Binocular Balancing

Question 1

what is the purpose of binocular balancing?

Answer 1

to balance the accommodative effort bet the 2 eyes

Question 2

why bother?

Answer 2

• the accommodativ 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 can result in asthenopia

Question 3

when should you do binocular balancing?

Answer 3

after subjective refraction

Question 4

what methods?

Answer 4

humphriss immediate contrast test MAIN

turnvilles infinity balance test

Question 5

who should you balance?

Answer 5

all pxs with binocular vision and good acuity in each eye

Question 6

who shouldnt you balance?

Answer 6

patients with

• squint/strabismus (not binocular)
• amblyopia (not binocular)
• monocular (only one functioning eye)
• va diffs of 3 or more lines (not binocular)
• presbyopes - 60 or over (has none/minimal accom)

Question 7

Humphriss immediate contrast (hic)

Answer 7

• uses a fogging lens bet the powers to +0.75 and +1.25 to fog the eye to 6/12 although the powe usually is +0.75/+1.00
• over fogging an eye (+2.00) can cause it to become monocular

Question 8

reasons for fogging

Answer 8

• relaxes accom
• central vision supressed ie fovea
• peripheral vision maintained
• v similar to normal binocular viewing conditions

Question 9

methods for hic

Answer 9

1) comfort
2) clarity
3) duochrome

Question 10

1) comfort method (hic)

Answer 10

• px views line close to limit of acuity to their non fogged eye eg le fogged re BCVA 6/5 - view 6/5 line
• view target first through +0.25 (position 1) for 1 second followed by -0.25 lens (p2) for half a second and then back to p1
• a plus lens that relaxes accom (no change in acuity) 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 small and black) should be less comfortable
• if p1 and p2 are the same keep pushing the plus

why?

• the px will accommodate if the minus lens is left in place for too long
• do not offer px the choice of no lens
• repeat as neccesary asking px ‘are letters more comfortable with lens 1 or 2)

Question 11

2) clarity method (hic)

Answer 11

• not all pxs understand the concept of comfort
• if p1 is clearer/more comfortable than p1
• first ask if it is def clearer or just smaller and blacker
• if smaller and blacker than STOP
• if def clearer, add the lens and repeat procedure until reversal obtained

Question 12

3) using duochrome (hic)

Answer 12

• can also be used in px who dont understand concept of comfortable vision
• identical end point should be achieved in each eye
• ie RE = red so LE must also be on red

Question 13

problems associated with hic and importan points to remember

Answer 13

• eye fogging too little
• eye fogging too much
• fogging lens left in trial frame and incorporated in final result
• remember always push plus
  only give more minus if it is def more comfortable and va is better
  -do not repeat +1.00 blur test after bb

Question 14

Turvilles infinity balance test

Answer 14

• septum placed on mirror to occlude vertical section in central field of each eye
• remainder of field still seen by both eyes, hence binocularly maintained
• can cause duochrome, letters, concentric circles on white background

Question 15

Duochrome method (tib)

Answer 15

• ask px to look at circles on the right and ask if circles appear darkest against red, or green, or about the same
• if the same stop and repeat for other eye
• if red better add minus to balanace (-0.25). if balance not possible leave at red better
• if green better add plus to balance (+0.25) if balance not possible leave at red better
• repeat for other eye - ask px to look at circles in the left

Question 16

when to use duochrom (tib)

Answer 16

• px who responds well to duochrome

- have unequal VAs

Question 17

when not to use duochrome (tib)

Answer 17

• px who always sees red/green better
• when has not been poss to acheive same end point in each eye
• media opacities - lead to red bias
• v small pupils

Question 18

letters/ concentric circles on white background (tib)

Answer 18

• ask px to compare clarity of images on right and left side of chart
• if one of circles/ letters is missing, check septum is positioned correctly
• if still missing or misaligned, could indicate significant heterophoria
• best to use 2 letters - one seen by RE and other seen by LE, the letters F and L are usually used
• if one of the circles/letters is clearer than the other, perform BVS of eye with least clear vision
• if circles/ letters are still not equally clear, perform BVS in other eye

Question 19

Binocular addition

Answer 19

• done after bb, done to check accom is completely relaxed

Question 20

how to carry out binocular addition

Answer 20

• direct px to smallest line, 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 21

what is an alternative to binocular balancing

Answer 21

binocular refraction

Question 22

what is binocular refraction

Answer 22

alternative to monocular subj refraction, followed by bb

• quick and easy to use but requires an accurate ret result
• rather than occluding fellow eye, fog fellow eye with +1.00 and perform subj routine

Question 23

indications for binocular refraction

Answer 23

• anisometropia
• latent hyperopia
• pseudomyopia
• unequal va due to pathology/ amblyopia
• sig horizontal/vertical phorias
• latent nystagmus