Week 5 - Assessment of binocular vision Flashcards
Main categories of tests for binocular vision:
• Presence
- Cover test
- Bagolini lenses (4yrs +)
- Worth’s lights (school age)
• Strength
- 4^ Prism reflex test
- Prism fusion range
• Quality
- Stereotests
Summary cover test
• detects all manifest and latent strabismus
• indicates size and variation in deviation with distance and the effect of any refractive error
• gives an indication of the level of visual acuity in either eye - fixation
• indicates if a latent deviation is controlled (well compensated) - rate of recovery
How to tell if: Bsv present; visual axis aligned; eyes work together?
• Bagolini lenses
• Worth’ Lights
• 4 prism reflex test
Bagolini lenses (glasses):
• Sensory fusion test
i.e retinal correspondence
• lenses with oblique striations etched at 45° and 135° (so fine they do not affect vision)
• produce a luminous streak at 90° to the striations when the patient views a point source of light
• subjective and partially dissociative
• tests the projection of retinal points used fixation under binocular conditions
depending on the condition present it tests either
1. Foveal-Foveal projection, or secondly in the absence of bifoveal fixation
2. Foveal-Extra-macular projection
Instructions for Bagolini lenses:
• patient seated comfortably
• patient wears any refractive error
• patient is instructed to fixate a spotlight at both 33cms and 6m
• examiner places lenses before patients eyes
• examiner notes the direction of striations before each eye (NB 90°)
• ask patient what they see (younger children who find it difficult to explain may draw the response)
Advantages and disadvantages of bagolini lenses:
Advantages
• one of the least dissociative tests used to determine the presence and type of BSV
• carried out in natural viewing conditions
• quick and fairly easily understood
• portable
• can be carried out on other positions of gaze
Disadvantages
• for some patients it can be confusing with several striations being seen
Worths lights:
• sensory fusion test i.e. retinal correspondence
• this test consists of four lights arranged in a diamond shape (two green lights horizontally, one red light and one white light)
• based on complementary colours
• subjective and partially dissociative
• tests the projection of retinal points used for fixation under binocular conditions
depending on the condition present it tests either
1. Foveal-Foveal projection, or secondly in the absence of bifoveal fixation
2. Foveal-Extra-macular projection
How does one do worths light test?
• patient seated comfortably
• patient wears any refractive error
• patient wears red and green goggles (red filter is usually placed before the right eye)
• the red and green of the lights and goggles are complementary
• the red and white lights are only seen through the red filter
• the green and white lights are only seen through the green filter
• the white light is visible to both eyes and therefore a stimulus for fusion
• patient is instructed to fixate Worth’s lights at both 33cms and 6m
• examiner asks patient how many lights are seen, what colours) they are and where they are in relation to each other
(the filters may be reversed to check answers for reliability)
Worths lights possible results:
• four lights indicate BSV (normal or abnormal retinal correspondence see later)
• five lights indicate a manifest deviation with diplopia
• two or three lights indicate suppression
Advantages/disadvantages to worths lights:
Advantages
• quick and fairly easily understood
• near and distance
Disadvantages
• very dissociative and unnatural viewing conditions
• can produce many false positive/negative results
- The eyes are easily dissociated with the red-green spectacles and therefore a patient with unstable but functionally useful binocular vision may exhibit a suppression response.
- retinal rivalry can occur which may cause false positive results
• also a suppression area may fall within the centre of the test and miss all the apertures
Normal BSV with foveal suppression scotoma?
• normal BSV exists with bifoveal fixation
• BSV can exist with a foveal suppressin
• foveal suppression in one eye represents a subnormal variant of BSV abnormal BSV
• anisometropia and microtropia are the commonest conditions with foveal suppression
• 45% anisometropic amblyopes have a microtropia
4 Base prism reflext test
• to determine the presence of bifoveal fixation
• the patient fixes an accommodative target at 33cms and a detailed target at 6m - must keep attention and work quickly
• 4^ prism is place before one eye and then the other
• usually tested base-out but can be tested Bl/BU etc
What is seen with bifoveal fixation using 4 prism test?
• base out prism iplaced 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 ‘fusional 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
What is seen with left central suppression scotoma using 4 prism test?
• when a base-out prism is placed before the left eye
• no movement of the eye is seen
• as the image of the fixation target falls with left suppression scotoma
• when a base-out prism is pled before the right eye
• a conjugate movement of both eyes is seen to a left
• but there is no refixation movement of the left eye
• seen as the image has fallen within the suppression scotoma of the left eye
Important notes about 4D prism test:
• the 4^ movement is very small and can occur quickly. It is therefore sometimes difficult to detect if the examiner is not paying full attention
• by virtue of the small movement occasionally the test may be inconclusive, especially if the child is not a good fixer
• the test can only be used in co-operative individuals
• steady fixation must be maintained at all times
Advantages and disadvantages of 4D prism test:
Advantages
• quick and easy to perform
• the prism in any form is portable
• can be carried out for both near and distance fixation
• can be used on young children (provided they are co-operative)
Disadvantages
• the movement is so small that it may not be seen by examiner
• by virtue the results may therefore be inconclusive
Prism fusion range:
Prism Fusion Range
Equipment prism bars detailed target at 33cms and 6m before estimating fusion ranges with prisms is useful to be aware of the following:
• size of deviation
• near point of convergence
- noting which eye diverges on failure of convergence and whether or not diplopia appreciated. If the patient fails to appreciate diplopia when convergence fails it may necessary to add a dissociative factor to the test e.g. Bagolini lenses or a red filter ensure the patient is aware when fusion has broken
Whats recorded during prism fusion range?
Record:
• ‘blur / break / recovery’ for each prism fusion range
• NB In some conditions the subject may not notice blur, if the subject does not report blur you will subsequently only be recording the break and recovery point.
20D prism Reflex test:
• babies and young children unable to cooperate with the prism fusion range
• useful in proving the presence of BSV in pseudostrabismus
• the child fixes a light or interesting target at 33cms - must keep attention and work quickly
• 20^ prism base-out is place before one eye and then the other
6 months of age 10D base-out
12 - 18 months of age 15D base-out
Over 18 months of age 20D base out
Measurement of deviations
Objective
• methods using dissociation
- prism and cover test (PCT)
• methods using corneal reflections
- Hirscheberg test
- prism reflection test (PRT)
- Krimsky test synoptophore
Subjective
- synoptophore
- Maddox rod
- Maddox wing
Prism cover test can be used in:
is an objective partial dissociation test used to measure the maximum angle of deviation
• heterotropia and heterophoria
• horizontal and vertical deviations
• measurements possible in all positions of gaze
• adults and co-operative children
• central fixation
• visual acuity 6/60 or better
Advantages/Disadvantages of prism cover test:
Advantages
• the test may be performed reasonably quickly
• it provides an accurate measurement of the full dissociated angle of deviation
• it can measure the deviation fixing either eye, in the nine positions of gaze
Disadvantages
• the test demands concentration and cooperation from the patient and cannot be carried out on infants
• it is difficult for patients to see through large strength prisms and therefore the PCT can be unreliable in deviations greater than 80D
• it cannot be used in eccentric fixation
• it is extremely difficult to measure the deviation in cases of nystagmus
• it cannot be used to measure cyclodeviations
Hirscheberg:
Is an objective test used lo measure the angle of deviation
• heterotropia
• horizontal and vertical deviations
• poor visual acuity
• babies and uncooperative children
Prism reflection test:
is an objective dissociation test used to measure the angle of deviation
• heterotropia
• horizontal and vertical deviations
• poor visual acuity
• babies and young (or uncooperative) children
