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ABO study material
Opticianry Certification
315
Physics
Professional
05/14/2012

Additional Physics Flashcards

 


 

Cards

Term
How many millimeters are in an inch?
Definition
25.4 mm = 1 inch
Term
What is the spectrum of visible light, in nm?
Definition
from ~400nm to ~700nm
Term
List the colors of the spectrum, from longest wavelength to shortest.
Definition
Red, Orange, Yellow, Green, Blue, Indigo, Violet
Term
What is the spectrum of UV light, in nm?
Definition
from ~200nm to ~400nm
Term
How are the bands in the UV spectrum categorized?
Definition
A, B, & C (with C being blocked by the Earth's atmosphere)
Term
What distance is considered at infinity? Why?
Definition
20 feet- because after light leaves its source, it diverges and becomes parallel at 20 feet
Term
What is the speed of light?
Definition
186,000 miles/second
Term
What happens when light enters a transparent medium at 90 degrees?
Definition
It slows down and continues onward.
Term
What happens when light enters a transparent medium at an oblique angle?
Definition
Refraction- it changes the angle of light
Term
Each time light encounters a different material, (blank) occurs.
Definition
Refraction
Term
Define "Index of Refraction"
Definition
the degree that light is bent in a given material based on that material's density
Term
How is Index of Refraction determined?
Definition
speed of light/speed through the material
Term
What is the index of refraction of polycarbonate?
Definition
1.589
Term
What is the index of refraction of CR39?
Definition
1.49
Term
Is material more or less dense with a higher index of refraction?
Definition
more
Term
What is the index of refraction of glass?
Definition
1.523
Term
What is the index of refraction of flint glass?
Definition
1.70
Term
What is the standard index of refraction in the optical industry, which all instruments are calibrated to?
Definition
1.53
Term
Define Dispersion
Definition
when light is broken down into basic colors causing a rainbow effect
Term
What is abbe value (or Nu value)?
Definition
measure of how easily dispersion happens
Term
Abbe values are between what numbers?
Definition
29 and 60
Term
Do higher or lower abbe values result in the least dispersion and best vision?
Definition
higher
Term
What is the abbe value for plastic?
Definition
59-60
Term
What is the abbe value for glass?
Definition
60
Term
What is the abbe value for high index resin?
Definition
43
Term
What is the abbe value for polycarbonate?
Definition
29-31
Term
What is the abbe value for flint glass?
Definition
38-40
Term
What 3 things happen as light hits a medium?
Definition
Refraction
Absorption
Reflection
Term
As light enters and exits any medium, what percent of light is lost (assuming medium is non-coated)?
Definition
~8% loss of light (~4% on each surface)
Term
What is the normal?
Definition
a line drawn at right angles to the material's surface at the ray's point of entry
Term
What is the incident ray?
Definition
the ray coming into the material (before it enters)
Term
When does the incident ray become the refracted ray?
Definition
As it enters and leaves the material
Term
More curve induces (more or less?) refraction
Definition
more
Term
What is a diopter?
Definition
the measure of the power of a lens to refract light
Term
A lens that can focus parallel light to a point at one meter has what power?
Definition
1 diopter
Term
What is the formula for determining diopter power? D=?
Definition
D = 1/f where f is the focal length of the lens in meters
Term
How do you determine focal point, given the power of a lens in diopters?
Definition
f = 1/D
Term
How do you convert magnification to diopter power?
Definition
multiply the magnification by 4 (2x is 8 diopters)
Term
What are the 3 types of plus lens configurations?
