binocular balancing Flashcards
what is the purpose of binocular balancing?
. to balance the accommodative effort between the two eyes
why do we do binocular balancing?
. the accommodative effort is not always the same under monocular conditions as it is under binocular conditions
. when both eyes are working together, they accommodate by the least amount needed to maintain a clear image
. this can cause accommodation to be unstable and result in asthenopia
when should you do binocular balancing?
. after subjective monocular redraction
how do you do binocular balancing ?
. humphriss immediate contrast test
. turville’s infinity balance test
which patients should you balance ?
. all patients with binocular vision and good acuity in each eye
which patients should you not balance ?
. patients with
- squint - not binocular
- amblyopia- not binocular
- monocular- only one functioning eye
- VA difference of 3 or more lines- not binocular
- presbyopes ( 60 years or over )- has none ( or minimal) accommodation
what are the general concepts behind the humphriss immediate contrast (HIC)?
. uses a fogging lens between the powers +0.75 and +1.25D to fog one eye to 6/12 although usually the power is +0.75/+1.00D
. over fogging an eye ( e.g. +2.00D) can cause it to become monocular
. many clinicians use +1.00D and leave it in after the +1.00 blur test as they already know how much it fogs the patient by
what are the reasons for fogging a patient?
. relaxes accommodation
. central vision is suppressed i.e. fovea
. peripheral vision maintained
. very similar to normal binocular viewing conditions
what are the three methods for doing the humphriss contrast test?
. comfort
. clarity
. duochrome
explain the (HIC) comfort method ?
. the patient views the line of letters close to limit of acuity to their non-fogged eye
e.g. LE is fogged and RE best corrected visual acuity is 6/5. view 6/5 line
. view target first through +0.25 lens ( position 1 ) for 1 second followed immediately by -0.25 lens ( position 2) for 1/2 second and then back to position 1
. repeat as necessary asking the Px: are the letters more comfortable with lens 1 or 2
why is the plus lens held longer than minus lens in the HIC comfort method?
. because the px will accommodate if the minus lens is left in place for too long
what should be comfortable in HIC comfort method?
. a plus lens that relaxes accommodation , or a minus lens that makes vision clearer should both be more comfortable
. a plus lens that blurs vision or a minus lens that makes the eye accommodate ( letters smaller and blacker ) should be less comfortable
what happens if position 1 and 2 are the same during the HIC comfort method?
. keep pushing the plus
. add +0.25 and repeat procedure until reversal of lens preference is achieved
when would we use the HIC clarity method?
. not all Pxs understand the concept of comfort
. then use clarity method
. emphasise that ‘smaller and darker’ does not mean clearer
what to do if position 2 ( minus ) is clearer/ more comfortable than position 1?
. first ask ‘ is it definitely clearer or just smaller or blacker’
. if just smaller and blacker , STOP
. if definitely clearer, add the lens and repeat the procedure until reversal is obtained
what is the difference between HIC the American way?
. exactly the same as described for HIC ( the British way)
. the difference is you only show a +0.25 DS lens, never a -0.25 DS lens
when to use HIC duochrome ?
. duochrome can also be used in patients who do not understand concept of comfortable vision
. identical end point should be achieved in each eye
i.e. RE=red so LE must also be left on red
what are the problems associated with HIC?
. eye fogged too little
. eye fogged too much
. fogging lens left in trial frame optom incorporates into final result
what are important things to note in HIC?
. remember always push plus
. only give more minus if it is definitely more comfortable and VA is better
. do not repeat +1.00 blur test after binocular balancing
what is Turville’s infinity balance test ( TIB)?
. septum placed on mirror to occlude vertical section in central field of each eye
. remainder of field still see by both eyes, hence binocularity maintained
. can use duochrome, letters, concentric circles on white background
what is the method of (TIB) duochrome ?
. ask patient to look at circles on the right and ask if circles appear darkest against red or green background or about the same
. stop and repeat for the other eye
. if red is better-
add minus to balance (-0.25 steps) if balance not possible leave at red
. if green better- add plus to balance ( +0.25) if balance not possible leave at red
. repeat for other eye - ask px to look at circles on left
what to remember when using (TIB ) duochrome ?
. end point must be same for each eye
when to use duochrome?
. patients who respond well to duochrome
. px have unequal VAs
when not to use duochrome?
. px who always see red/green better
. when has not possible to achieve same end point in each eye
. media opacities - red bias
explain the TIB procedure: letters/concentric circles on white background?
. ask the patient to compare clarity of images on right and left side of the chart
. if one of the circles / letter is missing check septum
. if still missing or misalignment of circles/letters could indicate significant heterophoria
. best to use 2 letters- one seen by RE and other seen by LE
what to do in TIB if one of the circles/letter is clearer in one eye?
. if one of the circles/letters is clearer than the other, perform best vision sphere assessment of eye with least clear vision
. if circles/letters are still not equally clear, perform best vision sphere on other eye
. always start off with +0.25
what to do after binocular balancing?
binocular addition
why do we do binocular addition?
. to check that accommodation is completely relaxed
how to do binocular addition?
. direct the px to smallest lien. add +0.25 to both eyes and ask ‘ if letters are just as clear with or without’
. if VA remains unaltered , add +0.25 binocularly
. repeat until further addition of +0.25 causes reduction in acuity
. no need to offer -0.25 unless binocular VA less than monocular and you feel you have under minused
. best done with flippers
what are the general rules of binocular addition?
. as a general rule, only offer +0.25DS
. only offer -0.25DS if binocular VA is less than monocular VA
. young person should never be encouraged to accept more minus
what are the alternative to binocular balancing?
binocular refraction
what is binocular refraction?
. alternative to monocular subjective refraction, followed by binocular balancing
. quick and easy but need to have accurate ret results
. rather than occluding fellow eye, fog fellow eye ( with +1.00DS) and perform subjective routine
when to use binocular refraction?
. anisometropia
. latent hyperopia
. pseudomyopia
. unequal visual acuities due to pathology/ amblyopia
. significant horizontal or vertical phorias
. latent nystagmus
what order test after ret?
. monocular subjective refraction
. +1.00 DS blur test
. binocular balancing
. binocular add
