3. Vision is perception of light emitted or reflected
from objects in the environment
Stimulus- light waves

10. Fibrous Layer
 Consist of a protective sclera and a transparent
cornea.
 The central anterior portion is crystal clear.
Sclera
 a thick, glistening white connective tissue, seen
anteriorly as the “white of the eye”.
Cornea
 Known as the “window” where light enters.
 Well supplied by nerve endings.

11. Supplied pain fibers.
Most expose part of the eye. Very vulnerable to
damage.
Ability to repair itself extraordinarily. The
cornea is the only tissue in the body that can be
transplanted from one person to another
without worrying rejection. It has no blood
vessels and its beyond the reach of the immune
system.

12. Vascular Layer
 Middle layer of the eyeball.
3 Distinguishable regions:
1. Choroid- most posterior. A blood-rich nutritive
tunic that contains a dark pigment. The pigment
prevents light from scattering inside the eye.
2. Smooth muscle structures
a) Ciliary body- Where lens is attached by a
suspensory ligament called ciliary zonule.
b) Iris- has rounded opening, the pupil, through which
light passes. Acts like the diaphragm of the camera.

13.  Regulates the amount of light entering the eye so that
one can see as clearly as possible in the available light.
 Close Vision and Bright light the circular muscles
contract, and the pupil constricts.
 Distant vision and Dim light, the radial fibers contract
to enlarge (dilate) the pupil, which allows more light to
enter the eye.
Sensory Layer
 Innermost sensory layer of the eye.
Contains the two layered retina.

14. Two Layers of Retina
I. Outer Pigmented Layer- Composed of pigmented cells
that absorbs light and prevent light from scattering
inside the eye. These cells act as phagocytes that remove
dead or damaged receptor cells and stores needed
vitamin A for vision.
II. Transparent Inner Neural Layer- contains millions of
receptor cells, the rods and cones which are called
photoreceptors.
Photoreceptors- Responds to light. Electrical signals pass
from the photoreceptors via two neuron chain bipolar
cells and ganglion cells before leaving retina via the
optic nerve as nerve impulses that are transmitted to
the optic cortex.

15. THE PROCESS OF SEEING
1. Formation of
retinal image
Processes involved:
a. refraction of light
rays- due to
cornea, aqueous
humor, lens,
vitreous humor
b. accommodation of
lens

17. 2. Constriction of pupil-directs light rays to
retina
3. Convergence of eyes- eyeballs converge so
that visual axes come together at the object
viewed

18. • Neural apparatus includes the retina & optic nerve
• Retina forms as an outgrowth of the brain attached
only at optic disc where optic nerve begins
•Detached retina
blow to head or lack of sufficient vitreous body
blurry areas in field of vision
leads to blindness due to disruption of blood supply

19. Optic disk or blind spot is where optic nerve exits the
posterior surface of the eyeball no receptor cells are
found in optic disk. Blind spot can be seen using the
above illustration in the right position, stare at X and
red dot disappears.
Visual filling is the brain filling in the green bar across
the blind spot area

20. blind spot macula

21. Ganglion
Amacrine
Bipolar
neuron
Horizontal
cells
photoreceptive cells
Choroid
Sclera

24. Night Blindness
Inability to see well at night or in poor light. It is not a
disorder in itself, but rather a symptom of an
underlying disorder or problem, especially untreated
myopia (nearsightedness).
Night blindness may exist from birth, or be caused by
injury or malnutrition (for example, a lack of vitamin
A). It can be described as insufficient adaptation to
darkness.

25. Causes
 Myopia
 Glaucoma
medications that
work by
constricting the
pupil
 Cataracts
 Retinitis
pigmentosa
 Vitamin A
deficiency

26. Treatment
 Depends upon its cause.
 Treatment may be as simple as getting a new eyeglass
prescription or switching glaucoma medications, or it may
require surgery if the night blindness is caused by
cataracts.
Cataracts
 Is the clouding of the lens of the eye, which impedes the
passage of light.
 Although most cases of cataract are related to the aging
process, occasionally children can be born with the
condition, or a cataract may develop after eye injuries,
inflammation, and some other eye diseases

27.  Causes vision to become hazy and distorted.
Causes
o Diabetes Mellitus
o Frequent exposure to sunlight
o Heavy smoking
Treatment
 Surgical removal of the lens and replacement with a
lens implant or special cataract glasses.

28. Glaucoma
 a term describing a group of ocular disorders with multi-
factorial etiology united by a clinically characteristic
intraocular pressure-associated optic neuropathy.]This can
permanently damage vision in the affected eye(s) and lead
to blindness if left untreated. It is normally associated with
increased fluid pressure in the eye .
 Stills sight slowly and painlessly until damage is done.
 Tonometer- used to measure the intraocular pressure.

29. Treatment
 Eyedrops- increases the rate of aqueous humor
drainage.
 Laser or Surgical enlargement of the drainage of
channels can be used.
 Opthalmoscope- instrument that illuminates the
inferior of the eyeball allowing the retina, optic disc,
and internal blood vessels at the fundus, or posterior
wall of the eye to be viewed and examined. Certain
pathological conditions, such as diabetes,
arteriosclerosis, and degeneration of the optic nerve
and retina can be detected by such examination.

30. Emmetropia- Literally means harmonious vision.
Myopia- Short vision. It occurs when the parallel rays
from distant objects fail to reach the retina and instead
focus in front of it. Distant objects appear blurry to
myopic people. Results from an eyeball that is too
long, a lens to strong, or a cornea that is too curved.
Treatment for Myopia:
Requires concave corrective lenses that diverge the light
rays before they enter the eye, so that they converge
farther back.

31. Hyperopia- Far vision. Occurs when parallel light rays
from distant objects are focused behind the retina at
least in the resting eye in which the lens is flat and the
ciliary muscle is relaxed. Results from an eyeball that is
too short or a lazy lens. See distant objects clearly
because their ciliary muscles contract continuously to
increase the light-bending power of the lens, which
moves the focal point forward onto the retina. Near by
objects are blurry. Hyperopic people are subject to eye
strains as their endlessly contracting ciliary muscles
tire from overwork.

32. Treatment for Hyperopia:
Correction requires convex corrective lenses that
converge the light rays before they enter the eye.
Astigmatism
Unequal curvatures in different parts of the cornea or
lens. Blurry images occur because points on the retina
but as lines. Eyes that are myopic or hyperopic and
astigmatic require a more complex correction.
Treatment
Special cylindrically ground lenses or contacts are used
to correct this problem.