Session 11 - Visual System

Define the Visual Field

The portion of space that can be viewed from the retina when the eye is fixated straight ahead

Define the Retinal Field

The portion of retina that alters its firing rate in response to a stimulus

What is the relationship between the visual and retinal fields

Reverse and inverted

How is the retina conceptually divided

Temporal and Nasal half

Superior and Inferior half

Order of sensory info received by eyes

Rods/Cones → Bipolar cells → Retinal ganglia cells

What forms CN II (Optic Nerve)

Axons of retinal ganglia cells

What is the light sensing part of the eye?

Retina

Describe cones

Found more in middle; photoreceptors for color vision and high visual acuity

Describe rods

Photoreceptors for black, white and gray vision; important for night vision

Do humans have more rods or cones in their eye?

More rods

What nucleus in the thalamus receives information from rods and cones?

Lateral geniculate body

The external world on the lateral side would be projected to which side of the right eye

Medial (inner portion) side of retina

Which visual field crosses the body in the optic chiasm

Nasal side

Is the Optic nerve part of the CNS or PNS?

CNS

What do optic tract fibers consist of?

Temporal retinal fibers of the ipsilateral eye and nasal retinal fibers of the contralateral eye

How much of the Lateral Geniculate Body’s input comes from the retina? Where does the rest of the input originate from?

10-20%; brainstem reticular formation and visual cortex

Describe the Third order neurons of the Visual system?

Project from the thalamus (LGB) as the optic radiation (geniculocalcarine tract) to the occipital lobe

What do the second order neurons of the visual system do?

Some cross midline (nasal retinal fibers) as they travel to synapse on the thalamus

Where do dorsal axons of third order neurons project to?

Almost directly to the occipital lobe

Where do ventral axons of third order neurons project to?

Anteriorly and downward as Meyer’s loop

Describe the dorsal pathway of higher visual processing

Primary visual cortex → Parieto-occipital cortex, where in the visual field an event occurred

Describe the ventral pathway of higher visual processing

Primary visual cortex → Occipito-temporal cortex, What the object in the visual field is

Damage to the Where pathway on a patient’s right side will lead to what?

Left sided hemineglect

What does the Direct retinohypothalamic projections influence

Entraining circadian rhythms in day-night cycle

What is presbyopia

Age related loss of power accommodation due to the lens hardening; results in ability to focus on near objects

What is age related macular deneration

Loss of central vision and acuity

Define Anisocoria

Pupillary size inequality

What is Hemianopsia

Visual field deficit of one-half of the visual field

What is quandrantanopsia?

Visual deficit of one quadrant of the visual field

What is bitemporal hemianopsia?

A lesion to the optic chiasm damages the crossing fibers from each nasal retina causing loss of peripheral vision

What is contralateral homonymous heminanopsia

Lesion of the mixed optic tract fibers

What is a transient ischemic attack of the retina called?

Amaurosis fugax

Describe Optic Neuritis

Inflammatory demyelinating disorder often related to multiple sclerosis

Symptoms of Optic Neuritis

Eye pain, decreased acuity, and impaired color vision, altered light reflex

Injuries to the What (ventral) pathways can lead to:

Visual agnosia: can perceive, but cannot understand meaning of what they see

Prosopagnosia: face blindness (damage to occipitotemporal cortex)