Definition
Bi-convex ()
plano convex [)
meniscus ))
Term
What type of lens magnifies an image?
Definition
plus lens
Term
What type of lens is thicker in the center and thinner at the edges?
Definition
plus lens
Term
What type of lens demonstrates "against" motion (if the lens is moved side to side, the image seems to go the opposite direction)?
Definition
plus lens
Term
What are the three types of refractive errors that plus lenses correct for?
Definition
hyperopia
presbyopia
aphakia
Term
What are the 3 types of minus lens configurations?
Definition
Bi-concave )(
plano concave )]
meniscus ))
Term
What type of lens minifies an image?
Definition
minus lens
Term
What type of lens is thicker at the edges and thinner in the middle?
Definition
minus lens
Term
What type of lens demonstrates "with" motion (if the lens is moved side to side, the image seems to go the same direction)?
Definition
minus lens
Term
What type of refractive error do minus lenses correct for?
Definition
myopia
Term
How do you determine power in diopters using a lens clock?
Definition
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
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
+1
Term
How do you transpose an rx?
Definition
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
When prism changes the direction of light, this is known as _________ or _______.
Definition
diffraction or deviation
Term
If a prism is strong enough, light can be separated into different colors. This is called ________.
Definition
dispersion
Term
Which direction does light entering a prism bend?
Definition
toward the normal
Term
The image appears toward the _________ of a prism when looking in while it is actually toward the __________.
Definition
apex
base
Term
What measurement is used to indicate the amount of deviation of a prism?
Definition
diopter
Term
The ________ a prism, the more light it will bend.
Definition
larger
Term
T or F: A prism focuses light.
Definition
False. A prism only deviates/shifts light, not focuses it
Term
T or F: A prism does not magnify or minify an image.
Definition
True. it only shifts/deviates
Term
Does a steeper angle on a prism result in more or less deviation?
Definition
more (greater angle of deviation)
Term
If light passes through the center of a lens, it will neither converge nor diverge. This represents the _________ or the ___________.
Definition
optical center
axial ray
Term
What type of lens converges light?
Definition
plus lens
Term
What type of lens diverges light?
Definition
minus lens
Term
In a minus lens, if the pupil is below the optical center of the lens, what type of prism is induced?
Definition
Base down prism
Term
In a minus lens, if the pupil is above the optical center of the lens, what type of prism is induced?
Definition
Base up prism
Term
In a minus lens, if the optical center of the lens is moved toward the nasal, this induces what type of prism?
Definition
Base out prism
Term
In a minus lens, if the optical center of the lens is moved toward the temple, this induces what type of prism?
Definition
Base in prism
Term
In a plus lens, if the pupil is below the optical center of the lens, what type of prism is induced?
Definition
Base up prism
Term
In a plus lens, if the pupil is above the optical center of the lens, what type of prism is induced?
Definition
Base down prism
Term
In a plus lens, if the optical center of the lens is moved toward the nasal, this induces what type of prism?
Definition
Base in prism
Term
In a plus lens, if the optical center of the lens is moved toward the temple, this induces what type of prism?
Definition
Base out prism
Term
What formula determines the prism in a lens at a given point, or how much to decenter a lens to induce prism?
Definition
Prentice's Formula
Term
Prentice's Formula
Definition
P = (h x D)/10

