# Vergences Vergences

 Date 19.12.2017 Size 42.5 Kb.
Vergences

• 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 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

• 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