binocular balancing

Question 1

what is the purpose of binocular balancing?

Answer 1

. to balance the accommodative effort between the two eyes

Question 2

why do we do binocular balancing?

Answer 2

. 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

Question 3

when should you do binocular balancing?

Answer 3

. after subjective monocular redraction

Question 4

how do you do binocular balancing ?

Answer 4

. humphriss immediate contrast test

. turville’s infinity balance test

Question 5

which patients should you balance ?

Answer 5

. all patients with binocular vision and good acuity in each eye

Question 6

which patients should you not balance ?

Answer 6

. 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

Question 7

what are the general concepts behind the humphriss immediate contrast (HIC)?

Answer 7

. 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

Question 8

what are the reasons for fogging a patient?

Answer 8

. relaxes accommodation
. central vision is suppressed i.e. fovea
. peripheral vision maintained
. very similar to normal binocular viewing conditions

Question 9

what are the three methods for doing the humphriss contrast test?

Answer 9

. comfort
. clarity
. duochrome

Question 10

explain the (HIC) comfort method ?

Answer 10

. 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

Question 11

why is the plus lens held longer than minus lens in the HIC comfort method?

Answer 11

. because the px will accommodate if the minus lens is left in place for too long

Question 12

what should be comfortable in HIC comfort method?

Answer 12

. 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

Question 13

what happens if position 1 and 2 are the same during the HIC comfort method?

Answer 13

. keep pushing the plus

. add +0.25 and repeat procedure until reversal of lens preference is achieved

Question 14

when would we use the HIC clarity method?

Answer 14

. not all Pxs understand the concept of comfort
. then use clarity method
. emphasise that ‘smaller and darker’ does not mean clearer

Question 15

what to do if position 2 ( minus ) is clearer/ more comfortable than position 1?

Answer 15

. 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

Question 16

what is the difference between HIC the American way?

Answer 16

. 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

Question 17

when to use HIC duochrome ?

Answer 17

. 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

Question 18

what are the problems associated with HIC?

Answer 18

. eye fogged too little
. eye fogged too much
. fogging lens left in trial frame optom incorporates into final result

Question 19

what are important things to note in HIC?

Answer 19

. 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

Question 20

what is Turville’s infinity balance test ( TIB)?

Answer 20

. 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

Question 21

what is the method of (TIB) duochrome ?

Answer 21

. 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

Question 22

what to remember when using (TIB ) duochrome ?

Answer 22

. end point must be same for each eye

Question 23

when to use duochrome?

Answer 23

. patients who respond well to duochrome

. px have unequal VAs

Question 24

when not to use duochrome?

Answer 24

. px who always see red/green better

. when has not possible to achieve same end point in each eye

. media opacities - red bias

Question 25

explain the TIB procedure: letters/concentric circles on white background?

Answer 25

. 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

Question 26

what to do in TIB if one of the circles/letter is clearer in one eye?

Answer 26

. 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

Question 27

what to do after binocular balancing?

Answer 27

binocular addition

Question 28

why do we do binocular addition?

Answer 28

. to check that accommodation is completely relaxed

Question 29

how to do binocular addition?

Answer 29

. 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

Question 30

what are the general rules of binocular addition?

Answer 30

. 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

Question 31

what are the alternative to binocular balancing?

Answer 31

binocular refraction

Question 32

what is binocular refraction?

Answer 32

. 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

Question 33

when to use binocular refraction?

Answer 33

. anisometropia
. latent hyperopia
. pseudomyopia
. unequal visual acuities due to pathology/ amblyopia
. significant horizontal or vertical phorias
. latent nystagmus

Question 34

what order test after ret?

Answer 34

. monocular subjective refraction
. +1.00 DS blur test
. binocular balancing
. binocular add