P = power in prism diopters
h = OC distance in mm
D = dioptric power of lens
Term
How much prism is induced when a 3D lens is decentered by 5 mm?
Definition
5x3/10 = 1.5 diopters of prism
Term
How much prism is induced in a -4.25 lens decentered by 4 mm?
Definition
4 x -4.25/10 = 1.7 diopters of prism
Term
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
3.75 diopters of prism

*use power at 90 degrees since shifting down, which is -6.25
Term
How far is a lens moved to have 5D of prism in a 2D power lens?
Definition
(5*10)/2=h
25 mm = h
Term
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
(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
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
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
How many diopters of difference between eyes will induce double vision when looking away from the optical center?
Definition
2+ diopters of difference
Term
What is another name for slab off prism?
Definition
bicentric grinding
Term
When 2 separate optical centers are ground into one lens, what is it called?
Definition
slab off prism or bicentric grinding
Term
How do you determine which eye slab off prism should be done in?
Definition
the most minus (or least plus) lens
Term
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
the left eye (it is the most minus)
Term
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
OD: 2x10/10= 2D BU prism
OS: 5x10/10= 5D BU prism
Term
What is diplopia?
Definition
double vision
Term
Why don't you need to use slab off prism with single vision lenses?
Definition
patient can move head to look through OC
Term
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
*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
What is the RX for the split prism version of this RX?
OD: -0.50 3 BD
OS: -1.00
Definition
OD: -0.50 1.5 BD
OS: -1.00 1.5 BU
Term
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
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
When splitting prism, base out and base in are split in what direction?
Definition
the same direction (both eyes BO or both eyes BI)
Term
When splitting prism, base up and base down are split in what direction?
Definition
opposite directions (one eye of each)
Term
How many tunics (layers) make up the outer part of the eye? What are they (listed from outermost to innermost)?
Definition
3- fibrous tunic, vascular tunic, and nervous tunic
Term
What is the name of the outer tunic of the eye that is mostly composed of dense connective tissue?
Definition
The fibrous tunic
Term
The fibrous tunic is divided into the __________ and the ____________.
Definition
sclera, cornea
Term
How much refractive power (in diopters) does the cornea have?
Definition
43 diopters
Term
Which outer tunic contains the blood vessels that supply the retina with nutrients?
Definition
choroid tunic
Term
What is the name for the white part of the eye?
Definition
sclera
Term
What part of the eye is translucent and serves as a passageway for light to enter the eye?
Definition
cornea
Term
Which tunic is also known as the choroid tunic?
Definition
vascular tunic
Term
The ___________ helps to refract light and to focus on the retina.
Definition
cornea
Term
What layer contains a high concentration of dark pigments that help absorb excess light?
Definition
choroid
Term
The _________ is primarily composed of nerve tissue and forms a thin internal membrane of the eye.
Definition
retina
Term
The vascular tunic consists of...?
Definition
iris, choroid, & ciliary body
Term
The inner layer of photoreceptors and neurons (the nervous tunic) consists of...?
Definition
the retina
Term
How many segments/chambers are contained within the inner part of the eye? What are they?
Definition
3- anterior chamber, posterior chamber, & vitreous chamber
Term
The fluid filled area between the cornea and the iris is the ________.
Definition
anterior chamber
Term
The fluid filled area between the iris and the lens is know as the __________.
Definition
posterior chamber
Term
The anterior and posterior chambers contain a fluid known as _____________.
Definition
aqueous humour
Term
Define aqueous humour.
Definition
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
Aqueous humor is continually drained from the eye through the ____________.
Definition
Canal of Schlemm
Term
The greatest volume of the inner chambers, forming about four-fifths of the eye, is the ________________.
Definition
vitreous chamber
Term
The vitreous chamber is found between the _________ and the __________.
Definition
retina, lens
Term
What is vitreous humour?
Definition
a thicker gel-like substance contained within the vitreous chamber which maintains the shape of the eye
Term
What does vitreous humour do?
Definition
maintains the shape of the eye
Term
What does aqueous humour do?
Definition
maintains IOP, provides nutrients to the lens and cornea
Term
The cornea consists of how many distinct layers?
Definition
5
epithelium
