Strabismus and Ventral Stream - Visual Neurophysiology and Perception Spring 2026

eye turn in early infancy/childhood

What is the etiology of strabismic amblyopia?

esotropia

Strabismic amblyopia is more common for (esotropia/exotropia)

anisometropia

An infant/child with strabismic amblyopia may have concomitant _______

-eye turn of the affected eye

-reduced optotype acuity in the affected eye

-suppression of the affected eye during binocular viewing

-other perceptual signs

-little or no stereopsis

What are the signs and symptoms of strabismic amblyopia?

Because of coordinated activity produced by stimulation of similar retinal locations by a given stimulus in the visual field (both foveas responding to a central stimuli)

Why do cells "fire together" after birth?

Signals initiate corresponding signals in the retina, which the eyes send to the brain, thus encouraging orderly, binocular, retinotopic projection

When 2 eyes are ALIGNED, what do the signals they receive initiate?

The stimuli DO NOT CORRESPOND. When the fovea of one eye is stimulated, the peripheral retina of the other eye is stimulated at the same time. A disordered projection will occur d/t this.

In patients with strabismus the two eyes are NOT ALIGNED, what are the consequences of this?

prenatal

_________ retinal waves refine the projection to the LGN correctly

Postnatally

_________, an eye turn will make different stimuli fall on the foveas (stimuli are not similar)

the same

Postnatally, an eye turn will make (the same/different) stimuli fall on non-corresponding positions of the 2 retinas

No

Can postnatal stimulation encourage orderly, in-register projection from the 2 eyes?

-Disordered retinotopic map

-Suppression of the turned eye to prevent diplopia

-Perceptual abnormalities

What does post-natal stimulation cause?

suppressed

When a disordered retinotopic map is present d/t the presence of strabismic amblyopia, the turned eye will be ______ to prevent diplopia

dual -- one from each eye

Strabismus produces _____ retinotopic maps and disordered retinotopic projection

Yes -- jagged appearance of lines is typical

Can perception of images be very distorted in an individual with strabismic amblyopia?

-waves in lines

-jumps in lines

-multiple angles

-interruptions

-scotomas

What are the perceptual consequences of strabismic amblyopia?

Reduced pattern recognition (reduced optotype acuity)

What is the clinical consequence of strabismic amblyopia on pattern recognition?

high

Distortion of (high/med/low) spatial frequencies is seen with strabismic amblyopia leading to reduced visual pattern recognition and optotype acuity

nearby stimulus information obscures attended item (with reduced optotype acuity)

What is the crowding effect as experienced by strabismic amblyopes?

periphery

Crowding is important to vision in the _____

No

Is crowding usually present with foveal vision?

Crowding -- Single Letters Easy to Distinguish (Pic)

Crowding -- Single Letters Easy to Distinguish (Pic)

Crowding -- Multiple Letters Make It Harder to Distinguish Middle Letter (Pic)

Crowding -- Multiple Letters Make It Harder to Distinguish Middle Letter (Pic)

true

True or False:

With the crowding effect, single letters are easy to identify, even when viewed in our midperipheral visual field

Yes

Are crowded letters much harder to identify than single letters for amblyopes?

Yes -- there is not much improvement when letter size is increased

Are bigger letters still affected by crowding?

more

The farther from fixation the letters are, the (more/less) the crowding effect will be present

more

The closer the crowding letters are to the target, the (more/less) the crowding effect will be present

Yes -- applies to lots of visual stimuli

Does crowding apply to more visual stimuli than just letters?

when neighboring items impair the perception of the target item

REVIEW: When does crowding occur?

Yes

In normal adults, does peripheral viewing have a big effect on crowded letters?

peripheral

Strabismic patients act as (foveal/peripheral) viewers

a much bigger deficit on crowding than single letters

What is the effect of peripheral viewing in strabismic patients?

Yes -- by using crowding bars or rows of optotypes

Is it important to use crowded letters in patients with amblyopia when testing their VA?

to better identify the deficit in the affected eye

WHY is it important to use crowded letters in patients with amblyopia when testing their VA?

single

(single/crowded) letters are easier to recognize for strabismic patients

Yes

Do crowding bars show a strong effect on VA in strabismic patients?

Single Letter Crowded Flash Cards (Pic)

Single Letter Crowded Flash Cards (Pic)

Effect of Crowding and Crowding Bars on VA in an Amblyopic Patient (Pic)

Effect of Crowding and Crowding Bars on VA in an Amblyopic Patient (Pic)

poor

Individuals with strabismus will have (good/poor) Vernier acuity

location of parts of the stimulus uncertain d/t the secondary map and scrambling

What is the effect of poor Vernier acuity in a strabismic amblyope?

poor

Individuals with strabismic amblyopia are likely to have (poor/good) stereoacuity

binocular cells must have binocular input to form and survive

WHY do individuals with strabismic amblyopia have poor stereoacuity?

poor

Individuals with strabismic amblyopia will have (good/poor) grating orientation identification acuity

Often this is near normal in these patients

Will the grating resolution acuity be reduced in individuals with strabismic amblyopia?

high

In a strabismic amblyope, ____ spatial frequency gratings DO NOT look like a uniform grey and thus can be detected OK

they are badly distorted -- sometimes the patient will NOT be able to tell the difference between vertical and horizontal oriented lines

Even though strabismic amblyopes can detect gratings, what do the gratings look like?

Vernier acuity; optotype acuity

______ and _____ acuity are generally very highly correlated in patients with strabismic amblyopia

affects them the same proportion

REFRACTIVE amblyopia affects Vernier or Grating acuity more?

-Good grating acuity

-Vernier much worse

STRABISMIC amblyopia affects Vernier or Grating acuity more?

