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Ophthalmic Optics Block 10 > Phys And Optical Characteristics Of Lenses 2 > Flashcards

Phys And Optical Characteristics Of Lenses 2 Flashcards

1
Q

Light incidence on a surface suffers a combination of three fates

A

Transmission
Absorption
Reflection

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2
Q

Tranmission + absorption + reflection=

A

100%

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3
Q

When a light passes through a lanes, it is _____ on both lens surfaces and _____ by the lens material

A

Reflected

Absorbed

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4
Q

The anoint of light energy that gets through an optical system

A

Transmittance (T)

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5
Q

When light falls upon a lens, it is lost in two ways

A

Reflected

Absorbed

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6
Q

Specifies the amount of light reflected from a surface

A

Fresnel law

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7
Q

Spectacle lens in air fresnels law

A

R= (n2-1/N2-1)^2

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8
Q

Converting transmittance

A

Ts-1-R

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9
Q

To find transmittance (not absorbed)

A

T=TsTsTm

Ts is transmittance at each surface
TM amount transmitted, not absorbed by the medium

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10
Q

How the amount of light transmitted changes based on a change of thickness of the absorbing material

A

Beer-lambert law

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11
Q

The fraction of light transmitted per unit lenejgth of solid tinted material

A

Transmittance factor (q)

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12
Q

If given:
Q=0.8/mm
Material thickness=4mm
How much light is transmitted

A

(0.8)^4=0.41=41%

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13
Q

The ratio of the density of a substance to the density of a reference substance

A

Specific gravity

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14
Q

Higher the specific gravity of a material,

A

The more material is packed into a smaller area

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15
Q

Substances with specific gravity >1

A

More dense than water (will sink)

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16
Q

Substances with specific gravity <1

A

Less dense than water (will float)

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17
Q

A diopter equals

A

D=1/f

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18
Q

Light passing through a plus lens

A

Converges

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19
Q

Light passing through a minus lens

A

Diverges

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20
Q

Rays of light entering a prism always do what at base of prism

A

Bends towards

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21
Q

The image through a prism

A

Shifted towards apex

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22
Q

A curved interface between two media

A

Single spherical refracting inferfaces

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23
Q

An optical system with two spherical refracting interfaces- the front and back surfaces

A

A spherical lens

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24
Q

Total lens power =

A

Front lens surface + back lens surface

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25
Interface wraps around the lower n medium
Concave
26
Interface wraps around the higher n medium
Convex
27
Concave interface is always
Diverging
28
Convey interface is always
Converging
29
Power of SSRI
F=(n2-n1)/r n2=RI of final media N1=RI of original media R=radius of curvature of SSRI F=power of the ssri
30
Total lens power
F=F1+F2
31
Refractive power of a surface
P=(N2-n1)/r N1=refractive index of medium N2=refractive index of emerging rays R= distance (m) Simplified to F= (n-1)/r
32
Total power of the lens ignores what
Thickness This is approximate power
33
Front surface power is
+
34
Back surface power is
-
35
Back vertex power
Fv= P1/(1-d/n*P1)+P2
36
Front vertexpower
Fn=F2/(1-t/nF2)+F1
37
Vertex distance and tilt
When lens is tilted about the optical center the vertex distance doesn't change along line of sight
38
Optical axis and tilt
The optical axis of the lens no longer passes through the center rotation of the eye -paraxial theory no longer applies
39
Tow forms of tilt
Pantoscopic tilt | Face form
40
Horizaontal tilt
Panto
41
Vertical tilt
Faceform tilt
42
Tilt on lens and cyl and sphere
Sphere power reduced in meridian that is tiled
43
Panto tilt of a minus lens
Axis at 180
44
Panto tilt of a plus
Axis at 90
45
Faceform tile of plus
Axis at 90
46
Faceform tilt of a plus
Axis at 180
47
Compensating power for tilt
A Rx modified for the as worn position when fitted to the frame or mount -Rx measured on a lensometer does not equal Rx/ordered RX
48
Single vision compensating for tilt
Ensure optical axis of the lens passes through the center of rotation by lowering the optical center
49
Compensating for panto tilt
Lower it 2mm per 1 degree of tilt
50
Equation for compensating for lens tilt
X=dcorsiny
51
Lens form characterizes
The relationship between the front and back surface geometries of a lens
52
Form of a lens
Specified by the power of the front surface BC
53
BC can be manipulated for 4 reaseons
Thickness and wt Peripheral lens aberrations Cosmetic considerations Image size and magnification
54
Plano-convex and Plano-concave
One surface is flat and the others s curved
55
Meniscus
Convex front surface and concave back surface Most common
56
Biconvex and biconcave
Both surfaces are either convex or concave
57
Equiconvex and equiconcave
Half total power is due to the front surface and half is due to the back surface
58
Plano cylinder
One flat surface and one cyl surface
59
Toric
One topic surface and spherical surface
60
Standard lens curves used by manufactures
Base curve
61
Spherical lens BC
From spehre curve
62
Toxic base curves and cross curve
Back surface
63
Base curve of minus cyl
From sohere curve
64
Spherical equivalent
Sum of the spherical component and one half of the cyl component of a lens or surface
65
Curve from which all other curves are measured
Base curve theory
66
To find the best curve for plus RX, add the sphere power or the spherical equivalent to +6,
Vogels rule
67
To find the best curve for a minus Rx, add half the sphere power or half the spherical equivalent to +6
Vogels theory
68
You want the BC of the front surface to be as close to _____ as possible
+6
69
The height or depth of a lens surface
Sag
70
The sagitta of a curve is the
Perpendicular distance from the vertex of the curve to a chord intersecting the curve
71
Sag formula
S=H2/2r
72
The distance between the posterior pole of ophthalmic lens and perpendicular plane constraint the posterior edge of lens
Vertex depth
73
The distance between the anterior pole of the lens and the plane containgin anterior edge of the lens
Lens bulge
74
The height of the lens when laid down on a flat surface
Plate height
75
Sag of back surface
Vertex depth
76
Sag of front surface
Lens bulge
77
Sag of front surface + edge thickness
Plate height
78
How to account for different RI in lens clock
Pclock= (n2-n1)clock/r Rearranged to R=(n2-n1)clock/Pclock Ultimately Ptrue=Pclock((n2-n1)true)/(n2-n1)clock
79
When a frame is put on a patients face, it should touch at three points
The fitting trial -ear and skull Bridge of nose
80
4 pt alignment
``` Tighten the screw X-int Co-planar Skewed bridge Faceform Panto tilt Parallel temples Nose pads Open temple angle Clean ```
81
Check for misalignment when viewing the frame from above
Co planar | -occurs when the bridge us pushed forward/backward while the lenses remain in correct tilt
82
Check for misalignment when viewing from above
X-int | Lenses twisted where eyewires meet the bridge
83
Check for misalignment when looking straight on
Skewed bridge/eyewires | Lenses are rotated inward or outward around the bridge
84
Check curvature of fram from above
Faceform | Too much=changes in perceived lens power
85
Check for alignment where viewed from
The side | Some panto is necessary for cosmetics and optics
86
Check for misalignment by placing the eyewear temples up on flat surface and checking from the side
Parallel temples | Both temples should make contact with flat surface
87
Check from above for 90 angle
Open temple angle | Should never be less
88
Check from back when temples are closed
Temple fold angle | Temple tips should not touch the lenses, be parallel and cross at middle
89
Check all three of these for alignment, frontal, splay, vertical)
Nose pads

Ophthalmic Optics Block 10 (4 decks)

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