binocular refraction techniques

1. Binocular refraction techniques,binocular
balancing &binocular best sphere
Sabina Poudel
B.Optometry
Institute of Medicine

2. Presentation layout
• Introduction
• Clinical indications for binocular refraction
• Techniques of achieving binocularity during
refraction
• Binocular balancing
• Binocular best sphere
• Binocular subjective refraction at near

3. Subjective Refraction
Technique of comparing one lens against another,
using changes in vision as the criterion, to arrive
at dioptric lens combination resulting in
maximum visual acuity (Polasky 1991)
Monocular Subjective Refraction
Binocular Subjective Refraction

4. Binocular Refraction
Clinical procedure in which the subjective refraction
is performed monocularly under binocular viewing
conditions
Component procedures described monocularly are
performed in the same or similar manners
Both eyes are open
Unoccluded
Views a common target
EXCEPT THAT

5. Advantages over monocular refraction
 Accommodation , convergence , light adaptation
more constant
 Refractive status evaluated in more nearly normal
environment i.e. binocular viewing condition
 Detection of suppression
 Measurement of stereopsis
 Measurement of fixation disparity

6. Indications for Binocular Refraction
1)Refractive Considerations
Hyperopic anisometropia
Antimetropia
Latent hyperopia
Pseudomyopia

7. 2) Visual Acuity Considerations
Anisooxyopia ( unequal acuities
between two eyes)
Unilateral amblyopia
Unilateral reduced acuity as a
result of ocular disease

8. 3) Ocular Motility Considerations
Significant horizontal, vertical or cyclo
associated phorias
Cyclophoria
Latent nystagmus

9.  Under binocular conditions, the amblyopic eyes
accept more of the indicated correction and
obtains better acuity
 VA in RE 6/6 VA in LE 5/60
On retinoscopy: RE +1.00 DS LE +4.00 DS
VA in LE with +4.00 DS = 6/60
on monocular subjective refraction
LE: 6/24 with +2.50 DS
on binocular condition
LE: 6/18 with +3.50 DS

10. • In monocular condition: accommodation of a
blurred eye unstable
• In binocular condition: vision of non
amblyopic eye stabilize the accommodation of
amblyopic eye

11. • In binocular condition : Fixation of the
amblyopic eye is steadied by the simultaneous
fixation of the non amblyopic eye
Degree of eccentricity diminish under binocular
condition compared with when amblyopic eye
fixates on its own

12. Principle of Binocular Refraction
By some means each eye views its respective
target, yet both eyes remain open. The right eye
views only right portion target, left eye only left
portion
 Outline of the chart, its borders and sometimes
a central “fusion lock” provide visual clues to
both eyes that enable the binocular fusion
necessary for association of target

13. This monocular viewing under binocular conditions
can be achieved by:
Septum
Polarization
Fogging

14. Septum
• Concept originally described by Turville in 1927
• Each eye views its respective target
• Characters on the other side of chart are masked
from its view
• Both eyes see the border of the chart and the
septum, thus single percept is associated

15. Turville Infinity Balance
Apparatus consisted of:
reversed acuity chart containing two vertical
columns of letters or test characters
Mirror divided into equal sections by an opaque
vertical septum having a width of approximately
3 cm
Acuity chart located superiorly on the wall
behind the patient

16. • Divided mirror placed out in front of patient so
that reflection of bordered wall chart can be seen
by patient
• With eyes in proper position each eye views
characters on its side of chart , characters on
other side of chart are masked from its view
• Both eyes see the border of the chart and the
septum

17. • Morgan adapted the Turville principle to
projection
• Special slides allowed a chart to be presented at a
desired distance in front of the patient
• A septum was located along a track between the
patient’s eyes and the distance chart

18. septum

19. Clinical procedure for septum technique
• patient seated behind the phoropter
• 20/40 or 20/50 line characters on screen
• septum in center of patient’s viewing mirror
• instructed to hold his or her head in an
upright position and not to move head from
side to side

20. • After alignment , patient attention directed to
right side of chart
• With retinoscopic findings in place appropriate
sized characters projected on screen .
• Best sphere determination made until
approximately 20/25 or 20/20 letters are clear.

