L12- Disorders Of Vision Flashcards
What are the learning objectives regarding disorders of vision?
Understand how some forms of blindness arise
* Understand the different disorders of vision and the brain areas that must be damaged to cause these disorders
How does the brain process visual information from the retina to V1?
Visual information from the retina is transmitted to the lateral geniculate nucleus (LGN) and then to the primary visual cortex (V1) in the occipital lobe. The right side of the brain processes the left visual field and vice versa.
What is blindsight and what are its characteristics?
Blindsight is the ability to localize objects in space without conscious visual perception, often due to damage to V1. Patients may not be able to identify objects but can localize them, especially moving objects, due to information reaching the dorsal stream and V5.
What is achromatopsia and what causes it?
Achromatopsia is the absence of color vision caused by damage to area V4. People with achromatopsia see only black, white, and shades of gray.
What is akinetopsia and what causes it?
Akinetopsia is the absence of motion vision caused by damage to area V5 (MT). Patients have difficulty perceiving objects in motion.
What is apperceptive agnosia and what causes it?
Apperceptive agnosia is a failure of object recognition due to fundamental visual perception failure, caused by bilateral damage to V1. Patients have preserved elementary visual functions but poor matching and copying abilities.
What is the “Peppery Mask Hypothesis” related to apperceptive agnosia?
The “Peppery Mask Hypothesis” suggests that damage to V1 results in multiple blind spots (scotomas), making vision severely impaired as if looking through a peppery mask.
What is dorsal simultagnosia and what causes it?
Dorsal simultagnosia is a failure of object recognition due to a spatial perceptual impairment, caused by bilateral damage to the parietal lobes. Patients can recognize objects but not more than one at a time.
What is ventral simultagnosia and what causes it?
Ventral simultagnosia is a failure of object recognition due to a complex perceptual impairment, caused by damage to the ventral stream beyond V4. Patients can see multiple objects but not clearly, recognizing only one at a time.
What is associative agnosia and what causes it?
Associative agnosia is a failure of object recognition due to a higher-order complex perceptual impairment, despite seemingly normal copying abilities. This condition is due to preserved elementary visual functions but impaired perception at higher levels.
What are some tests used to identify associative agnosia?
incomplete figures test
* Embedded figures test
