Visual Pathway

ipRGCs

express the photopigment melanopsin, 5 subtypes in humans, help mediate the non-image forming function of CN2

olivary pretectal nucleus

responsible for the pupillary light reflex (part of the non-image forming pathway that does not go to the visual cortex)

suprachiasmatic nucleus

located in the hypothalamus, responsible for the circadian rhythm, photoentrainment, sleep/wake cycle, and the pineal gland

upside down & backwards

describe how images appear on the retina

nasal

the _____ visual field is imaged on the temporal retina

temporal

the ______ visual field is imaged on the nasal retina

foveola

the retina is divided into 4 quadrants centered on the _______

papillomacular

the _________ bundle enters the temporal aspect of the optic disc

temporal

the ________ fibers enter the superior temporal and inferior temporal aspect of the optic disc

nasal

the ______ fibers (temporal to the disc) enter the superior temporal and inferior temporal aspect of the disc

nasal

the _____ fibers (nasal to the disc) enter nasally

temporal, nasal

_____ fibers remain ipsilateral, _____ fibers cross over to the other side

internal limiting membrane

formed by the continuation of Muller cells with astrocytes

central meniscus of Kuhnt

thickened ILM at the center of the optic disc

border tissue of Elshnig

fibrous tissue that extends from sclera and fuses with Bruch’s membrane; separates choroid from RGC axons

border tissue of Jacoby

astrocytes surrounding the optic canal

intermediary tissue of Kuhnt

extension of the border tissue of Jacoby that separates RGC axons from outer retina

dura mater

outermost sheath, tough connective and elastic tissue

arachnoid mater

middle thin collagenous membrane, continuous with intracranial subarachnoid space and contains cerebrospinal fluid

pia mater

innermost sheath, loose vascular connective tissue, supplies blood and connective tissue septa into the nerve

external lamina cribosa

where does the myelination start on the optic nerve?

intraocular optic nerve

• part of the optic nerve

• 0.7-1mm

• prelaminar

• laminar

intraorbital optic nerve

• part of the optic nerve

• 30mm

• length exceeds the distance from globe to apex of orbit to allow full eye excursions without stretching the nerve

• contains nerve fiber, pia, septa, myelin, arachnoid mater, and dura mater

prelaminar intraocular optic nerve

• part of optic nerve

• 1.5-1.8mm wide

• contains nerve fiber

• no myelin

laminar intraocular optic nerve

• part of optic nerve

• 3mm wide

• contains nerve fiber, pia, and septa

• myelin begins in external part

lamina cribosa

sieve like structure of the optic nerve, postulated to act as a barrier to oligodendrocytes

intracanalicular optic nerve

• part of optic nerve

• 6-10mm

• passes through the optic canal

intracranial optic nerve

• part of optic nerve

• 10-16mm

• passes through brain

intraocular (prelaminar & laminar), intraorbital, intracanalicular, intracranial

what are the divisions of the optic nerve anterior to posterior

optic chiasm

• 15mm horizontally

• 8mm anterior to posterior

• lies w/in circle of willis

• located between the hypothalamus and pituitary gland

• in front of the infundibulum

  • location of fiber crossing

50%

what percentage of fibers from each eye cross to the contralateral side?

anteriorly

inferior nasal fibers cross more _________

posteriorly

superior nasal fibers cross more _________

optic tract

• 3.5mm high

• 5.1mm long

• extends from optic chiasm to LGN

90%

what percentage of fibers synapses at the LGN

10%

what percentage of fibers leaves the optic tract before reaching the LGN (go to suprachiasmatic nucleus and pretectal olivary nucleus)?

lateral geniculate nucleus

• located on dorsolateral aspect of the thalamus

• where retinal axons terminate

• sends most fibers to visual cortex

• layered structure

• regulates flow of visual info

magnocellular layers

• 2 layers of LGN

• large cell bodies

• layers 1 & 2

• sensitive to motion, contrast, and depth perception

parvocellular layers

• 4 layers of LGN

• medium sized cell bodies

• layers 3, 4, 5, 6

• sensitive to fine spatial resolution (fine detail) and color vision

koniocellular layers

• 6 layers of LGN

• small cell bodies

• sits between the other layers

• receives information from retina and superior colliculus

• modulates information from different pathways

1, 4, 6

contralateral fibers project to which layers of the LGN?