21. • Cross cylinder introduced parallel to axis of
cylinder present
• This way presence , amount and orientation of
astigmatism may be measured .

22. • Next step is to blur or fog the characters to
approx. 20/40 level .
achieved by adding 0.75 or 1.00 sphere more plus
or less minus to the sphere power .
From this point power is decreased in 0.25 steps
until best or maximum visual acuity is attained .

23. • End point may be monitored by red green balance
to avoid overminusing
• Same procedure repeated for left eye
• Then each eye is blurred or fogged by +0.75 or
+1.00 D
• This amount reduced binocularly until best visual
acuity is attained

24. Polarization
• Analyzer and polarized target have same axis of
polarization , allowing right eye to view right half
of the target , but blocking left half of target from
view
• Variation of this technique is to polarize only the
letters , leaving background normal
Polarized Targets and Polarizing
Filters
Vectographic Slides for Projection

25. Polarized Targets and Polarizing Filters
 Simplified binocular subjective refraction
 Proper positioning of septum not necessary
 Distance acuity chart divided into two halves,
each covered by polarizing films

26.  An analyzer before right eye polarized at angle
parallel to right half of chart permitted right eye
to view only the right half of chart
 An analyzer before left eye parallel to the
polarization of left half of chart permitted left eye
to view only the left half of chart
 Both eyes could see the unpolarized border of
entire chart and area surrounding the chart

27. Cowen introduced
polarization of only the
letters on an unpolarized
illuminated background
Amount of light emitted by
polarized letters is reduced
to 50% by polarization

28. Analyzer at right angle
to polarization angle of
letters
For right eye
Light from the letter in
right half totally excluded
But 50% of the light from the
white background is transmitted
Black symbols in white background
50 % light from the letters
in left half transmitted
50 % light from the
background also transmitted
White blank field

29. Analyzer at right angle
to polarization angle of
letters
For left eye
Light from the letter in
left half totally excluded
But 50% of the light from the
white background is transmitted
Black symbols in white background
50 % light from the letters
in right half transmitted
50 % light from the
background also transmitted
White blank field

30. Binocular percept is that of a
uniform white background
with black letters on it
Both eyes are allowed to
view the unpolarized borders
and boxes of the chart in
which polarized letters are
contained : serve as fusion
lock

31. Vectographic Slides for Projection
 Its perception is identical to that for polarized
symbols
 The slide presents
1. VA chart visible only to RE
2. VA chart visible only to LE
3. Radial chart to determine astigmatism

32. 4. Equalization chart
5. Suppression reading chart
6. Binocular acuity chart
7. Fixation disparity chart
8. Stereopsis chart

33. Vectographic Chart
Stereo Test
Associated Phoria Test
(fixation disparity)
Astigmatic Test
VA Test: OD
VA Test: OS

34. Polarized Fan Dial
o split vertically so that left half visible to LE &
right half visible to RE
o a common vertical bar and two dots near center
of target unpolarized- serve as fusion lock for BE
oFusion lock hold BE in normal binocular position,
whether cyclophoria is present or not
o thus permitted eastimation of astigmatism for
each eye in normal viewing condition

35. Fogging
• Slightly blur the central vision in the eye not
under test
• This slight blurring suspends foveal vision , such
that each eye is refracted under conditions of
binocular vision with peripheral fusion

36. Immediate Contrast Technique
Humphriss used +0.75 DS over the non tested eye
for the performance of astigmatic tests and
Bichrome tests on the tested eye
This unilateral fogging also called a psychological
septum
Centrally suppressed the foveal image
of the blurred eye but permitted the
peripheral images to be fused

37. Outline & summary of binocular
subjective refraction
1) Starting point
- Identical to that of a monocular refraction, except
that the eyes must be set up for binocular fusion
- Lenses determined by objective methods
- Habitual spectacle correction
- Previous subjective refraction

38. 2) Control of accommodation
- As untested eye is unoccluded, accommodation need
to be controlled in that eye
- Both eyes are initially fogged to at least +0.75 DS
- Degree of fog maintained in untested eye
- Unfogging done in tested eye till the spherical
equivalent is placed at the retina

