Visual Flashcards
What is object agnosia?
Inability to recognize familiar objects by visual means alone
What is prosopagnosia?
Inability to recognize faces
What is visual agnosia?
The inability to recognize or attach meaning to visual images
What is lost with a lesion to one optic nerve?
Loss of the monocular field of the eye affected and depth perception (stereopsis)
What loss happens in a lesion severing the optic chiasm?
This cuts the fibers from the nasal hemiretina of each eye. The patient cannot see the temporal halves of both visual fields. This is called bitemporal hemianopsia or “tunnel vision”
What happens with a lesion of one optic tract?
Complete loss of the entire visual hemifield of the contralateral side. Known as left or right (contralateral) homonymous hemianopsia.
This would mean losing the temporal half of the visual field in the contralateral eye and the nasal half visual field of the ipsilateral eye.
Name the order of neurons in the eye.
First order neuron are the rods and cones – only cells that respond to light, function is to transduce light into graded potentials
Second order neurons are the bipolar cells – excitatory or inhibitory and they generate graded potentials that carry the information from the photo receptors
Third order neuron is the ganglion cell – their axons form the optic nerve. The only cell who’s axons leave the retina and generate action potentials.
Where do axons project from ganglion cells?
Most project posteriorly to the lateral geniculate nucleus/body in the thalamus, others go to superior colliculus, or pretectal area
Describe the organization of the three cells in the eye
The deepest near the pigmented Retina are the rods and cones and the ganglion cells are nearest to the vitreous body. Photo receptors must be near the outer pigmented layer because it absorbs excessive light and removes excess disc membrane.
*Makes the sharpest image!
What do cones see?
Mediate color vision, function only at high light intensity so. They have small receptive fields which means they are a high acuity resolution visual system. Most are found in the fovea.
DO NOT WORK AT NIGHT!
What do rods see?
Mediate black and white, function at low intensities. They have large receptive fields so they are part of low acuity or resolution system. They are more common than cones and found all the retinal areas except fovea
What information do each hemiretina (superior and inferior) see and where do they project?
The inferior hemiretina carries information concerning the superior visual hemifield and projects on the inferior bank of the calcarine fisssure.
The superior hemiretina carries information concerning the inferior visual hemifield and projects to the superior bank of the Calcarine fissure.
So superior bank sees inferior visual hemifield and inferior bank sees superior visual hemifield i.e. the image is upside down
