The eye is composed of a series of lenses and spaces that give focus to images, just as a camera does. It is composed of the vitreous humor, aqueous humor, the crystalline lens, and the cornea, and each of these has its own refraction index (the average being 1.34, because of the content of these tissues).Functions Pupil. Opens and closes in order to regulate and control the amount of light. Iris. Controls light level similar to the aperture of a camera. Sclera. Protects the outer coat. Cornea. A thin membrane which provides 67% of the eye's focusing power. Crystalline lens. ... Conjunctive. ... Aqueous humour. Vitreous humour.

1. PHYSIOLOGY OF EYE
PRESENTED BY : Ms. SAPNA
ASSISTANT PROFESSOR
PHARMACOLOGY

2. Human
Eye :
The human eye is an organ which reacts to
light and pressure. As a sense organ, the
mammalian eye allows vision. A Normal Eye
looks like,

3. The human eye is an
organ that reacts to light and has
several purposes. As a sense organ,
the mammalian eye allows vision.
Rodand cone cell in the retina allow
conscious light perception.

4. 4
Eye and Associated Structures
 70% of all sensory receptors are in the eye
 Photoreceptors – sense and encode light patterns
 The brain fashions images from visual input
 Accessory structures include:
Eyebrows, eyelids, conjunctiva
Lacrimal apparatus.

5. 5
Eyebrows
 Coarse hairs the overlie the supraorbital margins
 Functions include:
 Shading the eye
 Preventing perspiration from reaching the eye
 Orbicularis muscle – depresses the eyebrows
 Corrugator muscles – move the eyebrows medially

6. 6
Palpebrae (Eyelids)
 Protect the eye anteriorly
 Palpebral fissure –
separates eyelids
Figure 16.5a

7. 7
Accessory Structures of the Eye
 Eyelashes
 Project from the free
margin of each eyelid
 Initiate reflex blinking
 Lubricating glands
associated with the eyelids
 Meibomian glands and
sebaceous glands
 Ciliary glands
Figure 16.5a

8. 8
Conjunctiva
 Transparent membrane
that:
 Lines the eyelids as the
palpebral conjunctiva
 Covers the whites of
the eyes as the ocular
conjunctiva
 Lubricates and protects
the eye
Figure 16.5a

9. 9
Lacrimal Apparatus
 Consists of the lacrimal gland and associated ducts
 Lacrimal glands secrete tears
 Tears
 Contain mucus, antibodies, and lysozyme
 Enter the eye via superolateral excretory ducts
 Exit the eye medially via the lacrimal punctum
 Drain into the nasolacrimal duct

10. 10
Lacrimal Apparatus
Figure 16.5b

11. 11
Structure of the Eyeball
Figure 16.7

12. 12

13. The Camera The Human Eye
The individual components of the eye work in a manner
similar to a camera. Each part plays a vital role in providing
clear vision. So think of the eye as a camera with the cornea,
behaving much like a lens cover. As the eye 's main focusing
element, the cornea takes widely diverging rays of light and
bends them through the pupil, the dark, round opening in
the center of the colored iris. The iris and pupil act like the
aperture of a camera.
Next in line is the lens which acts like the lens in a camera,
helping to focus light to the back of the eye. Note that the
lens is the part which becomes cloudy and is removed during
cataract surgery to be replaced by an artificial implant
nowadays.

14. Parts of Human
Eye
The front part of the Eye includes:
Iris: the colored part.
Cornea: a clear dome over the iris.
Pupil: the black circular opening in the iris that
lets light in.
Sclera: the white of your eye.

15. Iris
IRIS
(colored part)
Colored part of eye
Controls light entering
Function:
Controls the amount of light
entering the eye

16. Cornea
CORNEA
(clear lens in front of
eye)
transparent covering of the
front of the eye
Allows for the passage of
light into the eye and
functions as a fixed lens.
Function:
Allows for the passage of light
into the eye and it also focuses
the light.

