Printable Flash Cards

Term 1

How many millimeters are in an inch?

Definition 1

25.4 mm = 1 inch

Term 2

What is the spectrum of visible light, in nm?

Definition 2

from ~400nm to ~700nm

Term 3

List the colors of the spectrum, from longest wavelength to shortest.

Definition 3

Red, Orange, Yellow, Green, Blue, Indigo, Violet

Term 4

What is the spectrum of UV light, in nm?

Definition 4

from ~200nm to ~400nm

Term 5

How are the bands in the UV spectrum categorized?

Definition 5

A, B, & C (with C being blocked by the Earth's atmosphere)

Term 6

What distance is considered at infinity? Why?

Definition 6

20 feet- because after light leaves its source, it diverges and becomes parallel at 20 feet

Term 7

What is the speed of light?

Definition 7

186,000 miles/second

Term 8

What happens when light enters a transparent medium at 90 degrees?

Definition 8

It slows down and continues onward.

Term 9

What happens when light enters a transparent medium at an oblique angle?

Definition 9

Refraction- it changes the angle of light

Term 10

Each time light encounters a different material, (blank) occurs.

Definition 10

Refraction

Term 11

Define "Index of Refraction"

Definition 11

the degree that light is bent in a given material based on that material's density

Term 12

How is Index of Refraction determined?

Definition 12

speed of light/speed through the material

Term 13

What is the index of refraction of polycarbonate?

Definition 13

1.589

Term 14

What is the index of refraction of CR39?

Definition 14

1.49

Term 15

Is material more or less dense with a higher index of refraction?

Definition 15

Term 16

What is the index of refraction of glass?

Definition 16

1.523

Term 17

What is the index of refraction of flint glass?

Definition 17

1.70

Term 18

What is the standard index of refraction in the optical industry, which all instruments are calibrated to?

Definition 18

1.53

Term 19

Define Dispersion

Definition 19

when light is broken down into basic colors causing a rainbow effect

Term 20

What is abbe value (or Nu value)?

Definition 20

measure of how easily dispersion happens

Term 21

Abbe values are between what numbers?

Definition 21

29 and 60

Term 22

Do higher or lower abbe values result in the least dispersion and best vision?

Definition 22

higher

Term 23

What is the abbe value for plastic?

Definition 23

59-60

Term 24

What is the abbe value for glass?

Definition 24

Term 25

What is the abbe value for high index resin?

Definition 25

Term 26

What is the abbe value for polycarbonate?

Definition 26

29-31

Term 27

What is the abbe value for flint glass?

Definition 27

38-40

Term 28

What 3 things happen as light hits a medium?

Definition 28

Refraction
Absorption
Reflection

Term 29

As light enters and exits any medium, what percent of light is lost (assuming medium is non-coated)?

Definition 29

~8% loss of light (~4% on each surface)

Term 30

What is the normal?

Definition 30

a line drawn at right angles to the material's surface at the ray's point of entry

Term 31

What is the incident ray?

Definition 31

the ray coming into the material (before it enters)

Term 32

When does the incident ray become the refracted ray?

Definition 32

As it enters and leaves the material

Term 33

More curve induces (more or less?) refraction

Definition 33

Term 34

What is a diopter?

Definition 34

the measure of the power of a lens to refract light

Term 35

A lens that can focus parallel light to a point at one meter has what power?

Definition 35

1 diopter

Term 36

What is the formula for determining diopter power? D=?

Definition 36

D = 1/f where f is the focal length of the lens in meters

Term 37

How do you determine focal point, given the power of a lens in diopters?

Definition 37

f = 1/D

Term 38

How do you convert magnification to diopter power?

Definition 38

multiply the magnification by 4 (2x is 8 diopters)

Term 39

What are the 3 types of plus lens configurations?

Definition 39

Bi-convex ()
plano convex [)
meniscus ))

Term 40

What type of lens magnifies an image?

Definition 40

plus lens

Term 41

What type of lens is thicker in the center and thinner at the edges?

Definition 41

plus lens

Term 42

What type of lens demonstrates "against" motion (if the lens is moved side to side, the image seems to go the opposite direction)?

Definition 42

plus lens

Term 43

What are the three types of refractive errors that plus lenses correct for?

Definition 43

hyperopia
presbyopia
aphakia

Term 44

What are the 3 types of minus lens configurations?

Definition 44

Bi-concave )(
plano concave )]
meniscus ))

Term 45

What type of lens minifies an image?

Definition 45

minus lens

Term 46

What type of lens is thicker at the edges and thinner in the middle?

Definition 46

minus lens

Term 47

What type of lens demonstrates "with" motion (if the lens is moved side to side, the image seems to go the same direction)?

Definition 47

minus lens

Term 48

What type of refractive error do minus lenses correct for?

Definition 48

myopia

Term 49

How do you determine power in diopters using a lens clock?

