OPT503 Lecture 4 Handout Single Slide PDF

Binocular Vision Lecture 4 – Objective measurement of eye deviations Professor P Buckhurst By then end of the session you will be able to: Perform a cover test Interpret the results of the cover test Conduct and interpret the Brückner test, Hirschberg method and the Krimsky test Introduct...

Binocular Vision Lecture 4 – Objective measurement of eye deviations Professor P Buckhurst By then end of the session you will be able to: Perform a cover test Interpret the results of the cover test Conduct and interpret the Brückner test, Hirschberg method and the Krimsky test Introduction Heterophoria occurs when the dissociated (passive) eye position is different to the associated (active) eye position When both eyes are fixated on a target the eyes are in the associated position When one eye is covered and prevented from fixating the eyes are in the dissociated position – Sensory fusion is prevented and fusional vergence does not occur On cover the eye moves from the associated position to the dissociated position Therefore covering the eye allows an assessment of heterophoria The cover test – When used It is used in every sight test Objective method of assessing heterophoria and heterotropia Allows you to differentiate between a phoria and tropia Cover-uncover and alternating cover There are two components to the cover test Part 1 The cover-uncover test – The primary function is to identify tropias Part 2 The alternating cover test – The primary function is to identify phorias Set up – distance cover test Room lights on, you must be able to see your Px’s eyes Explain the test “This test allows me to see how well your eye muscles work together” Test should be performed both with and without spectacle correction (More on this later) Decide on a fixation target for the Px – Px fixates on a letter on the line above the visual acuity of their worst eye – If the VA of the worst eye is < 6/18 then use the spotlight as a target Instruct your patient to keep on looking at the fixation target throughout the test Px should be looking in primary gaze position Note: For children you can use a picture target provided there is sufficient detail for fixation Conducting the procedure – cover/uncover test 1. To determine if there is a tropia in the right eye – Cover left eye and look at the response of the right eye – Hold cover in place for 3 seconds If no tropia is present then the right eye wont move If tropia is present then the right eye will move to take up fixation 2. To determine if there is a tropia in the left eye – Cover right eye and look at the response of the left eye – Hold cover in place for 3 seconds If no tropia is present then the left eye wont move If tropia is present then the left eye will move to take up fixation Investigation of a Heterotropia Classifying your findings With a tropia one eye fixates and the other deviates Large deviations can often be seen even without a cover test Examples of left exotropia What to expect when no tropia is present When the cover test is moved over the left eye the right eye does not move Uncovered eye does not move (no tropia - R eye) nose R L What to expect when no tropia is present When the cover test is moved over the right eye the left eye does not move Uncovered eye does not move (no tropia - L eye) nose R L Right Exotropia Right Exotropia – the right eye is abducting when the left eye is fixating When the cover test is moved over the left eye the right eye has to move in to take up fixation (as it was pointing outwards originally) Uncovered eye has to move to take up fixation (R exotropia) nose R L Right Exotropia Right Exotropia – the right eye is abducting when the left eye is fixating When the cover test is moved over the right eye the left eye does not move as it maintains its fixation Uncovered eye does not move (no tropia - L eye) nose R L Left Esotropia Left Esotropia – the left eye is adducting when the right eye is fixating When the cover test is moved over the left eye the right eye does not move as it maintains its fixation Uncovered eye does not move (no tropia - R eye) nose R L  Left Esotropia Left Esotropia – the left eye is adducting when the right eye is fixating When the cover test is moved over the right eye the left eye has to move out to take up fixation (as it was pointing inwards originally) Uncovered eye has to move out to take up fixation (L esotropia) nose R L Left Hypertropia Left Hypertropia – the left eye is superior when the right eye is fixating When the cover test is moved over the left eye the right eye does not move as it maintains its fixation Uncovered eye does not move (no tropia - R eye) nose R L Left Hypertropia Left Hypertropia – the left eye is superior when the right eye is fixating When the cover test is moved over the right eye the left eye has to move DOWN to take up fixation (as it was pointing inwards originally) Uncovered eye