Binocular Balancing Flashcards
(23 cards)
1
Q
what is the purpose of binocular balancing?
A
to balance the accommodative effort bet the 2 eyes
2
Q
why bother?
A
- 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
3
Q
when should you do binocular balancing?
A
after subjective refraction
4
Q
what methods?
A
humphriss immediate contrast test MAIN
turnvilles infinity balance test
5
Q
who should you balance?
A
all pxs with binocular vision and good acuity in each eye
6
Q
who shouldnt you balance?
A
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)
7
Q
Humphriss immediate contrast (hic)
A
- 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
8
Q
reasons for fogging
A
- relaxes accom
- central vision supressed ie fovea
- peripheral vision maintained
- v similar to normal binocular viewing conditions
9
Q
methods for hic
A
1) comfort
2) clarity
3) duochrome
10
Q
1) comfort method (hic)
A
- 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)
11
Q
2) clarity method (hic)
A
- 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
12
Q
3) using duochrome (hic)
A
- 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
13
Q
problems associated with hic and importan points to remember
A
- 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
14
Q
Turvilles infinity balance test
A
- 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
15
Q
Duochrome method (tib)
A
- 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
16
Q
when to use duochrom (tib)
A
- px who responds well to duochrome
- have unequal VAs
17
Q
when not to use duochrome (tib)
A
- 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
18
Q
letters/ concentric circles on white background (tib)
A
- 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
19
Q
Binocular addition
A
- done after bb, done to check accom is completely relaxed
20
Q
how to carry out binocular addition
A
- 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
21
Q
what is an alternative to binocular balancing
A
binocular refraction
22
Q
what is binocular refraction
A
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
23
Q
indications for binocular refraction
A
- anisometropia
- latent hyperopia
- pseudomyopia
- unequal va due to pathology/ amblyopia
- sig horizontal/vertical phorias
- latent nystagmus
