconds of surgical and/or medical decompression of intracranial pressure and were sensitive to specific changes in the visual pathway. Surgical procedures that directly affected the visual system, or elevation of intracranial pressure, resulted in changes in SSVEP. In contrast, procedures that did not affect the functional integrity of the visual system did not affect the recordings.


Subject(s)
Critical Care , Evoked Potentials, Visual , Monitoring, Physiologic/methods , Neurosurgery , Adenoma/physiopathology , Adenoma/surgery , Adult , Brain Diseases/physiopathology , Critical Care/methods , Female , Humans , Intracranial Pressure , Male , Middle Aged , Monitoring, Intraoperative , Pituitary Neoplasms/physiopathology , Pituitary Neoplasms/surgery
3.
Graefes Arch Clin Exp Ophthalmol ; 227(3): 212-5, 1989.
Article in English | MEDLINE | ID: mdl-2737481

ABSTRACT

In this report we recommend the estimation of visual acuity by detection of the visual evoked potential (VEP) threshold, defined by the smallest visual angle of a constant check size that evokes potentials. This approach was implemented using a fiber-optic pattern-reversal stimulator placed at measured, increasing distances from the examined eye. Snellen visual acuity as determined in 113 subjects was correlated with the VEP detection threshold. A highly significant correlation was found between visual acuity and the threshold visual angle of check size in subjects whose vision was impaired due to opacity in ocular media. For any given visual acuity a somewhat wide range of threshold check sizes, typically 5-10 min of arc was observed. Technical difficulties that need to be overcome to improve these results are discussed.


Subject(s)
Evoked Potentials, Visual , Fiber Optic Technology , Adult , Aged , Humans , Middle Aged , Optical Fibers , Pattern Recognition, Visual , Visual Acuity
4.
Electroencephalogr Clin Neurophysiol ; 64(5): 411-6, 1986 Nov.
Article in English | MEDLINE | ID: mdl-2428591

ABSTRACT

A comparison of VEP findings using a fiber optical stimulator with three color combinations (black/red, black/green and red/green) and a conventional video monitor stimulator in black/white was performed in 3 groups of subjects: a group with definite lesions in the visual pathway, a group with suspected lesions and a control group. No significant correlations of P100 latency were found in the normative group, probably because of the small range of their values. All correlations were significant in the two patient groups, except for the red/green stimuli in the definite group. In general, the red/green combination was inferior to other color combinations in eliciting VEPs. The patient groups with definite, as well as suspected, lesions indicated no benefit from the color stimuli, as compared with black/white. The major advantage of the fiber optical stimulator is its simplicity, the lack of stimulus artifacts and the accessibility to the patient's bed side, thanks to its small size. Stimulators with higher illuminance and improved pattern element shape should narrow the still unacceptable normative variability of the wave forms recorded.


Subject(s)
Evoked Potentials, Visual , Multiple Sclerosis/diagnosis , Adolescent , Adult , Aged , Female , Fiber Optic Technology , Humans , Male , Middle Aged , Pattern Recognition, Visual , Videotape Recording
5.
J Neurosurg ; 62(6): 935-8, 1985 Jun.
Article in English | MEDLINE | ID: mdl-3998849

ABSTRACT

A system for recording evoked potentials, in which a lock-in amplifier replaces the averaging computer, is described. With this system, the set-up is much the same as in the conventional apparatus, with the following exceptions: 1) the amplifier gain is set at only a few thousands; 2) analogue-to-digital conversion and computer averaging is replaced by a lock-in amplifier; and 3) the output of the system is an analogue signal representing the amplitude of the recorded steady-state evoked potentials and the phase of baseline crossings. This set-up is much less costly than the conventional apparatus, much easier to operate, and, with its real-time output, may provide an ideal technique for screening and monitoring purposes.


Subject(s)
Evoked Potentials , Neurophysiology/instrumentation , Electrophysiology/instrumentation , Evoked Potentials, Auditory , Evoked Potentials, Somatosensory , Evoked Potentials, Visual
6.
Appl Opt ; 17(3): 459-62, 1978 Feb 01.
Article in English | MEDLINE | ID: mdl-20174430

ABSTRACT

The conditions necessary to obtain simultaneous oscillation of two laser transitions sharing a common energy level are examined. The general form of the equations is the same for all three possible cases, and it is shown that the operating point should lie within the area limited by the axes of coordinates and two straight lines in the transmittance plane. Parameters determining those lines can either be calculated or measured experimentally; their slopes depend only upon the transition parameters and are thus the same for all lasers operating on given transitions.

7.
Appl Opt ; 17(21): 3503-6, 1978 Nov 01.
Article in English | MEDLINE | ID: mdl-20204009

ABSTRACT

A statistical approach is used to characterize image transmission through misaligned multifibers, i.e., differently arranged at the input and output faces, leading to a spatially invariant line spread function. The resulting MTF is the product of the MTF for the aligned system and a function characterizing stochastic departures from alignment. The case of circular fibers with Gaussian misalignment is treated theoretically and is found to account satisfactorily for experimentally observed results.

8.
Appl Opt ; 17(23): 3818-21, 1978 Dec 01.
Article in English | MEDLINE | ID: mdl-20208616

ABSTRACT

By magnifying the high-quality image produced by a rigid miniature endoscope onto a large flexible multifiber, an instrument has been developed which provides both high resolution and flexibility. It is shown theoretically, and verified experimentally, that the MTF of a system of coupled multifibers is the product of the individual MTFs. Measurements show that the coupled instruments outperform state-of-the-art all-flexible systems. The technique should greatly facilitate observation, display, and photography in percutaneous endoscopy and in a variety of industrial applications.

9.
Appl Opt ; 16(4): 1041-4, 1977 Apr 01.
Article in English | MEDLINE | ID: mdl-20168631

ABSTRACT

Multiwavelength lasers are used to compensate for color distortion in transmission of light through plastic optical fibers. Efficient methods to eliminate the speckle effect and to generate multicolor laser light are described.

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