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
What should you consider when measuring the prism fusion range?
Have to do fusion ranges in intermittent deviation or decompensating phoria
Measure fusion first before dissociating them – so you know how they actually are during the day
Think about time of day you are seeing them – their sxs may be worse in evening when tired but you see them at 10am for e.g.
What should you record in prism fusion range?
Blur/break/recovery for each prism fusion range. In some conditions, the subject may not notice blur, if subject does not report blur then only record break & recovery point (usually in BI)
Describe normal fusion range?
- By age of 5, child should cooperate with measurement of prism range using a prism bar
- Most pxs blur at about 15/16, break at about 30, recovery at 25 – if within these then do no need to treat
- If cannot control deviation due to not enough fusion then will get sxs or squint
- Blur = fusion starts to suffer maintaining fusion
o Prism should have no optical strength at all - Break = diplopia
o If regaining binocular single vision by just one prism down – shows that they are good binocularity - BO in distance is usually about half of near
- BO range of 30^ - XOP of 10^ then BO range of 40^
- Want to know how much the px is controlling on their own
o Need to know what is possible & what is normal - May need to use bagolini & worths lights – to use control to get more subjective response from the px
Describe the 20^ prism reflex test?
- Babies & young children unable to cooperate with prism fusion range
- Useful in providing presence of BSV in pseudostrabismus
- Child fixes a light or interesting target at 33cm – must keep attention and work quickly
o Fixation target is best – detailed target - Prism BO is place before one eye and then the other
- Can you make them squint by using the prism – can you overcome their fusion range
- Can they overcome a 20Δ then you know they have enough fusion to control their eyes
- a base out prism is placed before the right eye - non-corresponding retinal points
- in order to regain bifoveal fixation the eye under the prism adducts
- because of Hering’s Law both eyes make a conjugate movement to the left - non-corresponding retinal points
- in order to regain bifoveal fixation the left eye makes a refixation movement to the right
- when the prism is removed the right eye will ‘flick back out’ to regain bifoveal fixation - recovery movement
- repeat with the other eye
Which prisms should be used in which ages for 20^ prism reflex test?
6 mths of age 10^ base out
12-18 mths of age 15^ base out
over 18mths of age 20^ base out
