Functional Retinal Physiology

1. Functional Retinal Physiology
Nilufa Akter
B.Optom .2nd year
Institute of community ophthalmology

2. Functions of retinal layer
• RPE
• -Plays important role in photoreceptor
and recycling of vit-A.
• - plays phagocytic action
• -provides mechanical support to the
processes of photoreceptors

3. Photoreceptor
• ROD
• -provides peripheral of vision
• -helps in scotopic vision
• CON
-Provides in central vision
-helps in photopic vision and color
vision.

4. Inner neuclear layer
• BIPOLAR CELL
-transmits signal from photoreceptors to
the ganglion cell.
HORIZONTAL CELL
-helps integrate and regulate the inpute
from multiple photoreceptors cell.
-responsible for eyes to adjust to see well
both bright and dim light condition.

5. GANGLION CELL LAYER
has 2 types of cells
1.PERVO( midget) cell
-have small receptive field
-are sensitive to color .
2.MAGNO(parasol ) cell
-large receptive field
-sensitive to visual motion
-participate very little in color perception.

7. MACULA
-Provides 15 degree of visual field
-helps in photopic and color vision
-provides central high resolution of vision
( main 2 function :
-visual acuity
-color vision ).

8. RETINAL PHYSIOLOGY
Vision ?
Receptor ?
Electrophysiology:
Extracellular recording: a microelectode placed in
close proximity to a neuron records action potentials
generated by the neuron.
Intracellula recording : microelectode pierces the
membrane of a neuron and records the membrane
potential. This technique technically more challanging than
extracellular recoding

9. RETINAL NEURONS
3 TYPES OF NEURON

10. Cont..
• A direct 3 neuron chain
• -from photoreceptor to bipolar to
ganglion cell- is the major route of
information flow from the light source to
the optic nerve.
• The horizontal and amacrine cells are
primary responsible for lateral
interactions.

11. Cont…

12. • Retinal receptive fields
• The part of the retina that needs to be
stimulated to elicit action potentials from a
ganglion cell is the receptive field.
• Retinal receptive fields are small and
concentric and correspond to the part of
the world that the cell can “SEE’.

13. Photoreceptors
• There are 2types of photoreceptor: rods
and cones.
• These differences are the basis of the
Duplex Theory of Vision.

14. Duplex theory of Vision
• Rods contain a single visual pigment
(rhodopsin),sensitive to blue-green light.
• Cons contain visual pigment
(iodopsin),sensitive to short ,medium or
long wavelengths of light,permitting to
color perception.

16. Duplex theory of vision
• Rods are very sensitive to light and are
responsible for scotopic vision,where
cones are much less sensitive to light and
are responsible for photopic vision.
• Both photoreceptors are active during
mesopic vision.

17. Cont..

18. Duplex theory of vision
• Rods and cones are unevenly distributed.
• The density of rods exceeds that of cones
, except that of the fovea where the cone
density is highest and it’s central region
(Fovea) is rod-free.

19. Cont..

20. ROD SYSTEM CON SYSTEM
ACROMATIC
HIGH CONVERGENCE
HIGH LIGHT SENSITIVITY
LOW VISUAL ACUITY
CROMATIC
LOW CONVERGENCE
LOW LIGHT SENSITIVITY
HIGH VISUAL ACUITY

21. BIPOLAR CELL
Receptive field of 2 different types of bipolar
cell.
1.ON- CENTER bipolar cell :
-tends to form a specialized synapse (TRIAD),
at their synapse with photoreceptors. At this
specialized synapse,a bipolar cell and 2
horizontal cells form an invagination within
photoreceptor.

23. Cont..
2. OFF CENTER bipolar cell
-bordered by an excitatory on-
surround. Synaptic arrangement
associated with this off-center bipolar
cell is a conventional flat synapse.

24. Cont..
Under dark conditions, photoreceptors
continuously release neurotransmitter.
Under light condition, phoreceptors
progressibely decrease neurotransmitter.

25. Cont..
That’s for on-center bipolar cells
,glutamate is inhibitory .causes a relative
excitation (depolarization) of the bipolar
cell.
For off-center bipolar cells ,same
neurotransmitter has the opposite effect.

26. Ganglion cell
1.Light falling on the receptor field center
excites the cell
- Increase frequency of action potential
2.Light falling on the receptive field
surroud inhibit the cell
-produces reduce in the frequency of
action potentials .

27. cont..
• (other ganglion cells have the reverse
arrangement).
.Light falling on the receptive field center
–produces a decrease in the action
potential .
- where as light falling on the surround –
produces an increase in frequency.

29. References
1 . Visual perception
2.Anatomy and physiology of eye
by A.K. Khurana
3.Internet

30. THANKS to all