Definition 49

take the front side measurement (usually +) and combine algebraically with the backside measurement (usually -). F + B = P where F= front curve, B= back curve, and P = power

Term 50

If the front curve of a lens is clocked at +6 and the back curve is clocked at -5, what is the power of the lens?

Definition 50

Term 51

How do you transpose an rx?

Definition 51

algebraically add the sphere power and the cylinder power to get the new sphere power, use the same cylinder power but switch the sign, and add 90 degrees to the axis

Term 52

When prism changes the direction of light, this is known as _________ or _______.

Definition 52

diffraction or deviation

Term 53

If a prism is strong enough, light can be separated into different colors. This is called ________.

Definition 53

dispersion

Term 54

Which direction does light entering a prism bend?

Definition 54

toward the normal

Term 55

The image appears toward the _________ of a prism when looking in while it is actually toward the __________.

Definition 55

apex
base

Term 56

What measurement is used to indicate the amount of deviation of a prism?

Definition 56

diopter

Term 57

The ________ a prism, the more light it will bend.

Definition 57

larger

Term 58

T or F: A prism focuses light.

Definition 58

False. A prism only deviates/shifts light, not focuses it

Term 59

T or F: A prism does not magnify or minify an image.

Definition 59

True. it only shifts/deviates

Term 60

Does a steeper angle on a prism result in more or less deviation?

Definition 60

more (greater angle of deviation)

Term 61

If light passes through the center of a lens, it will neither converge nor diverge. This represents the _________ or the ___________.

Definition 61

optical center
axial ray

Term 62

What type of lens converges light?

Definition 62

plus lens

Term 63

What type of lens diverges light?

Definition 63

minus lens

Term 64

In a minus lens, if the pupil is below the optical center of the lens, what type of prism is induced?

Definition 64

Base down prism

Term 65

In a minus lens, if the pupil is above the optical center of the lens, what type of prism is induced?

Definition 65

Base up prism

Term 66

In a minus lens, if the optical center of the lens is moved toward the nasal, this induces what type of prism?

Definition 66

Base out prism

Term 67

In a minus lens, if the optical center of the lens is moved toward the temple, this induces what type of prism?

Definition 67

Base in prism

Term 68

In a plus lens, if the pupil is below the optical center of the lens, what type of prism is induced?

Definition 68

Base up prism

Term 69

In a plus lens, if the pupil is above the optical center of the lens, what type of prism is induced?

Definition 69

Base down prism

Term 70

In a plus lens, if the optical center of the lens is moved toward the nasal, this induces what type of prism?

Definition 70

Base in prism

Term 71

In a plus lens, if the optical center of the lens is moved toward the temple, this induces what type of prism?

Definition 71

Base out prism

Term 72

What formula determines the prism in a lens at a given point, or how much to decenter a lens to induce prism?

Definition 72

Prentice's Formula

Term 73

Prentice's Formula

Definition 73

P = (h x D)/10

P = power in prism diopters
h = OC distance in mm
D = dioptric power of lens

Term 74

How much prism is induced when a 3D lens is decentered by 5 mm?

Definition 74

5x3/10 = 1.5 diopters of prism

Term 75

How much prism is induced in a -4.25 lens decentered by 4 mm?

Definition 75

4 x -4.25/10 = 1.7 diopters of prism

Term 76

How much prism is a person inducing if he looks 6 mm below the OC in a lens -3.00 -3.25 x 180?

Definition 76

3.75 diopters of prism

*use power at 90 degrees since shifting down, which is -6.25

Term 77

How far is a lens moved to have 5D of prism in a 2D power lens?

Definition 77

(5*10)/2=h
25 mm = h

Term 78

Given a +2.00 -5.00 x 180, how far must the lens be decentered to get 1 BU prism and in what direction?

Definition 78

(1*10)/-3.00 = 3.3 mm

*power at 90 degrees is -3.00. for minus lens, BU prism is induced by moving OC down

Term 79

A pair of glasses has been found to be 4 mm off in the PD.
OD: -2.00 +2.00 x 90
OS: -0.75 sph

What is the prism induced?

Definition 79

OD: P= (2x0)/10 = 0 diopters
OS: P= (2 x -0.75)/10 = .15 diopters prism
*assume off by 2 mm in each eye
*OD at 180 degrees is plano

Term 80

How many diopters of difference between eyes will induce double vision when looking away from the optical center?

Definition 80

2+ diopters of difference

Term 81

What is another name for slab off prism?

Definition 81

bicentric grinding

Term 82

When 2 separate optical centers are ground into one lens, what is it called?

Definition 82

slab off prism or bicentric grinding

Term 83

How do you determine which eye slab off prism should be done in?

Definition 83

the most minus (or least plus) lens

Term 84

If a patient has an RX of OD +2.00 sph and OS +0.25 -4.00 x 135, which eye should have slab off prism?

