Clinical Investigations: Assessment of Binocular Vision Flashcards
What tests are used to test presence, strength and quality of BV?
To test presence: cover test, Bagolini lenses (4yrs+), Worth’s lights (school age)
To test strength: 4/20Δ prism reflex test, prism fusion range (adults)
To test quality: stereo tests
What is cover test used for?
- Detects all manifest & latent strabismus
- Indicates size & variation in deviation with distance and effect of any refractive error
- Gives an indication of level of VA in either eye – fixation
- Indicates if a latent deviation is controlled (well compensated) – rate of recovery
o NO RATE OF RECOVERY IN TROPIA - Technique:
o To a light – cover the straight eye or cover eye with central corneal reflex
o Need to hold cover over eye long enough to break dissociation
o Uncommon for px to be no apparent deviation – most people have something
What is sensory fusion?
Sensory fusion is the ability to perceive two similar images, one formed on each retina, and interpret them as one.
Single vision & sensory fusion – assuming 2 eyes working together – ask them to look at target – are they really seeing one or are they suppressing?
Describe bagolini lenses (glasses)?
- Sensory fusion test i.e. retinal correspondence
- Lenses with oblique striations etched at 45° and 135°
- Produces a luminous streak at 90° to the striations when the patient views a point source of light
- Subjective & partially dissociative
o Partially dissociative as 2 eyes seeing light – what pattern do the lights form? - Tests projection of retinal points used for fixation under binocular conditions
- Depending on condition present, it tests either:
o Foveal-foveal projection,
o or secondly in absence of bifoveal fixation Foveal-extra-macular projection - Should see 2 lines in a cross if have binocular bifoveal single vision
o Manifest deviation & see a cross – then abnormal retinal correspondence as functioning as normal - Technique:
o Px sits comfortably & wear refractive error
o Px is instructed to fixate a spotlight at both 33cms & 6m
o Examiner places lenses before pxs eyes
o Examiner notes direction of striations before each eye (NB 90°)
o Ask px what they see (younger children who find it difficult to explain may draw response) - Px may squint at one distance and not other
- If diplopia in bagolini – they will see 2 lights
- Problems with bagolini:
o Px may tell you they see 10 lights due to aberrations
What are the advantages and disadvantages of bagolini lenses?
- +ves:
o One of least dissociative tests used to determine presence & type of BSV
o Carried out in natural viewing conditions
o Quick & fairly easily understood
o Portable
o Can be carried out on other positions of gaze - -ves:
o For some pxs it can be confusing with several striations being seen – may say they see 10 lights
o Can overestimate binocularity – may get a +ve response – even when px hasn’t got great binocularity
Describe Worth’s lights?
- Sensory fusion test i.e. retinal correspondence
- Consists of 4 lights arranged in diamond shape (2 green lights horizontally, one red light & one white light)
- Based on complementary colours
- Subjective & partially dissociative
- Tests projection of retinal points used for fixation under binocular conditions
- Depending on condition present, it tests either:
o Foveal-foveal projection,
o or secondly in absence of bifoveal fixation Foveal-extra-macular projection - Technique:
o Px sits comfortably & wear refractive correction
o Px wears red & green goggles (red filter is usually placed before RE)
o Red & green of lights & goggles are complentary
o Red & white lights are only seen through green filter
o White light is visible to both eyes & therefore stimulus for fusion
o Px instructed to fixate Worth’s lights at 33cm and 6m
o Examiner asks px how many lights are seen, what colour(s) they are & where they are in relation to each other
What are the possible responses in Worth’s lights?
4 lights indicate BSV (normal or abnormal retinal correspondence)
5 lights indicate a manifest deviation with diplopia - if 2 red on left and 3 green on right then EXO, if 3 green on left and 2 red on right then ESO
2 or 3 lights indicate suppression - 3 green lights = right, 2 red lights = left
What are the advantages and disadvantages of Worth’s Lights?
- +ves:
- Quick & fairly easily understood
- Near & distance
- -ves:
- V dissociative & unnatural viewing conditions
- Can produce many false +ve/-ve results
- For e.g., the eyes are easily dissociated with red-green spex & therefore a px with unstable but functionally useful BV may exhibit a suppression response
- Also a suppression area may fall within centre of test and miss all the apertures
- Retinal rivalry can occur which may cause false +ve results
What happens when you have BSV with a foveal suppression scotoma?
