MIDTERM REVIEW Flashcards
1
Q
Physical optics
A
is primarily concerned with the nature and properties of light itself deals with the mechanism of vision and the physiology and psychology of seeing
2
Q
Geometric optics
A
is the branch of optics in which the laws of geometry can be used to design lenses that include spectacles (glasses), optical instruments, telescopes, microscopes, cameras, etc.
3
Q
Physiologic optics
A
deals with the mechanism of vision and the physiology and psychology of seeing
4
Q
2 main theories of light
A
Wave Theory and Corpuscular theory
5
Q
Wavelength
A
Crest to crest or trough to through The wavelength of a given wave is the distance from the crest (peak) of one wave to the crest of the next (or trough to trough)
6
Q
Frequency
A
is the number of wavelengths passing a given point in 1 second.
7
Q
Velocity (formula)
A
V = F x Wavelength
8
Q
Wavelengths of light that the eye can see
A
ASK MAGDA OR LOOK IT UP
9
Q
Longest to shortest wavelength
A
RED THE LONGEST VIOLET IS THE SHORTEST
10
Q
(ROY G BIV)
A
.
11
Q
Dispersion
A
The Visible spectrum is actually the frangmentation of white light. When white light is separated into its spectral components, this is known as dispersion.
12
Q
Medium
A
is any substance that light can pass through, such as gas, liquid, and glass
13
Q
Light rays passing
A
.
14
Q
perpendicularly through a medium
A
.
15
Q
Normal
A
.an imaginary line that is perpendicular to the surface of a medium
16
Q
Refracted/emergent ray
A
.the same light ray emerging from the medium
17
Q
Incident ray
A
.a ray of light entering a medium
18
Q
Angle of incidence
A
the angle that the incident ray makes with the normal, which is perpendicular to the surface of the medium
19
Q
Angle of refraction
A
.the angle the ray makes within the medium by its change of direction, or the angle that the refracted ray makes with the normal
20
Q
Reflection (including specular and diffuse)
A
Specular reflection is a clear sharp imagine Diffusion reflection the light
21
Q
Law of reflection
A
When light strikes a reflective surface, it will be reflected at an angle equal to the angle of the incoming light. In other words, the angle of incidence is equal to the angle of reflection
22
Q
How is light refracted?
A
Light rays are refracted as they pass through a medium at an oblique angle. This is because the oblique rays that are closest to the surface of the new medium will enter the medium first and thus be slowed down first
23
Q
Index of refraction
A
It tells us the amount by which light slows down in a given medium
24
Q
What is the speed of light in a vacuum?
A
186,262
25
What causes the speed of light to increase or decrease?
medium
26
Which way does a refracted ray bend when going from one medium to another?
.
27
Snell’s Law
A fundamental law in optics that governs the refraction of light in a transparent medium. It tells us how the angle of incidence is related to the angle of refraction and the refractive index. It can be used to calculate the angle of the incident ray, the refracted ray or the index of refraction.
Lens designs are based on this relationship. It is also the basis of all ophthalmic equipment, many ophthalmic tests, measurements, and protocols.
28
Footcandles
10K Foot candles
29
The visual system is part of the central nervous system
.
30
How does the process of vision occur?
WHITE LIGHT reflected off an object Light Passes through TEAR FILM Then CORNEA ANTERIOR CHAMBER Anterior chamber has AQUEOUS IRIS PUPIL LENS
31
Visual axis
Is the path of light that starts the object being viewed and ends at the FOVEA
32
What are the 5 optical media?
1.Tears 2.cornea 3. aqueous 4.lens 5.vitreous
33
Which part of the eye has the greatest refracting power?
Most of the refraction of they eye takes place through the tears and cornea, about 75%.
34
Radius of curvature
Shorter radius and curve?
longer radius
The other variable we need to look at is radius of curvature (r) in meters (though commonly written in mm).
Spheres with a shorter radius (a smaller sphere) have base curves that are higher (or steeper)
than spheres with a longer radius (a larger sphere) which are flatter.
35
Factors that determine the power of a lens 2
The index of refraction (density of the medium) The curvature (radius of curvature)
36
Light going through center of lens is NOT refracted
In any lens, the ray of light going through the center of the lens is not refracted. But all rays on either side will be refracted. They will either converge (come together) to form a point or diverge from a point (more on this later). This is known as the focal point.
