Lecture 16 Visual System: Structure of the Eye

cornea & lens

focus image on the retina, refracts light, transparent

iris

aperature, regulates amount of light

ciliary body

secretes aqueous humor

retina

transduces photons, integrates starts processing of visual info

pupillary sphincter & dilator muscles

change the size of pupil

ciliary body details

• fills anterior chamber between lens and cornea

• replaced 15x a day

• gelatinous vitreous humor behind lens

ciliary muscle contraction

fattens lens; focus on near objects

how contracting ciliary muscle fattens the lens?

contraction releases tension on lens, thus fattens if young and elastic

retina parts

• fovea

• optic disk

• optic nerve

fovea

• depression in center of macula

• especially rich in cones

• directly in line with visual axis

• highest visual acuity

optic disk

• no photoreceptors

• origin of optic nerve

• blind spot

cell types

• photoreceptors

• bipolar cells

• horizontal cells

• amacrine cells

• ganglion cells

photoreceptors

rods and cones

phototransduction

process of transduction of light energy into electrical energy in the retina; hyperpolarization

central pathways

• lateral geniculate nucleus of thalamus to primary visual cortex (visual perception)

• superior colliculus and pretectum (orientation of head and eye movements)

• hypothalamus (circadian rhythms)

blind right eye

the maximum deficit that could result from damage on the right side of the visual pathway in front of the optic chiasm. partial damage could cause loss of sectors, loss of an area straddling the midline

bitemporal hemianopia

maximum deficit that could result from damage in the middle of the optic chiasm, affecting the crossing fibers. damage on one side of the chiasm could cause an ipsilateral nasal field loss, but damage anywhere in the chasm should generally cause losses in different parts of the two eyes fields

left homonymous hemianopia

maximum deficit that could result from damage on the right side of the visual pathway behind the optic chiasm. partial damage could cause loss of only quadrants or sectors or spare the left half of the foveal field, but the losses in the two eyes visual fields should more or less overlap