OPT503 Lecture 2 Binocular Vision PDF

Binocular Vision Lecture 2 – Normal Extraocular Movement part 2 Professor Phill Buckhurst  This lecture is being recorded as part of Plymouth University's Content Capture project and will be available via the Panopto block located on your module DLE pages shortly....

Binocular Vision Lecture 2 – Normal Extraocular Movement part 2 Professor Phill Buckhurst  This lecture is being recorded as part of Plymouth University's Content Capture project and will be available via the Panopto block located on your module DLE pages shortly. Please note - If you ask a question or make a comment it may appear on the recording, you can ask me to pause the recording if you do not wish you question to be recorded. By the end of the session you will be able to: Identify the positions of rest and fixation Explain the difference between saccadic and pursuit movement and how each mechanism is tested Understand how to perform extra ocular movement examination Recognise which muscles and type of movement are being assessed during ocular motility testing The positions of rest and fixation Position of anatomical rest The position of the eyes in the absence of muscle tone and postural reflexes Occurs in death Reflects angle between orbital axes (~ 45°) Generally divergent Due to anatomy of the orbit No muscle invervation Position of physiological rest Position of the eyes in the absence of a fixational reflex Position determined by postural reflexes and muscle tone Occurs in total darkness Postural reflexes and muscle tone Effect of accommodation The accommodation – convergence relationship As accommodation  convergence  Accommodation Convergence  Fusional convergence The final adjustment of the eyes to fuse on a target Retinal images fall on corresponding points  Dissociated (Passive) position Position of the eyes when fusional convergence is not present but all other anatomical and physiological factors are present Occurs when one eye is covered – Cover test (see later) Also occurs in other tests where eyes are prevented from fusing an image – Maddox rod – Maddox wing Associated (Active) position Position of the eyes when fusional convergence is present along with other physiological factors Retinal disparity stimulates the fusional vergence that moves the eyes into this position  What does this mean If there is a difference between the associated and the dissociated position then there is a deviation in the eyes known as a Heterophoria If there is no difference then this is known as orthophoria Categories of version movements Categories of version movements Saccades Smooth Pursuit Movements Fixational Eye Movements Vestibulo-Ocular Reflex Optokinetic Nystagmus Saccades Short, rapid and abrupt movement Occurs during reading and fixating from one point to another Rods and cones respond to changes in luminance Peak velocity of a 10° saccade can exceed 300°/s vision is suppressed during a saccade Smooth Pursuit Movements Movement of an eye while it is fixating a moving object The eye maintains fixation as long as the object moves smoothly and below about 40 degrees per second Fixation Eye Movements Maintained imaging at the centre of the fovea Rapid eye movements – physiological Nystagmus The movements vary in amplitude and frequency Avoids stabilised retinal image – This would result in fatigue of the receptors and parts of the image would disappear Vestibulo-Ocular Reflex Movement of both eyes in opposite direction to head triggered by stimulation of semicircular canals attempts to keep image on retina during head movement responds best at high visual stimulus velocities and frequencies (e.g. can be seen when person spun around on a chair) optokinetic reflex attempts to keep image on retina at low visual stimulus velocities and frequencies Optokinetic Nystagmus (OKN) Physiological Also called train nystagmus Occurs when watching objects traverse the visual field Ocular motility Assessment of ocular motility Assesses the ability of a patient to look (with version movements) in all parts of the motor field It can be used to see the performance of the extraocular eye muscles It can determine if a deviation is comitant or incomitant – Comitance (concomitance) – angle visual axes is consistent with all positions of gaze – Incomitance – angle varies with direction of gaze Motility test - setup Routine test Room lights on - Can be dimmed - must be able to see corneal reflections NO glasses The target is a pen torch Sit directly in front of Px (so both eyes can be seen) Explain the test to the patient Instruct your patient to follow the light and to keep their head still Explain to your patient that they need to tell you if they notice any diplopia  Motility test – procedure Hold pen light about 40 cm away from px Move pen light in radial directions in the six cardinal diagnostic positions of gaze Keep within the binocular field – Around 20-25 degrees from primary position Look for any misalignments of the corneal reflex Are there any points where the patient experiences double vision? Check the vertical for “A” and “V” patterns (more on this later) nose  The Six Cardinal positions Examines the integrity of synergists (yoke muscles) RSR RIO LIO LSR RLR RMR LMR nose LLR R L RIR RSO LSO LIR testing in vertical midline is only required for assessing A and V patterns (Later)  Muscles involved with ductions DUCTION AGONIST ANTAGONIST contracts relaxes Abduction LR MR Adduction MR LR Supraduction SR, IO IR, SO Infraduction IR, SO SR, IO Incycloduction SO, SR IO, IR Excycloduction IO, IR SO, SR Abduction On abduction the action of the the lateral rectus is examined as this is where it has its greatest action The lateral rectus is contracting The medial rectus is relaxing Nose Nose Medial wall Medial Lateral Rectus Lateral wall is relaxed Rectus is contracted Primary Gaze Abduction Adduction On adduction the action of the the medial rectus is examined The medial rectus is contracting The lateral rectus is relaxing Nose Nose Medial wall Medial Lateral Rectus is Lateral wall Contracted Rectus is relaxed Primary Gaze Adduction Abduction and elevation On abduction and elevation the action of the the superior rectus is examined When abducting by 23 degrees the superior rectus purely elevates with contraction The inferior rectus is relaxing Superior Rectus Contracts Nose Nose 23° 23° Inferior Rectus relaxes Primary Gaze Abduction and elevation Abduction and depression On abduction and depression the action of the the inferior rectus is examined When abducting by 23 degrees the inferior rectus purely depresses with contraction The superior rectus is relaxing Superior Rectus Relaxes Nose Nose 23° 23° Inferior Rectus contracts Primary Gaze Abduction and depression Adduction and elevation On adduction and elevation the action of the the inferior oblique is examined When adducting by 51 degrees the inferior oblique purely elevates with contraction The superior oblique is relaxing Superior oblique relaxes Nose Nose 51° 51° Inferior oblique contracts Primary Gaze Adduction and elevation Adduction and depression On adduction and depression the action of the the superior oblique is examined When adducting by 55 degrees the superior oblique purely depresses with contraction The inferior oblique is relaxing Superior oblique contracts Nose Nose 55° 55° Inferior oblique relaxes Primary Gaze Adduction and depression Recording findings If no abnormality detected: – Full smooth If abnormality detected: – Record if discomfort is experienced – Record if jerky or inaccurate pursuit eye movements occur – Determine if any underaction or overaction is detected (more on this later) – Consider testing ductions (more on this later) Monocular motility test (testing for ductions) Repeat motility test monocularly Checks to see if a restriction is either a paretic or mechanical incomitancy – if less underaction occurs during version then paresis is more likely – If similar underaction occurs during version and duction then mechanical restriction more likely  https://yourvoice.plymouth.ac.uk Providers name: Phillip Buckhurst Session title: OPT503 Lecture 2