Binocularity

What does sensory fusion require?

1. adequate visual sensitivity 2. adequate vergence (motor) function

What are the types of motor fusion?

1. convergence (point near the eye) 2. divergence (point far from eye)

What problems result from deficient motor fusion?

1. manifest deviation 2. latent deviation

What are the classic orders of sensory fusion?

1. simultaneous perception 2. flat fusion 3. stereopsis

Which cover test is best to measure the amount of deviation?

ACT- it breaks fusion the best

What does it mean that projection is opposite deviation?

an image formed on the temporal retinal area of OD will be projected to the left of the OD visual axis

What fixes hyper?

base down

What fixes exo?

base in

What fixes eso?

base out

What fixes hypo?

base up

Describe diplopia

both eyes fixate at the same location, and the image is formed on corresponding areas of the retina - the deviating eye's image lands on a different part of the retina and leads to double vision - projection is opposite deviation

What is latent deviation?

both eyes point at the desired location, but that is not their position of rest; eyes have to work harder and therefore deviate if fusion is broken

What type of diplopia results from "exo" postures?

crossed diplopia; image created on the eye turned out lands on the temporal retina, but the brain thinks its on the nasal side

If pt reports "against" motion in ACT, what is happening?

eso; target moves in opposite direction as occluder

How is deviation quantified?

estimation (1mm movement= 7-8 prism diopters) or prism neutralization (shift image toward base)

What is esophoria?

excessive convergence with respect to orthophoria

What is exophoria?

excessive divergence with respect to orthophoria (too little convergence)

If pt reports "with" motion in ACT, what is happening?

exo; target moves with occluder

Define hypo

eye turns downward

Define eso

eye turns inward

Define exo

eye turns outward

Define hyper

eye turns upward

What is manifest deviation?

eyes don't aim at the same place even when the option for sensory fusion is given to them; always present

If pt reports down motion in ACT, what is happening?

hyper

If pt reports up motion in ACT, what is happening?

hypo

What is consistency?

manifest and latent - comitant: deviation is the same in all fields of gaze - non-comitant: deviations varies in all fields of gaze

What is constancy?

manifest only - constant: present all the time - intermittent- manifest part of the time and latent the rest of the time (repeat UCT after ACT to determine)

What is sensory fusion?

neurological and perceptual integration of visual info... brain's job

What happens if motor fusion fails?

no incentive for sensory fusion; results in diplopia and suppression

Where does light that is from an object straight ahead land on the retina?

on the fovea

Where does light from an object in the temporal field land on the retina?

on the nasal retina

What is an example of latent deviation?

phoria

What is an important rule to know in diplopia?

projection is opposite deviation

Describe hypertropia diplopia

the eye aimed high will see the image low

Describe hypotropia diplopia

the eye aimed low will see the image high

What is motor fusion?

the movements of both eyes to help maintain sensory fusion; helped by the 6 EOMs

What are examples of manifest deviations?

tropia, squint, and strabismus

What is suppression?

unconscious regression of sensory info from all or part of the retina

What type of diplopia results from "eso" postures?

uncrossed diplopia; image created on the eye turned in lands on the nasal retina, but the brain thinks its on the temporal side

What is the subjective cover test?

uses info from patient to confirm what you're seeing- they should see an image jump - quantifies the amount of movement on ACT