37
Focal point
They will either converge (come together) to form a point or diverge from a point (more on this later). This is known as the focal point.
38
Focal Length
The distance from the center of a lens to the focal point is the focal length
39
Calculating the focal length or dioptric power of a lens
The power of a lens is measured in diopters (D). The power is related to the focal length. A 1 D lens will bend parallel light rays to a focal point that is 1 meter from the lens. D = 1/F or F = 1/D
40
Focal length in relation to lens power
Lenses with shorter focal lengths have higher powers longer focal lengths have lower powers
41
Convergence
Light rays moving toward each other are convergent. Convergent light rays usually do not occur in nature but are the result of the action of an optical system (eg, a lens). Convergence is expressed in plus power. Therefore, a lens that causes convergence is expressed in plus power (+). The power (or vergence power) of a lens describes its ability to converge or diverge light rays.
42
Divergence
Divergent light rays are moving away from each other. Light rays emanating from a source of light are divergent. Divergence is expressed in minus power. Therefore, a lens that causes divergence is expressed in minus power (-).
43
The power of the eye
, the overall power of the eye must be plus. +62
44
Axial length
xial length of the eye that determine the refractive error
The eye is a compound lens system that refracts light. It is the power of this lens system and the axial length of the eye that determine the refractive error of the eye. With near-sightedness, the refractive power of the eye is too strong for its axial length. There is too much plus power. This occurs either because the lens of the eye is too strong or the eye itself is too long. We will focus on axial length and assume the lens and cornea are of average power. The average axial length of the eye is approximately 24.40 mm. For every 1 mm change in axial length, a 3.00 D change in refractive error with occur!
45
A 1 mm change in axial length results in how many diopters difference in the power of the eye?
The average axial length of the eye is approximately 24.40 mm. For every 1 mm change in axial length, a 3.00 D change in refractive error with occur!
46
Emmetropia
The emmetropic eye is a normal eye in which all the rays of light from a distant object are focused sharply on the retina. NO refractive error is present. There is no need for corrective distance lenses. PLANO Sph BEFORE WE GET INTO THE TYPES OF ASTIGMATISM, LET’S RECALL HOW AN EMMETROPIC EYE FOCUSES LIGHT ONTO THE RETINA
47
Ametropia
The plus power of the eye can be excessive or inadequate, possibly resulting in decreased vision. In both instances, the power can be corrected. This is done so by changing the total plus power of the eye with lenses so that it IS at an adequate level.
48
Myopia
Also called near-sightedness, this is a condition where parallel light rays come to a focus at a point just in front of the retina Myopia can be corrected with a concave lens (either glasses or contacts). Near sighted Long eye Eye has too much power Minus lens Concave Diverges light rays Minifies With motion Virtual image
49
Hyperopia
Also called far-sightedness, this is a condition where parallel light rays from a distant object come to a focus at a point behind the retina. Hyperopia can be corrected with a convex lens (either glasses or contacts). Far sighted Short eye Eye has too little power Plus lens Convex Converges light rays Magnifies Against motion Real image
50
Minus lenses and all the characteristics
Also, when an image is viewed through a minus lens, the image will appear to move in the same direction as the lens when it is moved side to side or up and down. This is referred to as “with motion”. Minus lenses diverge rays of light. Light going through the thinnest part of the lens (the optical center) is NOT refracted. This is because it is perpendicular to the lens surface. Everywhere else, the angle of incidence is not 90 degrees and will therefore be refracted according to Snell’s law.
51
Plus lenses and all their characteristics
AGAINST MOTION An image viewed through a plus lens appears magnified. OTC reading glasses are plus lenses, thus people call them “magnifiers”. When an image is viewed through a plus lens, the image will appear to move against the motion of the lens as it is moved side to side or up and down. This is referred to as “against motion”. Plus lenses converge rays of light. Light rays going through the thickest part of the lens (the optical center) are NOT refracted.
52
Which way is light bent through a prism?
Light is always bent towards the base of a prism. If a convex lens is 2 prisms placed base to base, the light will converge inward towards the base of each prism.