Definition 84

the left eye (it is the most minus)

Term 85

OD: +2.00
OS: +5.00
What amount of prism will a patient experience with a reading gaze 10 mm below the OC with this RX?

Definition 85

OD: 2x10/10= 2D BU prism
OS: 5x10/10= 5D BU prism

Term 86

What is diplopia?

Definition 86

double vision

Term 87

Why don't you need to use slab off prism with single vision lenses?

Definition 87

patient can move head to look through OC

Term 88

OD: -2.00 -2.00 x 135 +2.50
OS: +2.00 -0.50 x 45 +2.50

Patient is ordering a FT28 in a 56/17 metal frame and has a PD of 68. Seg ht is 15. The OC difference between the distance and near is 12 mm.

1. What is the total prism needed for a slab off?
2. Which side will the slab off be on?
3. Which side would the slab off be on if it were reverse slab?

Definition 88

*power at 90 degrees for each lens is
OD: -3.00, OS: +1.75
*difference in power is 4.75D

1. using Prentice's rule (h=12, D=4.75)
12x4.75/10=5.7 diopters prism
2. OD
3. OS

Term 89

What is the RX for the split prism version of this RX?
OD: -0.50 3 BD
OS: -1.00

Definition 89

OD: -0.50 1.5 BD
OS: -1.00 1.5 BU

Term 90

What is the RX for the split prism version of this RX?
OD: -1.00 -1.00 x 90 5 BU
OS: -1.25 -2.50 x 90 3 BO

Definition 90

OD: -1.00 -1.00 x 90 2.5 BU 1.5 BO
OS: -1.25 -2.50 x 90 2.5 BD 1.5 BO

Term 91

When splitting prism, base out and base in are split in what direction?

Definition 91

the same direction (both eyes BO or both eyes BI)

Term 92

When splitting prism, base up and base down are split in what direction?

Definition 92

opposite directions (one eye of each)

Term 93

How many tunics (layers) make up the outer part of the eye? What are they (listed from outermost to innermost)?

Definition 93

3- fibrous tunic, vascular tunic, and nervous tunic

Term 94

What is the name of the outer tunic of the eye that is mostly composed of dense connective tissue?

Definition 94

The fibrous tunic

Term 95

The fibrous tunic is divided into the __________ and the ____________.

Definition 95

sclera, cornea

Term 96

How much refractive power (in diopters) does the cornea have?

Definition 96

43 diopters

Term 97

Which outer tunic contains the blood vessels that supply the retina with nutrients?

Definition 97

choroid tunic

Term 98

What is the name for the white part of the eye?

Definition 98

sclera

Term 99

What part of the eye is translucent and serves as a passageway for light to enter the eye?

Definition 99

cornea

Term 100

Which tunic is also known as the choroid tunic?

Definition 100

vascular tunic

Term 101

The ___________ helps to refract light and to focus on the retina.

Definition 101

cornea

Term 102

What layer contains a high concentration of dark pigments that help absorb excess light?

Definition 102

choroid

Term 103

The _________ is primarily composed of nerve tissue and forms a thin internal membrane of the eye.

Definition 103

retina

Term 104

The vascular tunic consists of...?

Definition 104

iris, choroid, & ciliary body

Term 105

The inner layer of photoreceptors and neurons (the nervous tunic) consists of...?

Definition 105

the retina

Term 106

How many segments/chambers are contained within the inner part of the eye? What are they?

Definition 106

3- anterior chamber, posterior chamber, & vitreous chamber

Term 107

The fluid filled area between the cornea and the iris is the ________.

Definition 107

anterior chamber

Term 108

The fluid filled area between the iris and the lens is know as the __________.

Definition 108

posterior chamber

Term 109

The anterior and posterior chambers contain a fluid known as _____________.

Definition 109

aqueous humour

Term 110

Define aqueous humour.

Definition 110

watery fluid produced in ciliary body which fills the anterior and posterior chambers that maintains pressure in the eye and provides nutrients to the lens and cornea

Term 111

Aqueous humor is continually drained from the eye through the ____________.

Definition 111

Canal of Schlemm

Term 112

The greatest volume of the inner chambers, forming about four-fifths of the eye, is the ________________.

Definition 112

vitreous chamber

Term 113

The vitreous chamber is found between the _________ and the __________.

Definition 113

retina, lens

Term 114

What is vitreous humour?

Definition 114

a thicker gel-like substance contained within the vitreous chamber which maintains the shape of the eye

Term 115

What does vitreous humour do?

Definition 115

maintains the shape of the eye

Term 116

What does aqueous humour do?

Definition 116

maintains IOP, provides nutrients to the lens and cornea

Term 117

The cornea consists of how many distinct layers?

Definition 117

5
epithelium
Bowman's Membrane
Stroma
Descemet's Membrane
Endothelium

Term 118

The outermost layer of the cornea is called the ___________.

