Visual System - Shorer Flashcards
Where are rods and cones located and what do they do?
Rods:
Night vision, located anteriorly, none in fovea.
Cones:
Concentrated at the fovea, produce color vision and sharp vision.
There are 100 million rods and cones but only 1 million axons that converge at the optic nerve. Bipolar cells are between the rods anc cones, not photosensitive. Bipolar cells converge on ganglion cells (layer within retina) which then converge to the optic nerve.
What is homonymous hemianopsia?
Damage to one optic tract after the chiasm.
Example: damage to right optic tract: can’t see left part of right or left eye.
Examine by covering one eye and asking to name fingers in different parts of the visual vield.
What is bitemporal homonymous hemianopsia? Example?
Ex: pituitary tumor at the optic chiasm. The lateral visual field is blocked and only nasal visual field is seen.
What is one sided nasal hemianopsia? Example?
If a tumor is pressing on the outer optic nerve around the optic chiasm, nasal retinal reflections normal but temporal retinal tracts damaged. Medial visual field blocked but lateral normal.
What happens to the visual fibers that reach the lateral geniculate body?
90%
Synapse at LGB and continue to the superior colliculus and continue to Meyer’s loop and geniculo-calcarine tract to calcarine sulcus.
10%
Goes through the LGB without synapsing and continue to the pretectal nucleus behind the superior colliculus. Synapse to the Edinger-Westphal nucleus, some from ipsilateral and contralateral, which sends parasympathetic fibers of CN III to the ciliary body in the ipsilateral eye (to the nucleus).
Oculomotor nucleus is lateral and medial to the Edinger-Westfal nucleus and those fibers go to the rectus muscles of the ipsilateral (to the nucleus) eye.
What are the two muscles of the iris and what do they do?
What pathway controls this?
Inner Circular muscle
Parasympathetic stimulation
Pupillary constriction/myosis
Outer Radial muscle
Sympatheric stimulatino
Pupillary dilation/midriasis.
Controlled by LGB through the pretectile nucleus, EW nucleus, and constrictor pupillae muscle.
Present in cortical blindness.