53
Spherical cornea
Shape in detailed do not say round
A SPHERICAL CORNEA IS SLIGHTLY STEEPER IN THE CENTER AND GETS FLATTER TOWARDS THE OUTER EDGES.
54
Astigmatism
AN ASTIGMATIC CORNEA MEANS THAT THE CURVATURE IS NOT SPHERICAL, IT IS NOT THE SAME IN ALL MERIDIANS. THERE WILL BE ONE MERIDIAN THAT HAS A STEEPER CURVE, AND ANOTHER MERIDIAN THAT HAS A FLATTER CURVE.
55
2 parts of eye that can cause astigmatism
cornea and lens
56
Symptoms of astigmatism
EYE STRAIN HEADACHES DISTORTION GHOSTING
57
Causes of astigmatism
HEREDITARY INJURY/ TRAUMA EYE SURGERY CORNEAL DYSTROPHY
58
Types of astigmatism (simple, compound, mixed)
REGULAR SIMPLE MYOPIC SIMPLE HYPEROPIC COMPOUND MYOPIC COMPOUND HYPEROPIC MIXED IRREGULAR
59
Ways to measure astigmatism
KERATOMETRY CORNEAL TOPOGRAPHY RETINOSCOPY OPTICAL BIOMETRY
60
With the rule
THE STEEPER AXIS IS LOCATED AT OR NEAR 90 DEGREES IMAGINE A FOOTBALL LAYING ON ITS SIDE MORE COMMON IN CHILDREN
61
Against the rule
THE STEEPER AXIS IS LOCATED AT OR NEAR 180 DEGREES IMAGINE A FOOTBALL STANDING UP ON ITS END MORE COMMON IN ADULTS
62
Oblique
THE STEEPEST CURVE OF THE CORNEA ISN’T VERTICAL OR HORIZONTAL OCCURS BETWEEN 30-60 DEGREES AND 120-150 DEGREES THE AXIS OF THE ASTIGMATISM IN ONE EYE TENDS TO BE (NOT ALWAYS) A COMPLEMENT OF THE AXIS IN THE OTHER EYE (THEY ADD UP TO 180) - 45 DEGREES AND 135 DEGREES - 30 DEGREES AND 150 DEGREES
63
Irregular
THERE ARE SEVERAL DIFFERENT MERIDIANS WITH DIFFERENT CURVATURES THEY ARE NOT 90 DEGREES APART
64
Keratoconus
A PROGRESSIVE THINNING OF THE CORNEA THAT RESULTS IN A BULGING, CONE SHAPED CORNEA. IT MAY BE RELATED TO GENETICS, ENVIRONMENTAL FACTORS, OR POSSIBLY HORMONES. IT CAN RESULT IN VERY HIGH AMOUNTS OF ASTIGMATISM (IN ADDITION TO MYOPIA).
65
Ways to correct astigmatism
* GLASSES/ CONTACTS
* ORTHOKERATOLOGY
* REFRACTIVE SURGERY
* OTHER SURGERY (CATARACT – TORIC LENS IMPLANTS)
66
What information can we get from an optical prescription?
Optical prescriptions are very important. They tell us a lot about the refractive errors of a particular patient.
And patients use the optical prescription given to them to get glasses or contacts to help them see Is the patient myopic or hyperopic?
How myopic or hyperopic are they?
Do they have astigmatism?
If so, how much and at what axis?
Do they have prism in their glasses?
Do they need help with reading?
67
Spherical lens
So remember, spherical lenses only have one parameter which is power (D).
have a spherical curved surface and, therefore, the same power in all meridians. This makes sense since we are using a spherical lens for a “spherical” cornea.
Spherical lenses can be plus or minus and will display characteristics of those lenses (image movement, magnification, central or peripheral thickness, convergence or divergence, etc).
68
High myope
For myopia, you may see a prescription anywhere from -0.25 to -19.00 or possibly even greater. A “high myope” describes someone who has a prescription of -6.00 D or more. FOR EXAMPLE: OD: -6.00 OS: -5.50 THIS PRESCRIPTION SHOWS THAT THIS PATIENT IS MYOPIC IN EACH EYE. HOWEVER, THIS PRESCRIPTION IS NOT COMPLETE! IT DOES NOT TELL US WHETHER OR NOT THE PATIENT HAS ASTIGMATISM.
