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Ophthalmic and Mechanical Optics > general PMO topics > Flashcards

general PMO topics Flashcards

1
Q

Lens having 1 focal length/power

A

Spherical and Toroidal Lens

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2
Q
  • Use conical curves, notably ellipsoids, to produce flatter and thinner lenses
  • most often made in the new high index plastic materials, which further improve the reduction in lens thickness
A

ASPHERIC LENS

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3
Q

Advantage of Aspheric lens:

A
  • thinner, lighter and flatter as compared to Spherical lens
  • Eliminates spherical aberration, oblique astigmatism and distortions
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4
Q

two separate lenses held together by the frame

upper halved distance lens and lower halved near correction

-invented by Benjamin franklin

A

Split Bifocal

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5
Q

Advantage of Split Bifocals:

A
  • Larger field of view
  • no vertical image jump
  • less chromatic aberration
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6
Q

Disadvantage of Split bifocals:

A
  • Lenses are held together by eye wire and come apart easily
  • dividing line produces annoying reflections
  • dust accumulation at dividing line
  • as the power increases the segment edge gets bigger and heavier
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7
Q

a modified franklins bifocal

reading portion was rounded and reduced in size

A

Perfection Bifocal

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8
Q

The first one piece bifocal as it is made from a single piece of glass material

top portion of biconvex lens was ground flat on one surface so that the finished lens was a combination of a Plano convex and biconvex lens

A

Solid Bifocal/ Solid Upcurve Bifocal

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9
Q

advantage of Solid Bifocal:

A
  • wide field of view for reading
  • little chromatic aberration
  • structurally stronger
  • better appearance than split bifocal
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10
Q

disadvantage of Solid Bifocals:

A
  • limited surface power
  • restricted field of view for Distance
  • presence of prismatic effect and image jump
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11
Q
  • uses two pieces of the same kind of glass, one fixed to the surface of the other
  • this bifocal featured a crown glass major lens to which was cemented a small section of crown glass called “wafer”
  • Canada Balsam was the adhesive used to cement the two glass
A

Cemented Bifocal

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12
Q

advantage of Cemented Bifocal:

A
  • Less optical aberrations
  • can be made of any power ranges
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13
Q

disadvantage of Cemented bifocal:

A

adherence of wafer is affected by the changes in temperature

wafer has a tendency to fall off

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14
Q
  • the first fused bifocal
  • uses two different glass materials
  • segment material has higher refractive index than the main lens
  • segment is fused into main lens
A

Fused Kryptok

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15
Q

advantage of fused kryptok:

A

segment edges do not collect dirt and dust

segment do no fall out, become discolored or chip

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16
Q

disadvantage of Fused kyptok:

A

flint segment produces high chromatic aberration

increase possibility of lens tension and strain during manufacturing process

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17
Q

Types of Bifocals based on manufacturing method:

A
  • Split Bifocals
  • Solid Bifocals/Solid Upcurve Bifocal
  • Cemented Bifocal
  • Fused Bifocal
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18
Q

Types of Bifocal Lenses based on segment shape/Design:

A
  • Round Segment/KRYPTOK Bifocal
  • Flat-Top Bifocal
  • Curved-Top Bifocal
  • Executive Bifocal
  • Ultex Bifocal
    *
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19
Q
  • segment width available in 22mm, 24mm and 28mm
  • has a circular arc segment which is least visible compared to other bifocals
A

Round segment bifocal/Kryptok

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20
Q

disadvantage of Round segment/Kryptok bifocals:

A
  • Segment is not wide enough for reading
  • There is presence of noticeable Image Jump
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21
Q

Segment widths ranges from 22mm to 45mm

Also known as D Bifocal/D-shaped Bifocal

Available in plastics (CR-39) and fused glass forms

A

Flat-Top Bifocals

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22
Q

Advantages of Flat-top bifocals:

A
  • more useful reading width
  • less image jump than round/Kryptok bifocals
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23
Q

disadvantages of Flat-top bifocals:

A
  • Less attractive compared to the round segment
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24
Q
  • Segment widths available in 28mm, 35mm and 45mm
  • Also called the C-style segment bifocal
  • Segment top has a slight curve rather than a perfectly flat segment top
A

