4. Accommodation, Vergence, and ZCSBV - Eye Movements & Binocular Vision Summer 2026

1/distance

What is the equation for accommodative demand?

0

What is the accommodative demand for a far away target in a fully corrected patient?

true

True or False:

The accommodative demand formula is a generalization

the accommodative demand for an object for a given patient

The accommodative demand equation DOES NOT necessarily describe what?

-refractive error

-refractive correction

What needs to be factored into the accommodative demand equation?

true

True or False:

We can accommodate and we can relax accommodation

fully relaxing accommodation -- we cannot accommodate less than 0D

What is the absolute limit to accommodation?

true

True or False:

Sometimes the spec rx that we give patients DOES NOT match the refraction

-d/t aniseikonia

-usually d/t accommodation

We would be not give patients the spec rx that matches their refraction?

0

What is the distance accommodative response in a 2D hyperope wearing +2.00D specs?

clear

What is the amount of blur at distance in a 2D hyperope wearing +2.00D specs?

+2.50

What is the near accommodative response in a 2D hyperope wearing +2.00D specs?

clear

What is the amount of blur at near in a 2D hyperope wearing +2.00D specs?

+1.00

What is the distance accommodative response in a 1D hyperope wearing no specs?

clear

What is the amount of blur at distance in a 1D hyperope wearing no specs?

+3.50

What is the near accommodative response in a 1D hyperope wearing no specs?

clear

What is the amount of blur at near in a 1D hyperope wearing no specs?

+1.00 (build in add)

What is the distance accommodative response in a -1D myope wearing -2.00 specs?

clear

What is the amount of blur at distance in a -1D myope wearing -2.00D specs?

+3.50

What is the near accommodative response in a -1D myope wearing -2.00 specs?

clear

What is the amount of blur at near in a -1D myope wearing -2.00D specs?

0.00

What is the distance accommodative response in a -3D myope wearing -2.00 specs?

-1.00 blur

What is the amount of blur at distance in a -3D myope wearing -2.00D specs?

+1.50

What is the near accommodative response in a -3D myope wearing -2.00 specs?

clear

What is the amount of blur at near in a -3D myope wearing -2.00D specs?

vergence

Disjunctive binocular movements

opposite

With vergence, eyes will go in the (same/opposite) direction

-convergence

-divergence

Vergence movements around the vertical axis (horizontal movements)

inward movement of both eyes

What is convergence?

outward movement of both eyes

What is divergence?

when the lines of sight are parallel such as when viewing an object at infinity

What is zero lateral vergence posture?

angle between the lines of sight

What is a vergence angle?

Verg Angle = pd / D

Lateral Vergence Angle Equation

radians

With the lateral vergence angle equation, if pd and D are both the same units, the angle unit will be in _____

prism diopters (cm/m)

With the lateral vergence angle equation, if pd is in cm and D is in m, the angle unit will be in _____

Yes

Can radians be converted to degrees?

-1/D

-Meter angles are not typically used clinically

What are meter angles and are the typically used clinically?

In understanding some relationships of units -- we can look at accommodation and vergence responses in similar units

What are meter angles useful for?

meter angles * pd (cm) = PD

How to convert meter angles to prism diopters?

Lateral Vergence Angle (Pic)

Lateral Vergence Angle (Pic)

-hypovergence

-hypervergence

What are the vergence movements around the horizontal axis (vertical movements)?

If the right eye goes up and the left eye goes down, this is a R hypervergence

What is hypervergence?

If the right eye goes down and the left eye goes up, this is a R hypovergence

What is hypovergence?

Yes

Are vergence disorders common?

convergence insufficiency

What is THE MOST COMMON binocular vision disorder?

-vision therapy

-prism in specs

What can we do to correct convergence insufficiency?

improves fusional compensation

What is the benefit of vision therapy for convergence insufficiency?

-fusional (disparity) vergence

-accommodative vergence

-proximal vergence

-tonic vergence

What are the 4 components to total horizontal ocular vergence?

binocular disparity

What is the stimulus for fusional (disparity) vergence?

