Med. & Biol. Eng. & Comput., 1977, 15, 705-706
Technical note Transducer for recording fine eye movement through the closed eyelid SEVERAL techniques have been devised for measuring fine eye movement (DITCHBURN, 1973). These methods necessitate that the subject's eye should be open during recording. A method of measuring fine eye movement through the closed eyelid would be of practical value in view of the recent observations on ocular microtremor during sleep (COAKLEY, 1976), anaesthesia (COAKLEY, et al., 1976) and coma (SHAKHNOVICHand THOMAS, 1974; COAKLEY and FHOMAS, 1977).
BENGI and THOMAS(1968) described a sensitive method of measuring microtremor using a piezo-electric straingauge transducer which touched the sclera of the open eye. With a specially constructed transducer, and using the same method of differentiation and amplification, recordings can now be obtained through the closed eyelid. The transducer is shown in Fig. 1. The piezo element consists of a strip of Multimorph (Vernitron Ltd.) with a silicone-rubber end-piece. The sensor protrudes 2mm beyond its mounting and therefore, when the whole unit is placed on the eyelid, the sensor presses into the skin and detects the eye movement underneath. (The levator palpebrae muscle is completely relaxed when the eyes are closed (BJORK and KUGELBERG, 1953).) The connecting w i r e s are soldered to the two faces of the cantilever and the twin-screened output cable is taped securely to the subject's forehead. The unit itself is taped onto the eyelid but it should also be possible to hold it in position with a suction device similar to that used in the Yarbus disc (YARBUS, 1968). The length of the piezo
,rene
85
mm
flement
Cross section : I crn/I
mm
Fig. 1 Cross-section of the transducer drawn to scale
Fig. 2 Recording simultaneously from both eyes
[
j
0.1S
First received 10th January and in final form 19th January, 1977
M e d i c a l & Biological Engineering & C o m p u t i n g
Fig. 3 Eye tremor recorded through the eyefid. The vertical bar corresponds to a transducer output of l mV N o v e m b e r 1977
705
element and the dimensions of the silicone rubber are such that their combined resonance is at a frequency above 203 Hz, whereas the microtremour activity is concentrated around 100 Hz (COAKLEY and THOMAS, 1977). The signal derived from the transducer may be displayed in the form of angular displacement against time or angular velocity against time. t h e calibration of the transducer and the amplification and differentiation of the signal are as described for the 'open-eye' transducer (BEN~I and THOMAS, 1968). An example of ocular microtremour recorded through the closed eyelid is shown in Fig. 3. Preliminary observations lead us to believe that the mean tremour frequency is higher if one eye is open during recording than if both eyes are closed. This phenomenon is currently under investigation. The recording method is simple and compact and there is no risk to the subject's eye. The technique could also be used as an accurate and valuable method of continousty recording larger eye movements such as nystagmus or the rapid eye movement (r.e.m.) of sleep.
References BENGt, H. and THOMAS, J. G. (1968) Three electronic methods for recording ocular tremour. Med. Biol. Eng. 6, 171-178. BJORK, A. and KUGELBERG, K. (1953) Fhe electrical activity of the muscles of the eye and eyelids in various positions and during movement. Electroenceph. Clin. Neorophysiol. 5, 595-602. COAKLEY, D. (1976) The ocular microtremor record during sleep. Trans. Ophthal. Soc. UK 96, 436-438.
706
COAKLEY, D. and THOMAS, J. G. (1977) The ocular microtremour record and the prognosis of the unconscious patient. Electroenceph. C/in. Neurophysiol. (in press). COAKLEY, D. and THOMAS, J. C. 0977) The effect of age and eye position on the normal ocular microtremour record. J. Physiol. 263, 260-261. COAKLEY, D. THOMAS, J. G. and LuNN, J. N. (1976) The effects of anaesthesia on ocular microtremor. Brit. J. Anaesth. 48, 1122-23. DITCHBURN, R. W. (1973) Eye movements and visual perception. Oxford University Press, London. SHAKHNOVICH, A. R. and THOMAS, J. G. (1974) Microtremour of the eyes as an index of motor unit activity and of the functional state of the brain stem. J. Physiol. 238, 36. YARBUS, A. L. (1967), Eye movement and vision. Plenum Press, New York. J. G. THOMAS*
Department of Electrical & Electronic Engineering University College Cardiff, Wales DAVIS COAKLEY Deportment of Clinical Gerontology University Hospital of Wales Cardiff, Wales
*Present Address: Burdenko Institute of Neurosurgery, Moscow USSR
Medical & Biological Engineering & Computing
November 1977
Technical note Transducer for recording fine eye movement through the closed eyelid SEVERAL techniques have been devised for measuring fine eye movement (DITCHBURN, 1973). These methods necessitate that the subject's eye should be open during recording. A method of measuring fine eye movement through the closed eyelid would be of practical value in view of the recent observations on ocular microtremor during sleep (COAKLEY, 1976), anaesthesia (COAKLEY, et al., 1976) and coma (SHAKHNOVICHand THOMAS, 1974; COAKLEY and FHOMAS, 1977).
