2. The final step in the subjective refraction is called “Binocular Balancing” –
a process which is known as sometimes “Equalizing the accomodative
effort” or “spherical equalization”
This allows both eyes have the retinal image simultaneously in
focus.
An imbalanced correction often leads to asthenopia because of
unstable accomodation.
Binocular balancing tests is not to balance the VA but to balance
the state of accomodation of the two eyes.
Aims
3. • The test not only test best sphere but also be used for
checking astigmatic compound under binocular viewing
condition.
alternative to binocular balancing tests
1. cycloplegic refraction
2. binocular refraction
4. Criteria
• These techniques are not the methods of choice when
amblyopia in one eye is present.
• Deep suppression should not be present.
• There should be BCVA and essentially almost same VA in both
eye.
5. Commonly used methods
• Fogging method
• Alternate occlusion method
• Duochrome test with fogging
• Prism dissociaton method
• Turville’s infinity balance technique
• Polaroid filters
6. Humphriss fogging method
• In this method one eye is fogged by +0.75Ds or +1.00Ds .
• As a result, foveal or central vision (2-3degree) is suspended but
the paracentral and peripheral vision are maintained.
• It is called “ psychologic septum”
7. Alternate occlusion test
1. Start with best corrected monocular visual acuity with both eyes
open.
2. Instruct the patient about the target line according to his VA
threshold.
3. Do alternate occlusion while the patient observing the snellen’s
letter
8. 4. Ask the patient if the letters are clearer than other eye.
5. If the images are equally clear, the balance is correct and
no further adjustment of lens power is necessary.
6. If the patient notices a difference in clarity ,let the patient
identify which eye possesses the clearer image.
7. Once the eye with the clearer image has been identified,
the clinician has 2 options.
• add plus sphere in +0.25Ds steps before the better eye to achieve
equally poor vision in both eye.
• add minus sphere in -0.25Ds before with the poorer VA in order to
achieve equally sharp image in both eye.
9. 8. To confirm the balance, add +0.25Ds sphere before each eye
and repeat ACT . If the eyes are perfectly balanced, both eye
will lose equal amount of vision.
cover paddle should be removed quickly.
VA in both eye should be approximately same.
10. Duochrome test with fogging
1. Start with best corrected monocular VA in trial frame.
2. Each eye observes red-green bar in vision box while the other eye
is fogged by +1.00Ds.
3. Let the patient assume whether red or green bar seem to be
more clear.
4. If red or green preference is equal then no adjustment will be
needed.
5. If not, the sphere before the observing eye is then adjusted to
give equal red preference or green preference as felt appropriate
by clinician.
11. Prism dissociation method
• It is considered the most sensitive method of binocular balance and
is practiced more commonly .
• It requires some degree of binocular vision.
1. Begin with the result of the monocular subjective refraction.
2. Adjust an isolated row of letters of 20/30.( 2 lines better than weaker eye)
3. Both eyes are fogged with +1.00Ds or +0.75Ds.
4. A vertical prism of 4pd or 5 pd is placed before one eye.
12. 5. The patient will be able to see the line of latter with both eyes
simultaneously.
6. Add +0.25Ds is placed before one eye followed by the another one.
7. If the eyes were balanced, the patient will report that ,the image
having additional +0.25Ds is more blur.
8. Having balanced the prism is removed and unfogged the patient
binocularly until maximum acuity is achieved with maximum plus or
lowest minus sphere.
• Risley prism
• Goodwin method
• Bichrome balance.
14. 1. Start with BCVA with a septum in the middle of the face
which will allow monocular viewing for each eye
simultaneously.
3. Originally a special set of test cards was used with TIB but a
line of suitable size of a snellen’s chart can be selected. TIB
can be done with or without fogging.
4. If all letters are seen equally clear by both eyes that implies a
binocular balancing.
5. The bichrome test and TIB may be combined.
6. It deals with great compatibility with stability of
accomodation.
15.
16. Polaroid filters
The two halves of the bichromatic pattern are polarized in mutually
perpendicular directions so that when viewed through a similarly
polarized visor ,one half of is visible to the right eye and the other half is
visible to the left eye only.
17.
18. To give the viewing conditions as near as
normal as possible ,the upright lines and
the surrounding are seen binocularly.
The patients attention is directed towards
upper half of the cluster of dots.
The spherical correction for the
appropriate eye is adjusted to give
equality of contrast on the red
and green backgrounds.
The process is then repeated for the
other eye in the same process showing
the lower cluster of the of dots.
19. Nice to Know
•The dots should be about 0.6 or 0.7 mm in diameter.
•Test should have adequate luminance to compensate for the
light loss due to polarizing filters and analyzing visors.
20. Binocular end point
The target letter should be 20/20 or BCVA.
Add +0.25Ds in front of both eyes and ask for any difference in clarity.
The same question should be asked for the 2nd and 3rd time after adding
+0.25Ds each time.
Expected response
slightly blurred (1st time)
badly blurred (2nd time)
blurred out (3rd time)
Unexpected response - still readable
Result – patient accomodation was not completely relaxed during subjective
response.
21. References
Rabbetts RB (2007). Bennett and Rabbetts’ Clinical Visual Optics
Primary Care of Optometry by Theodore Grosvenor
Clinical Procedure of Primary Eye Care by Davit E Elliot
Lecture notes of Ohio state University, School of Optometry
Internet
