slide1 n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Dr W Kolbinger, Visual System (2009) PowerPoint Presentation
Download Presentation
Dr W Kolbinger, Visual System (2009)

Loading in 2 Seconds...

play fullscreen
1 / 58

Dr W Kolbinger, Visual System (2009) - PowerPoint PPT Presentation


  • 153 Views
  • Uploaded on

Visual System. Lecture Outline. Structures of the Eye Refraction and Image Formation Visual Acuity Autonomic Control of Pupil Diameter Clinical Correlations . 1. 1. Dr W Kolbinger, Visual System (2009). Anatomic Considerations. The Ocular Fundus. Optic disc. Fovea. Macula.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Dr W Kolbinger, Visual System (2009)' - nizana


Download Now An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
slide1

Visual System

Lecture Outline

  • Structures of the Eye
  • Refraction and Image Formation
  • Visual Acuity
  • Autonomic Control of Pupil Diameter
  • Clinical Correlations

1

1

Dr W Kolbinger, Visual System (2009)

slide3

The Ocular Fundus

Optic

disc

Fovea

Macula

The optic disc region itself only contains axons of retinal ganglion cells, the output elements of the retina, but it lacks photoreceptors. As a consequence, the optic disc is responsible for the blind spot, a region inside the boundaries of the visual field, where we don’t receive

visual information.

3

slide4

Optics of the Eye

Convex Lens Focuses Light Rays

Concave Lens Diverges Light Rays

Measurement of the Refractive

Power of a Lens—“Diopter”

The refractive power in diopters of a

convex lens is equal to 1 meter divided by its focal

length.

slide5

Optics of the Eye

Cornea refractive power: 42 D

Flat lens refractive power: 13 D

Rounded lens refractive power: 26 D

Plasticity: 13 D

5

slide6

Accommodation

Flat lens refractive power: 13 D

  • Far Vision

Ciliary muscle relaxed

Suspensory ligaments tightened

Focus on the Retina

Accommodation Adjusts the Refractive Power of the Eye

6

slide7

Accommodation

Rounded lens refractive power: 26 D

  • Near Vision

Ciliary muscle constricted

Suspensory ligaments floppy

Focus on the Retina

7

slide8

Presbyopia

Flat lens

  • Near Vision

The variability of the refractive power of the lens between far vision (13 D)

and near vision (26 D) is called refractive plasticity.

Unfortunately,

the lens looses its elasticity

during aging, thereby

reducing the ability to focus

on near objects, a condition

called presbyopia.

Blurred picture on the Retina

8

slide9

Emmetropia (Normal Vision).

Cataracts

“Cataracts” are an especially common eye abnormality

that occurs mainly in older people. A cataract is a cloudy

or opaque area or areas in the lens

slide10

Visual acuity is the ability to distinguish between two nearby points. Visual acuity is high when the two-point discrimination threshold is low (high spatial resolution).

What is Visual Acuity?

  • Two point discrimination of the visual system
  • Normal: an angle of 5 minutes of a degree
  • highly dependent on the densities of retinal photoreceptors

visual acuity also depends on a proper function of the optical apparatus of the eye, including accommodation. When the optical apparatus fails to produce a focused (sharp) picture on the retina, the objects in the visual field appear “blurry”.

5 ‘

Far vision

Near vision

10

slide11

Neurological Examination of Visual Acuity

20

800

Distance

equivalents

20

20

  • Eye charts and near cards

Patient

Normal

11

slide13

RETINA-

Receptor and

Neural Function of the Retina

  • Photoreceptors and Phototransduction
  • Color Vision
  • Processing of Visual Information
  • Clinical Correlations

13

13

Dr W Kolbinger, The Retina (2009)

slide14

Layers of the Retina

Photoreceptor

layer

slide15

Photoreceptors

Outer segment

  • -Visual pigment

Inner segment

  • Synapses with bipolar
  • and horizontal cells

rhodopsin

Disks

Nucleus

Synaptic

ending

Rods are highly sensitive to light and enable us to see under low intensity light

conditions (at night).

