1. Physiology of Vision
Retina
Dr. Sumera Gul

2. Learning Objectives
At the end of the lecture the students should be able to:
Explain the physiological anatomy of retina
Explain the importance of each layer of retina
Discuss the fovea and its importance
Explain the importance of melanin in the pigmented layer

3. Review of Previous Lecture

4. Reduced Eye
In the reduced eye, a single refractive surface is considered to exist,
Its central point 17 millimeters in front of the retina
total refractive power of 59 diopters when the lens is accommodated for distant vision.
About two thirds of the 59 diopters of refractive power of the eye is provided by the anterior surface of the cornea

8. This ability to determine distance is called depth perception

9. A person normally perceives distance by three main means:
(1) the sizes of the images of known objects on the retina
(2) the phenomenon of moving parallax,
(3) the phenomenon of stereopsis.

10. Out flow of Aqueous Humor
through the pupil into the anterior chamber of the eye into the angle between the cornea and the iris through a meshwork of trabeculae canal of Schlemm extraocular veins

12. Vitreous Humor
Vitreous Humor is the clear gelatinous fluid in the posterior chamber (back 2/3) of the eye.
The outer surface of the Vitreous humor is attached to the retina.
Vitreous body, is a gelatinous mass held together by a fine fibrillar network composed primarily of greatly elongated proteoglycan molecules.
Both water and dissolved substances can diffuse slowly in the vitreous humor, but there is little flow of fluid.

13. Retina

14. Retina
Light sensitive
Contains rods and cones

16. Layers of Retina From the outside to the inside as follows:
Pigmented layer,
Layer of rods and cones projecting to the pigment
Outer nuclear layer containing the cell bodies of the rods and cones,
Outer plexiform layer
Inner nuclear layer,
Inner plexiform layer,
Ganglionic layer,
Layer of optic nerve fibers,
Inner limiting membrane.

18. Fovea

19. Fovea 1 square mm area in center of retina Central fovea is 0.3 mm
Central fovea is composed almost entirely of cones with a diameter of only 1.5 micrometers.
Long and slender cones in central fovea
All the layers are displaced to the sides

21. Rods and Cones 100 million rods and 3 million cones in each retina
In general, the rods are narrower and longer than the cones
In the peripheral portions of the retina, the rods are 2 to 5 micrometers in diameter,
whereas the cones are 5 to 8 micrometers in diameter

22. Functional Segment of Rod and Cones
(1) the outer segment,
(2) the inner segment,
(3) the nucleus,
(4) the synaptic body.

23. The light-sensitive photochemical is found in the outer segment.
In the case of the rods, this photochemical is rhodopsin
In the cones, it is one of three “color” photochemicals, usually called simply color pigments,
conjugated proteins.

24. In the outer segments of the rods and cones are large numbers of discs.
Each disc is actually an infolded shelf of cell membrane.
There are as many as 1000 discs in each rod or cone.

25. Functions of
Inner segment
Nucleus
Synaptic Body

26. Pigmented Layer Pigmented layer has melanin
Melanin in the pigment layer prevents light reflection throughout the globe of the eyeball
Makes the image clear
Stores large quantities of Vitamin A

27. Absence of melanin in Albinos
When they enter a bright room
Light is reflected in many directions after impinging retina
Visual acuity is usually 20/100 to
20/200

29. Questions?