- Normal BSV exists with bifoveal fixation
- BSV can exist with a foveal suppression
o May get appearance that eyes can work together but they aren’t actually - Foveal suppression in one eye represents a subnormal variant of BSV – abnormal BSV
o E.g. do Bagolini glasses – may report a gap in the cross - Anisometropia & microtropia are commonest conditions with foveal suppression
o Having microtropia doesn’t always come with manifest squint
o If px anisometropic then need to look for microtropia – they may have central suppression as blurred image going to hyperopic eye. Eyes look straight – no big angle – eyes appear to work together but they aren’t really - 45% anisometropic amblyopes have a microtropia
If manifest deviation and report cross on bagolini glasses then they have abnormal retinal correspondence.
No squint and latent deviation – see cross on bagolini glasses – normal retinal correspondence
What is the 4^ prism reflex test?
- To determine presence of bifoveal fixation
- Px fixes an accommodative target at 33cm & detailed target at 6m – must keep attention & work quickly
- 4Δ prism is placed before one eye and then the other
- Usually tested base out but can test BI/BU etc
- Use this test on EVERYONE WITH ANISOMETROPIA
- Base out in front of each eye – eye that’s foveal, eye will follow as they know image has moved
o If one eye moves then other eye follows (due to Hering’s law)
o If don’t know its moved then eye will not move - 4 yr old attending clinic – R +4.50 L+2.00
o Tests: vision, motility, 4Δ must be included
Describe the 4^ prism reflex test in someone with bifoveal fixation?
o a base out prism is placed before the right eye - non-corresponding retinal points
o in order to regain bifoveal fixation the eye under the prism adducts
o because of Hering’s Law both eyes make a conjugate movement to the left- non-corresponding retinal points
o in order to regain bifoveal fixation the left eye makes a refixation ‘fusional’ movement to the right
o when the prism is removed the right eye will ‘flick back out’ to regain bifoveal fixation - recovery movement
o repeat with the other eye.
Describe the 4^ prism reflex test in someone with LEFT central suppression scotoma?
o when a base-out prism is placed before the left eye
o no movement of the eye is seen
o as the image of the fixation target falls within a left suppression scotoma
o when a base-out prism is plced before the right eye
o a conjugate movement of both eyes is seen to left
o but there is no refixation movement of the left eye
o seen as the image has fallen within the suppression scotoma of the left eye
o NO REFIXATION MOVEMENT – it doesn’t know to refixate because of suppression scotoma
What are the points to note about 4^ prism reflex test?
- The 4Δ movement is v small & can occur quickly – sometimes difficult to detect if examiner is not paying full attention – look for small movements on cover test
o Might not be till remove the prism that see the movement - By virtue of small movement occasionally test may be inconclusive, especially if child is not a good fixer
- Test can only be used in co-operative individuals
- Steady fixation must be maintained at all times
- Done at near – must be fixating on foveal target – smallest fixation on budgie stick or small 6/9 on budgie stick
o Need to have foveal fixation
- +ves:
o Quick and easy to perform
o Prism in any form is portable
o Can be carried out for both near and distance fixation
o Can be used on young children (provided they are co-operative) - -ves:
o Movement is so small that it may not be seen by examiner
o By virtue the results may therefore be inconclusive
Describe prism fusion range?
- Equipment: prism bars, detailed target at 33cm & 6m (may vary between the two distances)
- Before estimating fusion ranges with prisms is useful to be aware of following:
o Size of deviation
o Near point of convergence
Noting which eye diverges on failure of convergence & whether or not diplopia is appreciated. If patient fails to appreciate dipopia when convergence fails it may be necessary to add a dissociated factor to the test e.g. Bagolini lenses or a red filter to ensure px is aware when fusion has broken - Go on cover test findings – if squinting at near then they don’t have fusion at near – so test in distance
- Base out then base in and can do vertical too
- More base out range at near – can pull eyes in much more as can converge
- BO is positive fusional vergence or convergence
- Base in is divergence
- Near range of base out is roughly double distance range of base out
- Image:
o Eye has to turn in – going towards apex of prism to keep fusion
o As soon as diplopia – that’s an incentive to fuse
o Because image has moved – eye has turned in - Light displaced towards prism base
- Image displaced towards prism apex
