A lot of young patients complain that they have headaches with the glasses I prescribe for them. A practitioner I work with asked me whether I carry out binocular balancing and binocular addition testing. What are these?
When people don’t get on with my glasses. Three things happen. I’m disappointed I didn’t get it right first time, my self-confidence takes a little knock and I learn something new.
Young people have lots of accommodative amplitude and it is important that the accommodative response in each eye is the same. An asymmetrical accommodative response can cause eye aches and headaches leading to non-tolerance of glasses and a patient back in practice complaining.
Good ways to ensure a symmetrical accommodative response is to conduct binocular balance and binocular addition testing. These are only necessary for people who are capable of accommodative response. I wouldn’t undertake these tests on a person older than 40 years but would do on people younger than that especially teenagers and those in their 20s. I also wouldn’t under these tests on people with only one seeing eye.
There are several techniques for binocular balancing but the monocular fogging technique is my preferred technique.
Fogging one eye suppresses central vision but maintains peripheral fusion so that both eyes work together (accommodation balanced/relaxed) and the ‘sphere for best VA’ can be found in the other eye.
Here is the procedure for binocular balancing:
- Carry out static retinoscopy & monocular subjective refraction on both eyes.
- Explain: ‘I now want to see how well your eyes work together but this test requires the vision in one eye to be blurred’.
- Fog LE with +0.75DS.
- Occlude the RE and explain: ‘Although your vision is now blurred, please read the smallest line you can see”. Visual acuity should be about 6/12 and add extra plus if it is better than this.
- Remove occluder from RE and explain: ‘Please look at the smallest line you can see’.
- Add +0.25DS and ask: Are the letters clearer, more blurred or the same?’.
- If clearer or the same, keep adding +0.25DS lenses until the letter first blur. This is the sphere for best visual acuity.
- If blurred, don’t add +0.25DS but proceed to next step.
- Add -0.25DS and ask: ‘Are the letters clearer now or just smaller and blacker?’.
- If clearer, keep adding -0.25DS lenses until no further improvement in visual acuity occurs = sphere for best VA.
- If smaller and blacker, don’t add -0.25DS = sphere for best visual acuity.
- Repeat the procedure with: RE fogged, determine ‘sphere for best VA’ in LE.
Accommodation relaxes in binocular single vision and therefore binocular addition may not be necessary as balancing with monocular fogging may have already relaxed accommodation maximally. However, this technique can be used as a final check to ensure that the accommodation is completely relaxed.
Here is the procedure for binocular addition:
- Remove fogging lens used during binocular balancing so the patient can see clearly through both eyes.
- Explain: ‘Please look at the smallest line of letters you can see’.
- Add +0.25DS to both eyes and ask: ‘Are the letters clearer, more blurred or the same?’
- If clearer or the same, keep adding +0.25DS lenses until the letter first blur; the endpoint has been reached.
- If more blurred, do not add +0.25DS.
Note, some patients prefer under-plus or over-minus distance correction for everyday tasks especially driving and looking at the board in class or a lecturer theatre. Remember that a 6m chart is at a dioptric distance of -0.16DS.
Following these procedures in young patients will help cut down the number of non-tolerances and the number of patients coming into the practice to complain.