Definition 118

epithelium

Term 119

The outermost layer of the cornea, the epithelium, rests on ______________.

Definition 119

Bowman's Membrane

Term 120

The _________ and the ____________ serve to protect the cornea from injury.

Definition 120

epithelium, Bowman's Membrane

Term 121

The ____________ protects the cornea through its ability to quickly regenerate.

Definition 121

epithelium

Term 122

___________ protects the cornea by providing a tough, difficult to penetrate barrier

Definition 122

Bowman's Membrane

Term 123

The innermost layer of the cornea which rests on Descemet's Membrane is called the ___________________.

Definition 123

endothelium

Term 124

What is the function of the endothelium?

Definition 124

It removes water from cornea, helping to keep the cornea clear.

Term 125

What layer of the cornea accounts for 90% of its thickness?

Definition 125

the stroma

Term 126

The __________ controls how much light enters the pupil.

Definition 126

iris

Term 127

How many muscles are found in the iris? What are their names?

Definition 127

2- dilator muscle and sphincter muscle

Term 128

The ________ muscle opens the pupil, allowing more light into the eye.

Definition 128

dilator

Term 129

The ___________ muscle closes the pupil, restricting light into the eye

Definition 129

sphincter

Term 130

The ___________ is just behind the pupil. Its purpose is to focus light on the retina.

Definition 130

crystalline lens

Term 131

Define accommodation.

Definition 131

the process of focusing on objects based on their distance

Term 132

The __________ surround the lens, helping it achieve accomodation.

Definition 132

Ciliary Body

Term 133

What are zonules?

Definition 133

fibrous strands that attach the ciliary body to the lens

Term 134

Describe the process of how the lens allows the eye to focus up close.

Definition 134

the ciliary body contracts and the zonules relax, allowing the lens to thicken and add power

Term 135

Describe the process of how the lens allows the eye to focus at distance.

Definition 135

the ciliary body relaxes and the zonules contract, drawing the lens outward, making the lens thinner and decreasing power

Term 136

The retina consists of photoreceptor cells called _______ and ________.

Definition 136

rods
cones

Term 137

Which photoreceptor cells are the more numerous ones (apprx. 120 million)?

Definition 137

rods

Term 138

Which photoreceptor cells are contained mostly at the periphery?

Definition 138

rods

Term 139

Which photoreceptor cells are suited to night vision and peripheral vision?

Definition 139

rods

Term 140

Which photoreceptor cells have the primary function of detail and color detection?

Definition 140

cones

Term 141

Which photoreceptor cells are the less numerous ones (apprx. 6 million)?

Definition 141

cones

Term 142

Which photoreceptor cells are largely concentrated in the fovea?

Definition 142

cones

Term 143

How many types of cones are there? Describe them.

Definition 143

3- Each type receives only a narrow band of light corresponding largely to a single color.

Term 144

What colors do the three types of cones correspond to?

Definition 144

red, green, or blue

Term 145

The signals received by the cones are sent via the ________ to the brain where they are interpreted as color

Definition 145

optic nerve

Term 146

_________ refers to an eye free of refractive errors.

Definition 146

emmetropia

Term 147

Define myopia. When does it occur?

Definition 147

near-sightedness
It occurs if the eye is longer than normal or the curve of the cornea is too steep, causing light rays focus in front of the retina.

Term 148

What type of refractive error causes light rays to focus in front of the retina?

Definition 148

myopia

Term 149

Define hyperopia. When does it occur?

Definition 149

far-sightedness
It occurs if the eye is too short or the curve of the cornea is too flat, causing light rays to focus behind the retina.

Term 150

What type of refractive error causes light rays to focus behind the retina?

Definition 150

hyperopia

Term 151

When does astigmatism occur?

Definition 151

It occurs when the cornea has an oblong, football-like shape in one or more directions (or axes) causing light rays to focus on more than one point on the retina.

Term 152

What type of refractive error causes light rays to focus on more than one point on the retina?

Definition 152

astigmatism

Term 153

When does presbyopia occur?

Definition 153

When, because of aging, the crystalline lens begins to lose elasticity and is no longer able to accomodate to focus at near points.

Term 154

Around what age does presbyopia occur?

Definition 154

begins at 40

Term 155

Around what age is the loss of elasticity of the crystalline lens complete?

Definition 155

Term 156

What is the term for the condition in which two eyes have unequal refractive power.

Definition 156

Anisometropia

Term 157

_________is an extreme case of anisometropia where one eye is myopic and the other is hyperopic.

Definition 157

Antimetropia

Term 158

The unequal refractive states in antimetropia can lead to __________ and ___________.

Definition 158

diplopia (double vision)
asthenopia (eye strain)

Term 159

If there is a large difference between the two eyes, the brain will often suppress the vision of the blurrier eye. What is this condition called?

