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Is it a tumor or is it eye movements?
IS IT A T U M O R
OR IS IT EYE M O V E M E N T S ?
A Method of Greatly Reducing Eye Movement Artefacts in the Frontal Leads T. J. CASt, M . D .
EEG Laboratory, Department o[ Surgery, University of Chicago Clinics, Chicago Ill. (Received for publication: .~Iay 30, 1958) One of the most difficult problems t h a t faces the i n t e r p r e t e r of E E G records is posed by the a r t i f a c t s f r o m eye movements. This problem is p e r h a p s most i m p o r t a n t f o r p a t i e n t s a r o u n d 45 to 60 years of age who have s y m p t o m s s u g g e s t i n g a b r a i n t m n o r and p e r h a p s a recent seizure or two. Small, slow, i r r e g u l a r delta like waves in th~ f r o n t a l s must, in such a case, be recognized with precision as i n t r a c r a n i a l or as eye movements. There exists t h r o u g h o u t the entire head a static field set up by the corneo-retinal dipole. This field (one for each eye) moves when the eyes move, resulting in a change of potential between any two points, depending upon how they are situated in this field. A l t h o u g h the two leads to an amplifier remain equally f a r a p a r t , it is possible to alter greatly the pickup of such field changes by c h a n g i n g the orientation of these leads or by c h a n g i n g their position on the head. We have, since 1935, r e f e r r e d our leads to the vertex in routine cases. W i t h such an a r r a n g e m e n t the f r o n t a l to vertex and ear to vertex leads show vertical eye movements strongly, the occipital to vertex only moderately, and the central to vertex little or not at all. Consideration of the lines in these fields suggests t h a t there will be little change of the potential of the lines s t r i k i n g two points, one of which is nearly lateral to the other, when a vertical movement of the eyes is made. When the point usually used for f r o n t a l recording is r e f e r r e d to the midline (both in the same coronal p l a n e ) , vertical eye movements are substantially a b s e n t in this channel. Vertical eye movement waves with the eyes open (with vertex or ear used as ~ reference) are usually large and usually a b o u t equal in the two f r o n t a l areas and are in the same direction. When unequal the inequality remains a b o u t constant throughout the record. The rising phase is steeper t h a n the falling phase. W h e n the eyes are closed the movem e n t s usually stop, b u t in some people they do not stop b u t are much smaller and the waves resulting are greatly reduced in amplitude, b u t are often faster.
[
Their rising and falling phases are similar amt they resemble delta waves. Horizontal eye movements produce waves which are usually in opposite directions ir the f r o n t a l leads and are often unequal. ( I t seems likely t h a t the eyes do not always move t o g e t h e r when dosed.) Although eye movements cause ~rouble only in a few people, they are sometimes ,lost difficult to evaluate and the electroencephalogr:~pher n m s t decide with reasonable confidence whether ~he waves he sees are due to eye movements or arc fr,.m an intraeranial SOllrce. There arc several ways of apI.~oaching this decision: (1) I f the eyes are left (,pen, most of tile waves resulting f r o m eye movement~ are of the large, vertical type, which rise rapidly :.nd fall a little more slowly and are about equal i~ the two f r o n t a l areas. The spate between these l a r ~ . waves is usually free f r o m the smaller delta-like wa,. :~s caused by eye movements when the eyes are closed (2) Theoretically eye movement waves will disa p p e a r when the eyes are not m¢~ed. No o]1(, can avoid blinking his eyes when they : " e open but some people move them with s u r p r i s i n g ~:,pidity when they are closed, m a k i n g waves as f a s t a~ 6 per see., which :~re often sinusoidal and delta-lil:,~ in appearance. These waves are of much lower am}litude t h a n those seen when the eyes are open and b(,.ome thereby even more readily confused with waves f : o m tumors. These j i t t e r y people do not know t h a t t h e " eyes are moving and the movements can be some limes stopped by placing nickels on the lids. This a!lows them to feel the movements of their eyes. T ,e same result is p e r h a p s ,'l little more easily aehiev, d by letting them press their f i n g e r s lightly in the co h e r s of their eyes. (3) When two leads are placed I~orizontally in tile same coronal plane the channel 7, which they are connected shows little or no r e s p o . s e to even large vertical movements of the eye f i n d . Thus, if one places an electrode in the midline lirectly medial to the f r o n t a l lead f r o m which ques" .onable waves are coming, this pair of electrodes w i l not show vertical eye movements in a s u b s t a n t i a l am,rout, and as about 90 per cent of movements made ~vi~h the eyes close,] are vertical, being blinks and flut:,.r movements, the problem of eye movements will be I:,rgely resolved by 156 ]
I S I T A T U M O R 01~ I S I T E Y E
MOVEMENTS
157
?
