6: binocular balancing

what is done in binocular refraction

dont use an occluder, and in its place a fogging lens is used

use a +0.75 or +1.00DS

what does no occluder mean

means no dissociations and no stimulus to accomodation; low fogging lens means peripheral fusion and more relaxation of accomodation

quicker as dont need to do binocular balance

one problem with binocular refraction

you need an accurate retinoscopy and you need to spot px who have difficulty with this tes eg px with highly dominant eyes and know when to not use it eg px who are not binocular , such as those with a strabismum and/or amblyopia

binocular balance of accomodation tests

performed after a monovular refraction to relax and balance accomodation in the two eyes

either completely dissociate the two eyes and attempt to match the fogged VA in each eye. or partially dissociated and match fogged VA or the duochrome

who doesnt need the bincoular balance

those who cant accomodate

monocular fogging

this is minimally dissociated and aim to determine the spherical correction in conditions similar to the px normal viewing situation so that vergence and pupil size are in their normal binocular state and there is no occluder to potentially indice proximal acom

procedure for monocular fogging balance

1. fog left eye until VA is reduced by 3-4 lines less than eye tested. usually a +0.75 or +1.00 needed

2. repeat the BVS assessment using a +0.25 in right eye. ie direct px to the lnie of best va and ask are the letters clearer with this lens, same or without

3. if better, add +0.25DS to correction and repeat until px says better without or if minus better without or same

4. remove fog from left eye and then fog the right eye by same amount and repeat until have max plus minimum minus

what changes?

typically, BB tests either find no change in refractive correction from monocular refraction or find a small amount of additional positive lens power in one eye

moncular subjective refraction can lead to a possible over minusing or under plussing as occluder can stimulate accom in non tested eye causing it in the tested eye

blurring 3-4 lines supresses central vision in fogged eye, but retains peripheral fusion ( not fully dissociated with an occluder or prism )

there can be a significant increase in amount of plus accepted with BB

record subjective refraction after bb rather than after bb monocularily

common errors

is to try bb a patient who has no accom eg over 60s nd psuedophakes

less commonly; some px are so dominant in one eye that when you fog their dominant eyethey have great difficulty making subjective judgements binocularily

also with some hypropes and psuedomyopes youll find much more plus when bb. shdn you have added +0.50 ds in right eye, accom in both eyes will have relaxed and you might fing that the fog in the le is now not blrring too much. in that case add more plus to fog left eye before continuing

what 2 techniques are used in binocular balancing

one way is to compare the vision directly in 2 eyes and are directed towards balancing accomodation whereas others are based on binocular refraction techniques eg polaroid, monocular fogging and determine the spherical correction in conditions close to the px normal viewing situation

procedure for monocular fogging balance

fog left eye until va is reduced by 3-4 lines . typically +0.75 or +1.00

repeat the bvs using plus/minus technique

if +0.50 or more is added, such as for some px with latent hyperopia , it is likely that this will relax the accom in both eyes. to ensure amount of fogging lens is still effective, add additional plus power to left eye and check va is blurred 3-4 lines

remove fog then fog right eye and repeat

procedure for humphriss immediate contrast

1. fog left eye until va reeduced 3-4 lines. young px would require +0.75 /+1.00 to give va of 6/9 to 6/12

2. ask px to look at smallest line and place +0.25 in front for 1 sec and replace with -0.25 for ½ sec

3. ask if better with lens 1 or 2

4. if they say minus, check if va imporves and if so then add

5. if px reports after some consideration that the minus is clearer then dont add

6. if +0.25 clearer add it

7. because youve added +0.25 it is asusmed that acocm is relaxed in both eyes. to ensure the amount of fogging lens is still effective add +0.25 to left eye

8. continue until rejected

procedure for polaroid balance of accom

1. place polarised filters before both eyes

2. add +0.50 DS to both eyes

3. ask px if letters clearer on line seen by right or left eye or if the same

4. if one line is clearer add +0.25 to that eye until the 2 monocularily seen lines are equally blurred

5. if balance cannot be achieved use leneses that provide thr best vision to the dominant eye

6. remove polarised filters

7. remove fog in binocular +0.25 ds steps until obtain max va

8. if px can read to the bottom lind of chart you can allow extra minus or extra plus

binocular subjective refraction

performed under conditions that are close to the px normal distance viewing situation as possible

better control over and greater relaxation of, acom and is slightly quicker than monocular refraction as no BB is required

binocular refraction procedure

begin with the retinoscopy before each eye

occlude right eye and fog left eye until the va is reduced by 3-4 lines and remove occluder

determine bvs and cylinder power and axis using jcc

check end result sphere using duochrome and measure va

remove fogging lens from untested eye and fog right eye and do same

remove fogginf lens and measure binocular va

recording and interpreting binocular refraction results

a subjective reuslt that is less positive than retinoscopy result or subjective being more minus than suggested by unaided VA could indicate latent hyperopia or pseudomyopia