Von Graefe Phorias



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Binocular Testing

  • Complete evaluation of a patient’s functional system involves testing the accommodation and vergence systems

  • Von Graefe Phorias

    • Purpose: To measure subjectively the relative horizontal or vertical deviation of the eyes, one with respect to the other, when fusion is interrupted

    • Advantages: 1) allows fine control of prism magnitude, 2) relatively quick, 3) done in phoropter (easier for patient) and 4) can easily determine the gradient AC/A

    • Disadvantages: 1) less information than the cover test, 2) peripheral fusion is restricted, 3) limited to primary gaze, 4) unable to observe patient’s eyes or head tilts and 5) depends on the patient response (subjective test)

    • To determine distance lateral von Graefe phorias

      • Use MPBVA in phoropter and distance PD

      • Target: Isolated vertical LOL (includes letters that are one line larger than BVA)

      • Use 6ΔBD in front of OD and 12 ΔBI in front of OS to dissociate

        • 6ΔBD is the dissociating prism

        • 12 ΔBI is the measuring prism

      • Verify that the patient can see 2 targets (one up and one down)

      • Instruct patient to look at the upper target and keep it clear and tell them “I am going to move the lower target and I want you to tell me when it’s directly below the upper target, like buttons on a shirt”

      • Reduce BI prism (~2 Δ/sec) until the patient reports vertical alignment

      • Record magnitude and direction of deviation

      • Expected: Ortho to 2 exo

    • To determine distance vertical von Graefe phorias

      • Use MPBVA in phoropter and distance PD

      • Target: Isolated horizontal LOL (one line above BVA)

      • Use 6ΔBD in front of OD and 12 ΔBI in front of OS to dissociate

        • 6ΔBD is the measuring prism

        • 12 ΔBI is the dissociating prism

      • Verify that the patient can see 2 targets (one up and one down)

      • Instruct patient to look at the lower target and keep it clear and tell them “We are going to do the same sort of thing and tell me when the other target is right beside it, like headlights on car”

      • Reduce BD prism (~1-2 Δ/sec) until the patient reports horizontal alignment

      • Record magnitude and ALWAYS identify the eye with the hyper deviation

      • Expected: Ortho to +/-0.25Δ

    • To determine near lateral von Graefe phorias

      • Use near correction (if no near correction, use BVA) and near PD

      • Target: Isolated vertical LOL or small 20/20 block on rotary card at 40 cm

      • Use 6ΔBD in front of OD and 12 ΔBI in front of OS to dissociate

        • 6ΔBD is the dissociating prism

        • 12 ΔBI is the measuring prism

      • Verify that the patient can see 2 targets (one up and one down)

        • If the patient does not see two separate targets, try switching to BO or increase the amount of BI

      • Instruct patient to look at the upper target and keep it clear and tell them “I am going to move the lower target and I want you to tell me when it’s directly below the upper target, like buttons on a shirt”

      • Reduce BI prism (~2 Δ/sec) until the patient reports vertical alignment

      • Record magnitude and direction of deviation

      • Expected: Ortho to 6 exo

    • To determine near vertical von Graefe phorias

      • Use near correction (if no near correction, use BVA) and near PD

      • Target: Isolated horizontal LOL on rotary chart at 40 cm

        • Use high illumination with the stand lamp but with no shadows

      • Use 6ΔBD in front of OD and 12 ΔBI in front of OS to dissociate

        • 6ΔBD is the measuring prism

        • 12 ΔBI is the dissociating prism

      • Verify that the patient can see 2 targets (one up and one down)

      • Instruct patient to look at the lower target and keep it clear and tell them “We are going to do the same sort of thing and tell me when the other target is right beside it, like headlights on car”

      • Reduce BD prism (~1-2 Δ/sec) until the patient reports horizontal alignment

      • Record magnitude and ALWAYS identify the eye with the hyper deviation

      • Expected: Ortho to +/-0.25Δ

    • Flash technique is used to control accommodation and fusional eye movements

      • Used mainly with lateral phorias

        • Set up lateral phorias and occlude the eye with the measuring prism (OS)

        • Instruct the patient to make sure the image is clear and explain “when I uncover your eye, tell me where the lower target is, to the left or right of the upper target”

        • Remove occluder briefly (~1 sec) and based on their response move the prism under the occluded eye and repeat until the patient reports alignment

        • Record magnitude and direction of deviation

      • The patient has no opportunity to make fusional movements (indicated by the patient describing movement of the targets) and is therefore more accurate

  • Vergences are binocular disjunctive eye movements (A prerequisite is binocularity)

    • Four types of vergences

      • Tonic

      • Accommodative

      • Proximal

      • Fusional: 1) convergence or divergence 2) vertical vergence 3) cyclovergence

    • Fusional Demand: amount of vergence required to see single (another term for phoria)

    • Fusional Reserves: amount of vergence remaining after compensating for the phoria

    • Positive Relative vergence (PRV) and negative relative vergence (NRV) are measured from the zero point (demand point) [what we record]