Bowman's Membrane
Stroma
Descemet's Membrane
Endothelium
Term
The outermost layer of the cornea is called the ___________.
Definition
epithelium
Term
The outermost layer of the cornea, the epithelium, rests on ______________.
Definition
Bowman's Membrane
Term
The _________ and the ____________ serve to protect the cornea from injury.
Definition
epithelium, Bowman's Membrane
Term
The ____________ protects the cornea through its ability to quickly regenerate.
Definition
epithelium
Term
___________ protects the cornea by providing a tough, difficult to penetrate barrier
Definition
Bowman's Membrane
Term
The innermost layer of the cornea which rests on Descemet's Membrane is called the ___________________.
Definition
endothelium
Term
What is the function of the endothelium?
Definition
It removes water from cornea, helping to keep the cornea clear.
Term
What layer of the cornea accounts for 90% of its thickness?
Definition
the stroma
Term
The __________ controls how much light enters the pupil.
Definition
iris
Term
How many muscles are found in the iris? What are their names?
Definition
2- dilator muscle and sphincter muscle
Term
The ________ muscle opens the pupil, allowing more light into the eye.
Definition
dilator
Term
The ___________ muscle closes the pupil, restricting light into the eye
Definition
sphincter
Term
The ___________ is just behind the pupil. Its purpose is to focus light on the retina.
Definition
crystalline lens
Term
Define accommodation.
Definition
the process of focusing on objects based on their distance
Term
The __________ surround the lens, helping it achieve accomodation.
Definition
Ciliary Body
Term
What are zonules?
Definition
fibrous strands that attach the ciliary body to the lens
Term
Describe the process of how the lens allows the eye to focus up close.
Definition
the ciliary body contracts and the zonules relax, allowing the lens to thicken and add power
Term
Describe the process of how the lens allows the eye to focus at distance.
Definition
the ciliary body relaxes and the zonules contract, drawing the lens outward, making the lens thinner and decreasing power
Term
The retina consists of photoreceptor cells called _______ and ________.
Definition
rods
cones
Term
Which photoreceptor cells are the more numerous ones (apprx. 120 million)?
Definition
rods
Term
Which photoreceptor cells are contained mostly at the periphery?
Definition
rods
Term
Which photoreceptor cells are suited to night vision and peripheral vision?
Definition
rods
Term
Which photoreceptor cells have the primary function of detail and color detection?
Definition
cones
Term
Which photoreceptor cells are the less numerous ones (apprx. 6 million)?
Definition
cones
Term
Which photoreceptor cells are largely concentrated in the fovea?
Definition
cones
Term
How many types of cones are there? Describe them.
Definition
3- Each type receives only a narrow band of light corresponding largely to a single color.
Term
What colors do the three types of cones correspond to?
Definition
red, green, or blue
Term
The signals received by the cones are sent via the ________ to the brain where they are interpreted as color
Definition
optic nerve
Term
_________ refers to an eye free of refractive errors.
Definition
emmetropia
Term
Define myopia. When does it occur?
Definition
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
What type of refractive error causes light rays to focus in front of the retina?
Definition
myopia
Term
Define hyperopia. When does it occur?
Definition
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
What type of refractive error causes light rays to focus behind the retina?
Definition
hyperopia
Term
When does astigmatism occur?
Definition
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
What type of refractive error causes light rays to focus on more than one point on the retina?
Definition
astigmatism
Term
When does presbyopia occur?
Definition
When, because of aging, the crystalline lens begins to lose elasticity and is no longer able to accomodate to focus at near points.
Term
Around what age does presbyopia occur?
Definition
begins at 40
Term
Around what age is the loss of elasticity of the crystalline lens complete?
Definition
65
Term
What is the term for the condition in which two eyes have unequal refractive power.
Definition
Anisometropia
Term
_________is an extreme case of anisometropia where one eye is myopic and the other is hyperopic.
Definition
Antimetropia
Term
The unequal refractive states in antimetropia can lead to __________ and ___________.
Definition
diplopia (double vision)
asthenopia (eye strain)
Term
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
amblyopia
Term
What is the name of the group of muscles responsible for the stabilization of eye movement?
Definition
extraocular muscles
Term
How many extraocular muscles are there? Name them.
Definition
6:
Lateral rectus
Medial rectus
Superior rectus
Inferior rectus
Superior oblique
Inferior oblique
