Binocular Balance.docx

Binocular Balance

Binocular balancing is a technique to equalising both eyes and also known as Equalising. Binocular Balanceing refers to the fogging technique that detects and eliminates the condition of one eye being over – minus or under – plus as compared to the other eye. In binocular balancing we check one eye at a time because one eye may be accommodating more than the other eye during the process. If glasses are made from unbalanced prescription, the patient may experience a sensation that the eyes are not focusing together. Unfortunately every patient does not benefit from binocular balancing. The best candidates are those who see 20 / 20 or 6/ 6 or better with each eye. If the vision is less than 20/30 (6/9), in one or both eyes, balancing probably will not effective. Always one should try to balance the both eyes of the patients as 20 / 20 or 6/6 vision. If one eye is over- accommodating, which will be exposed by balancing.

The procedure : 1. The distance correction must be completed where the best corrected visual acuity (BCVA) in both eyes are 6/6 or 20/20. 2. Add 0. 75 D or 1.00 D plus sphere power to each eye while ask the patient that his or her vision will be little blurry . This is the fogging part of this procedure. 3. Tell the patient to keep both eyes open and then occlude or cover one eye and then the other. Instruct the patient to tell, which eye is clear as the occluder moves from one eye to the other. 4. Add 0.25 D plus sphere power to the eye that sees clear and then repeat step 3. 5. Continue this until each eye sees equally blurry or until the clearer vision switches to the other eye. This is the end point.

Many people have a dominant eye, the eye that they see best with it, is the eye people look through a camera viewfinder with. In most of cases, the right eye is dominant. So it is better to leave the dominant eye with the better vision. During the monocular refraction, a different state of relaxation of accommodation may occur because one eye was under test while the other was not. Thus, binocular balancing is performed to balance accommodation between both eyes.

Alternate Occlusion : Alternate Occlusion is usually used only when Visual Acuity in both eyes are Equal. The procedure : 1. Fog both eyes with + 0.75D Sph 2. Direct patient to view 3 lines above best VA 3. Alternately occlude each eye for about 0.5 secs each while, asking patent “Which eye sees clearer/sharper?” 4. Add +0.25DS to the better eye. 5. Repeat step 3 and 4 until both eye’s vision is equalised. 6. Slowly reduce fog until best VA is reached.

Prism Dissociation : Prism Dissociation is a another technique for Binocular Balance involves dissociated two images using the vertical prism of 6 PD. So, 3 PD BD in front of one eye and 3 PD BU in front of the other eye. Typically the base down prism is placed in front of the Right Eye so that the image for the Right Eye appears above the image for the Left Eye. Using a 20/40 (6/12) line and + 0.50 to + 0.75 diopters of fog, the patient is asked to compare the two lines of letter seen. The clinician adds plus lenses (+ 0.25 D at a time) to the better eye or minus lenses (- 0.25 D at a time) to the worse eye until the patient reports that both lines appear equally blurred.

The significant difference between this technique and alternate occlusion is that the patient is comparing simultaneous images with this technique which is often easier for the patient. The prism dissociated blur balance is the most widely used balancing technique in clinical practice.

Humphriss Immediate Contrast : Humphriss Immediate Contrast procedure may be used when VA are equal or Unequal between both eyes. The procedure : 1. Fog OS with +0.75D Sph. 2. Direct the patient to view OD’s best VA line. 3. And, perform BVS in OD. 4. Then add +0.25 D Sph in OD to achieve VA same or better with this add +0.25DS. If Visual Acuity worse with this add +0.25D Sph, remove +0.25, until you achieve max. plus min. minus. 5. Repeat these Steps 1-3 to test OS.

Binocular Best Vision Sphere : After binocular balancing, spherical lenses are added in front of both eyes at the same time to determine the Binocular Best Vision Sphere. The most plus/ least minus lens that would not reduce VA would be the end-point. Best Corrected Visual Acuity (BCVA) with strongest positive spherical lens.

The procedure : 1. Ask the patient to view best corrected visual acuity in both eyes. 2. Then add +0.25D Sph. in both eyes at the same time, if the visual acuity is same as previous, add +0.25D Sph. in both eyes (Repeat with additional +0.25DS), but if the visual acuity is worse than previous, remove these +0.25D Sph. This is the end point of this procedure. ----------------------