No

Can babies do optotype VA tasks?

Vernier acuity is a promising approach to diagnosing amblyopia in infants and toddlers.

If babies cannot do optotype VA tasks, how are we able to monitor for amblyopia in infants?

No -- NOT ideal. This is a grating acuity

Is Teller acuity (grating) ideal for identifying amblyopia in children?

Vernier

_____ corresponds well to Snellen acuity in all types of amblyopia

Vernier Acuity in Amblyopia v Snellen Acuity (Pic)

Vernier Acuity in Amblyopia v Snellen Acuity (Pic)

**Proportional loss of both in Anisometropes, Strabs, and Mixed Amblyopes

Vernier Acuity in Amblyopia v Grating Acuity (Pic)

Vernier Acuity in Amblyopia v Grating Acuity (Pic)

Proportional loss of both

Vernier Acuity v Grating Acuity in an Anisometrope

Much greater loss of Vernier than Grating

Vernier Acuity v Grating Acuity in a Strabismic Patient

Intermediate loss of both

Vernier Acuity v Grating Acuity in a Mixed Aniso/Strab Patient

Yes

Can a "pure" strabismic amblyopic patient can normal CSF and good resolution acuity for simply detecting the presence of gratings?

No

Will a refractive amblyope have a normal CSF/good resolution acuity for detecting gratings?

Both are defects in the vision of ONE eye in the absence of any obvious pathology in the eye

SUMMARY: What are refractive and strabismic amblyopia?

abnormal visual experience during the critical period

SUMMARY: Both refractive and strabismic amblyopia are the result of what?

Yes -- "mixed" amblyopia.

They can have independent and severe effects on vision

SUMMARY: Are refractive and strabismic amblyopia often mixed and found in the same patient?

deprivation of the high-spatial frequency tuned channels d/t anisometropia during the critical period

Refractive v Strabismic Amblyopia

What is the cause and result of refractive amblyopia?

Results from different stimulation of corresponding points, which disrupts the "postnatal" wave during the critical period

Refractive v Strabismic Amblyopia

What is the cause and result of strabismic amblyopia?

loss in grating acuity

Refractive Amblyopia

Grating Resolution Result

loss of optotype acuity

Refractive Amblyopia

Optotype Acuity Result

Proportional

Refractive Amblyopia

______ loss in Vernier and resolution acuity

little loss at low spatial frequencies

Refractive Amblyopia

Contrast Sensitivity Result at LOW SPATIAL FREQUENCIES

No -- crowded optotype acuity is similar to single-letter optotype acuity

Refractive Amblyopia

Crowding effect?

Reduced optotype acuity

Strabismic Amblyopia

Optotype Acuity Result

No loss in grating acuity

Strabismic Amblyopia

Grating acuity result

Much higher loss in Vernier acuity than grating acuity

Strabismic Amblyopia

Vernier vs grating acuity loss

Little loss in contrast sensitivity AT ALL SPATIAL FREQUENCIES

Strabismic Amblyopia

Contrast sensitivity result

Crowded optotype acuity is WORSE than single letter acuity

Strabismic Amblyopia

Crowding present?

Ocular dominance columns asymmetrical (deprivation or refractive) or the cells in V1 may receive input from non-corresponding retinal neurons (strabismic) resulting in image distortion

SUMMARY: What are the major issues in amblyopia?

more

SUMMARY: In general, the earlier you treat amblyopia, the (more/less) effective patching will be

7

SUMMARY: Amblyopia is more responsive to treatment among children younger than ____ years old

Yes -- Stereo Sue example

SUMMARY: Are there reports of individuals developing improvements in vision (acuity, stereopsis) with vision therapy that is prescribed in adulthood?

Yes

Parallel Inputs to the Striate Cortex

REVIEW: Do magno and parvo pathways maintain segregation in V1?

4Cα

Parallel Inputs to the Striate Cortex

REVIEW: Magno neurons project to _____

4B

Parallel Inputs to the Striate Cortex

REVIEW: Margo neurons project to 4Cα, neurons from here then project to ______

4Cβ

Parallel Inputs to the Striate Cortex

REVIEW: Parvo neurons project to _____

2/3

Parallel Inputs to the Striate Cortex

REVIEW: Parvo neurons project to 4Cβ, neurons from here then project to ______

2/3

Parallel Inputs to the Striate Cortex

REVIEW: Konio neurons project to ____

low

Magno Channel LGN to VI -- Parasol cells

(high/low) spatial frequency

high

Magno Channel LGN to VI -- Parasol cells

(high/low) temporal frequency

achromatic

Magno Channel LGN to VI -- Parasol cells

(Chromatic/achromatic) processing

fast

Magno Channel LGN to VI -- Parasol cells

(Fast/slow) processing

dynamic

Magno Channel LGN to VI -- Parasol cells

Input for _____ stimuli

low

Parvo Channel LGN to V1 -- Midget Cells

(high/low) temporal frequency

high

Parvo Channel LGN to V1 -- Midget Cells

(high/low) spatial frequency

red/green

Parvo Channel LGN to V1 -- Midget Cells

_______ chromatic

slow

Parvo Channel LGN to V1 -- Midget Cells

(Slow/fast) processing

Dorsal v Ventral Stream (Pic)

Dorsal v Ventral Stream (Pic)

magno

Dorsal stream mainly contains the (magno/parvo) pathway information

Parvo

Ventral stream mainly contains the (magno/parvo) pathway information

Parvo

Review of Response Properties -- Magno v Parvo

Temporal spatial frequency is sluggish and sustained

Magno

Review of Response Properties -- Magno v Parvo

Temporal spatial frequency is brisk and transient