Term
What is the name of the muscle that moves the eye outward, away from the nose?
Definition
Lateral rectus
Term
What is the name of the muscle that moves the eye inward, toward the nose?
Definition
Medial rectus
Term
What is the name of the muscle that moves the eye upward and slightly outward?
Definition
Superior rectus
Term
What is the name of the muscle that moves the eye downward and slightly inward?
Definition
Inferior rectus
Term
What is the name of the muscle that moves the eye outward and downward?
Definition
Superior oblique
Term
What is the name of the muscle that moves the eye outward and upward?
Definition
Inferior oblique
Term
What is diplopia?
Definition
double vision
Term
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
suppression
Term
What is suppression?
Definition
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
Define phoria.
Definition
when the eye has a tendency to turn from its normal position (such as when the patient is tired)
Term
Define tropia.
Definition
when the eye has a definite or obvious turning from its normal position
Term
What is it called when the eye has a tendency to turn downward?
Definition
hypophoria
Term
What is it called when the eye has a tendency to turn inward?
Definition
esophoria
Term
What is it called when the eye has an obvious upward deviation?
Definition
hypertropia
Term
What is it called when the eye has an obvious outward deviation?
Definition
exotropia
Term
What is the name of electromagnetic radiation that lies just above the visible spectrum (750nm-1mm)?
Definition
infrared
Term
What is the name of electromagnetic radiation that lies just below the visible spectrum (1nm-400nm)?
Definition
ultraviolet
Term
List the types of electromagnetic radiation in order of increasing wavelength.
Definition
gamma rays
x rays
UV
Visible spectrum (VIB G YOR)
Infrared
Microwave
Radio waves (FM-AM)
Long radio waves
Term
What notation is used to indicate index of refraction?
Definition
n
Term
What is the index of refraction (n) of air?
Definition
1
Term
What is the index of refraction (n) of vitreous humour?
Definition
1.33
Term
What is the index of refraction (n) of aqueous humour?
Definition
1.33
Term
What is the index of refraction (n) of the cornea?
Definition
1.37
Term
What is the index of refraction (n) of the crystaline lens?
Definition
1.42
Term
What is the index of refraction (n) of CR-39?
Definition
1.49
Term
What is the index of refraction (n) of crown glass?
Definition
1.52
Term
What is the index of refraction (n) of polycarbonate?
Definition
1.58
Term
Light rays pass through a lens and converge 0.50 m from the lens. What is the power of the lens?
Definition
P=1/f = 1/.5 = 2D
Term
What is the ideal base curve for a mild rx (-1.75 to +2.00)?
Definition
6
Term
For plus powers, base curves should ideally be __________ than 6.
Definition
more
Term
For minus powers, base curves should ideally be __________ than 6.
Definition
less
Term
What would be the ideal base curve for moderate plus powers (+2.25 to +5.25)?
Definition
8
Term
What would be the ideal base curve for high plus powers (+5.50 to +8.75)?
Definition
10
Term
What would be the ideal base curve for very high plus powers (+9.00 to +10.50)?
Definition
12
Term
What would be the ideal base curve for super high plus powers (+10.75 to +12.25)?
Definition
14
Term
What would be the ideal base curve for extremely high plus powers (+12.25 and up)?
Definition
16
Term
What would be the ideal base curve for moderate minus powers (-2.00 to -4.50)?
Definition
4
Term
What would be the ideal base curve for high minus powers (-4.75 to -8.00)?
Definition
2
Term
What would be the ideal base curve for very high minus powers (-8.00 to -9.00)?
Definition
0.5
Term
What would be the ideal base curve for super high minus powers (-9.00 and up)?
Definition
plano or minus
Term
A lens clock is calibrated to read materials with a refractive index of __________.
Definition
1.53
Term
Hi-index materials will have true power _________ than the measurement given by a lens clock. Why is this?
Definition
greater than
The lens clock is calibrated to read materials with a refractive index of 1.53
Term
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
+1.00 -2.00 x180
Term
How many types of refractive errors are there? What are they?
Definition
7
Hyperopia
Myopia
Simple hyperopic astigmatism
Simple myopic astigmatism
Compound hyperopic astigmatism
compound myopic astigmatism
mixed astigmatism
Term
_____________ has a plano meridian with a plus meridian.
Definition
simple hyperopic astigmatism
Term
_____________ has a plano meridian with a minus meridian.
Definition
simple myopic astigmatism
Term
_____________ has two plus meridians.
Definition
compound hyperopic astigmatism
Term
_____________ has two minus meridians.
Definition
compound myopic astigmatism
Term
_____________ has one plus and one minus meridian.
Definition
mixed astigmatism
Term
What type of refractive error is the following rx?