Disparity = Target position - Eye position

What is the equation for disparity?

positive

Positive disparity (eyes are underconverged) is a stimulus for ________ fusional convergence

get rid of fusional convergence

To get rid of fusional convergence, what would we have to do?

phoria

When we break fusion, we are left with a _____ on alternating cover test

true

True or False:

When you uncover an eye, fusional vergence will come back

160ms

What is the latency for the fusional vergence system?

-dynamic

-static

What are the 2 components to fusional (disparity) vergence?

Fusional vergence used to change vergence posture (fixate a target at a different distance)

What is dynamic fusional (disparity) vergence?

Holds vergence posture (compensates for the phoria)

What is static fusional (disparity) vergence?

fusional (disparity) vergence

What is the only components of the vergence system that is controlled by a feedback loop?

accommodation

Accommodative vergence is driven by __________

Accommodative convergence / accommodation (AC/A)

What is the Rate of accommodative convergence equation?

PD / d

What is the unit for accommodative convergence?

-calculated AC/A

-gradient AC/A

How is the AC/A ratio measured in clinic?

4 pd/D

What is the avg AC/A ratio?

stimulus is the perceived distance of the target

What is proximal vergence?

Yes -- mirrored room, instrument (phoropter)

Can proximal vergence affect clinical testing?

-ocular vergence posture when the output of the other 3 stimuli driven vergence components is 0

-vergence posture in the absence of vergence stimuli

What is tonic vergence?

-blur (defocus) accommodation

-vergence accommodation

-proximal accommodation

-tonic accommodation

What are the 4 components to ocular accommodation?

retinal defocus

What is the stimulus for blur (defocus) accommodation?

true

True or False:

blur (defocus) accommodation is driven by a feedback loop

by the act of converging

What is convergence accommodation driven by?

convergence accommodation / convergence (CA/C)

What is the rate of convergence accommodation equation?

D / pd

What is the typical units on the CA/C ratio?

0.1-0.4 D/pd

What is a normal CA/C value?

No

Is CA/C typically measured clinically?

Yes

Does the CA/C contribute substantially to normal binocular vision?

Base line value in the absence of any stimulus to accommodation

What is tonic accommodation?

1.5D

What is the avg value for tonic accommodation?

vergence posture of the eyes in the absence of fusional vergence (latent deviation)

What is a phoria?

-"How close does accommodative, proximal, & tonic vergence come to the required vergence angle?"

What question does a phoria value answer?

fusional vergence

Whats left over when accommodative, promixal, and tonic accommodation are in play is accounted for by _______

What fusional vergence must ovecome when the person is looking with both eyes

What does the phoria demonstrate?

more

The bigger the phoria, the (more/less) strain you are putting on fusional vergence

3pd exophoria

What are avg values for near phoria?

1pd exophoria

What are avg values for distance phoria?

-alternating cover test

-VG phorias

-Modified Thorington

How is a phoria measured clinically?

person uses negative fusional convergence (turn eyes out) to compensate for the tendency to turn eyes in

What is an esophoria?

person uses positive fusional convergence (turn eyes in) to compensate for the tendency to turn eyes out

What is an exophoria?

-accommodative vergence

-proximal vergence

In order to measure a phoria, what vergence components need to be held stable?

fusional vergence

To measure a dissociated phoria, you need to eliminate __________

-occlusion (CT)

-vertical prism (VG)

REVIEW: How do we eliminate fusional vergence?

how far the covered eye drifted away from the fixation target

To measure a phoria, we have to measure what?

how much fusional vergence must be used to maintain fusion

What does the phoria represent?

measure the vergence ranges

To assess the impact of the phoria, what must we do?

Graphical analysis of the ZCSBV

One method for analyzing the workload that patients have for visual tasks at differing distances?

For a Target at 40cm, the accommodative demand will be 2.5D and the vergence demand for a 60cm PD will be 15PD

What does this graph (see pic) show?

BO prism

How to increase the convergence demand of a target?

Patient will have to use positive fusional vergence to fuse the target

What happens if you increase the convergence demand of a target?

positive convergence accommodation

What does positive fusional vergence create?

blur

In some patients, increasing positive convergence accommodation will create ______