Cones(3) are less

sensitive to light.

enable

us to see colors.

glutamate

Rod

Cone

15

slide16

Convergence is high in the rod

  • system. It is low in the cone system. As a consequence, spatial resolution (visual acuity) is better in bright light, when the cone system is active.
  • Rods and cones are not evenly distributed over the whole retina and the fovea only contains cones, but no rods. As a consequence, there is no central vision under dim light conditions
  • Night Blindness
slide17

The Visual Pigment

Rhodopsinis the visual

pigment of rods. It consists

of two components:

· Opsin, a protein

which is synthesized

in the photoreceptor

(cones have different

types of opsins).

· Retinal, a

chromophore, is the

light absorbing

compound or the

visual pigment. It is

derived from Vitamin

A and is the chromophore of the visual pigment in rods and cones. Vitamin A is synthesized from beta-carotene contained in our food.

slide18

Photoreception -The Dark Current

GDP

,

cGMP

Na+

G protein

(Transducin)

cGMP-gated channel

  • Visual pigment-Rhodopsin

cGMPphosphodiesterase

18

Dr W Kolbinger, The Retina (2009)

slide19

Phototransduction

GTP

cGMP

Na+

5’GMP

cGMPphosphodiesterase

Light

19

Dr W Kolbinger, The Retina (2009)

slide20

Color Vision Is Based on Comparison of Activity of

Three Cone Types

Visible Light Is Part of the Electromagnetic Spectrum

The visible part of the spectrum is characterized by

wavelengths ranging from 400 to 700 nm (nanometers).

20

slide21

Monochromatic Light: Colors of a Rainbow

21

Dr W Kolbinger, The Retina (2009)

slide22

Three Types of Cones Have Different Spectral Sensitivities

The human retina contains

three types of cones:

· S (short wavelength

sensitive) cones, also

called “blue” cones,

with a maximum

sensitivity at 430 nm

· M (medium

wavelength

sensitive) cones, also

called “green” cones,

with a maximum

sensitivity of 530 nm

· L (long wavelength

sensitive) cones, also

called “red” cones, with a maximum sensitivity of 560 nm.

slide23

Stimulation of Cones by Monochromatic Light

Log relative sensitivity

450 nm

monochromatic

light

400

500

600

700

Wavelength (nm)

23

slide24

Stimulation of Cones by Monochromatic Light

600 nm

monochromatic

light

Log relative sensitivity

400

500

600

700

Wavelength (nm)

24

slide25

Red-Green Color Blindness

Normal

Protanopia

Deuteranopia

Individuals affected by red-green color blindness can no longer distinguish

certain red colors from certain green colors.

25

slide26

pseudo-isochromatic color

plates like the one on the

right are presented to the

patient.

The numbers

embedded in the pattern of

colored dots can be

distinguished by individuals

with a fully intact color

vision.

Dichromats, who are weak

in red-green discrimination,

have difficulties in

identifying the numbers on all plates

slide27

Visual Pathways

Lecture Outline

  • The Visual Field
  • Passage of Light
  • Neuronal Pathways
  • The Primary Visual Cortex
  • Parallel Pathways for Depth, Motion, Form and Color
  • Clinical Correlations

27

slide28

The Visual Field

Total amount of space we can see with this eye, when the eye is fixed straight ahead, pointing towards the center of the visual field (point of fixation).

The extension of the visual field is

measured in degrees of maximum deviation from this straight line in all directions.

For right eye-

- left visual hemifield/nasal

- right visual hemifield/temporal

The vertical axis together with the horizontal axis divide the visual field into Four quadrants:-

superior left, superior right,

inferior left and inferior right

quadrant of the visual field.

slide29

Projections of the Visual Field on the Retina

The four quadrants of the visual field are projected onto the retina.

The superior half of the visual field is projected to the inferior half of the retina, and vice versa.

The left half of the visual field is projected on the right half of the retina, and vice versa.