r~p-v
LE'V
Fig. 1 This poorly relaxed person made many eye movements both with eyes open and closed. The vertb:al eye movements are almost absent from the frontal to mid-line derivation. At the arrow there is pre,~mably a horizontal component to the eye movement.
t h i s p l a c e m e n t , H o r i z o n t a l eye m o v e m e n t s p r o d u c e as l a r g e a v o l t a g e in t h i s p l a c e m e n t as in m o s t o t h e r p l a c e m e n t s b u t t h e y occur much less commonly. The d e l t a waves due to f r o n t a l t u m o r s a p p e a r j u s t as well in t h i s f r o n t a l to m i d l i n e p l a c e m e n t as when the f r o n t a l is r e f e r r e d to a n y o t h e r region.
SUMMARY F r o n t a l E E G w a ve s r e s u l t i n g from v e r t i c a l eye m o v e m e n t s can be l a r g e l y e l i m i n a t e d b y u s i n g a f r o n t a l to m i d l i n e d e r i v a t i o n i n w h i c h b o t h electrodes a re in the s a me c orona l plane. Such a d e r i v a t i o n shows the d e l t a w a ve s due to t u m o r s w,~ll.
Reference: CASE, T. J. I s i t a t u m o r or is i t eye m o v e m e n t s ? EEG Clin. Neurophysiol.,
1959, 11:
156-157.
OR IS IT EYE M O V E M E N T S ?
A Method of Greatly Reducing Eye Movement Artefacts in the Frontal Leads T. J. CASt, M . D .
EEG Laboratory, Department o[ Surgery, University of Chicago Clinics, Chicago Ill. (Received for publication: .~Iay 30, 1958) One of the most difficult problems t h a t faces the i n t e r p r e t e r of E E G records is posed by the a r t i f a c t s f r o m eye movements. This problem is p e r h a p s most i m p o r t a n t f o r p a t i e n t s a r o u n d 45 to 60 years of age who have s y m p t o m s s u g g e s t i n g a b r a i n t m n o r and p e r h a p s a recent seizure or two. Small, slow, i r r e g u l a r delta like waves in th~ f r o n t a l s must, in such a case, be recognized with precision as i n t r a c r a n i a l or as eye movements. There exists t h r o u g h o u t the entire head a static field set up by the corneo-retinal dipole. This field (one for each eye) moves when the eyes move, resulting in a change of potential between any two points, depending upon how they are situated in this field. A l t h o u g h the two leads to an amplifier remain equally f a r a p a r t , it is possible to alter greatly the pickup of such field changes by c h a n g i n g the orientation of these leads or by c h a n g i n g their position on the head. We have, since 1935, r e f e r r e d our leads to the vertex in routine cases. W i t h such an a r r a n g e m e n t the f r o n t a l to vertex and ear to vertex leads show vertical eye movements strongly, the occipital to vertex only moderately, and the central to vertex little or not at all. Consideration of the lines in these fields suggests t h a t there will be little change of the potential of the lines s t r i k i n g two points, one of which is nearly lateral to the other, when a vertical movement of the eyes is made. When the point usually used for f r o n t a l recording is r e f e r r e d to the midline (both in the same coronal p l a n e ) , vertical eye movements are substantially a b s e n t in this channel. Vertical eye movement waves with the eyes open (with vertex or ear used as ~ reference) are usually large and usually a b o u t equal in the two f r o n t a l areas and are in the same direction. When unequal the inequality remains a b o u t constant throughout the record. The rising phase is steeper t h a n the falling phase. W h e n the eyes are closed the movem e n t s usually stop, b u t in some people they do not stop b u t are much smaller and the waves resulting are greatly reduced in amplitude, b u t are often faster.