Curved-Top bifocals

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25
Q
  • it is monocentric - optical centers for distance and near portion located both on the line segment
  • often recommended as an occupational lens for patients involved with a lot of reading or near works
  • The near add is ground on the front surface of the lens
A

Executive Bifocals

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26
Q

advantage of Executive Bifocals:

A
  • Very large reading zone
  • No image jump
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27
Q

disadvantage of Executive Bifocals:

A
  • thick and Heavy
  • not cosmetically appealing
  • dust accumulates in the crevice
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28
Q
  • a one-piece bifocal bifocal made out of ophthalmic crown glass
  • is ground with a central disk diameter of 38mm (segment width).
  • After grinding the black is cut into two lenses, each having a segment height of 19mm
A

Ultex Bifocal

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29
Q

advantage of Ultex bifocals:

A

Recommended as occupational lens as it has a LARGE FIELD OF VIEW for READING PORTION

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30
Q

disadvantage of Ultex Bifocals:

A

greater image jump than the other bifocal lenses

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31
Q

refers to a sudden change or shift in image location that occurs when gaze shifts from the distance to the add segment

A

Image Jump

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32
Q

a sudden introduction of a base down prism at the dividing line of the segment

A

Image jump

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33
Q

Magnitude of image jump is dependent on:

A

distance of dividing line from optical center of the segment and power addition

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34
Q

lens that help correct the intermediate zone by featuring a second small lens segment directly above the area used to correct near vision

A

TRIFOCAL LENSES

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35
Q

Most popular trifocals:

A
  • Flat-top Trifocal
  • Executive trifocal
  • E-D line trifocal
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36
Q

lens with two flat-top segments

designed for people who need to see objects at an intermediate distance above their heads (librarians, pilots)

A

Double D Trifocal or Librarian Trifocal

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37
Q

lens which the distance power is located in the middle band

A

Executive Occupational Multifocal

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38
Q

Same as Double-D trifocal except that a trifocal segment is incorporated at the bottom

A

Quadrifocal Lens

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39
Q
  • also known as dental upcurve bifocal
  • the segment on top is the distant portion of the lens and the main part of the lens being the near zone
A

Rede Rite Bifocal (Minus Add Up Curve)

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40
Q
  • has small, round segment for near vision placed low in the outside corner of one lens
  • the lens for the right eye, in the case of a right-handed golfer
A

Golf/Golfer’s Bifocal

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41
Q
  • the design of the lens is such that the power gradually increases as it goes from the distance zone - through a corridor - near zone.
  • were designed to meet visual demands of presbyopes who require spectacles for all distances.
A

Progressive Lenses

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42
Q

advantage of PALs:

A
  • Improved appearance
  • Complete range of working distances
  • No image jump
  • Thinner and Lighter
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43
Q

disadvantage of PALs:

A
  • Unwanted astigmatic power at the periphery (Peripheral Aberration)
  • adaption problems
  • More critical fitting required
  • More expensive
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44
Q

disadvantage of PALs:

A
  • Unwanted astigmatic power at the periphery (Peripheral Aberration)
  • adaption problems
  • More critical fitting required
  • More expensive
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45
Q

PAL that has:

  • Narrower distance and Near zones
  • Wider and Longer intermediate Corridor
A

Soft Design Progressive Lens

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46
Q

PAL that has:

  • Wider distance and Near zones
  • narrow and shorter intermediate corridor
A

Hard Design Progressive Lens

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47
Q

PAL that has:

  • rapid increase in unwanted astigmatism
  • more peripheral aberrations
A

Hard Design Progressive Lenses

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48
Q

PAL that has:

  • Gradual increase in unwanted astigmatism
  • Reduced peripheral aberrations
A

Soft Design Progressive Lenses

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49
Q

PAL lens permanent markings:

A
  • Micro etching/ Horizontal Locators
  • Lens Logo
  • ADD power
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50
Q

PAL lens Temporary markings (ink stamped markings):

A
  • Distance reference circle
  • Fitting Cross
  • Prism reference point
  • Near reference Point
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51
Q