69
Cylinder lens – 2 optical surfaces
flat one
curve one
Cylindrical lenses are slightly more complex than spherical lenses. Unlike spherical lenses which refract light rays equally in all meridians, cylindrical lenses refract light only along one axis. This is because cylindrical lenses have 2 optical surfaces – a flat one and a curved one.
70
Focal line
The curved surface has curvature and power; it is called the power meridian. Its image does not form a point focus (focal point) like a spherical lens, but rather a line focus (focal line) along the cylinder axis
71
A plano lens
Cylinder lenses are used to correct astigmatic errors in which only one meridian needs to be corrected and the other is plano (pl). Plano is the same as “zero” spherical power. Cyl is used to correct simple myopic and simple hyperopic astigmatism.
72
Spherocylindrical lens
how many meridians
and what else it has?
In that case, a spherocylindrical lens is used. As the name implies, it is a combination of a spherical lens and cylindrical lens. Thus, spherocylindrical lenses have 2 meridians, one of maximum power and the other of minimum power.
73
Be able to identify simple, compound or mixed astigmatism
Spherocylindrical lenses are used to correct compound myopic and compound hyperopic astigmatism as well as mixed astigmatism. In that case, a spherocylindrical lens is used. As the name implies, it is a combination of a spherical lens and cylindrical lens. Thus, spherocylindrical lenses have 2 meridians, one of maximum power and the other of minimum power.
74
What can cause shifts in an optical prescription?
ANYTHING THAT DISRUPTS THE SURFACE OF THE CORNEA CAN AFFECT THE PRESCRIPTION OF THE EYE. THIS INCLUDES SCARRING FROM INJURY OR CORNEAL DISEASE, PTERYIGUMS, DRY EYES, ETC. SHIFTS CAN BE MYOPIC, HYPEROPIC, OR INDUCE ASTIGMATISM.
75
X
Simple astigmatism
Cylinder lenses are used to correct astigmatic errors in which only one meridian needs to be corrected and the other is plano (pl). Plano is the same as “zero” spherical power. Cyl is used to correct simple myopic and simple hyperopic astigmatism. If a patient has simple hyperopic astigmatism in both eyes, their prescription may look like this… OD: pl +1.00 x 045 OS: PL +0.75 X 120 The PL Indicates THAT THERE IS NO (ZERO) SPHERICAL POWER! IF A PATIENT HAS ASTIGMATISM, THERE WILL BE 2 POINTS ON THE NUMBER LINE, ONE FOR THE SPHERICAL POWER AND ONE FOR THE CYLINDER POWER. THESE POINTS CAN FALL ANYWHERE ON THE NUMBER LINE. IF IT IS A SIMPLE ASTIGMATISM IN PLUS CYLINDER, ONE OF THE POINTS ON THE NUMBER LINE MUST BE ZERO AS THERE IS ZERO SPHERICAL POWER!
76
X
compound astigmatism
Spherocylindrical lenses are used to correct compound myopic and compound hyperopic astigmatism as well as mixed astigmatism IF BOTH POINTS FALL ON THE NEGATIVE SIDE OF THE NUMBER LINE, THAT WOULD BE COMPOUND MYOPIC ASTIGMATISM. If a patient has compound myopic astigmatism, their prescription may look like this…
OD: -2.50 +1.75 X 002
OS: -4.25 +0.25 X 178
LINE, THAT WOULD BE COMPOUND HYPEROPIC ASTIGMATISM.