Definition 159

amblyopia

Term 160

What is the name of the group of muscles responsible for the stabilization of eye movement?

Definition 160

extraocular muscles

Term 161

How many extraocular muscles are there? Name them.

Definition 161

6:
Lateral rectus
Medial rectus
Superior rectus
Inferior rectus
Superior oblique
Inferior oblique

Term 162

What is the name of the muscle that moves the eye outward, away from the nose?

Definition 162

Lateral rectus

Term 163

What is the name of the muscle that moves the eye inward, toward the nose?

Definition 163

Medial rectus

Term 164

What is the name of the muscle that moves the eye upward and slightly outward?

Definition 164

Superior rectus

Term 165

What is the name of the muscle that moves the eye downward and slightly inward?

Definition 165

Inferior rectus

Term 166

What is the name of the muscle that moves the eye outward and downward?

Definition 166

Superior oblique

Term 167

What is the name of the muscle that moves the eye outward and upward?

Definition 167

Inferior oblique

Term 168

What is diplopia?

Definition 168

double vision

Term 169

Difficulty with fusion can cause double vision (diplopia), or it can cause the brain to "turn off" one image in an effort to eliminate diplopia. This condition is called ____________.

Definition 169

suppression

Term 170

What is suppression?

Definition 170

When one of more of the extraocular muscles are either too strong or too weak, causing difficulty with image fusion. Suppression results when the brain "turns off" one image in order to eliminate double vision.

Term 171

Define phoria.

Definition 171

when the eye has a tendency to turn from its normal position (such as when the patient is tired)

Term 172

Define tropia.

Definition 172

when the eye has a definite or obvious turning from its normal position

Term 173

What is it called when the eye has a tendency to turn downward?

Definition 173

hypophoria

Term 174

What is it called when the eye has a tendency to turn inward?

Definition 174

esophoria

Term 175

What is it called when the eye has an obvious upward deviation?

Definition 175

hypertropia

Term 176

What is it called when the eye has an obvious outward deviation?

Definition 176

exotropia

Term 177

What is the name of electromagnetic radiation that lies just above the visible spectrum (750nm-1mm)?

Definition 177

infrared

Term 178

What is the name of electromagnetic radiation that lies just below the visible spectrum (1nm-400nm)?

Definition 178

ultraviolet

Term 179

List the types of electromagnetic radiation in order of increasing wavelength.

Definition 179

gamma rays
x rays
UV
Visible spectrum (VIB G YOR)
Infrared
Microwave
Radio waves (FM-AM)
Long radio waves

Term 180

What notation is used to indicate index of refraction?

Definition 180

Term 181

What is the index of refraction (n) of air?

Definition 181

Term 182

What is the index of refraction (n) of vitreous humour?

Definition 182

1.33

Term 183

What is the index of refraction (n) of aqueous humour?

Definition 183

1.33

Term 184

What is the index of refraction (n) of the cornea?

Definition 184

1.37

Term 185

What is the index of refraction (n) of the crystaline lens?

Definition 185

1.42

Term 186

What is the index of refraction (n) of CR-39?

Definition 186

1.49

Term 187

What is the index of refraction (n) of crown glass?

Definition 187

1.52

Term 188

What is the index of refraction (n) of polycarbonate?

Definition 188

1.58

Term 189

Light rays pass through a lens and converge 0.50 m from the lens. What is the power of the lens?

Definition 189

P=1/f = 1/.5 = 2D

Term 190

What is the ideal base curve for a mild rx (-1.75 to +2.00)?

Definition 190

Term 191

For plus powers, base curves should ideally be __________ than 6.

Definition 191

Term 192

For minus powers, base curves should ideally be __________ than 6.

Definition 192

less

Term 193

What would be the ideal base curve for moderate plus powers (+2.25 to +5.25)?

Definition 193

Term 194

What would be the ideal base curve for high plus powers (+5.50 to +8.75)?

Definition 194

Term 195

What would be the ideal base curve for very high plus powers (+9.00 to +10.50)?

Definition 195

Term 196

What would be the ideal base curve for super high plus powers (+10.75 to +12.25)?

Definition 196

Term 197

What would be the ideal base curve for extremely high plus powers (+12.25 and up)?

Definition 197

Term 198

What would be the ideal base curve for moderate minus powers (-2.00 to -4.50)?

Definition 198

Term 199

What would be the ideal base curve for high minus powers (-4.75 to -8.00)?

Definition 199

Term 200

What would be the ideal base curve for very high minus powers (-8.00 to -9.00)?

Definition 200

0.5

Term 201

What would be the ideal base curve for super high minus powers (-9.00 and up)?

Definition 201

plano or minus

Term 202

A lens clock is calibrated to read materials with a refractive index of __________.

