Lecture 25 - Visual Development & Amblyopia (TV) Flashcards
Why does an infant have poorer visual acuity than an adult?
All-cone fovea is not fully developed - cones widely spaced and poorly developed (even if rod-dominated peripheral retina is) AND visual cortex is not fully developed either *It is not due to poor optics
During monocular deprivation, in non-deprived eye, it dominates most of the available cortical space in layer 4. In the deprived eye, there are thinner stripes, only occupying a narrow area of space. In the open eye, the axon arbors are much more diffuse - extending to the space of two ocular dominance columns In the deprived eye, there are very sparse axons, barely any competition
During monocular deprivation, in non-deprived eye, it dominates most of the available cortical space in layer 4. In the deprived eye, there are thinner stripes, only occupying a narrow area of space. In the open eye, the axon arbors are much more diffuse - extending to the space of two ocular dominance columns In the deprived eye, there are very sparse axons, barely any competition
What happens when you suture BOTH eyes shut - binocular deprivation?
Fewer binocular cells, but there are cells driven by either contra or ipsilateral eye (where else in monocular deprivation, only one area, ipsi or contra, has cells). Receptive fields are not very abnormal.
At birth, LGN afferents terminating in layer 4 of V1 overlap and over time they segregate into distinct ocular dominance columns
At birth, LGN afferents terminating in layer 4 of V1 overlap and over time they segregate into distinct ocular dominance columns
T/F - Diffuse light is essential to establish normal connectivity
F - it is form vision that is essential
T/F - There is competition between the geniculocortical inputs related to the two eyes for cortica space
T
During monocular dominance, there are very few changes earlier along the visual pathway - in the retina and LGN, except for some shrinkage of cells in the deprived LGN laminae
During monocular dominance, there are very few changes earlier along the visual pathway - in the retina and LGN, except for some shrinkage of cells in the deprived LGN laminae
T/F - All visual functions have the same critical periods
F- stereopsis, contrast sensitivity, face recognition etc. all have different critical periods
Tilt after effect? What’s happens to the right eye if you expose the left eye to tilted grating?
Looking at a set of lines that are titled clockwise then looking at a vertical grating - it will appear that it is tilted counterclockwise. Exposing left eye to tilted grating then showing the grating the vertical grating, it will appear slight counterclockwise. If you show it to the right eye, it also sees it as counterclockwise. It has intraocular transfer - this only happens with binocular cells.
Describe the concept of critical period in visual cortical development and how it is related to amblyopia
A period during someone’s development in which a particular visual function is believed to be most readily acquired. If there are disturbances to this critical period, it can lead to losses in visual acuity depending on which eye is affected. In amblyopia, visual acuity in one eye is very poor due to abnormal neuronal development where fewer cortical cells are driven by the amblyopic eye. There is a lack of binocular cells in the cortex - so no stereopsis (binocular vision)
3 Types of Amblyopia
1) `Occlusion When one eye is occluded by a congenital cataract or a lid ptosis (droopy lid)
2) Anisometropic When the two eyes have very different refractive errors (e.g. myopic, hyperopic)
3) Strabismic When one eye is deviated (eye turn, squint)
Is critical period restricted to vision?
No - occurs in auditory system, there is also competition between different sensory modalities (vision, touch and hearing) similar to competition between two eyes (there is a greater neuronal pool devoted to auditory and somatosensory processing in a visually deprived animal) and language development as well
How can plasticity be restored beyond the critical period?
Administration of fluoxetine to induce ocular dominance shift by monocular deprivation