77
X
mixed astigmatism
IF ONE POINT IS ON THE NEGATIVE SIDE, AND ONE IS ONE THE POSITIVE SIDE, THAT WOULD BE MIXED ASTIGMATISM. Spherocylindrical lenses are used to correct compound myopic and compound hyperopic astigmatism as well as mixed astigmatism. IF ONE POINT IS ON THE NEGATIVE SIDE, AND ONE IS ONE THE POSITIVE SIDE, THAT WOULD BE MIXED ASTIGMATISM. If a patient has mixed astigmatism, their prescription may look like this…
OD: -2.00 +3.00 X 075
OS: -4.00 +5.00 X 070
78
when viewing an object through a lens, you observe with motion therefore the lens is a minus lens T or F
true
79
Concave lenses cause light to diverge T or F
T
80
A patient who is emmetropic has a refractive error and therefore requires lenses to see clearly
False
81
If light rays pass through a medium perpendicularly, they will be refracted
False
82
The law of reflection states that the angle of incidence is equal to the angle of reflection
True
83
Dry eye can cause a blurry vision
True
84
Visible light is a small portion of the electromagnetic spectrum
True
85
A sphere with a shorter radius of curvature is steeper and has a higher base curve
True
86
The normal human eye has approximately how much plus power 20 40 60 80
60
87
What color light has the shortest wavelength Red Green Blue Violet
violet
88
The refracting power of a lens is determined by
The refractive index of the lens material
The curvature of the lens
Both the refractive index and the curvature the size of the lens
both the refractive index and the curvature
89
Which of the following is not a characteristics of a minus lens
Apex to apex
corrects myopia
minifies objects
converges light rays
Converges light rays
90
A nanometer is One thousandth of a meter One millionth of a meter one billionth of a meter none of the above
one billionth of a meter
91
The bending of light ray is known as refraction specular reflection diffuse reflection dispersion
refraction
92
What causes light rays to bend upon entering a new medium Change in reflection change in speed change in direction none of the above
change in speed
93
The refractive index of air is 1.67 1.50 1.33 1.00
1.00
94
The speed of light is affected by the _______ of the medium Density wavelength velocity none of the above
density
95
If the power of a lens is 7.00 D what is the focal length in inches 0.175 inches 5.71 inches 57.1 inches none of the above
5.71 inches
40/7
96
If the power of a lens is 4.00 D what is the focal length in cm 2.5 cm 20 cm 30cm none of the above
none of the above
97
If the focal length is 1000 mm, what is the power of the lens
100.00 D 10.00 D 1.00 D none of the above
98
How is light intensity measured Candles foot candles fluorescence none of the above
foot candles
99
The fundamental law in optics that governs the refraction of light in a transparent medium is The law of reflection snells law the law of refraction
both snells law and law of refraction
100
The lower the power of the lens, the _______ the focal length will be Shorter longer steeper none of the above
longer
101
Which part of the eye has the greatest refracting power the cornea the lens the vitreous the aqueous
the cornea
102
A hyperopic eye has _____ power and is blurry at near too much just enough too little none of the above
too little
103
Light is always bend towards the ________ of a prism apex base side none of the above
base
104
What is the formula for index of refraction?
1
105
see pic
see pic
106
107
seee
see
108
Whats the formula for snells law
Nsin0=N2Sin202
109
Are babies more likely to be hyperopic or myopic?
Hyperopic
110
A 1 mm change in axial length of the eye results in a chage in the power of the eye by how many diopters
3.00 diopters
111
How many focal points are they in regular stigmatism
2 meridians
112
Spherical lens
Have the same power in all meridians
113
What is the focal length in meter of an 8.00 D lens
0.125 m
F= 1/D= 1/8= 0.125 m
114
What type of lens has two prism base to base
convex
115
A longer eye is
myopic
116
Fos astigmatism where the steep and flat meridian located in relation to each other?
90 degrees away from each other
117
The ray of light that exit a transparent medium is called
The emergent ray
118
The light is slowed as it travels through a denser medium due to
index of refraction
119
What type of lens is thinner in the center and thicker towards the end
Minus lense
look like a sand timer
120
What type of lens would be best correct myopic an a astigmatism=
spherocylindrical
121
Black and white concentric rings reflected on the cornea is called
placido disk
122
Which part of the eye does not cause astigmatism
retina
123
Compund hyperioc astigmatism occurs when 2 focal points fall
behind the retina
124
when a prism cause a white light to be spread apart into its color compoment this is known as
dispersion
125
What is the power of a lens with a focal length of 4 inches
10 D
D= 40/f= 10 D
126
A 1mm difference in the axial length of the eye results in a refractive change of
3D
127
Which is not a parameter for a cylindrical lens
Sphere
128
who writes prescription in plus cylnder form
ophthalmologist
129
With the rule astigamtism occurs when the steeper curve is at
90 degrees
130
What color light has the longest wavelegth
red
131
A 1 diopter lens will
bend parallel light rays to a focal point taht is 1 m away
132
A prism bend light toward the
base
133
The equation that explains the relation between IR angles of incidence and refraction is
law of refraction
134
A plus lens has a ___ focal point
real
135
In myopic eye light rays come to a point focus
behind the retina
136
The speed of light can be increased
true
137
The distance between the center of a lens and focal poiny is known as
focal length
138
Which branch of optic discusses the properties of light and its behavior
physical
139
Irregular astigmatism can be corrected with a cylinder lense
t of f
false
regular astigmatism make it true
140
All of these are way to ??? and or measure astigmatism except
visual acuity
141
The higher the power of a lense the _____ the focal length will be
shorter
142
If a lens produces with motion the lens is a _______ lens
minus
143
A convex lens will
Magnify
144
The lens is the most powerful refracting component in the eye
false
its the cornea
145
How many optical media are present in the eye
5
tear
film
cornea
aqueos
vitreous
146
**_PHERICAL EQUIVALENTS_**
What is it?
