CMD 377- Quiz 7

cornea

the main site of refraction (bending light for focusing on the retina)

Iris

regulates the amount of light entering the eye

lens

·elastic structure

o   Flattened by the tension of the zonule fibers for far focusing

o   During accommodation, the anterior part bulges forward for near-focus

retina

innermost layer of eyes

o   Photoreceptors located in the retina

Rods

o   Concerned with peripheral vision & vision under conditions of low illumination (night vision)

o   Numerous in the periphery

Cones

Concerned with central discriminative vision & detection of color (color vision)

Fovea

center of the retina

o   The region of the highest visual acuity

o   Made up of cones

Parts of the retina

-retina

-rods

-cones

-fovea

Transduction of photic information

Photoreceptors (rods & cones) convert photic information into electrical charge in the retina  action potential  info is transmitted down the optic nerves

Visual pathway

Photoreceptors in the retina  ganglion cell axons leave the retina  optic nerve  optic chiasm (partial decussation)  optic tract  lateral geniculate nucleus (the thalamic relay (nucleus for vision)  optic radiation  primary visual cortex (calcarine sulcus)

·Some branch off (from the LGN) to synapse on the superior colliculi in the midbrain

The blind spot

a hole in our vision created by the optic disk (where the ganglion cell axons leave the retina)

right nasal retina

looking at right visual field/world (right eye)

right temporal retina

looking at left visual field (Right eye)

left temporal retina

looking at right visual field (left eye)

left nasal retina

looking at left visual field (left eye)

L visual field

represented in the Right optic tract, LGB & Right in visual cortex

visual field representation

at the level of the optic nerve

Upper half of the visual field

represented in the visual cortex below the calcarine sulcus (lingual gyrus)

Lower half of the visual field

represented in the visual cortex above the calcarine sulcus (cuneus)

lesions of superior optic radiation & cuneus

lower visual field cut

Unilateral optic nerve lesion

ipsilateral (same side) hemianopia

severing of nasal fibers at the optic chiasm

bitemporal hemianopia (tunnel vision)

unilateral lesion of optic tract

contralateral (opposite side) hemianopia

lesions of superior optic radiation and lingual gyrus

upper visual field cut

1. Lesion right eye optic nerve

blindness of right eye

2. Lesion optic chasm in midline

Bitemporal hemianopsia (outer visual field for both eyes)

3. right optic tract

left homonymous heminopsia (left side of visual field in both eyes)

upper left visual field in both eyes

lower left visual field in both eyes

left macular sparing in both eyes visual field