The nasal visual hemifieldof the right eye 

temporal hemiretinaof the right eye.

temporal visual hemifield of the right eye nasal hemiretina of the right eye

visual field defects e.g

“bitemporalhemianopia``

29

slide30

Chief Complaint: Headache and Nausea

History:

A 76 year old retired college dean presents with recurrent headaches over the past four

years. Her headaches have significantly increased in duration and intensity over the

past few months. She also reports episodes of nausea and vomiting. Her husband

adds that she has recently developed difficulties with comprehending spoken language.

The patient experiences uncoordinated movements of the right hand. She stopped

drinking and smoking cigarettes during her first pregnancy, when she was 27.

General Examination:

76 year old female in no acute distress. No significant cardiac, respiratory, or

abdominal abnormalities. Vital signs unremarkable.

Neurological Examination:

The patient can speak fluently, but the content is frequently incomprehensible to the

listener. Her ability to read and write is markedly reduced (dyslexia and dysgraphia

respectively.) The patient can not identify a hairbrush, but was able to demonstrate its

use. Numbness was detected in the right lower face and right hand. In addition, the

examination of the right hand revealed impaired 2-pt discrimination, joint position, and

fine touch.

Motor examination and reflex testing of the lower extremities were unremarkable.

Marked weakness of right arm flexion and extension was present, as well as elevated

right biceps and brachioradialis reflexes.

slide33

Neuronal Pathways, From the Retina Onwards

relay station between the retina and the primary visual cortex.

 circadian clock

 afferent limb of the pupillary light reflex

contribute to eye movements

slide34

The Primary Visual Cortex V1

Occipital

pole

Area 17

34

slide35

The Primary Visual Cortex V1

Calcarine

sulcus

Parieto-occipital

sulcus

Area 17

35

slide36

Neuronal Pathways, From the Retina Onwards

  • Fibers originating in nasal hemiretina cross over at the optic chiasm, fibers
  • originating in the temporal hemiretina don’t.
  • LGN fibers carrying sensory information of the superior half of the visual field follow the temporal radiation pathway, fibers originating in the inferior half of the visual field follow the parietal radiation pathway.

Example1- the axons originating in the right LGN which are carrying

sensory information from the superior left quadrant of the visual field, use the

temporal radiation and synapse in the inferior portion (below the calcarine

sulcus) of the primary visual cortex (V1).

Example 2 - ?

slide37

Retinotopic Organization of V1

Visual field

left eye

Visual field

right eye

Left

hemisphere

Right

hemisphere

37

slide38

Neurological Examination of the Visual Fields

The visual pathways are commonly tested in neurological examinations and they

have high localizing value.

Loss of vision is clinically tested in each quadrant of the visual field in a

“confrontation visual field test”. In this test, each eye is tested separately by

having the patient look straight at the examiners eye, while standing in double

arms length distance. While the examiner occludes his left eye with one hand,

the patient occludes his right eye (and vice versa). Then the examiner moves his

other hand, with one (or more) of his fingers stretched out, gradually from the

periphery to the center of the visual field, to determine where it is first seen.

Assuming the examiner has normal vision, the patient should see the

appearance of the hand at the same time as the examiner. He should also be

able to tell the number of fingers stretched.

slide39

Sparing of the Macula

When the macula is not included, Macular sparing is often associated with vascular lesions involving the

posterior cerebral artery or its branches,blood supply of the occipital pole of the cerebbral cortex (the area representing macular vision) may stay intact, due to sufficient blood flow

from the middle cerebral artery.

slide40

Eye Movements

Lecture Outline

  • Types of Eye Movements
  • Extraocular Muscles, their Innervation and Control
  • Saccadic Eye Movements
  • Clinical Correlations

40

slide41

Types of Eye Movements

  • Conjugate Eye Movements
      • Saccadic eye movements (and gaze)
      • Vestibulo-ocular reflex
      • Optokinetic reflex (and smooth pursuit)
  • Non-Conjugate Eye Movements
      • Vergence (convergence and divergence)

41

slide43

Neurological Examination of Eye Movements

Extraocular movements are examined using the “H-test”.

slide44

III

IV

III

IV

VI

VI

  • Cranial Nerve Nuclei and Control Units in the Brainstem

Midbrain

nucleus of MLF-control of vertical eye movements

CN III

CN IV

Cerebellum

CN VI

vestibulo-cerebellum (flocculo-nodular lobe)-optokinetic eye movements

pontineparamedian

reticular formation (PPRF)/

horizontal gaze center.

