2. OBJECTIVES:
1. Discuss principles of pinhole imaging,
mirror and lenses.
2. Define object and image characteristics
3. Discuss principles of light propagation
3. GEOMETRICAL OPTICS
Deals primarily with imaging
PHYSICAL OPTICS
Wave nature of light
QUANTUM OPTICS
Particle nature of light and interaction of
light and matter
4. DEFINITION OF TERMS
CONJUGATE- correspondence between
object and image points
RAY- the route that light follows as it
travels from an object point to the image
point
PENCIL of light- small bundle of rays that
travel in the same direction
9. OBJECT CHARACTERISTICS
REAL objects
◦ Can be felt, touched, located in front of the
optical system
VIRTUAL objects
◦ Cannot be felt or touched, located behind an
imaging system
LUMINOUS
◦ Objects that produces its own light (eg.
candle)
10. IMAGE CHARACTERISTICS
MAGNIFICATION
Most important
enlargement
Making images smaller or larger than the
object
◦ Transverse = image height/ object height
◦ Axial
◦ angular
11. 4 cm
Object
Height
Image
2 cm height
Transverse magnification = 2/4 = -0.5
12. AXIAL MAGNIFICATION
◦ Aka longitudinal magnification
◦ Axial magnification = ( transverse magnification) 2
ANGULAR MAGNIFICATION
◦ The ratio of the angle subtended by an object
without the lens or magnifier
13. IMAGE LOCATION
The distance between a reference point
and the image
Reference point- back surface of the lens
Positive- image is right to the reference
point
18. IMAGE QUALITY
Images are imperfect facsimiles.
Each object point produces a 2- mm
diameter spot in the image= BLUR circles
STIGMATIC IMAGE- a perfect point
image of an object point
The smaller the blur circle- less image
details lost
19. BRIGHTNESS and IRRADIANCE
BRIGHTNESS-
A visual perception
The response of the nervous system to
light entering the eye
IRRADIANCE
A purely physical measure of the amount
of light per unit of an image
Important in calibration of perimeter
22. OPTICAL MEDIA AND
REFRACTIVE INDEX
Medium- any material that transmits light
Light travels at different speeds in
different media
REFRACTIVE INDEX-
N= speed of light in vacuum
speed of light in medium
◦ is always greater or equal to 1
23. REFRACTIVE INDEX FOR SOME
MATERIALS OF CLINICAL INTEREST
MATERIALS REFRACTIVE INDEX
AIR 1.0000
WATER 1.3333
CORNEA 1.376
AQUEOUS/VITREOUS 1.336
SPECTACLE CROWN 1.523
GLASS
PMMA 1.492
24. Dispersion- short
wavelengths travel
slowly than long
wavelengths
Leads to chromatic
abberation
Eye- 0.5 D of
chromatic abberation
26. LAW OF RECTILINEAR
PROPAGATION
Light in a single medium travels along
straight- line paths called rays
Pencil of light- a bundle of rays traveling
close to each other in the same direction
27.
28. OPTICAL INTERFACE
The boundary separating 2 different
optical media
Smooth- light undergo specular reflection
and transmssion
Rough- diffuse reflection and transmission
32. SPECULAR REFLECTION:
LAW OF REFLECTION
The direction of the reflected ray bears a
definite relationship to the direction of
the incident ray
Reflected ray lies in the same plane as
the incident ray and the surface normal
and that θ i = θr
35. Reflection coefficient
Used to calculate the amount of light
transmitted at an optical surface
R= n2-n1 2
n2+n1
36. How much more reflective is an acrylic IOL than a silicone
IOL? Assume that the index of refraction of acrylic is 1.55 and
the silicone is 1.43. ( aqueous= 1.33)
R acrylic = 1.55-1.33 2
1.55+1.33
0.0584 =0.584%
R silicone= 1.43 - 1.33 2
1.43 + 1.33
0.00131= 0.131%
0.584/0.131= 4.46
37. SPECULAR TRANSMISSION: Law
of Refraction
The transmitted ray’s direction bears a
definite relation to the incident’s ray
direction
Snell’s law= the refracted or transmitted
ray lies in the same plane as the incident
ray and the surface normal
Light- lower- higher refractive index–
bends toward the surface normal
38. N1<n2 optical interface
N1>n2
Incident ray
θi
θi
θ
Surface normal θt
39. TOTAL INTERNAL REFLECTION
Occurs when light travels from a high-
index medium to a low –index medium
and the angle of incidence exceeds a
certain critical angle
Critical angle- angle of incidence that
produces a transmitted ray 90° to the
surface normal
43. Fermat’s principle
Light travels from one point to another along
the path requiring the least time
Optical path length- distance light travels in a
given medium multiplied by the medium’s
refractive index
e.g
Light travels 5 cm in air (n= 1.000) and 10 cm in
glass ( n= 1.523)
OPL= 5 cm x 1.000+ 10 cmx 1.523=
20.2 cm