PAL markings that are small micro-engraved circles which are positioned about 34mm apart

A

Micro-Etching / Horizontal Locators

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52
Q

PAL temporary marking:

portion of the lens through which the distance power should be read

A

Distance Reference Circle

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53
Q

PAL temporary marking:

the point which should be fitted directly in front of the pupil

A

Fitting Cross

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54
Q

PAL temporary marking:

portion used to check for the presence of prism within the lens or the amount of differential prism

A

Prism reference Point

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55
Q

PAL temporary marking:

portion used for checking the power of the addition through the lensmeter

A

Near Reference Point

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56
Q

a homogeneous glass, free from defects such as striae and bubbles, used for lenses or prisms.

A

Optical Glass

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57
Q

made of 70% Silica (sand),

14-16% Sodium Oxide,

11-13% Calcium Oxide

and 5% of Potassium, borax antimony and arsenic

A

Ophthalmic Crown glass

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58
Q

it is used for the majority of single-vision glass lenses available today, and for the distance portion of most glass bi- and tri- focals.

A

Ophthalmic CROWN glass

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59
Q

made of 45-65% lead oxide,

25-45% silica

and about

10% mixture of soda and potassium oxide

A

Flint Glass

60
Q

it is used mainly for bifocal segments in some fused bifocals

A

Flint Glass

61
Q

is made of 25-40% barium oxide and the result is silica and potassium oxide

A

Barium crown Glass

62
Q

it is mainly used for the segment portion of a specific type of fused bifocal

A

Barium crown Glass

63
Q

CR-39 specific gravity:

A

1.31

64
Q

crown glass specific gravity:

A

2.51

65
Q

the best materials for lens impact resistance:

A

Polycarbonate and Trivex

66
Q

a lens that blocks over 90% of UVA

A

CR-39

67
Q

a lens that blocks almost 100% UVA:

A

Polycarbonate lens

68
Q

Characteristics of Lens Materials:

A
  • Refractive index
  • Abbe Value
  • Impact resistance
  • Specific gravity
  • Scratch resistance
  • Transparency
  • UV absorption
  • Chemical resistance
69
Q

ratio of the speed of light in vacuum to the speed of light in the medium:

A

Refractive index

70
Q

Lenses made from a ______ material will be thinner and more cosmetically appealing than _____ materials.

A

Higher refractive index

Lower index materials

71
Q

High index materials have low ______ value

A

Abbe Value

72
Q

Lower Abbe Value means that is has more ______

A

Chromatic Aberrations

73
Q

is the reciprocal of the dispersive power of the material

A

Abbe Value

74
Q

Gives a measure of material’s ability to hold the spectrum

A

Abbe Value

75
Q

The higher the Abbe value, the _____ the chromatic aberration

A

LOWER

76
Q

If lens has a great chromatic aberration, it is because it has _______.

A

Low abbe value

77
Q

is a material’s ability to withstand intense force or shock applied to it over a short period of time.

A

Impact resitance

78
Q

standard DROP BALL TEST:

A

Dropping a 5/8 inch steel ball to the lens

From a height of 50 inches

79
Q

a measure of the physical density of the material

A

Specific Gravity

80
Q

Unit of measurement of Specific Gravity:

A

grams per cubic centimeter (g/cm3)

81
Q

the ability of a lens material to resist and withstand scratches

A

Scratch Resistance

82
Q

is the oldest and most often quoted test to measure the scratch resistance of a lens material

A

Moh’s hardness scale

83
Q

a function of the refractive index. the higher the refractive index, the lesser the transmittance of light.

A

Transparency

84
Q

Significance of Transparency:

A
  • reduction of troublesome ghost images
  • reduction in the glassy appearance of the lenses
  • increased transmittance
85
Q

gives an indication of the lens material’s resistance to various solvents.