Medulla

Pons

44

slide45

Cortical Control Units

Frontal eye field

(Area 8)

Parieto-occipital

eye field

planning and initiation

of eye movements-

saccadic eye movements

dorsal (parietal)

pathway for motion (and depth) led up exactly into this area.-optokinetic movements and smooth pursuit

45

slide46

Saccadic Eye Movements to the Right

Frontal eye field

Right

Left

PPRF

Left MLF

46

slide47

Diplopia

Visual field

of the left eye

Visual field

of the

right eye

Fovea

Fovea

47

slide48

InternuclearOphthalmoplegia

Internuclear

ophthalmoplegia is based

on a lesion of the medial

longitudinal fasciculus

(MLF), which prevents

adduction of the eye on the

side of the lesion during

attempted lateral gaze.

In the example on the right

shows a patient with a

lesion of the left MLF

(adduction of the left eye is

impaired).

Convergence does not involve the MLF and is not affected by the lesion. EXAMPLE- Multiple Sclerosis.

slide49

Internuclear Ophthalmoplegia

Prevents adduction of the right eye

X

MLF lesion on the right

Right

Left

49

slide50

Chief Complaint: Nausea and Vomiting

History:

An 8 year old boy visited his pediatrician, and his mother reported that he was in good health until about two weeks ago. He describes that his initial symptoms include a mild bifrontal headache, which has become progressively worse. During the last few days, he developed nausea and bouts of occasional projectile vomiting accompanying the headaches. Furthermore, he recently noticed that he has tremendous difficulty when walking down the stairs from his bedroom to the kitchen and reported difficulties in sleeping. No family history of abnormal development or mental retardation exists. He has two perfectly healthy younger brothers.

General Examination:

This 8 year boy presents with pronounced pubic hair growth, a low pitched voice,

enlarged genitalia, and acne on his forehead. Cardiac and respiratory examinations

were unremarkable.

Neurological Examination:

Patient is alert and oriented x 3. No receptive or expressive aphasias were noted.

Pupillary light reflex was intact bilaterally. Both the left and right optic discs appeared more pale than normal. Downward gaze (while the eyes were adducted) was impaired bilaterally.

slide51

MLF lesion + PPRF lesion = 1 ½ Syndrome

Prevents conjugate gaze of both eyes to the right

X

X

PPRF lesion on the right

Right

Left

Prevents adduction of the right eye

X

MLF lesion on the right

51

slide52

The Basics of Hair Cell Morphology

Endolymph:

High in Potassium

Apex of Hair Cell

with Cilia

Base of Hair Cell

with Synapse on

Afferent Fiber

52

slide53

Cells of the Retina

Photoreceptor

Horizontal cell

Bipolar cell

Amacrine cell

Ganglion cell

53

slide54

Some Bipolar Cells are Activated by Light, Others by Darkness

There are two basic types of retinal bipolar cells. Some bipolar cells are activated

(depolarized) when the light is ON. They are therefore called ON bipolar cells.

Other bipolar cells are activated (depolarized) during darkness, when the light is

OFF. They are therefore called OFF bipolar cells.

Light Depolarizes ON Center Bipolar Cells

Photoreceptor hyperpolarizes during light ON

Sign-converting

synapse:

metabotropic

glutamate receptor

On Center

Bipolar Cell

depolarizes

during light ON

54

slide55

Parallel Pathways

Specialized for Visual

Information of Depth, Motion, Form and Color

Where?

What?

Dorsal (parietal)

pathway

Depth

Motion

LGN

Magno

Parvo

Ventral (inferior temporal)

pathway

Color

Form

55

slide56

Light Hyperpolarizes OFF Center Bipolar Cells

Photoreceptor hyperpolarizes during light ON

Sign-conserving

synapse:

ionotropic

glutamate receptor

OFF Center

Bipolar Cell

hyperpolarizes

during light ON

56