has to move down to take up fixation (L hypertropia) nose R L  Left Hypotropia Left Hypotropia – the left eye is inferior when the right eye is fixating When the cover test is moved over the left eye the right eye does not move as it maintains its fixation Uncovered eye does not move (no tropia - R eye) nose R L Left Hypotropia Left Hypotropia – the left eye is inferior when the right eye is fixating When the cover test is moved over the right eye the left eye has to move up to take up fixation (as it was pointing downwards originally) Uncovered eye has to move UP to take up fixation (L hypotropia) nose R L Alternating tropia This occurs typically when there is good vision in both eyes Either eye can fixate (although there is generally a preference) When the cover test is moved over the left eye the right eye moves to take up fixation The right eye then maintains fixation until the right eye is covered Right eye moves to take up fixation nose R L Investigation of a Heterophoria If no tropia then we need to determine if a phoria is present A phoria is when the active position of the eye does not match the passive position When not covered the eye is in its active position On cover the covered eye moves into its passive position This movement is known as a phoria Orthophoria – what happens under the cover For example -- orthophoria The passive position of the eyes matches the active position – The eye under the cover does not move nose R L Exophoria – what happens under the cover For example -- exophoria The eyes are more divergent in the passive position – Under the cover the eye will move out nose R L Esophoria – what happens under the cover For example -- esophoria The eyes are more convergent in the passive position – Under the cover the eye will move in nose R L R/L hyperphoria – what happens under the cover For example – R/L hyperphoria The eyes are vertically misaligned in the passive position – If the right eye is covered the right eye will move up – If the left eye is covered the left eye will move down nose R L L/R hyperphoria – what happens under the cover For example – L/R hyperphoria The eyes are vertically misaligned in the passive position – If the right eye is covered the right eye will move DOWN – If the left eye is covered the left eye will move UP nose R L So How do we investigate a phoria Generally our occluders are opaque which means it is difficult to see what is happening under the cover (although you can get frosted occluders) Methods of examining a phoria – Looking behind the occluder when preforming the cover/uncover test – Asking the Px regarding the movement of the target – Preforming a alternating cover test *** Best method Alternating cover test Set up is the same as for the cover/uncover test To determine if there is a phoria present – Cover right eye and hold cover in place for 3 seconds – Quickly move cover across to left eye and watch the movement of the right eye – Occluder should now be covering the right eye for 3 seconds – Swap back to the right eye and watch the movement of the left eye – Repeat approximately 3 times to ensure that any phoria is seen Note: Your transfer should be quick to stop the Px from achieving binocular vision Orthophoria – What is seen on alternating cover test For example -- orthophoria The passive position of the eyes matches the active position – The eye under the cover does not move nose R L Exophoria – What is seen on alternating cover test For example – Exophoria Under the cover the eye moves to its passive position (divergent) When the cover is removed the eye moves IN to retake fixation nose R L Esophoria – What is seen on alternating cover test For example -- Esophoria Under the cover the eye moves to its passive position (convergent) When the cover is removed the eye moves OUT to retake fixation nose R L R/L hyperphoria – What is seen on alternating cover test For example – R/L hyperphoria Under the cover the eye moves to its passive position – Superior for the right eye – Inferior for the left eye When the cover is removed from the right eye it will move DOWN to retake fixation When the cover is removed from the left eye it will move UP to retake fixation nose R L L/R hyperphoria – What is seen on alternating cover test For example – L/R hyperphoria Under the cover the eye moves to its passive position – Inferior for the right eye – Superior for the left eye When the cover is removed from the right eye it will move UP to retake fixation When the cover is removed from the left eye it will move DOWN to retake fixation nose R L Distance cover test Should be conducted – Without Rx in place To examine binocular vision in the absence of refractive correction – With current spectacles in place To examine binocular vision with current spectacles Px may be wearing prism without knowing it – With optimal correction in place To determine the effect of your refraction on the binocular vision