39. 3) Astigmatic correction
- Similar techniques as used for monocular testing
except that both eyes remain unoccluded
4) Monocular spherical end points
- Separately determined for one eye and then for
the other under binocular viewing condition
- Similar techniques as used for monocular
refraction

40. Spherical equalization or binocular
balancing
Purpose
To balance the state of accommodation of two eyes
NOT the visual acuities of two eyes
Allows both eyes have the retinal images
simultaneously in focus

41. Difference in accommodative response between
two eyes
Inequality in clarity or size of
retinal images
Reduce stereoacuity
Reduce fusional amplitudes
Cause discomfort
Create visual inefficiency

42. Methods for binocular balancing
 Alternate Occlusion
 Prism Dissociated Blur Balance
 Prism Dissociated Red-Green
(Bichrome) Balance

43. Alternate Occlusion
Target: smallest acuity letters patient can read
through the spherocylindrical correction
Alternately occlude the patient’s eye with cover
paddle
If the images equally clear- balance is correct

44. If not, two options
-add plus sphere in +0.25 DS steps before the eye
with better image till both the images are equally
blurred
-add minus sphere in 0.25 DS steps before the eye
with poorer image till both images are equally clear
Finally to confirm, add +0.25 DS before each eye.
If the balance is correct BE will be equally blurred

45. Disadvantages
- The subject compares a visible object with a
previous one remembered but no longer visible
- Endpoint is equal acuity, and no allowance is
made for patients having amblyopia or unequal
maximum visual acuities in two eyes
- Each eye may assume its monocular
accommodative status when alternately
unoccluded

46. Prism dissociated blur balance
 RE – 3 ∆ Base Down
 LE – 3 ∆ Base Up
Two charts will be seen separated vertically

47. Procedure
• Fog vision in both eyes to 20/40 (6/12), on to
spherocylinder lenses found monocularly;
- assuming eyes capable of 6/6 acuity
• If one eye has reduced VA;
-A row of letters at least two rows larger than
that of the power eye of best acuity

48. • Dissociate the chart by equal amounts of
vertical prism
 3 or 4 Δ BU in one eye
 3 or 4 Δ BD in other eye
• Equal magnitude: ensures that images are
affected by equal prismatic distortions
• Upon removal of occlusion patient should be
able to see two identical targets.

49. • If patient cannot see two targets simultaneously,
alternately cover two eyes while directing
patient to regard target with uncovered eye
• Upon removal of occlusion, patient should be
able to see two targets simultaneously

50. • Ask pt. to compare the legibility of two acuity lines or
charts
• If neither is readable;
-reduce plus or increase minus until letters are visible
but slightly fogged
• If lines appear equally distinct in both eyes, add +0.25
in each eye
-Targets appear equally distinct, though slightly blurred;
equalization exists

51. • If acuity line in one eye is clearer than in
other;
-Add plus power in +0.25D steps in clearer eye
until acuity is equal in both eyes
-Continue change in power until a reversal
• End point –balance at equality of acuity
• Alternative - leave dominant eye with better
acuity
• When end point of balance is reached; remove
prism and find binocular spherical end point

52. Prism Dissociated Red-Green (Bichrome)
Balance
• Bichrome test or
Duochrome test
- Based on eye’s natural
chromatic aberration
- Uses distance VA chart with
black letters, splitted equally
into two halves
- Letters on one half on red
background
- Letters on other half on green
background

54. - Similar to dissociated blur balance except fogging
lenses are not added
- Instead of seeing two blurred charts, patient will see
two relatively clear charts, with each chart half red
and half green
- Method of choice when maximum acuities for two
eyes differ by several letters

55. • Patient views the full size split R-G chart with 6/6
letters on the bottom
• Occlude both eyes and dissociate the chart using 3 ∆
BD in RE and 3 ∆ BU in LE
• The patient must be capable of perceiving diplopia
Procedure

56. • Attention first on upper chart (seen by right eye )
• Asked to report which those on red or green side ;
appear sharper , blacker or more distinct
• Sufficient plus power is placed in RE till letters
on red side are clearer

