Midterm I Flashcards
(94 cards)
1
Q
Where were corrective lens first developed?
A
China and Europe simultaneously
2
Q
What were the two critical factors that lead to the development of corrective lenses?
A
- Increase visual demands with inc age
2. Development of glass
3
Q
What type of correction were the first glasses made for?
A
presbyopia
4
Q
What type of correction were the second glasses made for?
A
myopia
5
Q
Who invented the biofocals? 1. Who assisted him?2
A
- Ben Franklin
2. John McAllister
6
Q
What was the last type of correction that was corrected with glasses?
A
astigmatism
7
Q
What is the amorphous solid material that is obtain by an inorganic mixture fused at high temperatures used to make spectacles?
A
glass
8
Q
What are the natural types of glass?
A
- obsidian
2. fulgarites
9
Q
What do flint glasses contain in them that is not like crown glass?
A
lead oxide
10
Q
What does high index glass contain in it that is not like crown glass?
A
titanium oxide
11
Q
What is how light behaves differently based on the wavelength? 1. How is it measured? 2
A
- Dispersion
2. Abbe Value
12
Q
What is the distortion of a point because a lens will behave differently based on the wavelength?
A
chromatic aberration
13
Q
What is the ratio of the density of a substance to the density of water?
A
specific gravity
14
Q
How is the Abbe value calculated? 1. Is a high value or low value better? 2
A
- reciprocal of relative dispersion
2. high
15
Q
What are the advantages of glass?
A
- inert
- scratch resistant
- high optical quality
16
Q
What are the disadvantages of glass?
A
- heavy (high specific gravity)
- lower impact resistance
- potential for liability
17
Q
What is an organic polymeric material of high molecular weight that can be shaped by flow?
A
plastic
18
Q
What kind of plastic softens when heated and can be remodeled? 1. What kind cannot be softened once hardened? 2
A
- thermoplastic (Zial)
2. thermosetting
19
Q
Why did people start preferring plastic to glass?
A
- impact resistance requirement
- light weight, reduced scratching
- larger frames can be used
- tints available
20
Q
What is the allyl diglycol carbonate monomer that is a thermosetting plastic and has UV absorbers?
A
CR-39
21
Q
What are the desirable properties of CR-39?
A
- lightweight
- impact resistant
- chemically inert
- resistant to pitting
- resistant to fogging
- tintable
22
Q
What type of plastic is polycarbonate?
A
thermoplastic
23
Q
What are the advantages of polycarbonate lenses?
A
- superior to glass and CR-39 for impact resistance
- lighter than CR-39
- UV absorption
24
Q
What are the disadvantages of polycarbonate lenses?
A
- more easily scratched
- low Abbe Value (high dispersion)
- more reflections
25
What is the relatively new lens material that is similar to polycarbonate but higher Abbe Value?
Trivex
26
How does index of refraction affect the thickness of the lens?
high the index, thinner the lens
27
Is weight more of a concern in plus or minus lenses?
plus
28
What does the durability and safety of a lens depend on?
1. resistance to scratching
2. tensile strength
3. impact resistance
29
What is the order from most to least scratch resistant lens type?
glass>CR-39 (should coat) >polycarbonate (need coat)
30
What is the order from most to least expensive lens type?
1. trivex
2. glass
3. polycarb
4. CR-39
31
What is the most common lens type in the U.S.? 1. Second? 2
1. Polycarb
| 2. CR-39
32
Are the standards set by ANSI voluntary or involuntary?
voluntary
33
What does the drop ball test consist of for the impact resistance test?
1. 5/8 inch steel ball
2. weight=0.56 ounces
3. drop height = 50 inches
4. dropped on front surface geometric center of lens
34
What are the exceptions for the drop ball test?
1. test for stats. significant
2. plastic lenses
3. non-prescription lenses
4. special use lenses
35
What is the regulatory body of the government that prevents unfair business practices?
Federal Trade Commission (FTC)
36
What did the Eyeglasses II (1989) change as far as regulations from Eyeglasses I?
1. remove minimum info on Rx
| 2. suggest expiration
37
What is the regulatory agency to protect the workers?
Occupational Safety & Health Administration (OSHA)
38
What did ANSI Z80.1 set a standard for?
1. Standards for ophthalmic lens tolerances
| 2. lens quality criteria
39
What did ANSI Z80.3 set a standard for?
1. nonprescription sunglasses
| 2. minimum UV protection
40
What did ANSI Z80.5 set a standard for?
Standards for dress eyewear frames
41
What did ANSI Z87.1 set a standard for?
Standards for safety eyewear
42
What is the minimum thickness for safety glasses?