A

Chemical resistance

86
Q

Test to measure chemical resistance

simulates prolonged exposure to atmospheric conditions using heat and humidity

A

Thermodyne test

87
Q

he developed Thermodyne test:

A

Chance-Pilkington

88
Q

the inability of a lens to bring all incident rays to a desired point:

A

Aberration

89
Q

a defect in an image due to imperfect focusing of light rays by the lens or an optical system

A

Monochromatic Aberration or Seidel Aberration

90
Q

defect in an optic image occurring when an incident light is not confined to paraxial rays (central)

A

Monochromatic Aberration or Seidel Aberration

91
Q

Types of Monochromatic Aberrations:

A
  • Spherical Aberration
  • Coma
  • Oblique Astigmatism
  • Curvature of Field
  • Distortion
92
Q

the failure of a lens to focus rays of light at one and same point therefore the image seen is somewhat blurred

A

Spherical Aberration

93
Q

happens when peripheral rays are focused sooner than the central rays

A

Spherical Aberration

94
Q

Correction of spherical abberation:

A

Limiting the aperture of the lens

Use of Plano convex lens

Use of aplanatic surfaces

Use of Aspheric lens

95
Q
  • occurs when rays of light from an off-axis object (oblique incident light) are refracted by the periphery of a refracting surface
  • also called off-axis spherical aberration
  • Spherical aberration for oblique light
A

Coma

96
Q

forms a comet shape image of a point source

A

Coma

97
Q

Correction of Coma:

A
  • Eliminating the peripheral rays
  • Adjusting the shape of the lens
98
Q

Correction of Coma:

A
  • Eliminating the peripheral rays
  • Adjusting the shape of the lens
99
Q

occurs when narrow beam of light enters obliquely to lens axis of a spherical lens, the refracted rays become astigmatic

the emerging rays instead of uniting in a single image point, form the interval of sturm

A

Oblique astigmatism

100
Q

also known as Marginal astigmatism or Radial Astigmatism

A

Oblique astigmatism

101
Q

correction of Oblique astigmatism:

A
  • use of meniscus lenses
  • orientation of lens such that incident light is parallel to the principal axis
  • Using an aspheric lens
102
Q

correction of Oblique astigmatism:

A
  • use of meniscus lenses
  • orientation of lens such that incident light is parallel to the principal axis
  • Using an aspheric lens
103
Q

it is also known as disk of confusion, circle of indistinctness, blur circle or blur spot

A

Circle of Confusion

104
Q

it is an optical spot caused by a cone of light rays from a lens not coming to a perfect focus when imaging a point source

A

Circle of Confusion

105
Q
  • the smallest of a blur circle
  • Found exactly midpoint between the two focal lines
A

Circle of Least Confusion

106
Q

inability of a lens to form a plane image of a plane object

also called “Curvature of the Image”

A

Curvature of Field

107
Q

presents problem for instrument makers, particularly, camera manufacturers who need to produce an image on a PLANE film

A

Curvature of Field

108
Q
  • the inability of a lens to form an image of the same shape as the object
  • Mostly seen in high power plus and minus lenses
A

Distortion

109
Q
  • it affects image shape and lateral position, but not image clarity
  • results when the magnification of an extended object varies with its distance from the optical axis
A

Distortion

110
Q

Term that means “free from distortion”

A

Orthoscopic/Orthoscopy

111
Q

distortion observed in high power PLUS lenses

A

Pincushion Distortio

112
Q

distortion observed in high power MINUS lenses

A

Barrel Distortion

113
Q

occurs as a result of the unequal refraction of the various wavelengths of light

A

Chromatic Aberration

114
Q

is the non-uniform focusing of the different color waves in a pencil of light, due to the different refrangibility of these waves:

  • short violet waves being refracted most
  • long red waves least
  • medium waves in proportional degrees
A

Chromatic Aberration

115
Q

a type of lens made up of two simple lenses paired together designed so that the chromatic aberration of each lens partially offsets the other

A

Achromatic Doublet

116
Q

Forms of Chromatic aberration:

A
  1. Longitudinal chromatic aberration or Axial chromatic aberration
  2. Lateral Chromatic aberration
117
Q

type of chromatic aberration that focuses different spectral hues at different distances along the optical axis

A

Longitudinal or Axial Chromatic aberration

118
Q

type of chromatic aberration wherein all colors are in focus in the same plane, but the foci are not placed along the optical axis

A

Lateral Chromatic aberration

119
Q

the transmission of electromagnetic radiation can be reduced by _______ or _______.