    • Positive Fusional vergence (PFV) and negative fusional vergence (NFV) are measured from the phoria position

    • To determine horizontal vergences at distance

      • Use distance correction with distance PD

      • Target= vertical LOL

      • Use Risley prisms OU with the zero in the vertical position (no effective prism in place to start)

      • Make sure the patient only sees one LOL and they keep it clear and tell patient “Let me know IF and WHEN they become burry and when they break into two”

      • Add equal amounts of BI at the same rate (~2 Δ/sec) to both eyes

      • Once they have achieved “break” (diplopia) reduce prism in the opposite direction to achieve “recovery” (single image) explaining “Let me know when the letters come back together”

      • Record the total amount of prism (OD + OS) at blur/break/recovery

      • Repeat for BO

        • Note: Always test BI/NFV before BO/PFV (to relax accommodation)

        • Note: Patients should not have a blur value on BI/NFV at distance unless he/she is over-minused or under-plussed

    • To determine horizontal vergences at near

      • Use near correction (if no near correction, use BVA) with near PD

      • Target= vertical LOL or block of letters on rotary chart at 40 cm

        • Use high illumination with the stand lamp but with no shadows

      • Use Risley prisms OU with the zero in the vertical position (no effective prism in place to start)

      • Make sure the patient only sees one LOL and they keep it clear and tell patient “Let me know IF and WHEN they become burry and when they break into two”

      • Add equal amounts of BI at the same rate (~2 Δ/sec) to both eyes

      • Once they have achieved “break” (diplopia) reduce prism in the opposite direction to achieve “recovery” (single image) explaining “Let me know when the letters come back together”

      • Record the total amount of prism (OD + OS) at blur/break/recovery

      • Repeat for BO

        • Note: Always test BI/NFV before BO/PFV (to relax accommodation)

    • To determine vertical vergences at distance

      • Use distance correction with distance PD

      • Target= horizontal LOL

      • Use Risley prisms OU with the zero in the horizontal position (no effective prism in place to start)

      • Make sure the patient only sees one LOL and they keep it clear and tell patient “Let me know when they break into two”

      • Adjust vertical prism on one eye only

        • For supravergence, slowly add BD prism (~1 Δ/sec)

        • For infravergence, slowly add BU prism (~1 Δ/sec)

      • Once they have achieved “break” (diplopia) reduce prism in the opposite direction to achieve “recovery” (single image) explaining “Let me know when the letters come back together”

      • Record the amount of prism at break/recovery and which eye was used for measurement

        • There will be no blur because accommodation is not being stimulated with vertical vergences

      • Note: BU measurement taken on the right eye should be exactly the same as the BD measurement taken on the left eye

    • To determine vertical vergences at near

      • Use near correction with near PD

      • Target= horizontal LOL or block of letters on rotary chart at 40 cm

        • Use high illumination with the stand lamp but with no shadows

      • Use Risley prisms OU with the zero in the horizontal position (no effective prism in place to start)

      • Make sure the patient only sees one LOL and they keep it clear and tell patient “Let me know when they break into two”

      • Adjust vertical prism on one eye only

        • For supravergence, slowly add BD prism (~1 Δ/sec)

        • For infravergence, slowly add BU prism (~1 Δ/sec)

      • Once they have achieved “break” (diplopia) reduce prism in the opposite direction to achieve “recovery” (single image) explaining “Let me know when the letters come back together”

      • Record the amount of prism at break/recovery and which eye was used for measurement

        • There will be no blur because accommodation is not being stimulated with vertical vergences

      • Note: BU measurement taken on the right eye should be exactly the same as the BD measurement taken on the left eye

    • Expected: Vertical measurements (phoria and vergences) should not change between near and distance measurements



Near BO

17/21/11

Near BI

13/21/13

Distance BO

9/19/10

Distance BI

X/7/4



  • Sheard’s Criterion:

    • Reserve should be equal to or greater than twice the demand

      • The phoria is the demand

      • The reserves is the compensating vergence

        • If phoria is eso, the compensating vergence is BI or NFV

        • If phoria is exo, the compensating vergence is BO or PFV

    • Can be used to determine the amount of prism to prescribe or the increase in fusional vergence reserve that should be achieved by visual training

      • To determine the amount of prism to prescribe:

        • Prism = 2 (phoria) – compensating vergence finding

3

  • Percival’s Criterion:

    • The demand point (start point) must be in the center third of the total fusional range (i.e. the total limits of the vergences--BO limit and BI limit)

      • Does NOT take into account the phoria

  • Out of phoropter Vergences

    • Advantages: 1) quicker and easier for the patient 2) better control of patient 3) subjective and objective test (no blur finding if objective) 4) peripheral fusion possible and 5) less intimidating for children

    • To determine horizontal prism bar vergences

      • Patient should wear their best correction for distance and should look through their bifocal (if applicable) for near

      • Target: @ distance, use a vertical LOL

@ near, use a near target held at 40cm (typically 20/30 or 1 line above the patient’s BVA at near)