57. • Reduce plus power in 0.25 DS steps until
both sides are equally clear (equality)
OR
green side first is clear ( first green)
• Repeat the process for lower chart (left eye)

59. • The balance is complete when the patient reports
the same red-green end point for each eye (i.e if
the criterion used for lower chart is appearance of
first green, same criterion should be used for
upper chart)
• It is not necessary for the upper and lower charts
to be equally clear as long as both have the same
end point

60. Special considerations in balancing
techniques
1) Dissociative Techniques
- Prism value need to be increased for patients
with large phorias
- Otherwise prism may only compensate and
diplopia will not occur

61. 2) Reduced Best Corrected Acuities
- If BCA is reduced but equal, larger acuity lines
should be used
- If BCA is unequal, Dissociated Red Green
balance is preferred
3) Presbyopes
- For presbyopes with some amount of
accommodation, balancing is needed
- For full presbyopes, balancing not needed

62. Binocular Best Sphere
• The eyes are simultaneously fogged and then
unfogged until maximum binocular acuity is
attained
• The spherical endpoints are the maximum plus or
minimum minus power providing maximum
binocular visual acuity
• These endpoints are usually about +0.50 DS more
plus or less minus than those found monocularly

63. Binocular subjective refraction at near
• Near refraction refers to the measurement of the
refractive state when the patient is fixating at
near point
• Although near refraction may be performed
monocularly, small amount of cyclodeviation will
generally occur with near fixation and may result
in different cylinder axis. So binocular near
refraction is preferred
• Useful in conditions that significantly alter the
refractive error when patient fixates at near

64. Important in:
1) Presbyopes
2) Persons with binocular vision problems
3) Accommodative abnormalities
4) Greater spherical or cylindrical power of spectacle
Rx which cause greater change in the stimulus to
accommmodation during near fixation ( > +/- 4 DS ,
> +/- 1.50 DC)
5) Persons with special near task requirements

65. Techniques of achieving binocularity during
refraction at near
1.Turville (septum ) and related methods :
• Septum mounted 10 cm in front of a dual or split
chart at near served to combine respective images
separately to each eye
• Outer border of the chart and peripheral field served
as fusion locks .

66. 2. Vectographic near-point cards
• Consisted of duplications of identical targets that
composed projected vectographic distance chart.
• Distance chart miniaturized to a separate near card
.
• Need for different near point add powers for each
eye could be determined

67. Binocular versus monocular
refraction at near
Presbyopic near addition:
• To designate identical add powers for both eyes .
• Eyes don’t act identically when accommodated for
near .
• Less accommodation demanded - fully corrected
myopic for distance
• More accommodation-fully corrected hyperopic

68. • Two eyes having different optical corrections –
have different accommodative demands at near
• The imbalance requires unequal accommodative
efforts by two eyes
• When near add determined by binocular
refraction at distance and at near, imbalance is
minimized

69. Astigmatism
• Difference between power of astigmatic correction at
far compared to near due to – change in
accommodative demand due to power effectivity
• Accommodative demand for more minus meridian –
less than more plus meridian

70. • When binocular fixation altered from distance
to near, lines of sight converge and most often
depressed- eyes undergo excyclovergence
• Axis of cylinder is not same for binocular
distance and near refractions
• A monocular assessment of cylinder axis ignore
this phenomenon because cyclofusional eye
movements are then not possible at distance or
at near

71. Summary
Binocular refraction is superior to monocular –
better control of accommodation, separate binocular
balancing not required
Binocular balancing important as unbalanced
accommodation between two eyes result in
asthenopia , discomfort
If patient is not binocular (suppression, strabismus),
monocular best sphere is the end point of subjective
refraction

72. SubjectiveRefraction RE
Monocular
sphere
Astigmatism
(axis/power)
Monocular
best sphere
LE
Monocular
sphere
Astigmatism
(axis/power)
Monocular
best sphere
BE
Binocular best sphere
Binocular balancing

73. References
• Borish’s Clinical Refraction, 2nd edition
• Clinical Procedures in Optometry
• Primary Care Optometry, 2nd edition
• ICEE Module 3 – The Refractive Examination
• Internet