A

reflection or absorption

120
Q
  • reduce reflection at each surface improving the visual function
  • sharpens the patient’s vision, because more light is able to pass through the lens instead of being bounced off the lens
A

Anti-Reflection coatings

121
Q

______ coatings are particularly important for high index lenses and flat form lenses, such as the aspheric lenses

A

Anti-Reflective coatings

122
Q

used to prevent the condensation of water in the form of small droplets on a surface of lens

A

Anti-Fog coatings

123
Q

coating used by skiers, mountaineers, astronomers and pseudophakics

A

UV COATING

124
Q

UV that creates a risk for the conjunctiva and cornea

A

UV-B and UV-C (low levels of UV)

125
Q

this UV causes severe damage to the:

  • cornea
  • contribute to cataract formation
  • retinal damage
  • macular degeneration
A

UV-A (High level UV)

126
Q

acute effects of UV-A:

A
  • Photochemical retinopathy
  • Tanning of eyelids
127
Q

Chronic effects of UV-A:

A
  • Cataract
  • Macular degeneration
  • Malignant Melanoma
128
Q

Acute effects of UV B:

A

Photo-kerato-conjunctivitis

Cataract

Erythema of eyelid skin (redness)

129
Q

Chronic effects of UV B:

A
  • Pterygium
  • Pinguecula
  • Band Keratopathy
  • Corneal degeneration
130
Q
  • Highly reflective coatings applied to front surface of sunglasses
  • decrease eyestrain by blocking 10-60% of light transmission to the eye
A

Mirror Coating

131
Q
  • are applied by a vacuum application of interference layers made of powdered oxides, metals, lacquered plastics or other available compounds
  • this coating is good for highly reflective outdoor activities, especially from water and snow (Functional)
  • it shields the appearance of the eyes (Aesthetic reasons)
A

Mirror Coating

132
Q
  • Contains Silver chloride or silver halide which when exposed to UV causes a chemical reaction that gives the ability of the lens to darken
  • Also known as “light-adaptive lenses”
A

PhotoChromic Filters

133
Q

it means restricting the light waves to one direction

A

Polarization

134
Q

block horizontally aligned light which causes glare, while allowing vertical lights to transmit

A

Polarized Lenses

135
Q
  • blocks radiant light and all types of glare
  • filters out harmful ultraviolet rays
  • permits only natural light that is gentle to the eyes to pass
A

Polarized Lenses

136
Q

Advantage of Polarized lenses:

A
  • Filters glare
  • Reduces reflection
  • enhance contrast and depth perception
  • improves clarity of vision
137
Q

lens coating that combats digital eye strain

A

Blue Light Coating

138
Q

Beneficial blue light can:

A
  • regulates circadian rhythm
  • boost alertness
  • elevates mood
139
Q

Harmful blue light can:

A
  • cause digital eyestrain
  • too much exposure cause eye damage
140
Q
  • a bright yellow brown coating that filters out ultraviolet rays
  • also called as blue blocker tint
A

UV 500

141
Q

a clear coat applied the the lens to protect them against scratches

A

Hard Coating

142
Q

a color applied to the bevel area of a lens that matches the frame camouflaging the edge

A

Edge Coating

143
Q

used for individuals who are constantly going into and out of changing temperature

A

Anti Fog coating

144
Q

consists of several coatings of:

  • anti reflection
  • UV
  • hard coating
A

Multicoated lens

145
Q

advantages of multicoated lens:

A
  • Eliminates reflections
  • filters out ultraviolet light
  • makes your glasses lens conspicuous and hence more attractive
  • reduces eye fatigue in office and artificial light
  • helps to avoid glare during night driving from an incoming car headlight
146
Q

Standard uncoated lenses can decrease light transmission by up to ____ of available light

A

15%

147
Q

Standard uncoated lenses can decrease light transmission caused by visible reflection on the ____ and _____ surface of the lens,

as well as _______

A

Front and Back surface

Internal reflections

Ophthalmic and Mechanical Optics (10 decks)

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