PC - Binocular Balancing - Week 2

Question 1

List the 5 techniques of binocular balancing in order of increasing sensitivity.

Answer 1

Successive alternate occlusion
Vertical prism occlusion
Blurring/fogging technique
Septum technique
Polaroid technique

Question 2

Consider the humphriss fogging technique. What power is used as a blur and why?

Answer 2

+0.75 or 1.00DS is used. The level of the fog matters, and not the power of the lens.
The blur is used to suspend foveal vision in one eye, but allows paracentral and peripheral vision to act as a binocular lock.

Question 3

What is a disadvantage of septum and polaroid techniques?

Answer 3

Difficult to set up with computer charts

Question 4

What is the purpose of binocular balancing?

Answer 4

To ensure that the accommodation of both eyes are evenly balanced.

Question 5

What is the purpose of binocular addition, and why is it done even though binocular balancing is performed?

Answer 5

Binocular balancing ensures both eyes are evenly accommodating.
This does not mean they are fully relaxed, which is the purpose of binocular addition.

Question 6

Describe the binocular addition technique.

Answer 6

Have the patient focus on the smallest line they can read.
Place +0.25DS in front of both eyes simultaneously, and ask:
Are the letters clearer, the same, or worse?

Question 7

During binocular addition, describe what should be done for each patient response.

Answer 7

Clearer - add another +0.25DS and ask again
The same - add another +0.25DS and ask again
Worse - remove the added +0.25DS and end binocular addition

Question 8

How can you check for reversal during binocular addition, and what response would tell indicate an overplus?

Answer 8

Add +0.25DS until the patient reports worse vision.
Add an additional -0.25DS (after removing previous 0.25) and expect to hear smaller and darker.
If the patient reports clearer, it may indicate an overplus.

Question 9

Describe binocular refraction, why it might be more ideal, and what technique it negates. On what patient population is it most useful for and why?

Answer 9

Refracting under binocular conditions, the eyes are in a more natural situation, and accommodation is more stable.
Negates the need for binocular balancing.
Useful for younger patients and latent hyperopes as its more effective at relaxing accommodation.

Question 10

Describe binocular refraction, and what technique performed beforehand its accuracy relies on.

Answer 10

Retinoscopy findings are critical for binocular refraction accuracy.
After its performed, one eye is fogged by 2-3 lines, and monocular refraction is carried out on the unfogged eye.
Both eyes are then fogged, and the initial fogged eye is unfogged - in other words, both eyes should never be unfogged at the same time until after refraction is complete.

Question 11

What is advisable when prescribing a new pair of glasses/lenses to a patient?

Answer 11

Involve them in the decision directly by putting their prescription into a trial frame, and having them compare with their current lenses.

Question 12

What should 4 things should one be cautious about when making a change to a new prescription?

Answer 12

Changes that are too small and would be insignificant
Changes that are too large and would require a lot of time getting used to
Anisometropic and cyl changes also require care when prescribing

Question 13

What change in prescription is likely too small and not worth it?

Answer 13

0.50D equivalent sphere will be appreciated.

Anything less isnt very significant.

Question 14

Describe binocular balancing in detail.

Answer 14

Occlude one eye, and direct patient to the smallest line they can read.
Fog this eye by 2-3 lines, and confirm.
Unocclude the other eye, and direct them to the smallest line they can read.
Add +0.25DS to the unfogged eye, asking clearer, the same, or worse.
If clearer or the same reported, continue adding +0.25DS.
Verify by asking to repeat the their smallest line.
If worse is reported, then try -0.25DS, and ask clearer or smaller/darker.
If clearer, confirm for a +3 letter improvement, otherwise discard.
If smaller/darker, discard.
Once balanced, repeat on the other eye, however:
Do not have both eyes unfogged at the same time. Always apply fog to the other eye before removing the fog on the balanced eye.

Question 15

If the patient is struggling with clearer/same/worse or clearer/smaller and darker, what does this indicate?

Answer 15

Chances are the lens is making VA worse.

Question 16

Consider if VA is worse than 6/9. What should be done? Consider after this that VA improves, name 2 possibilities for the cause.
Consider VA doesnt improve, what does this indicate (3)?

Answer 16

Do a pinhole check.
Improvement
-Uncorrected refractive error
-Paracentral media opacity (cortical cataracts)

No improvement

• Refraction correct
• Amblyopia
• Pathology

Question 17

Why are some patients uncertain as to what lens give clearest vision? What does this vary with, and what is it larger with?

Answer 17

Due to depth of focus. Varies with pupil size.

Larger with smaller pupils.

Question 18

What is the theoretical basis of binocular balancing?

Answer 18

Ocular accommodation is a consensual reflex.

Question 19

Name 4 cases when binocular balancing isnt practical.

Answer 19

Strabismus
Amblyopia
Pathology
Presbyopia

Question 20

Describe the successive occlusion technique.

Answer 20

Eyes are alternatingly occluded, and each view is compared.
Lenses are used to equalise vision.
+0.25DS is added to the clearer eye until equal vision is reached.

Question 21

Describe the vertical prism dissociation technique.

Answer 21

Equal power vertical prisms of opposite bases are used to vertically dissociate their view.
Directed to the 6/9 line.
Both eyes are fogged by 0.50DS beforehand.
Patient is asked whether the top or bottom line is more clear or the same.
+0.25DS is added to the clearer view.

Question 22

By how many lines should a fogged eye be blurred during humphriss fogging technique?

Answer 22

2-3 lines, the power doesnt matter, but confirm a 2-3 line drop.

Question 23

For how long should positive spherical lenses be left in place?

Answer 23

Up to 5 seconds to allow accommodation to relax. Always ask them to blink a few times.

Question 24

For how long should negative spherical lenses be left in place?

Answer 24

No need, patient can be asked for visual changes straight away.

Question 25

What is an advantage of binocular balancing, and how does this relate to binocular addition?

Answer 25

Not only equalises accommodation, but usually also fully relaxes it.
Little need to do binocular addition afterwards.

Question 26

Describe the humphriss immediate contrast technique.

Answer 26

Leave monocular findings on place.
Fog one eye +1.00DS
Add +0.25DS to the other eye, and ask patient to compare view with a -0.25DS addition
Positive lens always shown first.
-0.25DS typically preferred.
Repeat the procedure, the +0.25DS will not cause blur due to the -0.25DS addition.
The -0.25DS will cause more accommodation and not be as comfortable, and so the -0.25DS additions can be removed, back to the balanced correction.
Repeat with the other eye.