-1.00 -1.50 x079
Definition
compound myopic astigmatism
Term
What type of refractive error is the following rx?

+1.00 -1.00 x126
Definition
simple hyperopic astigmatism
Term
What type of refractive error is the following rx?

pl -2.50 x008
Definition
simple myopic astigmatism
Term
What type of refractive error is the following rx?

+5.25 -2.50 x169
Definition
compound hyperopic astigmatism
Term
What type of refractive error is the following rx?

+0.75 -2.50 x098
Definition
mixed astigmatism
Term
What type of refractive error is the following rx?

+3.00 sph
Definition
hyperopia
Term
What type of refractive error is the following rx?

-2.50 sph
Definition
myopia
Term
What material accepts tint best?
Definition
CR-39
Term
____________ is twice as heavy as CR-39 but very durable.
Definition
crown glass
Term
The tints available with glass are...?
Definition
grays, photochromics, pinks, some browns and greens
Term
Why is UV coating not applied to glass?
Definition
gives it a yellow tint
Term
____________ is the recommended material for safety glasses.
Definition
polycarbonate
Term
Plus cylinder- when the cylinder is surfaced on the front of the lens rather than the back- is mainly used in what circumstance?
Definition
diving masks when power calls for a plus lens with cylinder
Term
_________ are added to glass to create basic tints.
Definition
metallic oxides
Term
__________ are added to glass to create photochromic effects.
Definition
silver halides
Term
_________ is the original material used to make AR coatings.
Definition
magnesium flouride
Term
AR coatings work through ______________.
Definition
destructive interference
Term
A plano base curve should be used on what powers?
Definition
-6.00 and up
Term
A 2.00 base curve should be used on what powers?
Definition
-4.00 to -6.00
Term
A 4.00 base curve should be used on what powers?
Definition
-2.00 to -4.00
Term
A 6.00 base curve should be used on what powers?
Definition
-2.00 to +2.00
Term
A 8.00 base curve should be used on what powers?
Definition
+2.00 to +4.00
Term
A 10.00 base curve should be used on what powers?
Definition
+5.00 to +8.00
Term
A 12.00 base curve should be used on what powers?
Definition
+8.00 and up
Term
Specific gravity describes what?
Definition
the density of a material by comparing its density to the density of water
Term
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
higher
heavier
Term
What is the standard fitting distance for a reading power?
Definition
16 inches or 40 cm
Term
The standard fitting distance for the intermediate distance in a trifocal is generally _________.
Definition
30 inches
Term
The intermediate distance in a trifocal is ________ % of the add power.
Definition
50%
Term
Where is the fitting height measured for a bifocal?
Definition
lower lid line
Term
Where is the fitting height measured for a trifocal?
Definition
bottom of the pupil
Term
What type of bifocal is the heaviest?
Definition
executive
Term
Is image jump greater in round top or flat top bifocals?
Definition
round tops
Term
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
+1.75 +1.00 x043
Term
Image jump will be more dramatic in a bifocal when ____________.
Definition
The OC of the distance area and the OC of the reading portion are far apart
Term
Progressives are fit at what point?
Definition
pupil center
Term
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
full field and aspheric lenticular
Term
What power range is usually used for lenses for a cataract patient after surgical removal of the crystalline lens?
Definition
+10.00 to +16.00 or more
Term
As a lens moves away from the eye, it becomes more _________.
Definition
plus
Term
As a lens moves closer to the eye, it becomes more ________.
Definition
minus
Term
Modification to a power should be made to accommodate for change in effective power at what point?
Definition
7.00 diopters or more
Term
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
more plus
Term
What is the standard instrument vertex?
Definition
14mm
Term
For a +10 power lens, every millimeter closer vertex distance should result in approximately ______ diopters of ________ power.
Definition
.1 additional
Term
When light enters a prism, shorter wavelengths are bent to a __________ degree than longer wavelengths.
Definition
greater
Term
Define chromatic aberration.
Definition
the tendency of a material to separate/disperse light that enters it into its various colors
Term
A material's level of chromatic aberration can be gauged by its ___________.
Definition
abbe value
Term
The Abbe value of a material is __________ proportional to the chromatic aberration induced as light passes through it.
Definition
inversely
Term
Generally speaking, the _______ the index of a lens material, the _______the chromatic aberration, and the _________ the Abbe value.
Definition
higher
higher
lower
Term
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
reflectance
Term
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
R = (n - 1)^2/(n + 1)^2 * 100%

