Binocular Balancing Techniques

What is the main goal of binocular balance ?

• ensure both eyes receive and equal accommodative stimulus

• helps align accommodative response between 2 eyes when they’re used together

• promotes relaxation of accommodation

When is binocular balance not necessary?

• patients who lack binocular vision or accommodation

• e.g those over approx 60yrs old or those with intraocular lens implants

What is prism dissociation used for?

• directly compare vision between 2 eyes

• focuses on balancing accommodation

What is the aim of the Humphriss technique?

• based on binocular refraction

• aim to determine spherical correction under conditions that closely resemble patient’s typical visual experience

What is the Humphriss Fogging technique procedure?

• fog the LEFT EYE → enough plus power to reduce VA by 3 or 4 lines (+0.75DS to +1.00DS)

• carry out BVS in RE → push the plus

• if px requires +0.50DS or more (latent hyperopia) this can help relax accommodation in both eyes.

• To confirm fogging lens still effective add more plus power to LE + ensure acuity blurred by 3 to 4 lines

• switch fogging → remove fogging lens from left eye , then fog the right eye by same amount 3 or 4 lines and repeat BVS for left eye

Describe the procedure for Humphriss Immediate Contrast technique

• Fog LE → 3 or 4 lines , for young patients with normal vision results in VA of 6/9 to 6/12

• Ask px to focus on smallest line they can read

• briefly place +0.25DS lens in front of RE for about 1 second or longer , then switch to a -0.25DS lens for HALF the time →0.5 seconds

• Ask patient are letters clearer with lens 1 or lens 2

Results for Humphriss Immediate Contrast Technique

• if patient immediately says -0.25DS lens definitely clearer → repeat comparison and ask if definitely clearer or just smaller + darker

• only add -0.25DS if px confirms definitely clearer

• if px says +0.25DS lens clearer or sees no difference, add +0.25DS to prescription

• since adding +0.25DS to RE relaxes accommodation in both eyes, check fogging lens on LE by adding +0.25DS to ensure it still effectively blurs vision

• continue comparing +0.25DS and -0.25DS lenses until px clearly rejects +0.25DS lens

• repeat entire procedure for LE , this time fogging Right eye

Binocular balancing using Polaroid filters

• Polaroid balance tests include several VA lines with one (or more) line seen by the right ,left and both eyes

• line seen by both eyes provides fusional lock
  

• middle line both eyes can see

• top one seen by right eye

• bottom line seen by left eye

• FOG BOTH EYES → which line is clearer

• if bottom one clearer not fogged enough so add +0.25DS

Technique for polarised filters

• place polarised filters before both eyes

• Add +0.50DS to both eyes

• Ask px if letters clearer on line seen by right eye or left eye of if both the same

• if one line clearer add +0.25DS to that eye until two monocular seen lines equally blurred

• remove polarised filters

• remove fog in binocular +0.25DS steps until you obtain max VA

• if px can read bottom line of your chart you can allow extra minus or less plus that makes bottom line of letters clearer

• ensure bottom line definitely clearer and not just smaller and blacker

what do we do if balance can not be achieved?

• use lenses that provide best vision to dominant eye or closest match

Procedure for prism- dissociated binocular balance

• make sure neither eye occluded and both eyes can see the chart

• fog each eye by +0.75DS relative to endpoint of monocular refraction

• measure px binocular VA and continue adding +0.25 sphere in front of both eyes until binocular VA is 6/7.5 or worse

• isolate a line of letters one line above VA found

• Ask px to close their eyes

• Place 3-4 base UP over RIGHT and 3-4 base down over left eye using prism

• Ask px to open their eyes, inform that they should see 2 lines of letters both of which should be blurry

• have px look back and forth between 2 lines of letters and let them tell you which line (upper or lower) clearer

• Add +0.25 to clearer line → make it blurrier , keep repeating until px reports equal blurriness of 2 lines

• remove prism

• remove fogging lens