      • Always begin with BI prism for NFV

      • Instruct the patient to look at the target and keep it clear and begin with the prism bar above one eye and slowly move the prism bar down, increasing the demand, asking “Tell me IF and WHEN the letters blur and when they break into two”

      • Slowly reduce the amount of prism until the patient reports single vision

      • Record blur/break/recovery and repeat with BO for PFV

    • To determine vertical prism bar vergences

      • Patient should wear their best correction for distance and should look through their bifocal (if applicable) for near

      • Target: @ distance, use a horizontal LOL

@ near, use a near target held at 40cm (typically 20/30 or 1 line above the patient’s BVA at near)

      • Instruct the patient to look at the target and keep it clear and begin with the prism bar above one eye and slowly move the prism bar down, increasing the demand, asking “Tell me WHEN the letters break into two”

        • Note: move more slowly than with horizontal

      • Slowly reduce the amount of prism until the patient reports single vision

      • Measure both supra (BD) and infra (BU)

      • Record break/recovery

  • Worth 4 Dot

    • Is used to assess the patient’s fusional ability at distance and near

    • Can detect a tropia or suppression

      • Also consider doing this test when stereopsis is less than 40”

    • Does not dissociate the eyes so you cannot test for a phoria

    • To determine:

      • Have patient wear his/her habitual correction and wear the red/green glasses with the red lens over the right eye

        • The right eye will see 2 red and the left eye will see 3 green

      • Hold the Worth 4 Dot will the white dot at the bottom and the red dot at the top and ask the patient “How many spots of light do you see?”

        • 4 dots: normal fusion

          • Could also indicate ARC in a small angle strabismus

        • 2 dots (should say red): suppression OS

        • 3 dots (should say green): suppression OD

        • 5 dots (determine where the red dots are located in reference to the green dots)

          • Red dots to the right of green dots: eso deviation (uncrossed diplopia)

          • Red dots to the left of green dots: exo deviation (crossed diplopia)

          • Red dots above the green dots: L hyper deviation

          • Red dots below the green dots: R hyper deviation

      • Perform at both distance and near and in both light and dark

        • Testing in the dark versus the light can uncover a subtle suppression

  • Maddox Rod

    • Purpose: to measure the relative horizontal or vertical deviation of the eyes, one with respect to the other, when fusion is interrupted

      • Can also be used to evaluate cyclo deviations

    • The Maddox Rod is dissociative due to the cylinders within the MR

    • Does not differentiate between phorias and tropias

    • To determine vertical:

      • Use dim to moderate illumination

      • Have patient wear his/her habitual correction and hold the MR over the right eye with the streaks oriented vertically

        • Patient will see a horizontal line

      • Hold the transilluminator at 40cm for near or use the muscle light on the projector screen for distance

      • Confirm that the patient sees both a red line and a white light and ask the patient to note where the red line is in relation to the white light

        • Line directly through the light: no vertical phoria

        • If light is touching the line: 1Δ deviation

        • If light is overlapping but not centered: 0.5 Δ deviation

        • Line above the light: OD hypo (recorded as hyper OS)

          • Red line is projected from inferior retina of OD

          • Use BU prism OD (or BD prism OS) to neutralize

        • Line below the light: OD hyper

          • Red line is projected form superior retina of OD

          • Use BD prism OD to neutralize

      • Repeat in down gaze (advantage of out of phoropter)

      • Record phoria based on prism required to neutralize (using the hyper eye) in both primary and down gaze

      • If using for lateral, have patient hold the MR over the right eye with the streaks oriented horizontally

        • Patient will see a vertical line

    • If testing in the phoropter

      • For near lateral: use 12 Δ BI OD (either Risley or prism bar) and decrease (or increase?) the prism until they are superimposed

      • For near vertical: use 6 BD OD (either Risley or prism bar) and decrease the prism until they are superimposed

    • Note: using the transilluminator is not an accommodative target

      • Should affect lateral phoria measurements because you are not bringing in convergence but should not affect vertical

  • Hirschberg Test

    • Way to identify and estimate the amount of strabismus when other more precise methods are not able to be performed

      • Objective technique

      • Used with infants and small children and with language barriers

    • Should be performed both with and without correction

    • Hold the penlight 50cm from the patient’s eyes and instruct them to look at the light

    • Observe the position of the corneal light reflex in each eye, while occluding the opposite eye

      • In the center of the pupil: zero angle lambda

      • Slightly nasal: positive angle lambda

      • Slightly temporal: negative angle lambda

    • Observe the position of the corneal light reflex in each eye with both eyes viewing and compare their locations relative to where they were with each eye fixating

      • If light reflexes have the same position as angle lambda: no strabismus is present

      • A patient who has a manifest deviation (strabismus or tropia) will pick up fixation during the angle lambda test but will trope during Hirschberg

        • Reflex will look centered during angle lambda but not when both eyes are open

      • Measure in 0.5mm increments **1mm= 22Δ





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