17. Pupil
PUPIL (black hole)
black hole in iris
where light enters
Function:
Pupil size is controlled by iris
muscles

18. The iris control the amount of light entering the
eyes. The iris automatically adjust the size of the
pupil according to the intensity of light received by
the eye. If the amount of light received by the eye
is large (as during the day time ),then the iris
contracts the pupil (makes the pupil small) and
reduces the amount of light entering the eye. On
the other hand , if the amount of light received by
the eye is small(as the room is dark)the iris
expands the pupil (make the pupil large ) so that
more light may enter the eyes.
 The adjustment of the size of pupil takes some
time .

21. Pupil Expansion
When the eye needs more light to
enter (when it is dark), the pupils
get larger; allowing more light to
enter the eye

22. Pupil Contraction
When the eye needs less light to
enter (when it is very bright), the
pupils get smaller; allowing less
light to enter the eye.

23. Sclera
SCLERA – a tough white skin
(made of tissue) that covers all of
the eyeball except the cornea.
Function:
Supports eyeball and
provides attachment for
muscles

24. Retina
Internal membrane
Contains light-receptive cells
(rods and cones)
Converts light to electrical
signals
Function:
Converts light waves to
electrical signals

25. 25
Sensory Tunic: Retina
 A delicate two-
layered membrane
 Pigmented layer –
the outer layer that
absorbs light and
prevents its
scattering
Figure 16.9a

26. 26
Sensory Tunic: Retina
 Neural layer, which
contains:
 Photoreceptors
that transduce light
energy
 Bipolar cells and
ganglion cells
 Amacrine and
horizontal cells
Figure 16.9a

27. 27
The Retina: Ganglion Cells and the Optic Disc
 Ganglion cell axons:
 Run along the inner surface of the retina
 Leave the eye as the optic nerve
 The optic disc:
 Is the site where the optic nerve leaves the eye
 Lacks photoreceptors (the blind spot)

28. 28
The Retina: Ganglion Cells and the Optic Disc
Figure 16.9b

29. The retina of our eye has a large number of light –
sensitive cells. There are two kinds of light-
sensitive cells on the retina: rods and cones .

30. 30
The Retina: Photoreceptors
 Rods:
Respond to dim light
Are used for peripheral vision
 Cones:
Respond to bright light
Have high-acuity color vision
Are found in the macula lutea
Are concentrated in the fovea centralis

31. Rod cells, or rods,
are photoreceptor cells in the
retina of the eye that can
function in less
intense light than the other
type of visual
photoreceptor, cone cells.
Cone cells, or cones, are one of
the two types
of photoreceptor cells that are
in the retina of
the eye which are responsible
for color vision as well as eye
color
sensitivity; they function best in
relatively bright light, as
opposed to rod cells.

32. 32
Blood Supply to the Retina
 The neural retina receives it blood supply from two sources
 The outer third receives its blood from the choroid
 The inner two-thirds are served by the central artery and vein
 Small vessels radiate out from the optic disc and can be seen
with an ophthalmoscope

33. 33

34. 34
The Lens
 A biconvex, transparent, flexible, avascular structure that:
 Allows precise focusing of light onto the retina
 Is composed of epithelium and lens fibers
 Lens epithelium – anterior cells that differentiate into lens
fibers
 Lens fibers – cells filled with the clear protein crystalline
 With age, the lens becomes more compact and dense and loses
its elasticity

35. Optic Nerve
OPTIC NERVE
Transmits electrical impulses from
retina to the brain
Creates blind spot
Brain takes inverted image and
flips it so we can see
Function:
Transmits electrical signals from
retina to the brain

36. Functions
The eye has many parts that must work
together to produce clear vision:
The sclera, or white part of the eye, protects
the eyeball.
The pupil, or black dot at the center of the eye,
is a hole through which light can enter the eye.
The iris, or colored part of the eye, surrounds
the pupil.