where R = reflectance
and n = refractive index of material
Term
Calculate the reflectance of polycarbonate
Definition
R = (1.58-1)^2/(1.58+1)^2
R = .3364/6.6564
R = .05054 = 5.054% per surface
Term
The ____________ of a lens material describes the amount of light (usually specified for a given waveband) that will pass through that material.
Definition
transmittance
Term
________is most stable, scratch-resistant, and provides the best optical quality of all lens materials.
Definition
glass
Term
What type of aberration is more pronounced in high-index glass than regular glass?
Definition
chromatic aberration
Term
Name 3 positive aspects of glass lenses.
Definition
best optics
stable material
scratch resistant
Term
Name 3 negative aspects of glass lenses.
Definition
difficult to tint
lacks impact resistance (too brittle)
heaviness
Term
Glass is ____x heavier than plastic.
Definition
2
Term
Name 3 positive aspects of CR-39 lenses.
Definition
easily tintable
lighter than glass
less likely to fog
Term
Name 2 negative aspects of CR-39 lenses.
Definition
more susceptible to scratching
lower index of refraction than glass
Term
Name 3 positive aspects of polycarbonate lenses.
Definition
impact resistant
thinner & lighter than plastic
inherent UV protection
Term
Name 4 negative aspects of polycarbonate lenses.
Definition
not easily tinted
soft (scratches easily)
poor optics
susceptible to stress fractures in drill mounts
Term
What are the benefits of aspheric lenses?
Definition
reduced spatial distortion
reduced magnification or minification
maintains a thin and flat lens profile
Term
Patients who are sensitive to chromatic aberration may have issues with which types of lens materials?
Definition
polycarbonate
high-index
possibly trivex
Term
What is the abbe value of trivex?
Definition
43-45
Term
What is the index of refraction of trivex?
Definition
1.53
Term
What materials have natural UV protection?
Definition
trivex & polycarbonate
Term
What is the lightest lens material available?
Definition
Trivex (specific gravity of 1.11)
Term
What are the positive aspects of trivex?
Definition
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
[image]
Definition
Term
Internal reflections viewed as multiple rings inside the lens are most common with what type of lens?
Definition
high minus
Term
Blurred or ghost images due to light reflection within a lens can significantly impair vision, especially during what situation?
Definition
at night around bright lights common in dusk or night time driving conditions
Term
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
be reflected directly back into the eye

"fill" the lens with reflected light
Term
_____________ allow more light to reach the eye increasing contrast and clarity as well as help to reduce eye strain.
Definition
AR coatings
Term
Polarized lenses significantly increase driving safety, especially at what times?
Definition
morning and late afternoon
Term
What is a good analogy to use to describe how polarized lenses work?
Definition
venetian blinds- they force the light to enter only at a certain angle
Term
Why is polarization better than tinting?
Definition
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
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
Dip-Coating
Term
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
Spin-Coating
Term
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
In-mould Coating
Term
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
Vacuum Coatings
Term
These are highly reflective coatings and are used to reduce the light transmission through a lens. They are produced in a vacuum process.
Definition
Mirror Coatings
Term
What is the desired vertex distance when fitting a pair of glasses?
Definition
10-14mm
Term
What is the best range for degree of face form when fitting a pair of glasses?
Definition
5-10 degrees
Term
What is the desired range for pantoscopic tilt when fitting a pair of glasses?
Definition
10-15 degrees
Term
When the lenses are ground to specification, the lab will often incorporate prism. What is this process called?
Definition
equi-thinning, prism thinning, or yolk prism
Term
What is the focal distance used for a lens meant for computer use?
Definition
20-24 inches (50-60 cm)
Term
What is the focal distance used for a lens meant for reading?
Definition
14-18 inches (35-45 cm)
Term
What is the minimum center thickness for a basic impact safety lens?
Definition
3 mm
Term
What is the minimum edge thickness for a basic impact safety lens?
Definition
2.5 mm (if it is +3.00 diopters or higher)
Term
A basic impact safety lens must pass what type of test?
Definition
a drop ball test of a 1 inch diameter steel ball dropped 50 inches
Term
What is the minimum center thickness for a high impact safety lens?
Definition
2.5 mm
Term
A high impact safety lens must pass what type of test?
Definition
a high velocity test in which a ¼ inch steel ball is shot at a lens at 150 ft/second
Term
What are the material options for a high impact safety lens?
Definition
polycarbonate, Trivex, or SR-91
Term
How can you tell if a frame is impact resistant enough to be considered a safety frame?
Definition
marked with "Z87+" on the frame front and temple.
Term
What is the chassis?
Definition
The frame front
Term
What are guard arms?
Definition
the wires that attach the nosepads to the frame
Term
What is the endpiece?
Definition
the area of the chassis that attaches to the temple
Term
What is the ideal amount of pantoscopic tilt for most frames?
Definition
8-10 degrees
Term
What is orthoscopic tilt?
Definition
when a frame has 0 degrees of pantoscopic tilt (no tilt)
Term
What is retroscopic tilt?
Definition
when a frame is farther from the patient's face at the bottom of the lens than it is at the top
Term
What are the 4 basic adjustments that can be made to nosepads?
Definition
width
splay angle
frontal angle
vertical angle
Term
What is splay angle?
Definition
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
What is frontal angle?
Definition
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
What is vertical angle?
Definition
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
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