Definition 202

1.53

Term 203

Hi-index materials will have true power _________ than the measurement given by a lens clock. Why is this?

Definition 203

greater than
The lens clock is calibrated to read materials with a refractive index of 1.53

Term 204

Using a lens clock, if we find the curve on the front surface of the lens to be +6.00 D and determine the back surface to be toric with a measurement of -8.00 D in the 90º meridian and -5.00 in the 180º meridian, what is the true power of the lens?

Definition 204

+1.00 -2.00 x180

Term 205

How many types of refractive errors are there? What are they?

Definition 205

7
Hyperopia
Myopia
Simple hyperopic astigmatism
Simple myopic astigmatism
Compound hyperopic astigmatism
compound myopic astigmatism
mixed astigmatism

Term 206

_____________ has a plano meridian with a plus meridian.

Definition 206

simple hyperopic astigmatism

Term 207

_____________ has a plano meridian with a minus meridian.

Definition 207

simple myopic astigmatism

Term 208

_____________ has two plus meridians.

Definition 208

compound hyperopic astigmatism

Term 209

_____________ has two minus meridians.

Definition 209

compound myopic astigmatism

Term 210

_____________ has one plus and one minus meridian.

Definition 210

mixed astigmatism

Term 211

What type of refractive error is the following rx?

-1.00 -1.50 x079

Definition 211

compound myopic astigmatism

Term 212

What type of refractive error is the following rx?

+1.00 -1.00 x126

Definition 212

simple hyperopic astigmatism

Term 213

What type of refractive error is the following rx?

pl -2.50 x008

Definition 213

simple myopic astigmatism

Term 214

What type of refractive error is the following rx?

+5.25 -2.50 x169

Definition 214

compound hyperopic astigmatism

Term 215

What type of refractive error is the following rx?

+0.75 -2.50 x098

Definition 215

mixed astigmatism

Term 216

What type of refractive error is the following rx?

+3.00 sph

Definition 216

hyperopia

Term 217

What type of refractive error is the following rx?

-2.50 sph

Definition 217

myopia

Term 218

What material accepts tint best?

Definition 218

CR-39

Term 219

____________ is twice as heavy as CR-39 but very durable.

Definition 219

crown glass

Term 220

The tints available with glass are...?

Definition 220

grays, photochromics, pinks, some browns and greens

Term 221

Why is UV coating not applied to glass?

Definition 221

gives it a yellow tint

Term 222

____________ is the recommended material for safety glasses.

Definition 222

polycarbonate

Term 223

Plus cylinder- when the cylinder is surfaced on the front of the lens rather than the back- is mainly used in what circumstance?

Definition 223

diving masks when power calls for a plus lens with cylinder

Term 224

_________ are added to glass to create basic tints.

Definition 224

metallic oxides

Term 225

__________ are added to glass to create photochromic effects.

Definition 225

silver halides

Term 226

_________ is the original material used to make AR coatings.

Definition 226

magnesium flouride

Term 227

AR coatings work through ______________.

Definition 227

destructive interference

Term 228

A plano base curve should be used on what powers?

Definition 228

-6.00 and up

Term 229

A 2.00 base curve should be used on what powers?

Definition 229

-4.00 to -6.00

Term 230

A 4.00 base curve should be used on what powers?

Definition 230

-2.00 to -4.00

Term 231

A 6.00 base curve should be used on what powers?

Definition 231

-2.00 to +2.00

Term 232

A 8.00 base curve should be used on what powers?

Definition 232

+2.00 to +4.00

Term 233

A 10.00 base curve should be used on what powers?

Definition 233

+5.00 to +8.00

Term 234

A 12.00 base curve should be used on what powers?

Definition 234

+8.00 and up

Term 235

Specific gravity describes what?

Definition 235

the density of a material by comparing its density to the density of water

Term 236

The higher the specific gravity of a lens material, the _________ the density, and consequently, the ________ a lens of that material will be for a given power and size.

Definition 236

higher
heavier

Term 237

What is the standard fitting distance for a reading power?

Definition 237

16 inches or 40 cm

Term 238

The standard fitting distance for the intermediate distance in a trifocal is generally _________.

Definition 238

30 inches

Term 239

The intermediate distance in a trifocal is ________ % of the add power.

Definition 239

50%

Term 240

Where is the fitting height measured for a bifocal?

Definition 240

lower lid line

Term 241

Where is the fitting height measured for a trifocal?

Definition 241

bottom of the pupil

Term 242

What type of bifocal is the heaviest?

Definition 242

executive

Term 243

Is image jump greater in round top or flat top bifocals?

Definition 243

round tops

Term 244

What is the power through the intermediate segment of a trifocal lens with the following rx?

+0.50 +1.00 x043 Add: 2.50

Definition 244

+1.75 +1.00 x043

Term 245

Image jump will be more dramatic in a bifocal when ____________.

