Optics and Vision

What is the function of photoreceptors

Transducer that changes light energy into electrical energy

Function of the pupl

Control the amount of light entering the eye by dilating (Sympathetic) and constricting (parasympathetic)

What makes up the anterior chamber of the eye

Sclera, cornea, pupil + the muscles and ciliary bodies at move the eye

What makes up the posterior chamber

Vitreous humor

What does the vitreous humor do

Pushes the retina into a globe like shape; contains nutrients that support the eye

A defect of the vitreous humor will cause what defect

Retinal detachment; common in people that are extremely short sighted

What forms the optic nerve

The retina 

Which part of the eye DOES NOT have photoreceptor

Optic disc

Where do vessels come out from in the eye

Optic disc

A large blind spot can be caused by a problem in what structure

Optic disc englargement caused by increased intercranial pressure

Which areas of the eye has the highest visual acuity

Fovea and macula which surround it

What are the differences between rod and cone cells

Rod cells > cone cells; rod cells work better without light, cone cells work with light; rod cells do not produce color, cone cells do

What is the process in which photoreceptors receive energy to cause response

Interneuron synapse to excite bipolar cell and inhibit negative surroundings

What is the function of ON center ganglion cells

Creates action potential when light is focused on the CENTER of the receptive field

Function of OFF center ganglion cell

Create action potential when light is focused on the PERIPHERY of receptive field

Parasol cells

Large cells → Detect movement → Go to magnocellular layer of LGN

Midget cells

Small cells → Detect find stimuli and color → Go to parvocellular cells in LGN

How is the image that is seen in the retina altered

The image is inverted and reversed

Parts of the prechiasmatic region

Optic nerve, eye itself, pituitary gland beneath it

Parts of the post chiasmatic region

Cortexes of the brain, LGN, optic tract (optic radiation and Mayer’s loop)

What is the characteristic of pre-chiasmatic region defects

Respect the HORIZONTAL meridian

A patient presenting with this visual defect likely has a lesion where

Pre-chiasmatic region; lesion of the optic nerve or ocular media on the LEFT side

A patient presenting with this visual defect likely has a lesion where

Patient has a central scotoma → Problem with the optic nerve optic nerve on the LEFT side

A patient presenting with this visual defect likely has a lesion where

Chiasmatic region; lesion located in the optic chiasm

A patient with partial bitemporal hemianopia on the superior side has a lesion where

Sella region (pituitary) under the optic chiasm

A patient with partial bitemporal hemianopia on the inferior side has a lesion where

Suprasellar region (frontal lobe) above the optic chiasm

What is the characteristic of post chiasmatic and chiasmatic defects

Respects the VERTICAL meridian

A patient presenting with this visual defect has a lesion where

Junctional scotoma; caused by a lesion of the LEFT junction between the optic nerve and optic chiasm

Which nuclei does light information get sent to

Majority to LGN, some to brachium of superior tectum/colliculus

What is the pathway of the optic radiation

Goes to parietal lobe and terminates in the upper bank of the calcarine fissure; controls the lower visual quadrant of the CONTRALATERAL eye

What is the pathway of the Mayer’s loop

Goes to temporal lobe and terminates in the lower bank of the calcarine fissure; controls the upper visual quadrant of the CONTRALATERAL eye

Why do patients with MCA infarction have eye defects

The MCA does not supply the occipital lobe BUT does supply the optic radiation

Which area of the occipital lobe produces images that are the most clear

Area 1; inputs mainly from the fovea with the highest visual acuity

Parasol cell visual processing pathway

Movement → Magnocellular layer of LGN → 4ca → Dorsolateral parieto-occipital cortex

Midget cell visual processing pathway

Fine spatial information → Parvocellular layer of LGN → 4cb → Inferior occipitotemporal cortex

Color → Parvocellular layer of LGN → 2,3 → Inferior occipitotemporal cortex

Which lobe is the where and what pathway located

Where pathway = parietal lobe, what pathway = temporal lobe

Function of Layer 1

Made of mainly dendrite of neuron from deeper layer

Function of layer 2 and 3

Contain neurons that project to other areas

Function of layer 4

Main input area; LGN terminate here

Function of Layer 5

Project to subcortical structure that is not thalamus

Function of Layer 6

Project to thalamus

Right homonymous superior quadrantanopia caused by a lesion where

Inferior part of the head → Left temporal lobe → Mayer’s loop

Left homonymous inferior quadrantanopia

Superior part of the head → Right parietal lobe → Optic radiation

Right homonymous hemianopia with macular sparing caused by lesion where

PCA infarction which supplies the occipital lobe but not the part supplied by MCA

LGN lesion can be caused by stroke of which arteries

Posterior or anterior choroidal arteries

What is the pupillary response

Light → Superior colliculus/pretectal area → EWN (bilateral) → Ciliary ganglion → Pupillary constrictor muscle; enter CN II exit CN III

What is accomodation reflex

Eyes will convert and pupils constrict when an item is held close to the nose

What is the Marcus Gunn pupil/relative afferent pupillary defect

Lesion in optic nerve, retina or eye that causes decreased light sensitivity → pupil of affected eye will not constrict when exposed to light

Left CN III lesion responses

The affected eye will NOT constrict when exposed to light; consensual reflex will make the affected eye more dilated

Left Horner syndrome responses

The affected eye will have a dilation lag from light to dark; affected eye is more constricted than unaffected eye