BENGI and THOMAS(1968) described a sensitive method of measuring microtremor using a piezo-electric straingauge transducer which touched the sclera of the open eye. With a specially constructed transducer, and using the same method of differentiation and amplification, recordings can now be obtained through the closed eyelid. The transducer is shown in Fig. 1. The piezo element consists of a strip of Multimorph (Vernitron Ltd.) with a silicone-rubber end-piece. The sensor protrudes 2mm beyond its mounting and therefore, when the whole unit is placed on the eyelid, the sensor presses into the skin and detects the eye movement underneath. (The levator palpebrae muscle is completely relaxed when the eyes are closed (BJORK and KUGELBERG, 1953).) The connecting w i r e s are soldered to the two faces of the cantilever and the twin-screened output cable is taped securely to the subject's forehead. The unit itself is taped onto the eyelid but it should also be possible to hold it in position with a suction device similar to that used in the Yarbus disc (YARBUS, 1968). The length of the piezo
,rene
85
mm
flement
Cross section : I crn/I
mm
Fig. 1 Cross-section of the transducer drawn to scale
Fig. 2 Recording simultaneously from both eyes
[
j
0.1S
First received 10th January and in final form 19th January, 1977
M e d i c a l & Biological Engineering & C o m p u t i n g
Fig. 3 Eye tremor recorded through the eyefid. The vertical bar corresponds to a transducer output of l mV N o v e m b e r 1977
705
element and the dimensions of the silicone rubber are such that their combined resonance is at a frequency above 203 Hz, whereas the microtremour activity is concentrated around 100 Hz (COAKLEY and THOMAS, 1977). The signal derived from the transducer may be displayed in the form of angular displacement against time or angular velocity against time. t h e calibration of the transducer and the amplification and differentiation of the signal are as described for the 'open-eye' transducer (BEN~I and THOMAS, 1968). An example of ocular microtremour recorded through the closed eyelid is shown in Fig. 3. Preliminary observations lead us to believe that the mean tremour frequency is higher if one eye is open during recording than if both eyes are closed. This phenomenon is currently under investigation. The recording method is simple and compact and there is no risk to the subject's eye. The technique could also be used as an accurate and valuable method of continousty recording larger eye movements such as nystagmus or the rapid eye movement (r.e.m.) of sleep.
References BENGt, H. and THOMAS, J. G. (1968) Three electronic methods for recording ocular tremour. Med. Biol. Eng. 6, 171-178. BJORK, A. and KUGELBERG, K. (1953) Fhe electrical activity of the muscles of the eye and eyelids in various positions and during movement. Electroenceph. Clin. Neorophysiol. 5, 595-602. COAKLEY, D. (1976) The ocular microtremor record during sleep. Trans. Ophthal. Soc. UK 96, 436-438.
706
COAKLEY, D. and THOMAS, J. G. (1977) The ocular microtremour record and the prognosis of the unconscious patient. Electroenceph. C/in. Neurophysiol. (in press). COAKLEY, D. and THOMAS, J. C. 0977) The effect of age and eye position on the normal ocular microtremour record. J. Physiol. 263, 260-261. COAKLEY, D. THOMAS, J. G. and LuNN, J. N. (1976) The effects of anaesthesia on ocular microtremor. Brit. J. Anaesth. 48, 1122-23. DITCHBURN, R. W. (1973) Eye movements and visual perception. Oxford University Press, London. SHAKHNOVICH, A. R. and THOMAS, J. G. (1974) Microtremour of the eyes as an index of motor unit activity and of the functional state of the brain stem. J. Physiol. 238, 36. YARBUS, A. L. (1967), Eye movement and vision. Plenum Press, New York. J. G. THOMAS*
Department of Electrical & Electronic Engineering University College Cardiff, Wales DAVIS COAKLEY Deportment of Clinical Gerontology University Hospital of Wales Cardiff, Wales
*Present Address: Burdenko Institute of Neurosurgery, Moscow USSR
Medical & Biological Engineering & Computing
November 1977