Definition 245

The OC of the distance area and the OC of the reading portion are far apart

Term 246

Progressives are fit at what point?

Definition 246

pupil center

Term 247

If a patient has cataract surgery and the crystalline lens is removed and not replaced with an implant, the patient will need what type of lens to compensate?

Definition 247

full field and aspheric lenticular

Term 248

What power range is usually used for lenses for a cataract patient after surgical removal of the crystalline lens?

Definition 248

+10.00 to +16.00 or more

Term 249

As a lens moves away from the eye, it becomes more _________.

Definition 249

plus

Term 250

As a lens moves closer to the eye, it becomes more ________.

Definition 250

minus

Term 251

Modification to a power should be made to accommodate for change in effective power at what point?

Definition 251

7.00 diopters or more

Term 252

If a lens sits closer to a patient's eye than the distance at which he was refracted, the power should be altered in what way?

Definition 252

more plus

Term 253

What is the standard instrument vertex?

Definition 253

14mm

Term 254

For a +10 power lens, every millimeter closer vertex distance should result in approximately ______ diopters of ________ power.

Definition 254

.1 additional

Term 255

When light enters a prism, shorter wavelengths are bent to a __________ degree than longer wavelengths.

Definition 255

greater

Term 256

Define chromatic aberration.

Definition 256

the tendency of a material to separate/disperse light that enters it into its various colors

Term 257

A material's level of chromatic aberration can be gauged by its ___________.

Definition 257

abbe value

Term 258

The Abbe value of a material is __________ proportional to the chromatic aberration induced as light passes through it.

Definition 258

inversely

Term 259

Generally speaking, the _______ the index of a lens material, the _______the chromatic aberration, and the _________ the Abbe value.

Definition 259

higher
higher
lower

Term 260

The __________ of the material describes the percentage of incident light reflected from a highly polished surface of that material and is calculated from the refractive index of a material

Definition 260

reflectance

Term 261

What is the formula used to determine reflectance:
When light hits a lens surface in air normally, the percentage of light reflected at each surface is calculated using this formula.

Definition 261

R = (n - 1)^2/(n + 1)^2 * 100%

where R = reflectance
and n = refractive index of material

Term 262

Calculate the reflectance of polycarbonate

Definition 262

R = (1.58-1)^2/(1.58+1)^2
R = .3364/6.6564
R = .05054 = 5.054% per surface

Term 263

The ____________ of a lens material describes the amount of light (usually specified for a given waveband) that will pass through that material.

Definition 263

transmittance

Term 264

________is most stable, scratch-resistant, and provides the best optical quality of all lens materials.

Definition 264

glass

Term 265

What type of aberration is more pronounced in high-index glass than regular glass?

Definition 265

chromatic aberration

Term 266

Name 3 positive aspects of glass lenses.

Definition 266

best optics
stable material
scratch resistant

Term 267

Name 3 negative aspects of glass lenses.

Definition 267

difficult to tint
lacks impact resistance (too brittle)
heaviness

Term 268

Glass is ____x heavier than plastic.

Definition 268

Term 269

Name 3 positive aspects of CR-39 lenses.

Definition 269

easily tintable
lighter than glass
less likely to fog

Term 270

Name 2 negative aspects of CR-39 lenses.

Definition 270

more susceptible to scratching
lower index of refraction than glass

Term 271

Name 3 positive aspects of polycarbonate lenses.

Definition 271

impact resistant
thinner & lighter than plastic
inherent UV protection

Term 272

Name 4 negative aspects of polycarbonate lenses.

Definition 272

not easily tinted
soft (scratches easily)
poor optics
susceptible to stress fractures in drill mounts

Term 273

What are the benefits of aspheric lenses?

Definition 273

reduced spatial distortion
reduced magnification or minification
maintains a thin and flat lens profile

Term 274

Patients who are sensitive to chromatic aberration may have issues with which types of lens materials?

Definition 274

polycarbonate
high-index
possibly trivex

Term 275

What is the abbe value of trivex?

Definition 275

43-45

Term 276

What is the index of refraction of trivex?

Definition 276

1.53

Term 277

What materials have natural UV protection?

Definition 277

trivex & polycarbonate

Term 278

What is the lightest lens material available?

Definition 278

Trivex (specific gravity of 1.11)

Term 279

What are the positive aspects of trivex?

Definition 279

Impact resistance of polycarbonate Better optics than polycarbonate
Tintable
Lightest material on the market
Inherent UV protection
High tensile strength (ideal for drill mounts)

Term 280

Definition 280

Term 281

Internal reflections viewed as multiple rings inside the lens are most common with what type of lens?

Definition 281

high minus

Term 282

Blurred or ghost images due to light reflection within a lens can significantly impair vision, especially during what situation?

Definition 282

at night around bright lights common in dusk or night time driving conditions

Term 283

Bright sun light hitting the back surface of a sun lens that is not AR coated, depending on the angle, can either ________________ or can ________________.