3.0 mm
43
What is the minimum thickness for dress eyewear?
none
44
What is the procedure of heating a lens to near softening point and then rapidly cooling called? 1. What are the restrictions after this? 2
1. thermal tempering
| 2. cannot be resurfaced or re-edged
45
What is the procedure that uses ion exchange to meet impact resistance standard? 1. What are the restrictions after this? 2
1. chemical tempering
| 2. none
46
Does CR-39 or chem tempered glass have better impact resistance for large slow objects? 1. Slow fast moving? 2
1. chem tempered glass
| 2. CR-39
47
What is the most impact resistant material?
polycarb (or Trivex)
48
What is the equation for the curvature of a lens?
(R) = C = 1/r
49
What is the distance between a point on the circle and the midpoint of a chord of the circle?
sagitta
50
What does a lens clock directly measure? 1 What does it indirectly measure? 2
1. sag
| 2. power
51
What is the index of refraction for most lens clocks?
1.53
52
If n(c)>n(T), then P(c) is an overestimate, an underestimate, or an exact measurement of P(T)?
overestimate
53
What is the only lens form that is still currently made?
meniscus
54
What refers to the relationship between the front and back surface curvatures of a lens?
lens form
55
What is the lens form of meniscus lenses?
convex front surface (+) and concave back surface (-)
56
On most modern single vision lenses, where is the toricity?
plus sphere on front and minus cylinder on back
57
What is the name for a blank that has neither side ground or polished?
rough blank
58
What is the name for a blank that has one surface ground and polished?
semi-finished blank
59
What is the name for a blank that has both surfaces ground and polished but not edged to fit the frame?
uncut lens
60
What side of the lens is the base curve usually referring to?
the front (flattest surface)
61
What are selected to minimize the lens aberrations and is a compromise between lens thickness and image quality?
base curve
62
Are flatter lens thicker or thinner?
thinner
63
What are lenses designed to minimize lens aberrations called?
"best form" or "corrected curve"
64
What is the most important factor in aberrations?
oblique astigmatism
65
What is the line connecting the centers of curvature of the two lens surfaces?
optic axis
66
What are the points on the front and back surface of a lens which intersect the optic axis
lens poles
67
What does the spherical equivalent determine?
location of the circle of least confusion
68
What are the three methods of determining the resultant power of obliquely crossed cylinders?
1. vector analysis
2. mathematical
3. polar coordinates
69
When is finding the result of obliquely crossed cylinders used? 1. What is it used with? 2
1. fitting toric contact lenses
| 2. SCOR (sphero cylinder over refraction)
70
What is a tilt of the bottom of a lens towards the face called?
pantoscopic tilt
71
What is a tilt of the bottom of a lens away the face called?
retroscopic tilt
72
What is a tilt of the temples of a lens toward the patient?
positive faceform
73
What is the axis of added cylinder in pantoscopic tilt?
180
74
What is the axis of added cylinder in faceform?
90
75
What is the power found using the lens clock?
nominal power
76
What is the algebraic sum of the lens surfaces?
nominal power
77
What is the power that is equal to the power of a single, thin lens placed at the secondary principal plane? 1. What is it used for? 2
1. equivalent power
| 2. low vision devices
78
What is another name for the front vertex power? 1. How is it found? 2
1. neutralizing power
| 2. hand neutralization or lensometer
79
What is the power that ophthalmic prescriptions are specified with? 1. What is it usually measured with? 2
1. back vertex power
| 2. lensometer
80
What is refractive behavior of the lens when moved to a different distance?
effective power
81
What is the power that provides the lens required when the vertex distance is changed?
compensated power
82
Will a contact lens or a glasses prescription have more plus power?
CL prescription
83
If there is a "with" motion when doing hand neutralization what is the net power?
minus
84
If there is a "against" motion when doing hand neutralization what is the net power?
plus
85
What kind of telescope is a lensometer?
Keplerian telescope
86
Where is the lens stop located in lensometery?
secondary focal plane of standard lens in lensometer
87
For a plus lens measurement does the target move toward or away from the standard lens?
toward
88
For a minus lens measurement does the target move toward or away from the standard lens?
away
89
Does higher index make a lens thicker or thinner?
thinner
90
Around what amount does lens thickness usually become important?
+- 4.00 D
91
Do stronger surface powers produce shorter or longer radii of curvature?
shorter
92
If: front surface (D) > back surface (D), what is the result? 1. If: front surface (D)
1. plus lens
| 2. minus lens
93
What are the center thicknesses required for minus lens safety glasses?
between 1.0 and 2.2 mm
94
What are the edge thicknesses required for plus lens safety glasses?
between 1.0 and 2.0 mm
