Reference -

1. KASHMEERA.N.A
II SEM MSc ZOOLOGY
ROLL NO: 37

2. The Eye as a Cam a
er
• The eye is optically equivalent to the usual
photographic camera.
• It has a lens system,
• a variable aperture system (the pupil),
• and a retina that corresponds to the film.

3. F o r mat i o n o f i mag e o n
re t i na

4. F o u r b as i c p r o c e s s ar e i n vo l ve d i n t h e
f o r mat i o n o f an i mag e o n r e t i n a
Refraction of light rays
Accommodation of lens
Constriction of pupil
Convergence

5. Ref r ac t i on of Li g ht Ray s
• When light rays traveling through a transparent
substance pass into a second transparent
substance with a different density, they bend at
the junction between the two substances. This
bending is called refraction.

6. The lens system of the eye is composed of four refractive
interfaces:
(1) the interface between air and the anterior surface of the
cornea,
(2) the interface between the posterior surface of the cornea and
the aqueous humor,
(3) the interface between the aqueous humor and the anterior
surface of the lens of the eye,
(4) the interface between the posterior surface of the lens and
the vitreous humor.

7. Ac c om odat i on of l ens
m
Convex lens will refract incoming light rays toward each other, so that they
eventually intersect.
Concave lens causes light rays to refract away from each other.

8. The lens of the eye is convex on both
its anterior and posterior surfaces
Its focusing power increases as its
curvature becomes greater.
When the eye is focusing on a close
object, the lens becomes more curved,
causing greater refraction of the light
rays.
This increase in the curvature of the
lens for near vision is called
accommodation
.

9. Ho w d o e s ac c o mmo d at i o n o c c u r ?
viewing distant objects –
the ciliary muscle of the ciliary body is relaxed –
the lens is flatter [ because it is stretched in all directions by zonular
fibers. ]
viewing a close object,-
the ciliary muscle contracts –
releases tension on the lens and zonular fibers. –
the lens becomes more spherical (more convex) –
which increases its focusing power and causes greater convergence of
the light rays.
Parasympathetic fibers of the oculomotor (III) nerve innervate the ciliary
muscle of the ciliary body and, therefore, mediate the process of
accommodation

11. Cons t r i c t i on of pupi l
The pupil of the human eye can become as small as about 1.5 mm and as large
as 8 mm in diameter.
.The constriction of the pupil is a narrowing of the diameter of the hole
through which light enters the eye due to the contraction of the circular
muscles of the iris.
This autonomic reflex occurs simultaneously with accommodation and prevents
light rays from entering the eye through the periphery of the lens.
Light rays entering at the periphery would not be brought to focus on the retina
and would result in blurred vision.
The greatest possible depth of focus occurs when the pupil is extremely small. -
with a very small aperture, almost all the rays pass through the center of
the lens, and the central most rays are always in focus.

12. Conver genc e
In humans, both eyes focus on only one set of objects—a
characteristic called binocular vision.
B.V allows the perception of depth and an appreciation of the 3 D
nature of objects.
B.V occurs when light rays from an object strike corresponding
points on the two retinas.
When we stare at a distant object, the incoming light rays are aimed
directly at both pupils and are refracted to identical spots on the
retinas of both eyes.
As we move closer to an object, however, the eyes must rotate
medially for the light rays from the object to strike the same points
on both retinas.

13. • The term convergence refers to this medial
movement of the two eyeballs so that both are
directed toward the object being viewed.
• The nearer the object, the greater the degree of
convergence
• The coordinated action of the extrinsic eye
muscles brings about convergence.
convergence

14. F o r mat i o n o f i mag e o n r e t i n a
• The image on retina is inverted and
reversed with respect to the object.
• However mind perceives objects in the
upright position because the brain is
trained to consider an inverted image as
the normal.

15. PHOTOCHEMI S TRY OF VI S I ON

16. Rhodops i n- r et i nal vi s ual c yc l e i n t he r od

17. PHOTOCHEMI S TRY OF
COL OUR VI S I ON

18. • photochemicals in cones are similar to rhodopsin
(scotopsin + retinal)
• cones contain photopsin + retinal
• 3 different types of photochemicals are present in cones,
their light absorption spectra are different
cone pigment wavelength of peak absorption (nm)
blue-sensitive pigment 445
green-sensitive pigment 535
red-sensitive pigment 570
• rods have peak sensitivity at 505 nm

19. • Human eye can see any colour due to a
combination of red, green and blue
monochromatic light in different
proportions.

20. EL ECTROPHYS I OL OGY OF
VI S I ON