2, 3, 5

ipsilateral fibers project to which layers of the LGN?

retinotopic map

• point to point localization of the retina

• located in each layer of the LGN

• fibers carrying info from same site in visual field of each eye terminate in adjacent layers next to each other

• fibers leaving the LGN originating from neighboring areas will terminate in same place in visual cortex

optic radiations

• spreads out in a fan-shape

• upper and lower division

• carries info from both eyes

• ipsilateral temporal fibers with contralateral nasal fibers

• right side of brain = left side of vision

• left side of brain = right side of vision

inferior, superior

optic radiation fibers leaving the lateral aspect of the LGN carry info from the ________ retina which is the _______ visual field

Meyer’s loops

formed by fibers leaving the lateral aspect of the LGN that pass through the temporal lobe and loop around the tip of the temporal horn of lateral ventricle, then form inferior optic radiations

superior, inferior

fibers leaving the medial aspect of the LGN carry information from the ______ retina which is the ______ visual field

temporal

what lobe do lateral/inferior optic radiations pass through?

parietal

what lobe do medial/superior optic radiations pass through?

macula

_______ fibers run between the inferior and superior optic radiations

cuneus

upper division of optic radiations project to what gyrus?

lingual

lower division of optic radiations project to what gyrus?

cuneus

gyrus above the calcarine fissure

lingual

gyrus below the calcarine fissure

visual cortex

• divided into cuneus and lingual gyri

• 2mm thick

  • organized into horizontal and vertical layers

calcarine fissure

extends from parietooccipital sulcus to posterior pole, dividing visual cortex in an upper and lower portion

layer 4

• layer of V1

• receives input from LGN

• has further subdivided layers for magnocellular and parvocellular inputs

• neurons project to more superficial layers and other visual cortex areas

superior colliculus, frontal eye fields

what 2 key areas does V1 project to?

superior colliculus

structure that is important for visual orientation, foveation, saccadic eye movements

frontal eye fields

structure that is important for conjugate eye movements and the near pupillary response, voluntary & reflexive

1/3

what portion of V1 is on the surface of the occipital lobe?

posterior

fibers carrying information from the macula terminate in the most _______ part of the striate cortex

cuneus

the superior macula projects onto the ______ gyrus

lingual

the inferior macula projects onto the ______ gyrus

83%

central 30 degrees of vision is represented by ____ of V1

37%

central 15 degrees of vision is represented by ____ of V1

eye of origin, stimulus orientaiton

the vertical columns of V1 are organized by what 2 things?

ocular dominance columns

part of V1 formed by the alternation of contralateral and ipsilateral eye organization in the LGN

strabismus, uncorrected high refractive error, deprivation

what are some potential causes of amblyopia?

8-9y

what is the critical period for ocular dominance column development?

ocular dominance columns of the affected eye shrink

what occurs in V1 as a result of amblyopia

visual association areas

form concentric circular areas around occipital pole; provides further interpretation of visual information

dorsal stream

• key for spatial information interpretation

• determines where something is

• visually guided actions

• senses position, motion, and depth perception

ventral stream

• key for object recognition

• determines what something is

• senses size, color, shape

central retinal artery

what supplies blood to the inner retina?

choroidal vessels

what supplies blood to the outer retina?

circle of Zinn

what supplies blood to the optic disc?

pial vessels from pia mater

what supplies blood to the optic nerve?

anterior choroidal artery, middle cerebral artery

what supplies blood to the anterior optic radiations?

lateral striate artery (branch of middle cerebral)

what supplies blood to the middle optic radiations?

posterior cerebral artery, calcarine artery

what supplies blood to the posterior optic radiations?

posterior cerebral artery, calcarine artery, middle cerebral artery

what supplies blood to the visual cortex?

anopsia

defect in the visual field

homonymous

affecting the same part of VF in both eyes

hemianopsia

an anopsia affecting half of the VF of one eye

altitudinal

a hemianopsia affecting the superior ½ or inferior ½ of one eye’s VF

quadrantanopia

an anopsia affecting a quarter of the VF of one eye

complete

the entire quadrant or hemifield is affected

incomplete

quadrant or hemifield is partially affected

congruous

anopsia that is identical between 2 eyes

incongruous

anopsia that is different b/t the 2 eyes

binasal hemianopsia

incredibly rare visual field defect often due to poor testing instructions, can also result from congenital with idiopathic ocular or neurological causes

opposite sides

eyes positioned on ______________ of the head give the widest FOV possible

front

eyes positioned on ______ of the head maximize depth perception

60, 75, 60, 110

the human FOV is __ superiorly, __ inferiorly, __ nasally, and __ temporally

120

what is the binocular field range with both eyes

200-220

what is the total field of vision