37. Accommodation (Acc) is the process by which the
vertebrate eye changes optical power to maintain a
clear image or focus on an object as its distance
varies.
Accommodation acts like a reflex, but can also be
consciously controlled. Mammals, birds and reptiles
vary the optical power by changing the form of the
elastic lens using the ciliary body (in humans up to
15 dioptres). Fish and amphibians vary the power by
changing the distance between a rigid lens and the
retina with muscles.[1]
Accommodation (eye)

38. 38
Refraction and Lenses
 When light passes
from one transparent
medium to another its
speed changes and it
refracts (bends)
 Light passing through
a convex lens (as is in
the eye) is bent so that
the rays converge to a
focal point
 When a convex lens
forms an image, the
image is upside down
and reversed right to
left
Figure 16.15

39. 39
Focusing Light on the Retina
 Pathway of light entering the eye: cornea, aqueous
humor, lens, vitreous humor, and the neural layer of the
retina to the photoreceptors
 Light is refracted:
At the cornea
Entering the lens
Leaving the lens
 The lens curvature and shape allow for fine focusing of
an image

40. 40
Adaptation
 Adaptation to bright light (going from dark to light) involves:
 Dramatic decreases in retinal sensitivity – rod function is lost
 Switching from the rod to the cone system – visual acuity is
gained
 Adaptation to dark is the reverse
 Cones stop functioning in low light
 Rhodopsin accumulates in the dark and retinal sensitivity is
restored

41. 41
Visual Pathways
 Axons of retinal
ganglion cells form the
optic nerve
 Medial fibers of the
optic nerve decussate at
the optic chiasm
 Most fibers of the optic
tracts continue to the
lateral geniculate body
of the thalamus
Figure 16.22

42. 42
Visual Pathways
 Other optic tract
fibers end in superior
colliculi (initiating
visual reflexes) and
pretectal nuclei
(involved with
pupillary reflexes)
 Optic radiations
travel from the
thalamus to the visual
cortex
Figure 16.22

43. ABNORMALITIES OF EYE

44. Myopia
Myopia commonly known as near-sightedness
(American English) and short-sightedness (British
English), is a condition of the eye where the light
that comes in does not directly focus on the retina
but in front of it, causing the image that one sees
when looking at a distant object to be out.

45. This figure shows an defect called
myopia. In this case, the parallel rays
of light coming from the distant
object are converged to form an
image in front of the retina due to
which the eye cannot see the distant
object clearly. Myopia is corrected by
using spectacles containing
concave lenses. When concave lens is
placed in front of the myopic eye as
shown in figure then the parallel rays
of light coming from the distant
object at the far point of myopic eye.
Since the rays of light now appear to
be coming from the eye’s far

46. The defects of eye
called hypermetropia is
caused :
i. Due to low
converging power of
eye-lens,
ii. Due to eye –ball
being too small.
Hypermetropia (Hyperopia) - Long

47. Hypermetropia means long sight and is
where the image of nearby object is
formed behind the retina. This could be
because the eye is too short, or the
cornea or crystalline lens does not refract
the light enough.
A hypermetropic person may have blurred
vision when looking at objects close to
them, and clearer vision when looking at
objects in the distance. By placing a
convex (plus powered) lens in front of a
hypermetric eye, the image is moved
forward and focuses correctly on the
retina.

48. Presbyopia
Presbyopia is a condition associated with aging in
which the eye exhibits a progressively diminished
ability to focus on near objects. Presbyopia’s exact
mechanisms are not fully understood; research
evidence most strongly supports a loss of elasticity
of the crystalline lens, although changes in the lens’
curvature from continual growth and loss of power
of the ciliary muscles (the muscles that bend and
straighten the lens) have also been postulated as its
cause.

49. This defect is corrected in the same way as
hypermetropa is by using spectacles having
convex lenses.

50. Cataract
A cataract is a clouding of the lens inside
the eye which leads to a decrease in vision. It is
the most common cause of blindness and is
conventionally treated with surgery. Visual loss
occurs because opacification of
the lens obstructs light from passing and being
focused on the retina at the back of the eye.
It is most commonly due to aging, but has many
other causes.

51. Over time, yellow-brown pigment is deposited in
the lens, and this, together with disruption of the
lens fibers, reduces the transmission of light and
leads to visual problems.
Those with cataracts often experience difficulty in
appreciating colors and changes in contrast,
driving, reading, recognizing faces, and coping
with glare from bright lights.

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