Optical Phenomena related to Optometric Optics (Reflection, Refraction, Interference, Diffraction, Polarisation) and also their Optometric Uses or their uses in the Optometry Field

1. Presented by: Satish Kumar Gupta
Roll no. : 25
Regd. No. : 14O0025
1St Year ( 2014-2018)
Sankara College of Optometry
Date: 29th May, 2015

2. LIGHT
• Form of energy: Sensation
of vision/sight
• Electromagnetic waves and
it doesn’t require any
medium for propagation
• When light travels from one
medium to another, the
velocity and wavelength
change. But frequency and
colour of light don’t change.
• Colour of light is determined
by its frequency, but not by
its wavelength.
• Speed/Velocity of light:
3 X 108 m/sec

3. Dual nature of light

4. •Particle nature:
Quanta/Photon- A very tiny, light and elastic particle with rest mass
and charge zero and energy is equal to:
E=hv

5. • Wave nature: Electromagnetic wave/ radiation consisting of self-
sustaining oscillating electric and magnetic fields at rt. angles to each
other and to the direction of propagation. It doesn’t require any
supporting medium and travels through the empty space at the speed
of the light (i.e., 3 X 108 m/sec)

6. OPTICS
• The branch of physical science concerned with the
vision and the generation, nature, propagation, and
behaviour of the electromagnetic light.
OPTICAL PHYSICS
• Subfield of atomic, molecular physics.
• The study of the generation of electromagnetic
radiations, the properties of that radiations, and the
interactions of that radiations with the matter,
especially its manipulation and control.

7. Optical Phenomena
• Optical phenomena are any observable events
that result from the interaction of light and
matter.
Some common Optical Phenomena are:
1. Reflection of light
2. Refraction of light
3. Interference of waves
4. Diffraction of waves
5. Polarization of waves

8. ???

9. 1. REFLECTION

10. 1. Reflection
• The phenomenon of returning back of light to the
same medium when the light is incident on a
polished surface is known as reflection.
• Types:
1. Specular/Regular: Plane and polished surface
2. Diffuse/Irregular: Rough Surface

11. Laws of Reflection:
1st law:
The incident ray, reflected
ray and the normal at the
point of incidence always
lie on the same plane.
2nd law:
<i = <r

12. ?

13. I. Specular Microscopy
• Based on the principle of Specular reflection i.e., obeys
the laws of reflection.

15. II. Keratometry

16. Contd…
• A keratometer / ophthalmometer: A diagnostic instrument
for measuring the curvature of the anterior surface of the
cornea, particularly for assessing the extent and axis of
astigmatism.
• A keratometer uses the relationship between object size
(O), image size (I), the distance between the reflective
surface and the object (d), and the radius of the reflective
surface (R). If three of these variables are known (or fixed),
the fourth can be calculated using the formula:
R = 2d I
O
• Normal value: Anterior R= 7.5 mm
Posterior R= 6.3 mm

17. ???

18. Refraction

19. 2. Refraction

20. Contd…
• When the light ray travels from one medium
to the another, it bends towards or away from
the normal. This phenomenon of bending of
light ray from the interface is known as
refraction.
• From denser to rarer: away from the normal
• From rarer to denser: towards the normal

21. Laws of Refraction:
1st law:
The incident ray, refracted
ray and the normal at the
point of incidence always
lie on the same plane.
2nd law:
µ1 sin i = µ2 sin r
(Snell’s law)

22. Scattering of light

23. Dispersion of light

24. ?

25. I. Total Internal Reflection

26. a. Optical Fiber
- Endoscopy
- Communication

27. b. Gonioscopy

28. Gonioscopy

29. II. Retinoscopy

30. • Retinoscopy : A technique to obtain an objective
measurement of the refractive error of a patient’s
eyes.
• The examiner uses a retinoscope to shine light into
the patient’s eye and observes the reflection
(reflex) off the patient’s retina. While moving the
streak or spot of light across the pupil the
examiner observes the relative movement of the
reflex then manually places lenses over the eye
(using a trial frame and trial lenses) to “neutralize”
the reflex.

31. ???

32. 3. Interference of waves

33. • Interference: A phenomenon in which two waves superpose.
• Coherent sources
• Coherent waves
• Interference: All types of waves, for example, light, radio,
acoustic, surface water waves or matter waves.
I α a2
•Constructive Interference: Intensity is maximum
Resultant amplitude(A)= a1 + a2
• Destructive Interference: Intensity is minimum
Resultant amplitude(A)=a1 - a2
• Fringe width, β = λD
d

36. Optical effects due to
Interference

37. Coloured soap bubbles

38. Brilliant colours of the peacock
feathers

39. Oil floating on water

40. ?

