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Eye movements I Introduction. Objectives and Readings. The field of fixation. Types of eye movements and their characteristics. Measurement of eye movements. SFO1004 Dr Sarah J Waugh© Objectives and readings The student should be able to: • Describe the different types • of eye movements and k...

Eye movements I Introduction. Objectives and Readings. The field of fixation. Types of eye movements and their characteristics. Measurement of eye movements. SFO1004 Dr Sarah J Waugh© Objectives and readings The student should be able to: • Describe the different types • of eye movements and know their characteristics. – Pgs. 220 (components of eye rotation) – Pgs. 231-232 (saccadic eye • Understand how eye movements can be measured. SFO1004 Levin, Leonard A. (2011) -Adler's physiology of the eye: clinical application. Chapter 9 Neural control of eye movements (ebook). movements) – Pgs. 229 (smooth pursuit eye movements) – Pgs. 226 – 227 (OKN and VOR) • Youtube links as shown on slides. • https://www.youtube.com/watch?v =u3BcgOIjbGA (short tutorial on the mechanics of the muscles and eye movement – useful for next week too). Dr Sarah J Waugh© Ocular motor function • The oculomotor system enables viewing of the world under different circumstances. • Five main categories of eye movements can be described: – Saccades (saccadic) – Smooth pursuit – Optokinetic – Vestibular – Vergence • Normal control of eye movements rely on the coordination of the ocular muscles, the various orbital ligaments, and the integrity of the neurological control centres. SFO1004 From Diagnosis and management of ocular motility disorders. 3rd Ed. Ansons and Davis. Dr Sarah J Waugh© Ocular motor function • Ocular (eye) movement occurs around 3 principles axes (x, y, z) which pass through the centre of rotation of the eye. • Horizontal or x-axis which allows vertical eye movements (called elevation and depression). • • Anteroposterior (sagittal) or yaxis which allows cyclorotational eye movements (called torsional either intorsion or extorsion). Vertical or z-axis which allows horizontal eye movements (called adduction and abduction). SFO1004 Vertical (z) axis Horizontal or transverse (x) axis Centre of rotation Anteroposterior (y) axis Dr Sarah J Waugh© Ocular motor function • The field of fixation (or the extent) is around 4050°. • We rarely rotate the eyes to such an extent because we use head movements. • A typical eye movement is about 15° in magnitude. • The purpose of eye movements is to direct SFO1004 superior 43° 47° 45° nasal temporal 45° 47° 47° 47° 50° inferior Dr Sarah J Waugh© Saccadic eye movements • These eye movements are fast, leaping movements from point to point in visual space (about 400700 degrees/second). • Most saccadic eye movements occur in about 300msec (milliseconds – thousandths of a second) and include a short latency between the onset of the stimulus and the eye moving. • The magnitude of a saccadic eye movements are related to their peak velocity. The larger the eye movement, the faster it is. SFO1004 From Adler’s Physiology Ch 36. Neural control of eye movements. C Schor. Dr Sarah J Waugh© Saccadic eye movements • Saccadic eye movements are the typical eye movements in used in sampling the visual environment. • For example in reading, driving, perceiving potential threats. • Saccades can be evaluated by asking a patient to look from one object to another in quick succession. • This could be in the horizontal or vertical SFO1004 directions. • Saccades are observed by away from and towards the midline. • Saccadic eye movements are tested when limited ocular movement is suspected. • Testing may help in the diagnosis of some neurological disorders. Dr Sarah J Waugh© Saccadic eye movements http://www.embalance.eu/ SFO1004 Dr Sarah J Waugh© Smooth pursuit eye movements • Smooth pursuit (or following) eye movements require the target to move. They maintain stability of an object on the retina sometimes in combination with a head movement. • Smooth pursuits typically do not exceed about 40° per second. • The stimulus to a smooth pursuit is the movement of the image off the fovea SFO1004 (retinal slip). • Smooth pursuits are observed by asking the patient to track a moving target to the limit of gaze. • The head should be kept still. • The examiner should note the smoothness of the movement (that it is not jerky), the extent of movement and if gaze position is maintained. • We test smooth pursuits routinely in clinic. Dr Sarah J Waugh© Smooth pursuit eye movements http://www.embalance.eu/ SFO1004 Dr Sarah J Waugh© Vestibular (VOR) and Optokinetic (OKN) eye movement systems • The vestibular and optokinetic systems may be considered together as their purpose is to maintain a stable retinal image during head movements. • There are a number of different sensory signals that act to generate compensatory eye movements when the head moves. – From the ear (semi-circular canals) SFO1004 – From retinal signals • The eye movements observed comprise a slow following movement (smooth pursuit) and a rapid re-fixation (saccade). • The vestibular ocular reflex (VOR) can be elicited by moving (rotating) the head – eye movements are equal and opposite to the head movement. • Opto-kinetic nystagmus (OKN) is elicited by passing a repeating pattern in front of the eyes – the pattern has to cover a large area of the visual field to elicit an OKN response. Dr Sarah J Waugh© Optokinetic nystagmus http://www.embalance.eu/ SFO1004 Dr Sarah J Waugh© Vestibular ocular reflex (VOR) http://www.embalance.eu/ SFO1004 Dr Sarah J Waugh© Interval • This is a good time to pause and reflect on the first section of the presentation. • When you are ready, continue to the next series of slides. SFO1004 Dr Sarah J Waugh© Measurement of eye movements • There are several different methods that maybe used to measure eye movements. • These include: – Direct observation of the eyes (as discussed). – The EOG (electrooculogram). – Infra-red reflection methods. – Scleral search coil. – Purkinje eye tracker. – Video systems. SFO1004 • Apart from the direct observation, each of the methods provides a record of the eye movement that can reviewed. • This allows detailed study for patient care or research. Dr Sarah J Waugh© EOG – electro-oculogram • The EOG (electro-oculogram) records the eye position using electrodes attached to the face. • Inner and outer canthi to record horizontal movements. • As the eye moves towards one electrode positive corneal potential causes a rise on one electrode and a decrease in the other. • The rate of change in the measured potential is linked to the speed of eye movement. SFO1004 Dr Sarah J Waugh© Search coil method recorder • A coil is embedded in a contact lens annulus that is placed on the eye. • The patient is then placed in a magnetic field. • As the eye moves, there is a current induced in the coil. The current is proportional to the eye movement. • Using search coil methods recorder allows the measurement of horizontal, vertical and torsional eye movements. SFO1004 Dr Sarah J Waugh© Infra-red reflection methods • This method is commonly used. • It relies on the detection of reflected infra-red light from the anterior eye by sensors. The sensors can be mounted onto spectacle frames which can be useful to remove the influence of head movements. • As the eye moves from one side to the other, the amount of light detected changes and is proportional to the eye movement. SFO1004 http://www.bj-brainvision.com/news2/23.htm Dr Sarah J Waugh© Questions? • Remember you can ask questions via Brightspace discussion board or the chat function on Teams. SFO1004 Dr Sarah J Waugh©

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