system Set up – Near cover test Same set up as for distance however patient is looking at a near target. Decide on a fixation target for the Px – Px fixates on a letter on the line above the visual acuity of their worst eye using a budgie stick – If the Px cannot make out the letters on the budgie stick then use a spot light Instruct your patient to keep on looking at the fixation target throughout the test Px should be looking in primary gaze position Note: For children you can use a picture target provided there is sufficient detail for fixation Near cover test Should be conducted – Without Rx in place To examine binocular vision in the absence of refractive correction – With current spectacles in place To examine binocular vision with current spectacles Px may be wearing prism without knowing it – With optimal correction in place To determine the effect of your refraction on the binocular vision system Note 1: For a presbyope the correction should be with their reading spectacles Note 2: If they wear bifocals or varifocals they will need to hold up the spectacles to ensure that the near vision portion is in the primary position Things to watch out for – herrings law Herrings law states that When an impulse to perform an eye movement is received by one eye, muscles of the other eye that rotate it in the same direction are equally innervated With large phorias movements caused by Herrings law can sometimes be seen on the cover/uncover test These movements can mislead people to believe a tropia is present and not a phoria nose R L Things to watch out for – herrings law For example – Large exophoria Under the cover the left eye moves out to its passive position and the right eye maintains fixation When the cover is removed the left eye moves in to retake fixation This causes the right eye to move out and then back in (due to Herrings law) – The movement out is caused by herrings law – The movement in is a re-adjustment to regain fixation nose R L Recording a phoria Direction Eso, Exo, R/L, L/R Magnitude In prism dioptres Fixation distance Distance, near Compensation (more common to record the recovery) Good, Moderate, Poor (more on this later) Recording a tropia (the minimum) Which eye and Laterality Alternating, R or L Direction Eso, Exo, Hyper, Hypo Magnitude In prism dioptres Fixation distance Distance, Near Determining the size of the deviation Experienced practitioners usually estimate size of deviation – You can practice this at home – Hold a ruler (calibrated in cm) just below your eyes – Seat a friend 1 m away and ask them to look from the 1cm line to any other line at random (1cm = 1∆) and back again – Try and estimate their eye deviation and ask your friend to confirm the answer A prism bar may be used (but rarely in routine practice): – More on this later Cover test ‘Phi’ movements Adds a subjective element to the cover test Rarely used in practice Ask subject if they see any movement of the target during the alternating cover test If target moves in the opposite direct of the occulder then esophoria If target moves in the same direction then exophoria Can be used to detect small phorias Cover test ‘Phi’ movements Other objective tests Brückner test Hirschberg test Krimsky’s modification of Hirschberg test These are gross and fairly inaccurate tests but can be useful in very young children  Brückner test Shine ophthalmoscope light into px eyes – Use large aperture to illuminate both pupils – Px looks at centre of light – 75-100cm from Px Compare red reflexes – If the reflexes are not equally bright then there could be a strabismus – Brighter refex in deviating eye Left exotropia A difference in brightness can also be caused by anisometropia, anisocoria, or opacities in the eye Source: Manny (1997) Hirschberg test Room lights on (need to be able to see pupil reflex Shine pentorch into Px eye Observe position of corneal reflexes as Px views binocularly With no tropia the reflexions should be in the same position near central to the pupil If the reflex is decentred in one eye then there is a tropia Corneal reflex shifts in the opposite direction to deviation – Nasal decentration = Exotropia – Temporal decentration = Esotropia – Superior decentration = Hypotropia – Inferior decentration = Hypertropia 1 mm of decentration ≈ 20∆ deviation Krimsky’s test (adaption of Hirschberg test) Test is the same as the Hirschberg test with the addition of prisms to measure the deviation: Prism placed before deviating eye – moves corneal reflex in deviating eye until the reflexes in both eyes are symmetrical Alternatively the prism can be placed before the fixating eye (less common) Things to watch out for – Pseudostrabismus Pseudostrabismus Often seen in children The epicanthus (skin fold over inner canthus) makes it look as if there is a strabismus No strabismus is present Binocular Vision Lecture 4 – Objective measurement of eye deviations Professor P Buckhurst