This lecture summary covers retinal physiology and visual perception. It will discuss retinal changes from light exposure, electroretinography, color vision theories and tests, and visual field. By the end, students should be able to identify retinal changes from light, recognize color vision physiology, and identify the visual field.

1. Dr. Mai Mohammed Hasan
Porf. Of medical physiology.
Dr. Nanees El-Malkey
Lecturer of medical physiology

2. By the end of this lecture the students are expected to:
 Identify retinal changes on exposure to light .
 Recognize the physiology of color vision.
 Identify visual field

3. Retinal changes on exposure to light
1. Structural changes:
• spread of melanin in pigmented cell layer
2. Chemical changes
• Degradation of visual pigment
3. Electerical changes:
• Recorded by electro-retino-graph

4. Electro-retino gram
„Electroretinogram (ERG) is the record of electrical activity in
retina When light rays stimulate it.
receptors
ganglion cells
Pigmented epithelum
repolarization

5. ELECTRORETINOGRAM
• ‘A’, ‘B’ and ‘C’ waves occur when light stimulus falls on retina.
‘D’ wave occurs when light stimulus is stopped.
• ‘A’ wave: arises from rods and cones.
• ‘B’ wave: arises from ganglion cells
• ‘C’ wave: arises from pigment epithelial layer
• ‘D’ wave: arises from receptor repolarization.

6. Purkinje phenomenon
: the yellow part of the spectrum
appears as the brightest i.e. it has the lowest threshold ability
to stimulate retina.
: this high sensitivity is shifted from yellow
to blue green which will have the maximal luminosity.

8. COLOR VISION
Color vision is the sense of discrimination of the wave lengths that
constitute the visible spectrum.
Important definitions about color vision: -
1- Hue is the actual nature of the color i.e. red, yellow this depends
upon the wavelength of the color.
2- Saturation is the degree of purity of the color from the white
color.
3-Brightness or luminosity is the degree of intensity of the rays that
are reflected from colored object.

9. 4-Primary colors
when their wave lengths are mixed in an equal proportion
and stimulate the retina can give the sensation of white color.
5-Complementary colors for any color their is a
complementary color, when their wave lengths are mixed
together properly by certain proportion can give the
sensation of white color.
6- Black is that sensation which produced by complete
absence of light .

11. Theories of color vision
A-Trichromatic theory (Young - Helmholtz theory)
1. There are 3 types of cones each one is maximally sensitive to
one of the primary color.
First cone contains pigment that is maximally sensitive to blue
violet part of the spectrum
Second cone contains pigment that is maximally sensitive to
green portion of spectrum,
Third cone contains pigment that is maximally sensitive to the
red portion of the spectrum.

12. Each color stimulates the 3 cones in unequal
manner
The frequency and intensity of impulses
reaching the visual cortex are different

13. B-Neural theory of color vision
states that perception of colors is mainly a function of group of
neural cells starts at small ganglion cells in the retina which are
stimulated by certain color .
Types of ganglion cells :
• W (40%) cells receive most of their excitation from Rods,.
• X cells (55%) transmit fine details of visual images,
responsible for color vision. They are connected to P Cells
of lateral geniculate body.
• Y cells (5%) respond to rapid changes in visual images, they
are connected to M cells of lateral geniculate body

14. Color Blindness
Color blindness is most commonly hereditary disorder (recessive
sex - linked)
A- Trichromate:
The patient has the 3 cones but one of them is weak.
B-Dichromate :
One cone is totally absent and the other two are present. Thus
patient cannot perceive a certain color
Monchromate:
the patient have only one cone system and matches the different
colors as various degrees this color.

15. Tests of color vision:
1-Colour matching test: patient is given group of colored tufted
wool and is asked to separate similar colored pieces together.
2- Edridge - Green lantern test :-in which the person has to
identify the color of a small illuminated area the size of which can
be varied.

16. 3-Ishihara's chart test:
these are colored printed figures and each figure is printed by
many different colored small circles on a background of
colored circles also.

17. After Image Phenomena
These are visual sensations which can be detected after removal of
the primary visual stimuli.
1. Positive after image: When a person looks to specially a bright
object for a short time then he closes his eyes, the image of that
object, still appear in front of him for many seconds.
2. Negative after image: If a person looks to certain bright
colored picture or to a scene for at least 30 seconds then he turns
his eyes to white surface, the picture will remain in front of him for
sometime but the black parts in the picture will appear white and
the white parts will appear black.

18. Flickers: can be defined as the ability of the eye to perceive
successive visual stimuli as an intermittent light sensation.
The point at which flicker just disappear is known as the
critical fusion frequency (CFF), when the flicker moves at a
speed of 25 times / second .

19. refers to the total area in the world which can be seen by single ey
It is not circular as
 It is cut medially by the nose (60 degree)
 Upward by the supraorbital ridges (50 degree)
 Downwards by the checks (80 degree)
 Laterally extended up to (90 degree)
The visual field

20. Visual field

21. How the Test visual field:
1. Confrontation test
2. perimertry

22. Importance of determination of the visual field:
1. It greatly helps in localization of the sites of lesions in the
visual pathway.
2. A blind spot in the visual field is called "Scotoma".
3. It helps in diagnosis of some retinal diseases

23. Thank you