Balancing refers to the fogging technique that detects and eliminates the condition of one eye being over-minused or under-plused as compared to the other eye.

Why use balancing?  When performing refractometry we check one eye at a time. Because of this one eye may be accommodating more than the other eye during the process. If glasses are made from a resultant unbalanced prescription, the patient may experience a sensation that the eyes are not focusing together, that the glasses "just don’t seem right". The closer the prescription is to being perfectly balanced, the more the vision from each eye reinforces binocular vision.

Should I balance everyone?  Unfortunately every patient does not benefit from prescription balancing. The best candidates are those who see 20/20 or better with each eye. The greater the difference in best corrected acuity between eyes, and the worse the overall vision is, the less effective balancing becomes. If the vision is less than 20/30, in one or both eyes, balancing probably will not be effective. Of course there is an exception to every rule. Always try to balance patients who you think should be seeing 20/20 OU, but are seeing worse out of one eye when you finish your refraction. They may have been over-accommodating in that one eye, which will be revealed by balancing.

How do you balance?

1) Have the final distance refraction in place in the phoropter with the patient viewing the 20/50 line with both eyes.

2) Add .75 (some like to use 1.00 D) plus sphere power to each eye while telling the patient her vision will be a little fuzzy. This is the "fogging" part.

3) Tell the patient that she is to keep both eyes open and that you will cover one eye and then the other. Instruct the patient to tell you out of which eye she sees clearer as you move the occluder from one eye to the other. You will need to inform the patient which eye she is seeing with as you proceed.

4) Add .25 plus sphere power to the eye that sees clearer,  and then repeat step 3.

5) Continue until each eye sees equally blurry or until the clearer vision switches to the other eye. This is the end point.

6) Important!  Many people have a dominant eye, that is, the eye that they see best with. It is usually the right eye. It is the eye people look through a camera viewfinder with. You need to leave the dominant eye with the better vision.

Example: You have asked the patient which she thinks is her better eye, or which eye she looks through a camera with. She says the right eye. You are balancing the Rx and adding plus to the right eye as the patient indicates it has the better vision. You reach a point where the better vision switches to the left eye.

You must now subtract .25 sphere power from the right eye to restore it as the eye with the better vision. Be sure to recheck the vision by covering one eye and then the other to confirm the right eye has the better vision.

7) Now that you have the eyes in proper balance you must subtract the original .75 (or 1.00) diopter plus sphere power from each eye. Do this while the patient is viewing a full eye chart with the 20/20 line at the bottom. The patient will be impressed as her vision sharpens to exquisite detail, and she will feel like she has had the best refraction she has ever had.

8) Sometimes one last step is in order. With the patient looking at the chart with both eyes, simultaneously add .50 D plus sphere to each eye and ask which is better. Do the same in the minus direction. Most of the time the patient will like the starting position. But sometimes the patient will accept more plus power. Remember the refractionist’s golden rule: Most plus or least minus for the best vision. If you think the patient is accepting too much plus, you can check her binocularly with the red/green test.

Confused?  Let's work through an example.

Step 1: Our patient has been refracted OU to a +2.00 sphere OD and a +2.75 OS.  Vision is 20/20 OU.  The patient is viewing the 20/50 line with both eyes.

Step 2: We now add .75 sphere power to each eye.  Tell the patient; "Your vision will be blurry.  Keep both eyes open.  I am going to cover one eye and then the other.  You tell me out of which eye you see clearer."

Step 3: Hold the occluder over the left eye port and tell the patient; "You're looking with your right eye now."

Step 4: Hold the occluder over the right eye port and tell the patient; "You are looking with your left eye now. Tell me which eye you see better with."  Repeat steps 3 and 4 if necessary.

Step 5:  Suppose the patient tells you that she sees better with her right eye.  You would then change the sphere power OD to +3.00 from +2.75 and repeat steps 3 and 4.