[
Their rising and falling phases are similar amt they resemble delta waves. Horizontal eye movements produce waves which are usually in opposite directions ir the f r o n t a l leads and are often unequal. ( I t seems likely t h a t the eyes do not always move t o g e t h e r when dosed.) Although eye movements cause ~rouble only in a few people, they are sometimes ,lost difficult to evaluate and the electroencephalogr:~pher n m s t decide with reasonable confidence whether ~he waves he sees are due to eye movements or arc fr,.m an intraeranial SOllrce. There arc several ways of apI.~oaching this decision: (1) I f the eyes are left (,pen, most of tile waves resulting f r o m eye movement~ are of the large, vertical type, which rise rapidly :.nd fall a little more slowly and are about equal i~ the two f r o n t a l areas. The spate between these l a r ~ . waves is usually free f r o m the smaller delta-like wa,. :~s caused by eye movements when the eyes are closed (2) Theoretically eye movement waves will disa p p e a r when the eyes are not m¢~ed. No o]1(, can avoid blinking his eyes when they : " e open but some people move them with s u r p r i s i n g ~:,pidity when they are closed, m a k i n g waves as f a s t a~ 6 per see., which :~re often sinusoidal and delta-lil:,~ in appearance. These waves are of much lower am}litude t h a n those seen when the eyes are open and b(,.ome thereby even more readily confused with waves f : o m tumors. These j i t t e r y people do not know t h a t t h e " eyes are moving and the movements can be some limes stopped by placing nickels on the lids. This a!lows them to feel the movements of their eyes. T ,e same result is p e r h a p s ,'l little more easily aehiev, d by letting them press their f i n g e r s lightly in the co h e r s of their eyes. (3) When two leads are placed I~orizontally in tile same coronal plane the channel 7, which they are connected shows little or no r e s p o . s e to even large vertical movements of the eye f i n d . Thus, if one places an electrode in the midline lirectly medial to the f r o n t a l lead f r o m which ques" .onable waves are coming, this pair of electrodes w i l not show vertical eye movements in a s u b s t a n t i a l am,rout, and as about 90 per cent of movements made ~vi~h the eyes close,] are vertical, being blinks and flut:,.r movements, the problem of eye movements will be I:,rgely resolved by 156 ]
I S I T A T U M O R 01~ I S I T E Y E
MOVEMENTS
157
?
r~p-v
LE'V
Fig. 1 This poorly relaxed person made many eye movements both with eyes open and closed. The vertb:al eye movements are almost absent from the frontal to mid-line derivation. At the arrow there is pre,~mably a horizontal component to the eye movement.
t h i s p l a c e m e n t , H o r i z o n t a l eye m o v e m e n t s p r o d u c e as l a r g e a v o l t a g e in t h i s p l a c e m e n t as in m o s t o t h e r p l a c e m e n t s b u t t h e y occur much less commonly. The d e l t a waves due to f r o n t a l t u m o r s a p p e a r j u s t as well in t h i s f r o n t a l to m i d l i n e p l a c e m e n t as when the f r o n t a l is r e f e r r e d to a n y o t h e r region.
SUMMARY F r o n t a l E E G w a ve s r e s u l t i n g from v e r t i c a l eye m o v e m e n t s can be l a r g e l y e l i m i n a t e d b y u s i n g a f r o n t a l to m i d l i n e d e r i v a t i o n i n w h i c h b o t h electrodes a re in the s a me c orona l plane. Such a d e r i v a t i o n shows the d e l t a w a ve s due to t u m o r s w,~ll.
Reference: CASE, T. J. I s i t a t u m o r or is i t eye m o v e m e n t s ? EEG Clin. Neurophysiol.,
1959, 11:
156-157.