Download Binocular Balance Through Prism

CLE 162.3 Optometric Procedures
Notetaker: Kyle Reuter
Date: 3/20/12 1st Hour
Page 1
Ocular Dominance
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Visual input from one eye versus the other is preferred
Make small triangle with hands and put letter on Snellen chart
o If you close 1 eye it will disappear with the eye that is not
dominant
o Eye that still sees target is the dominant eye
Binocular Balance
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Goal: Eliminate accommodative imbalance between 2 eyes in the final Rx.
Candidates for BB:
o Patients that are not absolute presbyopes
 i.e. people with no accommodation left
o Patients that have VA that differ by 1 line between both eyes
 Ex. If right eye is best corrected at 20/20 and left eye is best
corrected at 20/40
 If you give target 2 lines better than BCVA, the brain will
always prefer the clearer eye
Binocular Balance Through Prism
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Isolate distant line 2 above BCVA
On JCC lens, select prism setting
Tell patient, “I’m going to add lenses, it might become blurry”
Add +0.50DS to each eye
Place 3∆ BD OD and 3∆ BD in OS via Risley Prism
o Confirm that the patient is seeing 2 targets (lines) that are
separated vertically
o May need to add more than 3∆ to each eye to disrupt fusion
Tell patient to ignore the brightness of the screen and report which set of
letters is most clear
o Top image correlates to BD and bottom image refers to the BU
Add +0.25DS to the more clear eye and repeat until lines look equal
o Goal is to make them both look the same
If you cannot make them the same, leave the dominant eye with less plus
power
o I.e. Leave the dominant eye with the more clear image
Add another +0.50DS OU and remove the Risley Prism
Check VA
o Should be reduced from before because of the added plus power
Slowly begin adding minus BINOCULARLY in -0.25D increments until
patient reports that the letters are clear and comfortable
o Monitor VA and visual efficiency so that you do not overminus the
patient
Once the patient reports that the letters are clear, check the VA for each
eye
Binocular Balance Through Alternate Occlusion
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Basically the same process as BB through Prism except that you occlude
one eye
CLE 162.3 Optometric Procedures
Notetaker: Kyle Reuter
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Date: 3/20/12 1st Hour
Page 2
Occlude one eye and have them look at target, then occlude other eye and
have them view the same target with the other eye
o Ask them if one image appeared to be more clear, and add +0.25DS
to the eye that appeared most clear
You still add the +0.50DS OU before you begin and the +0.50DS OU after
Usually done if the patient has a intermittent strabismus or very high
exophoria
Troubleshooting
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How can I tell if my patient is suppressing an eye during prism
dissociation?
o The patient should tell you they only see ONE line of letters
 Why we confirm that they see 2
o If suppressing, the patient may report that they see the single line
moving when doing prism dissociation
 If suppressing OS, the image will appear to move further
“up” due to the addition of BD to OD
 Vice versa if suppressing OD
After BB, the patient has slightly worse vision in one eye than after step 4
of manifest refraction. How can this be right?
o During the BB step, you equalized the amount each eye
accommodates
 Remember: eyes are lazy and will only accommodate to
the lesser amount required
o It is OK if one eye sees slightly less (one VA line) than before
 When patient is viewing target with both eyes, this
difference will be eliminated
o If the vision is worse by multiple lines, repeat the test for accuracy
After finishing BB, the result was more minus sphere in one/both eyes
compared to the step 4 result. Did I screw up?
o BB results generally have the same/more plus than the monocular
findings.
o More minus may mean that one/both eyes have been overminused
o Should not happen – Go back and make sure that they earn the
20/20
Why didn’t balancing my amblyopic patient work?
o First, the patient must be “binocular” so it should not work for a
strabismic amblyope
o Second, if the VA difference between the 2 eyes is more than one
line, the target of the clearer line with ALWAYS appear more clear
 Hence, not balancing accommodation, but balancing VA’s
will result in over-minusing the worse eye when minus
power is added binocularly
o Amblyopes have a disruption to the development of one of the
visual tracts that causes imbalance in their ocular dominance
CLE 162.3 Optometric Procedures
Notetaker: Kyle Reuter
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Date: 3/20/12 1st Hour
Page 3
Meaning, one eye cannot be best corrected to the VA of
their other eye
Typically, it’s about a difference of 1 line
Chromatic Aberration
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Use Red/Green screen to test for chromatic aberration
If your manifest refraction is perfect, then the patient will see the
brightness of the red/green as equal
o If you have over-minused someone, the green side will appear
clearer
o If you have over-plused someone, the red side will appear clearer
Different wavelengths of light are bent to different extents
Longer wavelengths are bent less (Red)
o i.e. require minus power to bring to equal
Shorter wavelengths are bent more (Green)
o i.e. require plus power to bring to equal
Duochrome or Bi-Chrome Test
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Choose during which step you will introduce this test
o Can be introduced at any time that you are adjusting sphere power
 i.e. Step 1, Step 4, Binocular Sphere Adjustment (after BB)
Isolate a line at least 2 lines above BCVA
Apply the Red/Green filter
Completely darken exam room
o So that no other wavelengths of light interfere
Add +0.50 DS to non-occluded eye(s)
Ask patient which side of chart looks more clear
o Expecting red side because you have added plus
o If the patient says the green side is clearer, add more plus because
you have over-minused the patient
o **If adding additional plus does not result in the red side
becoming more clear/dark, but instead blurs the target –
Discontinue the procedure**
o If patient says that the red side is more clear/darker, add -0.25DS
increments until the patient reports that the red and green letters
appear equally clear/dark
**If working in an exam room that is less than 20ft in length, the
appropriate endpoint is the first -0.25DS increment that leaves the
green side more clear/dark**