1. Physiology of Vision (1)
بسم الله الرحمن الرحيم
Physiology of Vision (1)
Dr. Abdelrahman Mustafa
Department Basic Medical Sciences
Division of Physiology
Faculty of Medicine
Almaarefa Colleges

2. Learning Objecetives By the end of this lecture, You should able to
Describe the functional anatomy of the eye
Describe the refraction of light as it passes through the eye to the retina, identifying the eye components that account for refraction of light at the center of the eye and away from the center.
Describe the process of accommodation, contrasting the refraction of light by the lens in near vision and in far vision.
Describe the refractive deficits that account for myopia, hypermetropia,, and astigmatism, and their correction by eyeglasses

3. Important of vision Definition
Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye
Important of vision
Learning through written speech
Maintenance of equilibrium

4. Anatomy of the Eyeball Eye ball diameter =2.5cm Consist of 3 layers
1.Sclera(outer layer )
Constitute the posterior 5/6 of the outer layer of the eye
It is formed of connective tissue, It is Opaque Structure (normally it is whitish)
SO does not transmit light rays
Modified interiorly to become transparent and more curved to form the cornea
2.Choroid(middle layer)
it contain many blood vessels and pigmented
it modified anteriority to form the ciliary body and iris which is the colored part in front of the lens
The iris has central round opening called the pupil
3.Retina(inner layer )
It Contains the visual receptors [rods and cones ] that respond to the light
Characterized by presence of an area that lacks visual receptors called the optic disc or the blind spot FOVEA CENTRALIS

5. Con THE CILLIARY BODY:- Is circular structure consist of 3 parts
A) Cilliary gland
B) Cilliary muscles: inserted near to corneoscleral junction
C) Suspensory ligaments :Joined to lens ligiment
It participates in accommodation , produces the aqueous humor and maintain the lens zonules
THE IRIS :-
The pigmented part of the eye
It contain 2 types of muscles that adjust the diameter of the pupil to control the amount of light reaching the retina
These muscles are :
a. dilator pupillae: contains radial muscle fibers that cause pupillary dilatation in response to symp. Stimulation
b. sphinctor pupillae : contains concentric muscle fibers that cause pupillary constriction in response to parasymp. Stimulation
Lens
Is a biconvex, crystallins,and transparent structure bind suspensory ligaments for focusing light
CILNICAL :Opacity of the lens: Cataract

6. Con
THE RETINA :-
Contains the visual receptors [rods and cones ] that respond to the light
The out put from the retina in form of AP passes through the optic nerve and other structure of the visual pathway to give perception of light
Characterized by presence of an area that lacks visual receptors called the optic disc or the blind spot Temporal to the optic disc there is another area known as the macula
At the center of the macula is the fovea centralis , the area with the highest visual acuity [contain cones only
nervous layers of the retina
(1) photoreceptor layer
(a) rods
(b) cones
(2) bipolar layer
(a) bipolar cells
(b) amacrine cells
(c) horizontal cells
(3) ganglion cell layer

7. Cavities of the Eye 1. anterior cavity a. posterior chamber
b. anterior chamber
c. aqueous humor
e. canals of Schlemm
2. posterior cavity
a. vitreous humor

8. Con
AQUEOUS HUMOR :-
The clear liquid that fills the space between the lens and the cornea
Provides the nutrients to the a vascular parts of the eye [the lens and cornea ] and eliminates their waste products
Its pressure maintains the normal convexity of the cornea
Increased production or decreased its drainage leads to increased intraocular CLINICAL: Glucoma
VITREOUS HUMOUR :-
The clear gelatinous material that fill the space between the lens and the retina
Consist of water , salts , sugars and collagen fibers
It provide structural support to the eyeball and allows passage of light rays to the retina
CANALS OF SCHLEMM: for venous drainage

9. Muscles of Eye Movement
Lateral rectus–moves the eye
outward, away from the nose
Medial rectus–moves the eye inward, toward the nose
Superior rectus–moves the eye upward and slightly outward
Inferior rectus–moves the eye downward and slightly inward
Superior oblique–moves the eye inward and downward
Inferior oblique–moves the eye outward and upward

10. Nerve supply
The extraocular muscles are supplied by third, fourth
and sixth cranial nerves.
The third cranial nerve
(Oculomotor) supplies the superior, medial and inferior recti and inferior oblique muscles.
The fourth cranial nerve (Trochlear) supplies the superior oblique and
The sixth nerve (Abducent) supplies the lateral rectus muscle.
CLINICAL : Paralysis of These Nerve= Squint

11. The formation of images on the retina involves three processes:
1. refraction of light rays
2. accommodation of the lens
3. constriction of the pupil

