Flashcards in Disorders of the Ascending Pathway (M2) Deck (24)
What are the signs and symptoms of strabismic amblyopia?
1. eye turn of affected eye
2. reduced optotype (Snellen) acuity in affected eye
3. suppression of affected eye during binocular viewing
4. little or no stereopsis
At what age is there a lifetime maximum of synapses in V1?
Which portion of the visual system is still developing postnatally? 1. Which is done? 2
1. V1 still developing
2. LGN fully retinotopically wired
Is refractive amblyopia congenital or developmental?
What is the process of how strabismic amblyopia develops from before and after birth?
1. prenatal waves from retina to LGN are ok
2. postnatally, the eye turn makes the same stimulus fall on non-corresponding positions of the two retinas
3. postnatal waves do not encourage orderly, projections
4. suppression of the turned eye occurs to prevent diplopia
What are the patients that have spatial-frequency-tuned channels and then lose them? 1. Why does this occur? 2
1. refractive amblyopes
2. more blur of proximal stimulus during critical period = more high spatial frequency loss (modulation transfer function)
What are the clinical consequences of strabismic amblyopia at the primary visual cortex?
1, impaired visual pattern recognition (reduced optotype acuity)
2. crowding (reduce optotype)
3. poor Vernier acuity
4. poor grating orientation identification acuity ("grating vertical or horizontal?")
5. near-normal grating resolution acuity (Teller acuity)
6. poor stereo acuity
What happens to the cells of the "handicapped" eye in the primary visual cortex if there is an amblyopia?
lose synaptic connections, making narrower columns
Why does refractive amblyopia tend to occur in cases of anisometropia?
accommodation is consensual and usually controlled by eye of smaller refractive error so eye with larger refractive error has constant blur
For complete achromatopsia, what is the inheritance? 1. What vision is normal and what is absent? 2. What are the signs and symptoms? 3
1. autosomal recessive
2. rod vision normal, cone vision completely absent
3. VA = 20/200, photophobia, no foveal reflex, and pendular nystagmus
For Vernier acuity compared to grating acuity, what is the loss of acuity like for anisometropes? 1. For strabismics? 2. For mixed? 3
1. proportionate loss
2. much greater loss of vernier than grating acuity
3. intermediate more loss of vernier
Where does the part of V1 that normally receives signals from the fovea receive info from for an achromatic patient?
signals from the parafoveal retina
Is the loss of contrast sensitivity at high spatial frequencies higher or lower than the loss of visual resolution acuity?
What develops normally in refractive amblyopia in regards to the patients vision?
lowest spatial frequency channels normal
When are patients most sensitive to refractive amblyopic damage? 1. Why? 2
1. under age 5
2. culling of synapses mostly done
What type of vision may not be affected by a pure strabismic amblyopia?
1. have normal CSF
2. good resolution acuity
Why do the retinal cells "fire together" during development before birth?
wave of spontaneous activity sweeps across the retina
Is there a relationship between the amount of blur and depth of the amblyopia?
yes, more blur means worse spatial frequency loss
What happens to patients that have blurred vision in both eyes?
1. critical period longer
2. eventually, connections lost and there is VA loss in both eyes
3. loss of motion perception
For Vernier acuity compared to Snellen acuity, what is the loss of acuity like for anisometropes? 1. For strabismics? 2. For mixed? 3
1. proportionate loss
2. proportionate loss
3. proportionate loss
What is the etiology of strabismic amblyopia?
1. eye turn in infancy/early childhood (more common for esotropia)
2. may have concomitant anisometropia (reduced contrast sensitivity and grating detection acuity in affected eye)
What will the failure to remove a cataract in a child lead to?
1. unilateral amblyopia
2. severe bilateral perceptual losses
Why do the retinal cells "fire together" during development after birth?
usual retinal stimulus