Binocular balancing Flashcards
what is the purpose of binocular balancing?
to balance the accommodative effort between the two eyes
why do we bother with BB?
Accommodative effort is not always the same under monocular conditions as it is under binocular conditions.
when both eyes are working together, least accommodation is needed/used to maintain clear image.
this can cause accommodation to be unstable and can result to asthenopia.
when should you do BB?
after subjective monocular refraction.
How should you do BB? name 2 techniques
Humphriss Immediate contrast test
turville’s infinity balance test
several techniques
which patients should you BB?
all patients with binocular vision and good acuity in each eye
which 5 types of patients should you NOT do BB? and state why
px’s with?
- squint: not binocular
- amblyopia: not binocular
- monocular: only has one functioning eye
- va differences of 3 or more lines: not binocular
- presbyopes ( 60 years or above): has non/minimal accommodation
what is the general concepts of the humphriss immediate contrast (HIC)?
- uses a fogging lens between the powers +0.75 and +1.25D to fog one eye to 6/12
- over fogging an eye e.g. with a +2.00D can cause the eye to become monocular
- many clinicians use a +1.00D and leave it in situ after the +1.00D blur test as they already know how much it food the px by
What is the 4 reasons for fogging ? when using the humphriss immediate contrast (HIC) method
- relaxes accommodation
- central vision suppressed i.e fovea
- peripheral vision maintained
- very similar to normal binocular viewing conditions
what are the three methods of HIC?
- comfort
- clarity
- duochrome
what is the HIC comfort method?
px views line of letters close to limit of acuity to their non fogging eye
LE FOGGED RE BCVA 6/5
px views 6/5 line
view target first through +0.25 lens for 1 sec then immediately by -0.25 lens for half sec then back to +0.25D again
repeat as necessary asking px, “are letter more comfortable with lens 1 or 2?”
why do we only hold the -0.25D lens for half a second in the HIC comfort method?
px will start to accommodate if the minus lens is left in place for too long.
px has to make a choice between the lenses, cannot have no lens.
what should be considered more comfortable in the HIC comfort method?
and what should be considered less comfort in the HIC comfort method?
A plus lens that relaxes accommodation (no change in clarity) 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 eyes accommodate (letters smaller and blacker) should be less comfortable
what if position 1 and 2 are the same?
remember to keep pushing for the plus
- add +0.25 and repeat procedure until reversal of lens preference is achieved
what is the HIC clarity method and how is it done?
done when a px does not understand the concept of comfortable vision, but with clarity you must emphasise that smaller and blacker does not mean clearer
- first ask “is it definitely clearer, or smaller and blacker?”
- if its just smaller and blacker, STOP
- if definitely clearer, add the lens and repeat the procedure until reversal is obtained
- if theres no difference between +0.25D and -0.25D lens, then add the +0.25D lens
what is the HIC duochrome method?
done when a px does not understand the concept of comfortable vision
an identical endpoint should be achieved in each eye i.e.
RE = red so LE must also be left on red
what 3 problems do you find with HIC?
- eye fogged too little
- eye fogged too much
- fogging lens left in trial frame and optometrist incorporates it into final results
what 3 points is always important to remember in in HIC?
- always push for the plus lens
- only give minus if it is more comfortable and VA is better
- do not need to repeat +1.00D blurr test after BB
what is the HIC clarity method and how is it done?
done when a px does not understand the concept of comfort, but with clarity you must emphasise that smaller and blacker does not mean clearer
- first ask “is it definitely clearer, or smaller and blacker?”
- if its just smaller and blacker, STOP
- if definitely clearer, add the lens and repeat the procedure until reversal is obtained
- if theres no difference between +0.25D and -0.25D lens, then add the +0.25D lens
how does TIB work?
- septum placed on mirror to occlude vertical section in central field of each eye
- remainder of the field still seen by both eyes hence binocularity maintained
- can use duo chrome, letters, concentric circles on white background
How does TIB test with the duochrome work?
- ask px to look at the circles on the right and ask if circles appear darkest against red or green background or about same
- RED=GREEN stop and repeat other eye
- RED IS BETTER - add minus to balance in -0.25D steps, if balance is not possible then leave at “red better”
- GREEN IS BETTER - add plus to balance in +0.25D steps, if balance is not possible leave at, “red better”
- repeat test on other eye but look at circles on the left side
- REMEMBER end point must be same for each eye, so should be either: RE = red & LE = green or RE = red & LE = red or RE = green & LE = green
when will you use the duochrome method on a patient during BB?
- px who responds well to duochrome
- px who has unequal VAs
when will you not use the duo chrome? list 4 circumstances
- px who always see either red/green better
- when has not been possible to achieve same end point in each eye
- media opacities - red bias
- very small pupils
explain the TIB procedure with, letters/concentric circles on white background
- ask px to compare clarity of images on right hand side to left hand side of the chart
- if one circle or letters is missing check the septum
- if still missing or misaligned circles/letters, this could indicate significant heterophoria
best to use 2 letters one seen by RE and other by LE.
The letter ‘F’ & ‘L’ are usually used - if one of the circles/letters is clearer than the other, perform best vision sphere assessment of the eye with the least clearer vision
- if circles/letters are still not equally clear, perform best vision sphere on the other eye
- always start off with +0.25D
what does a plus lens do in comfort method?
A plus lens that relaxes accommodation no change in clarity 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 eyes accommodate should be less comfortable
