Formulas and Optical Theory Flashcards
TP = sphere power + cylinder power x sin 2 (0)
Power in Oblique meridians
N1 sin i = N2 sin r
Snells’ Law
angle I =angle r
Law of reflection
Prism (^)=(hxD) / 10
Prentice Rule
D = 1/f
Focal length - Dioptic power
De = D1 +D2
Nominal Power
FPD = A +DBL
Frame PD
Dec = (FPD - PPD) / 2
Binocular decentration
Speed of light in air/ speed of light in medium.
Index of refraction
MBS = ED + (2 X Dec)
Minimum blank size
I need a lens with power +3.50D. If I use a lens blank with a front surface power of +8.00D, what back surface do I need?
De = D1 + D2 +3.50 = +8.00 + D2 D2 = -4.50
I have a lens with a front surface of +9.25D and a back surface of -2.25D. What is the power of the lens?
De = D1 +D2 De = +9.25 + -2.25 De = +7.00
I want my lens to have a power of -3.00D. What back surface do I need if the front surface is +8.00D?
De = D1 +D2 -3.00 = +8.00 +D2 D2= -11.00
What is the difference between a high index lens and a aspheric lens?
High index refers to the material of the lens; Aspheric refers to the surface design of the lens
What are the three things that can happen to a ray of light when it passes through a lens?
Absorbed, reflected, refracted
What is the difference between a monocular distance PD and a binocular distance PD?
Monocular PD: each eye is measured separately from the center line of the face
Binocular PD: the measurement is taken from the center pupil to center pupil
What role does the Food and Drug Administration play in the ophthalmic industry?
They are responsible for the lens safety aspect of the industry. Impact resistance is their main focus.
According to the Systems text, eyewear can be divided in to what three categories?
Dress eye wear - Designed for everyday use.
Safety eyewear - Designed to meet higher standards of impact resistance since it will be worn in situations that could be potentially hazardous to the eyes.
Sports eyewear - Designed to protect the eyes or enhance the vision in specific sports situations. What is appropriate will vary dramatically depending upon the sport.
What are the Rx’s in a plus cylinder form of the following optical crosses?
- 1.00 @095 -3.00 @ 175
- 2.00 @005 +1.50 @ 085
-2.00 + 1.00 x 005 -3.00 + 4.50 x 175
What is transposition?
Transposition is the changing of a prescription from a plus cylinder to a minus cylinder or the other way around. It does not affect the powers of the prescription.
What is the dioptric power a lens with a focal length of _____?
- ) 40 mm
- ) -33 mm
- ) D = 1/f D = 1 / .04 D = +2.50
2. ) D= 1/f D = 1 / .33 D = -3.00
What is the focal length of a -2.00 D lens in meters?
F = 1D F = 1/-2 F = -0.50 meters
What type of image is formed by a minus lens?
Virtual
A plus lens does what to light rays that pass through it?
Makes them converge
What does the term critical angle of a material mean?
The ray of light is striking the surface at an angle so that the ray is refracted along the surface of the lens.
What is the lens power in the 90th meridian for this lens prescription: +3.00 +1.00 x 180
a. +1.00
b. +2.00
c. +3.00
d. +4.00
+4.00
A minus lens with the optical center moved up created _____.
a. base up prism
b. base in prism
c. base out prism
d. base down prism
base down prism
A base-up prism _____.
a. bends light towards the base
b. bends light rays away from the apex
c. projects an image of the object downwards
d. all of the above
all of the above
The wavelengths of visible light range approximately from _____.
a. 200 - 400 nanometers
b. 300 - 600 nanometers
c. 400 - 720 nanometers
d. 500 - 800 nanometers
400 - 720 nanometers
The wavelengths of light that are the most pleasing to the eye are _____.
a. ultra-violet
b. infra-red
c. blue-green
d. orange
blue-green
The breakdown of light into its component colors is called _____.
a. dispersion
b. refraction
c. reflection
d. aberration
refraction
The point on a lens which a ray of light will pass through without being deviated is called _____.
a. apex
b. base
c. optical zone
d. optical center
optical center
The lower the abbe number, the _____.
a. less the chromatic aberration
b. more the chromatic aberration
c. thicker the lens
d. thinner the lens
more the chromatic aberration
If a lens deviates a ray of light 4 cm at a distance of 2 meters, the lens is said to have power of _____ diopters?
a. .25
b. .50
c. 1.00
d. 2.00
2.00
The transposed Rx of +3.00 - 1.00 x 30 is _____.
a. +3.00 +1.00 x120
b. +2.00 -1.00 x 30
c. +2.00 +1.00 x120
d. +2.00 -1.00 x 30
+2.00 +1.00 x 120
Which lens has the characteristic of magnification?
a. Minus spherical
b. Plus spherical
Plus spherical
Which lens has the characteristic of thin center/thick edge?
a. Minus spherical
b. Plus spherical
Minus spherical
Which lens has the characteristic of diverging light rays?
a. Minus spherical
b. Plus spherical
Minus spherical
Which lens has the characteristic of with motion?
a. Minus spherical
b. Plus spherical
Minus spherical
The lens design in which the front base curve gradually flattens is called _____.
a. aspherical
b. spherical
c. corrected curve
d. meniscus
aspherical
Plus lenses _____.
a. are diverging lenses
b. are thicker at the center than the edge
c. minify image size
d. show with motion
are thicker at the center then the edge
