Binocular Balancing CSA Flashcards
What is the purpose of binocular balancing?
To balance the accommodative effort between the two eyes.
What is asthenopia?
Asthenopia is more commonly known as eyestrain or ocular fatigue. It’s a common condition that occurs when your eyes become tired from intense use.
Why bother with binocular balancing?
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 can result in asthenopia.
When should you do binocular balancing?
After subjective monocular refraction.
How do you carry out binocular balancing?
There are several techniques but the one we concentrate on in labs is called Humphriss Immediate Contrast test.
[Another noted one is Turville’s Infinity Balance Test]
Which patients should you binocularly balance?
All patients with binocular vision and good acuity in each eye
Which patients should you not binocularly balance?
Px with:
- Squint
- Amblyopia
- Monocular
- VA differences of 3 or more lines
- Presbyopes (60 years or over)
What are the general concepts behind the Humphriss Immediate Contrast Test?
- 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 situ after the +1.00 blur test as they already know how much it fogs the patient by.
What are the reasons for fogging?
Relaxes accommodation
- Central Vision suppressed i.e. fovea
- Peripheral Vision maintained
- Very similar to normal binocular viewing conditions
What are the three methods of carrying out the Humphriss Immediate contrast test?
- Comfort method
- Clarity method
- Duochrome method
What does the Humphriss Immediate Contrast comfort method involve?
So basically once you have found the monocular Rx (imagine it’s 6/5 in both eyes) you are going to go ahead and fog an eye.
Let’s imagine in this case you fog the left eye. The left eye would be fogged using a +0.75/+1.00D lens (whichever lens is needed to get VA to 6/12).
[At this point the Px would view line of letters close to the acuity of their non fogged eye - so in this case 6/5 would be the Best Corrected Visual Acuity (BCVA)].
You would then place a +0.25D lens in front of the non-fogged eye (so our right eye in this case). This would be done for only 1 second. Then you would place a negative lens, -0.25D in front of the eye for half a second, and then go back to the +0.25D lens.
Then proceed to ask the Px are the letters more COMFORTABLE with lens 1 (the positive lens) or lens 2 (the negative lens).
[Do not offer the Px the choice of no lens].
You then add whatever lens they have said is more comfortable and repeat the procedure of asking which lens makes the letters more comfortable until they pick the lens opposite to the last lens they choose (i.e. if they previously picked lens 1 - our positive lens, then if they next pick lens 2 - our negative lens, you have reached reversal and vice versa). You are looking to find the point of reversal - (so when adding the same type of lens doesn’t make the letters any more comfortable to read).
Why in the Humphriss Immediate Contrast Comfort Test is the minus lens only allowed to be placed in front of the non-fogged eye for half a second?
Because the Px will accommodate if the minus lens is left in place for too long.
What do you do if in the Humphriss Immediate Contrast COMFORT Test the Px says that lenses one and two are the same?
Keep pushing the positive lens. -so add on the +0.25D lens and do the next round of adding lens 1 and lens 2 and asking which one is more comfortable.
Just double-check though that the negative lens isn’t just making the letters smaller and blacker by asking.
What’s the theory around reaching reversal in the Humphriss Comfort Contrast test?
- A plus lens that relaxes accommodation (no change in clarity), 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 eyes accommodate (letters smaller and blacker) should be less comfortable.
What’s a con of the Humphriss Immediate Contrast Comfort Test?
Not all Pxs understand the concept of comfortable thus you might have to use the Clarity Method to follow up or just the duochrome.
What is the clarity method and how do you carry it out?
So the patient has got to the point where they can’t tell whether the lens is making the letters more comfortable or not. If position 2 was more clearer/comfortable than position 1:
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 obtained (i.e. they choose a lens opposite to the previous lens) OR they say they can’t tell the difference between the two lenses in which case just give them the positive lens (to their Rx) and call it a day.
What’s the difference between the Humphriss Immediate Contrast Test carried out the British way as a pose to it carried out the American way?
Exactly the same except you only show a +0.25DS lens, never a -0.25DS lens
What’s the benefit of using a duochrome to conduct Humphriss Immediate Contrast (HIC) Test?
Pxs do not need to understand the concept of comfortable vision.
What is the end goal for HIC using a duochrome?
• Identical end point should be achieved in each eye i.e. if RE = red so LE must also be left on red.
What are problems associated with the HIC Test?
- Eye fogged too little
- Eye fogged too much
- Fogging lens left in trial frame and optometrist incorporates into final result
What are important things to remember with the HIC test?
-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.
How does Turnville’s Infinity Balance (TIB) test work?
- Septum placed on mirror to occlude vertical section in central field of each eye.
- Remainder of field still seen by both eyes, hence binocularity maintained.
- Can use duochrome, letters, concentric circles on white background.
What is the method for TIB?
• Ask patient to look at circles on the right and ask if circles appear darkest against red or green background or about the same.
If the patient says:
–Red=Green i.e. about the same Then stop and repeat for other eye
—If Red better Then add minus to balance (-0.25 steps). If balance not possible leave at “red better” and do the other eye.
–If Green better then add plus to balance (+0.25). If balance not possible leave at “red better” and do the other eye.
What is your end goal for TIB?
• Endpoint must be same for each eye:
i.e. RE red = green, LE red = green
OR RE = red, LE = red
OR
RE = green, LE = green (this is done is special circumstances)