41. I. ARC

42. ARC
• One of the important practical application of interference.
• An optical coating applied to the surface of lenses and
other optical elements to reduce reflection.
• In typical imaging systems, this improves the efficiency
since less light is lost.
• In complex systems such as a telescope, the reduction in
reflections also improves the contrast of the image by
elimination of stray light.
• The thickness of the coating should be equal to λ/4 and a
coating is maximally effective for only one wavelength of light.

43. • Layer thicknesses are chosen to produce destructive
interference in the beams reflected from the interfaces, and
constructive interference in the corresponding transmitted
beams.
• “anti-reflection lenses”
- decreased reflection makes them look better, and they
produce less glare, which is particularly noticeable when
driving at night or working in front of a computer monitor.
- The decreased glare means that wearers often find their eyes
are less tired, particularly at the end of the day. Allowing
more light to pass through the lens also increases contrast
and therefore increases visual acuity.

47. Q. A CR-39 lens requires an antireflection
coating. What should be the refractive
index of the coating?
µc = sq. root of µL
µc = sq. root of 1.498
µc = 1.22
Also, t = λ/4
t = 5890 X 10-10 m (for Yellow Colour light)
4
t = 1.4725 X 10-7 m
For a CR-39 lens, the antireflection coating should
have a refractive coating of 1.22

48. If you were to look at this
coating, it would appear
purplish!
WHY???
As discussed, a lens RI is
specified for light of 589 nm,
which appears yellow. This is
the wavelength for which
the destructive interference
will be maximized.
Wavelengths shorter (which
appears blue) and longer
(which appears red) are
reflected off the lens and
combine to form a purplish
colour. In clinical practice,
these reflections are can be
minimized by applying
additional layers of anti-
reflective coatings of other
indices of corresponding
colour light.

49. II. OCT

50. ???

51. 4. Diffraction of light

52. Diffraction:
The bending
of the light
waves
across the
edges of an
obstacle or
the
encroachme
nt of the
light within
the
geometrical
shadow.

54. Diffraction pattern of red laser beam made on a plate after passing
a small circular hole in another plate

55. Optical effects due to the
atmospheric diffraction of light

56. Silver lining of the clouds

57. Corona

58. Cloud iridescence

59. ?

60. I. Ocular diffraction

61. Airy’s Disk
r = 1.22 λ
d

62. II. Bifocal Contact lenses
• A contact lens is a
thin lens placed
directly on the
surface of the eye.
Contact lenses are
considered medical
devices and can be
worn to correct
vision, or for
cosmetic or
therapeutic reasons.

63. III. PAL
• Progressive
addition lenses
(PAL), or multifocal
lenses, are
corrective lenses
used in eyeglasses
to correct
presbyopia and
other disorders of
accommodation.

64. ???

65. 5. Polarization

66. • Polarization is a property of waves that can oscillate with more than one
orientation.
- Electromagnetic waves such as light exhibit polarization.
- In an electromagnetic wave, both the electric field and magnetic field
are oscillating but in different directions.
- Light propagates as a transverse wave—both the electric and magnetic
fields are perpendicular to the wave’s direction of travel.
- The oscillation of these fields may be in a single direction (linear
polarization), or the field may rotate at the optical frequency (circular or
elliptical polarization). In that case the direction of the fields’ rotation,
and thus the specified polarization, may be either clockwise or counter
clockwise.

69. Polarization effect: Glare

70. ?

71. I. Polarized Glass

73. • Stereopsis : Perception of depth
and 3-dimensional structure
obtained on the basis of visual
information deriving from two
eyes by individuals with normally
developed binocular vision.
• Because the eyes of humans, and
many animals, are located at
different lateral positions on the
head, binocular vision results in
two slightly different images
projected to the retinas of the
eyes.

74. III. Titmus Fly test

75. IV. Randol Stereo Test

77. References
1. Michael P. Keating. Geometrical, Physical and Visual Optics. 2nd edition. Butterworth-
Heinemann Publications. Boston. 2002.
2. Elkington Andrew R. Clinical Optics. 3rd edition. Blackwell Science Ltd. Oxford. 1999.
3. Schwartz Steven H. Geometrical and Visual Optics. 2nd edition. Mc Graw Hill
Education. New York. 2013.
4. Subrahmanyam N., Brij Lal. A text book of Optics. 1st edition. S. Chand & Company Ltd.
New Delhi. 1999.
5. Wikipedia. [Internet]. 2015 [sited May 2015]. Available from:
http://en.wikipedia.org/
6. Google Books. [Internet]. 2015 [sited May 2015]. Available from:
http://googlebooks.com/
7. Youtube. [Internet]. 2015 [sited May 2015]. Available from: http://youtube.com/
8. Google. [Internet]. 20015[ sited May 2014]. Available from: http://google.co.in/

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