optic pathways Flashcards
what physiological mechs protect the eye?
-blinking
-tears
what artery mainly supplies the eye?
the ophthalmic artery (branch of the internal carotid artery)
what are the 3 layers of the eye?
- sclera / cornea
- choroid
- retina
how many neurons does a sensory pathway consist of?
-primary
-secondary
-tertiary
what are the 3 order neurons in the visual pathway?
-primary - bipolar cells of the retina
-secondary - decussates - optic nerve / optic tract
-tertiary - cell body in the lateral geniculate nucleus (in the thalamus)
what is the function of the visual pathway?
the visual pathway transmits information interpreted from **visual light from the eyes to the visual cortex in the brain
describe the visual pathway (beginning - light - ocular bulb-retina-optic nerve - chiasm)
visual pathway begins with light entering the ocular bulb and being processed by the retina
information then passed on from the retina by the optic nerve which travels to the optic chiasm
describe the visual pathway from the optic chiasm
from the optic chiasm, the axons are now called the optic tract
the axons then synapse at the** lateral geniculate nucleus**
how do axons from the lateral geniculate nucleus reach the visual cortex of the brain?
they travel via the optic radiation
what is a visual field?
the visual field is what is seen by a person with both eyes wide open and looking straight ahead
where are inputs from the right and left visual field carried by?
information from the left visual field carried in right optic tract
information from right visual field carried in left optic tract
what is homonymous hemianpia?
loss of vision occurs in the same visual field of each eye.
- eg) if someone has homonymous hemianopia on the left side, it means they have lost the left half of their visual field in both eyes.
what is homonymous quadranopsia?
- loss of vision in one quadrant of the visual field in both eyes.
-caused by damage to the optic radiation or occipital lobe of the brain, often due to stroke, trauma, or tumors affecting the visual pathway.
what is akinetopsia?
Individuals with akinetopsia may perceive the world as a series of static or frozen images rather than a continuous flow of motion.
describe the corneal reflex
- cornea is gently touched
- this stimulates the ophthalmic nerve
-opthalamic sends info to the trigeminal ganglion
-as a result if stimulation, the brain triggers a response by activating the motor nucleus of the facial nerve
-facial nerve activates the orbicular oculi which results in rapid blinking of the eye
what is the ciliary ganglion?
small parasympathetic ganglion located behind the eye in the posterior orbit.
- note the post ganglionic fibres travel with the ophthalmic nerve to reach the iris and ciliary muscle of the eye
describe the pupillary light reflex
- protective mechanism of the eye that helps regulate the size of the pupil in response to changes in light intensity
-it involves co-ordinated action from the iris muscles (which control the size of the pupil)
what type of visual deficit is associated with damage to the optic radiation?
-homonymous hemiapnia- with macular spacing ]-ie the central vision (macula) is preserved and the peripheral vision is lost in the affected visual field
what type of visual deficit is associated with damage to the optic chiasm eg from pituitary tumour?
-bitemporal hemianopia
-loss of peripheral vision in both the temporal visual fields - resulting in tunnel vision
describe the location of the primary motor cortex including its number in brodmann’s classification
located in the occipital lobe
-brodmann area 17
what is the accommodation reflex?
-mechanism of the eye that allows for the adjustment of focus to maintain clear vision at different distances.
- coordinated changes in the shape of the lens and the size of the pupil in response to changes in the distance of objects being viewed.
what is papilloedema?
swelling of the optic disc, which is the portion of the optic nerve visible at the back of the eye. This swelling is caused by increased pressure within the skull, known as intracranial pressure (ICP).
what is strabismus/squint?
-misalignment of the eyes
- unknown cause
-eyes dont learn to co-ordinate properly