Definition 283

be reflected directly back into the eye

"fill" the lens with reflected light

Term 284

_____________ allow more light to reach the eye increasing contrast and clarity as well as help to reduce eye strain.

Definition 284

AR coatings

Term 285

Polarized lenses significantly increase driving safety, especially at what times?

Definition 285

morning and late afternoon

Term 286

What is a good analogy to use to describe how polarized lenses work?

Definition 286

venetian blinds- they force the light to enter only at a certain angle

Term 287

Why is polarization better than tinting?

Definition 287

Although tinting reduces brightness and therefore increases wearer comfort, it doesn't reduce glare like polarization does.
Also, tinting can be actually lead to increased UV damage since the eyes dilate behind the dark tint and allow more light in. Polarization blocks harmful UV rays.

Term 288

These type of coatings are produced relatively cheaply. They are applied by dipping the lens into a chemical solution and curing the lens in an oven.

Definition 288

Dip-Coating

Term 289

These coatings are applied to a spinning lens. The lenses must be cured after the hardcoat chemicals are applied. The curing can be done in an oven or by ultraviolet light.

Definition 289

Spin-Coating

Term 290

These coatings are made by adding the hardcoat chemical at the time that the lenses are being formed. Most lens manufacturers are using this type of coating process. This process is generally used on semi-finished lenses only. These coatings tend to be non-tintable.

Definition 290

In-mould Coating

Term 291

This is a process that is becoming more popular with the rise in anti-reflective coating use. The cost is generally much higher than the other methods. When this type of hard coat is produced at the same time and in conjunction with an anti-reflective coating, the costs difference is not as prohibitive.

Definition 291

Vacuum Coatings

Term 292

These are highly reflective coatings and are used to reduce the light transmission through a lens. They are produced in a vacuum process.

Definition 292

Mirror Coatings

Term 293

What is the desired vertex distance when fitting a pair of glasses?

Definition 293

10-14mm

Term 294

What is the best range for degree of face form when fitting a pair of glasses?

Definition 294

5-10 degrees

Term 295

What is the desired range for pantoscopic tilt when fitting a pair of glasses?

Definition 295

10-15 degrees

Term 296

When the lenses are ground to specification, the lab will often incorporate prism. What is this process called?

Definition 296

equi-thinning, prism thinning, or yolk prism

Term 297

What is the focal distance used for a lens meant for computer use?

Definition 297

20-24 inches (50-60 cm)

Term 298

What is the focal distance used for a lens meant for reading?

Definition 298

14-18 inches (35-45 cm)

Term 299

What is the minimum center thickness for a basic impact safety lens?

Definition 299

3 mm

Term 300

What is the minimum edge thickness for a basic impact safety lens?

Definition 300

2.5 mm (if it is +3.00 diopters or higher)

Term 301

A basic impact safety lens must pass what type of test?

Definition 301

a drop ball test of a 1 inch diameter steel ball dropped 50 inches

Term 302

What is the minimum center thickness for a high impact safety lens?

Definition 302

2.5 mm

Term 303

A high impact safety lens must pass what type of test?

Definition 303

a high velocity test in which a ¼ inch steel ball is shot at a lens at 150 ft/second

Term 304

What are the material options for a high impact safety lens?

Definition 304

polycarbonate, Trivex, or SR-91

Term 305

How can you tell if a frame is impact resistant enough to be considered a safety frame?

Definition 305

marked with "Z87+" on the frame front and temple.

Term 306

What is the chassis?

Definition 306

The frame front

Term 307

What are guard arms?

Definition 307

the wires that attach the nosepads to the frame

Term 308

What is the endpiece?

Definition 308

the area of the chassis that attaches to the temple

Term 309

What is the ideal amount of pantoscopic tilt for most frames?

Definition 309

8-10 degrees

Term 310

What is orthoscopic tilt?

Definition 310

when a frame has 0 degrees of pantoscopic tilt (no tilt)

Term 311

What is retroscopic tilt?

Definition 311

when a frame is farther from the patient's face at the bottom of the lens than it is at the top

Term 312

What are the 4 basic adjustments that can be made to nosepads?

Definition 312

width
splay angle
frontal angle
vertical angle

Term 313

What is splay angle?

Definition 313

the angle of the pads when viewed from the top of the frame- the front edges of the pads should be closer together than the back edges

Term 314

What is frontal angle?

Definition 314

the angle of the pads when viewed from the front of the frame- the tops of the pads should be slightly closer together than the bottoms of the pad following the contours of the nose as it gets wider from top to bottom

Term 315

What is vertical angle?

Definition 315

the angle of the pads when viewed from the side of the frame. Since most frames will have some amount of pantoscopic tilt, the bottoms of the pads should be slightly closer to the frame front than the tops