12. Con
Refraction is the change in direction of a wave due to a change in its speed when a ray of light crosses from one material to another of different density
Refractive media of the eye :-
There are 4 refractive media in the eye :
The cornea its refractive
The aqueous humour
The crystalline lens
The vitreous humour

13. Accomodation Accommodation :
Is the process by which the optical system of the eye is adjusted to see the near objects clearly
Light rays are refracted by the cornea and lens to be focused on the retina

14. Con Accommodation : On looking to a distant object [more than 6 meter]
The light rays are coming in parallel
Ciliary muscle is relaxed and the lens is flat
The rays are brought to a focus on the retina
On looking to a near object [close than 6meter ] :
Light rays are diverging
They will be focused behind the retina , this is prevented by the near response which consist of :
Increased convexity of the lens [accommodation ]
Convergence of visual axis
Pupillary constriction

15. From the Eye Sight website of student Kyle Keenan at Steton Hall University.

16. Constriction of the Pupil
1. part of accommodation reflex
2. limits peripheral light

17. The iris constricts or dilates to adjust size of the pupil.
You are looking at an anterior view of the iris, the colored part of the eye that you can see from the outside of the eye. * The function of the iris is to constrict or dilate to adjust the size of the pupil which is the opening in the center of the iris. * Light must pass through the pupil to enter the posterior segment of the eye where the receptors are located. * The size of the pupil, determines how much light can enter the eye. *
The iris constricts or dilates to adjust size of the pupil.
The pupil allows light to enter the posterior segment of the eye.

18. Convergence of the Eyes

19. ERRORS OF REFRACTION Lens: Refracts (bends) light
Focuses precise image on the retina (fovea) through accommodation (changing thickness)
The lens is a transparent, flexible, biconcave structure which is held in place by the suspensory ligaments. * Its primary job is to refract light passing through it so that an image may be focused on the fovea centralis. * Because the lens is flexible, tension exerted by the ciliary muscles through the suspensory ligaments changes the thickness of the lens. * This adjustment in the thickness of the lens to focus images precisely on the fovea is called accommodation.

20. Myopia Eyeball too long Distant objects focused in front of retina
Cannot see far
Image striking retina is blurred
Myopia * is a condition where the eyeball is longer than normal. As a result, the image is focused in front of the fovea rather than directly on it. * Thus the actual image striking the fovea is not in sharp focus. * * Individuals who are near sighted can see nearby objects clearly because the lens can accommodate sufficiently to adjust the focal point. That is not the case for things farther away. *
This condition may be corrected by using glasses which have concave lenses* which are ground precisely to correct the problem. * The condition may also be corrected by laser surgery which flattens the cornea to adjust the focal point for distant objects. *
Correction:
Concave lens or
laser surgery to slightly flatten the cornea

21. Hypermetropia Eyeball too short, lens too thin or too stiff.
Nearby objects are focused behind retina.
Needs some accommodation .
Image striking the fovea is blurred.
Hyperopia or farsightedness * is due to the eye being too short, the lens too thin, or the lens being too stiff to focus the image precisely on the fovea. * As a result, the image of a nearby object is focused behind the fovea * causing the image striking the fovea to be blurry. * * Farsighted individuals can see distant objects clearly.
This condition * may be corrected by using a convex lens * to bring the image of nearby objects forward far enough * for the image to be focused precisely on the fovea. *
Correction:
Convex lens

22. Astigmatism Irregular Curvature in parts of the cornea or lens
Causes blurry image
Irregular curvatures of different parts of the lens or the cornea * may cause portions of the image on the fovea to be blurry. * This is referred to as an astigmatism. *
* This condition may be corrected through the use of specially ground cylindrical lenses to compensate for the differences in curvature of the cornea or lens or through laser surgery. *
This may be corrected by specially ground lenses which( cylindrical ) compensate for the irregularity or laser surgery.

23. Q1
The structure that Modified interiorly to become transparent and more curved to form the cornea is
A)Iris
B)Choroid
C)Retina
D)Sclera

24. Q2 Cataract defined as : A)Opacity of the lens
B) Increase the intraocular pressure
C) Errors of refraction
D)Paralysis of abducent nerve

25. Q3 On looking to a distant object ,Which event DOSE NOT occur
A) The light rays are coming in parallel
B)Ciliary muscle is relaxed and the lens is flat
C)The rays are brought to a focus on the retina
D) Convergence of visual axis

26. Q4 The cause of myopia is A)Eyeball too short B)lens too thin
C)Lens too stiff
D)Eye ball to long

27. References Human physiology by Lauralee Sherwood, 7th edition
Text book physiology by Guyton &Hall,12th edition
Text book of physiology by Linda .s contanzo,third edition