Surgery – Truss – Pad
Patent
1996-07-08
1998-10-20
Millin, Vincent
Surgery
Truss
Pad
128733, 128639, A61B 504
Patent
active
058231900
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method as defined in the introductory part of claim 1, as well as to an apparatus for the realization of said method for carrying out an electro-oculographic (EOG) examination, said method being used for detecting certain types of damages in the retina. Especially the invention relates to a method for speeding up and facilitating to the EOG examination by automatizing it. More generally the invention is directed to a method for determining a reference value for a potential leap from a sample signal comprising potential leaps and spurious noise.
The invention further is related to an apparatus as defined in the introductory part of claim 7, for the realization of the method according to the invention.
Electro-oculography is an electro-physiological examination centrally related to opthalmology, said examination being based on the measurement of slow fluctuations in the electrical potential differences between the retina (- pole) and the cornea (+ pole). The ratio between said cornea-retinal potentials is called the EOG-ratio. EOG is used for the examination of certain degeneration diseases in the retina. It may further be used for ascertaining whether a medication used e.g. for curing rheumatism is damaging the retina. Thus, EOG examination is considered to be essential in patient examination, but it is also considered to be a good examination method in experimental studies and especially when carrying out retina toxic examinations for medicines.
The potential cannot be directly measured at the eye. This could be done by arranging an electrode on the cornea, but in this case the eye must be anesthetized, which would lead to erroneous results due to the abnormal function of the eye.
This problem is avoided by measuring the EOG ratio indirectly using electrodes arranged in the vicinity of the patient's eyes, whereby mutually different biopotentials, which can be measured, are formed by the movement of the eyes. The biopotential ratio for an eye can then be defined by calculation from the mutual ratio of said bio potentials. Depending on the test arrangement a varying amount of electrodes are arranged on the skin, and further there are numerous different positioning alternatives for them. The movement of the eyes is accomplished using e.g. blinking light sources. In a widely used test arrangement the patient looks at two light sources arranged at opposite sides of his eyes. The lights blink in opposite phases at a frequency of e.g. 1 Hz, so that the patient's eyes are in a constant movement back and forth. Also such a test arrangement is known where a fixed light or some other distinct target is moved in front of the patient's eyes.
The potential always varies when the patient moves his eyes. The wave frequency of the potential amplitudes thus initiated is identical with the blinking frequency of the light source.
The size of the potential amplitude is proportional to the EOG ratio, since the potential is zero when the eye looks straight ahead and correspondingly differs from zero when the eye looks sideways or upwards.
Since the potential depends on the position of the eye and on the cornea-retinal potential it is impossible to define the real cornea-retinal potential. This fact, however, is unsignificant, since the potential ratio achieved as a result of the examination is more important. It is, however, important that during the examination the eye moves between the same suitably defined points.
The examination itself is usually started in darkness. The potential difference signal is recorded for about 10 seconds once in every minute during a fifteen minute period. The signal is not measured continuously, because the continuous moving of the eyes is very exhausting, which would distort the results. Also, the changes in this type of cornea-retinal potential are very slow.
First the cornea-retinal potential decreases slowly when the eye adapts to the darkness. This should happen in about 8 to 9 minutes from the beginning of the examination. After this dark fifteen-minute per
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Millin Vincent
Wieland Robert N.
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