binocular refraction techniques, binocular balancing & binocular

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

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Page 1: Binocular refraction techniques, binocular balancing & binocular

Binocular refraction techniques, binocular

balancing & binocular best sphere

Sabina PoudelB.OptometryInstitute of Medicine

Page 2: Binocular refraction techniques, binocular balancing & binocular

Presentation layout

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

Page 3: Binocular refraction techniques, binocular balancing & binocular

Subjective RefractionTechnique 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

Page 4: Binocular refraction techniques, binocular balancing & binocular

Binocular RefractionClinical 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

Page 5: Binocular refraction techniques, binocular balancing & binocular

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

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Indications for Binocular Refraction1)Refractive Considerations

Hyperopic anisometropia

Antimetropia

Latent hyperopia

Pseudomyopia

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2) Visual Acuity Considerations

Anisooxyopia ( unequal acuities between two eyes)

Unilateral amblyopia

Unilateral reduced acuity as a result of ocular disease

Page 8: Binocular refraction techniques, binocular balancing & binocular

3) Ocular Motility Considerations

Significant horizontal, vertical or cyclo associated phorias

Cyclophoria

Latent nystagmus

Page 9: Binocular refraction techniques, binocular balancing & binocular

Under binocular conditions, the amblyopic eyes accept more of the indicated correction and obtains better acuity

VA in RE 6/6 VA in LE 5/60On 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

Page 10: Binocular refraction techniques, binocular balancing & binocular

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

Page 11: Binocular refraction techniques, binocular balancing & binocular

• 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

Page 12: Binocular refraction techniques, binocular balancing & binocular

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

Page 13: Binocular refraction techniques, binocular balancing & binocular

This monocular viewing under binocular conditions can be achieved by:

Septum

Polarization

Fogging

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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

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Turville Infinity BalanceApparatus 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

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• 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

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• 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

Page 18: Binocular refraction techniques, binocular balancing & binocular

septum

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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

Page 20: Binocular refraction techniques, binocular balancing & binocular

• 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.

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• Cross cylinder introduced parallel to axis of cylinder present

• This way presence , amount and orientation of astigmatism may be measured .

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• 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 .

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• 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

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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

Page 25: Binocular refraction techniques, binocular balancing & binocular

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

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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

Page 27: Binocular refraction techniques, binocular balancing & binocular

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

Page 28: Binocular refraction techniques, binocular balancing & binocular

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

Page 29: Binocular refraction techniques, binocular balancing & binocular

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

Page 30: Binocular refraction techniques, binocular balancing & binocular

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

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Vectographic Slides for Projection Its perception is identical to that for polarized symbols

The slide presents 1. VA chart visible only to RE2. VA chart visible only to LE3. Radial chart to determine astigmatism

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4. Equalization chart5. Suppression reading chart6. Binocular acuity chart7. Fixation disparity chart8. Stereopsis chart

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Vectographic Chart

Stereo Test

Associated Phoria Test (fixation disparity)

Astigmatic Test

VA Test: OD

VA Test: OS

Page 34: Binocular refraction techniques, binocular balancing & binocular

Polarized Fan Dialo 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

Page 35: Binocular refraction techniques, binocular balancing & binocular

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

Page 36: Binocular refraction techniques, binocular balancing & binocular

Immediate Contrast TechniqueHumphriss used +0.75 DS over the non tested eye for the performance of astigmatic tests and Bichrome tests on the tested eyeThis unilateral fogging also called a psychological septum

Centrally suppressed the foveal image of the blurred eye but permitted the peripheral images to be fused

Page 37: Binocular refraction techniques, binocular balancing & binocular

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

Page 38: Binocular refraction techniques, binocular balancing & binocular

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

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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

Page 40: Binocular refraction techniques, binocular balancing & binocular

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

Page 41: Binocular refraction techniques, binocular balancing & binocular

Difference in accommodative response between two eyes

Inequality in clarity or size of retinal images

Reduce stereoacuityReduce fusional amplitudes Cause discomfortCreate visual inefficiency

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Methods for binocular balancing

Alternate Occlusion Prism Dissociated Blur Balance Prism Dissociated Red-Green

(Bichrome) Balance

Page 43: Binocular refraction techniques, binocular balancing & binocular

Alternate OcclusionTarget: smallest acuity letters patient can read through the spherocylindrical correctionAlternately occlude the patient’s eye with cover paddleIf the images equally clear- balance is correct

Page 44: Binocular refraction techniques, binocular balancing & binocular

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 clearFinally to confirm, add +0.25 DS before each eye. If the balance is correct BE will be equally blurred

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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

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Prism dissociated blur balance

RE – 3 ∆ Base Down LE – 3 ∆ Base Up

Two charts will be seen separated vertically

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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

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• 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.

Page 49: Binocular refraction techniques, binocular balancing & binocular

• 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

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• 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

Page 51: Binocular refraction techniques, binocular balancing & binocular

• 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

Page 52: Binocular refraction techniques, binocular balancing & binocular

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

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Page 54: Binocular refraction techniques, binocular balancing & binocular

- 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

Page 55: Binocular refraction techniques, binocular balancing & binocular

• 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

Page 56: Binocular refraction techniques, binocular balancing & binocular

• 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

Page 57: Binocular refraction techniques, binocular balancing & binocular

• 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)

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Page 59: Binocular refraction techniques, binocular balancing & binocular

• 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

Page 60: Binocular refraction techniques, binocular balancing & binocular

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

Page 61: Binocular refraction techniques, binocular balancing & binocular

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

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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

Page 63: Binocular refraction techniques, binocular balancing & binocular

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

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Important in:1) Presbyopes2) Persons with binocular vision problems3) Accommodative abnormalities4) 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

Page 65: Binocular refraction techniques, binocular balancing & binocular

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 .

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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

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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

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• 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

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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

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• 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

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SummaryBinocular refraction is superior to monocular – better control of accommodation, separate binocular balancing not requiredBinocular balancing important as unbalanced accommodation between two eyes result in asthenopia , discomfortIf patient is not binocular (suppression, strabismus), monocular best sphere is the end point of subjective refraction

Page 72: Binocular refraction techniques, binocular balancing & binocular

Subj

ecti

ve R

efra

ctio

n RE

Monocular sphere

Astigmatism

(axis/power)

Monocular best sphere

LE

Monocular sphere

Astigmatism (axis/power)

Monocular best sphere

BE Binocular best sphere

Binocular balancing

Page 73: Binocular refraction techniques, binocular balancing & binocular

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

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Page 75: Binocular refraction techniques, binocular balancing & binocular