OPT503 Lecture 10 Handout PDF

Binocular Vision Lecture 10 – Introduction to incommitant deviation Professor Phillip Buckhurst By the end of the session you will be able to: Describe what an incommitant deviation is Differentiate between a comitant and incomitant deviation Differentiate between a Paralytic restriction and...

Binocular Vision Lecture 10 – Introduction to incommitant deviation Professor Phillip Buckhurst By the end of the session you will be able to: Describe what an incommitant deviation is Differentiate between a comitant and incomitant deviation Differentiate between a Paralytic restriction and a mechanical restriction  Commitant deviations Angle of deviation is the same in all positions of gaze – Eg a commitant exotropia Remember Herring’s and Sherrington’s law nose  Incommitant deviations Angle of deviation varies in different directions of gaze The angle of deviation varies depending on the eye used for fixation nose  Testing for incommitant deviations The Six Cardinal positions RSR RIO LIO LSR RLR RMR LMR nose LLR RIR RSO LSO LIR testing in vertical midline is only required for assessing A and V patterns (Later) Classification of incommitant deviation Neurogenic (palsy) – Problem with the muscle innovation Myogenic – Problem with the muscle Mechanical – Where there is a physical restriction of movement – The eye is not free to move within the globe  Neurogenic Palsy Where there is a problem with the nerve supplying the muscle Therefore there is a reduced nerve innovation to the muscle so that muscle is underacting Right lateral rectus palsy No Palsy Left eye fixating Left eye fixating Both lateral rectus and medial rectus Left lateral rectus is receiving less are receiving the correct amount of innovation from the nerve and and is innovation to maintain fixation in underacting primary gaze  Primary and secondary deviations With Neurogenic paresis the size of the deviation will be dependent on which eye is fixating This can be explained by thinking about Herrings law Primary deviation – when the fixating eye is the one without the neurogenic paresis Secondary deviation – when the fixating eye is the one with the neurogenic paresis No deviation Fixating Fixating + + + + Both lateral rectus and medial rectus are receiving the correct amount of innovation to maintain fixation in primary gaze Note: + or - represents the signal sent from the brain that is required to get the fixating eye to primary position  Primary deviation Non-fixating Fixating + + + + R L The Left eye is fixating, the brain is trying to send an equivalent amount of innervation to both the left and right eye however due to the palsy the right lateral rectus receives less innovation. Thus we have a RIGHT lateral rectus underaction  Secondary deviation Fixating Non-fixating +++ - - - +++ --- The RIGHT eye is fixating, the brain is having to send a stronger signal to the lateral rectus of the right eye. Therefore it is sending a much stronger signal to the left medial rectus. Therefore the LEFT medial rectus is overacting The deviation is greater with the secondary deviation Determining over- and under-actions through motility By looking at the corneal reflections Subjectively through questioning the patient Through alternating cover test RSR RIO LIO LSR RLR RMR LMR LLR RIR RSO LSO LIR  The underacting muscle Looking at the corneal reflections If a muscle in the non fixating eye is underacting then it will be “left behind” when following a fixation target into the relevant cardinal position The corneal reflection will continue to follow the fixation target – The corneal reflection will be closer to the fixation target than the pupil centre in the underacting eye E.g. the medial rectus of the left eye is underacting nose R L  The overacting muscle Looking at the corneal reflections If a muscle in the fixating eye has the paresis then the brain will send more signal to the nerve in order to maintain fixation In the non fixating eye the corresponding muscle receives too much power and “overshoots” the fixation target – overacts The corneal reflection will be further from the fixation target than the pupil centre in the overacting eye E.g. the lateral rectus of the right eye is overacting nose R L Determining over- and under-actions through motility By looking at the corneal reflections Subjectively through questioning the patient Through alternating cover test RSR RIO LIO LSR RLR RMR LMR LLR RIR RSO LSO LIR The underacting muscle Looking at the subjective patient response If a muscle in the non fixating eye is underacting then it will be “left behind” when following a fixation target into the relevant cardinal position The patient will report that they see two targets (diplopia) when this happens as the image does not fall onto the fovea for both eyes The eye that sees the target which is furthest away is the underacting eye You can test this by covering each eye and asking the patient which image is still there the one which was closest or furthest away The underacting muscle Looking at the subjective patient response nose R L I see the light which was furthest away from me The overacting muscle Looking at the subjective patient response If a muscle in the non fixating eye is overacting then it will be “overshoot” when following a fixation target into the relevant cardinal position The patient will report that they see two targets (diplopia) when this happens as the image does not fall onto the fovea for both eyes The eye that sees the target which is closest is the overacting eye You can test this by covering each eye and saying if the image remaining was the one closest or furthest away The overacting muscle Looking at the subjective patient response nose R L I see the light which was closest away from me Determining over- and under-actions through motility By looking at the corneal reflections Subjectively through questioning the patient Through alternating cover test RSR RIO LIO LSR RLR RMR LMR LLR RIR RSO LSO LIR  The underacting muscle Using the alternating cover test If a muscle in the non fixating eye is underacting then it will be “left behind” when following a fixation target into the relevent cardinal position If you cover the fixating eye the underacting eye will then move towards the target to take up fixation nose R L  The overacting muscle Using the alternating cover test So what happens to the other eye Under the cover the eye will also move further out towards the target This means that the covered eye will have moved away further and will have overshot This muscle is the overacting muscle nose R L  The alternating cover test We know that: – The Left medial rectus is underacting – The right lateral rectus is overacting nose R L  Example 1 Which muscle is underacting? Which muscle is overacting? nose R L  Example 2 Which muscle is underacting? Which muscle is overacting? nose R L  Recording the results If no incommitancy is present and the pursuit movements are normal then record as Full, smooth  Recording the results If an incomittant deviation is present then draw a diagram A ‘+’ sign demonstrates an overaction A ‘-’ sign demonstrates an underaction For example – a right lateral rectus underaction (and left medial rectus overaction) - +  Recording the results -- advanced You can grade the size of the over/underactions from 1-4 4 = does not move from primary position 3 = moves ¼ of the distance from primary position 2 = moves ½ of the distance from primary position 1 = moves ¾ the distance from primary position Example: grade 4 underaction of left medial rectus nose  Recording the results -- advanced You can grade the size of the over/underactions from 1-4 4 = does not move from primary position 3 = moves ¼ of the distance from primary position 2 = moves ½ of the distance from primary position 1 = moves ¾ the distance from primary position Example 2: grade 2 underaction of left medial rectus nose Further reading Evans, BJW. (2007) Pickwell’s binocular vision anomalies: Investigation and treatment. 5th edn. Philadelphia: Butterworth- Heinemann. Formative Exam Monday 11th December Arrive on time Bring pencil for the MCQ Bring a calculator – With the tamperproof sticker present – No calculators are available on the day What is in the passive exam? The assessment consists of: – multiple choice section worth 40 marks Binocular Vision Lecture 10 – Introduction to incommitant deviation Professor Phillip Buckhurst