**_SPHERICAL EQUIVALENT_**
We sometimes need to find the average of a spherocylindrical prescription. This is called the spherical equivalent.
147
How to plot a prescription on an optical cross
see pic
148
## Footnote
**_OPTICAL CROSS_**
How to derive a prescription from an optical cross in plus and minus cylinder
?
149
SPHERICAL EQUIVALENTS
## Footnote
When is it used?
The spherical equivalent is used in contact lenses, certain tests such as the visual field, and is also important for surgical patients. So, how does it work?
150
SPHERICAL EQUIVALENTS
## Footnote
How to calculate it?
1) Take ½ of the cylinder power and add it to the sphere
2) Drop the cylinder power
3) Drop the cylinder axis
151
Focal lines
Half way in between the 2 focal lines a blurred circle is formed called the “circle of least confusion
152
Circle of least confusion
THE SPHERICAL EQUIVALENT OF A SPHEROCYLINDRICAL LENS
153
Conoid of Sturm
envelope of light rays between the 2 focal lines
154
Sturm’s interval
is the distance between the 2 focal lines
155
What is accommodation?
This readjustment requires an increase in the plus power of the eye (remember, we need more convergence). Amazingly, the eye has the ability to automatically change it’s refracting power in response to a change in distance. This is called accommodation. Accommodation helps to keep things in focus as they move closer. The closest point where we can maintain a clear image with the help of accommodation is called the near point.
156
How does it occur?
First, the ciliary muscle that surrounds the lens receives a signal to contract. The zonules (fibers that connect the ciliary muscle to the lens) become relaxed. The inherent elasticity of the lens causes it to increase in thickness. This increases its effective power.
157
Maximum power of the lens
. The maximum power of the lens is +33.00 with full accommodation
158
What is presbyopia and what are the symptoms?
?The accommodative ability decreases with age because of this loss of strength of the ciliary muscle and hardening of the lens. This is referred to as presbyopia. It usually becomes noticeable between 40-45 years of age and gradually worsens from there
159
ADD power to correct presbyopia
Presbyopia is corrected with reading glasses or bifocals/trifocals or possibly contacts or refractive surgery.
160
What is amplitude of accommodation?
The amplitude of accommodation is the maximum dioptric amount of accommodation that an eye can exert
161
How do you calculate amplitude of accommodation?
In order to measure amplitude of accommodation, a reading card or other object with small print is held at arm’s length and gradually brought closer to the eyes. The distance at which the patient reports a blurring of the letters is measured in centimeters. This measurement can then be converted into diopters
162
How to determine the reading and computer Rx
Let’s determine the reading Rx is the patient’s Rx is as follows…
-2.00 +1.00 x 050 ADD +2.00
We take the ADD power of +2.00 and ADD it to the spherical power of the distance Rx. The cylinder and axis stay the same.
-2.00 +2.00 = 0.00 or plano
So, the reading Rx is
pl +1.00 x 050
Let’s determine the intermediate/computer Rx is the patient’s Rx is as follows…
-2.00 +1.00 x 050 ADD +2.00
We take the 1/2 of the ADD power of +2.00 and ADD it to the spherical power of the distance Rx. The cylinder and axis stay the same.
-2.00 +1/2(2.00) = -1.00
So, the computer Rx is
-1.00 +1.00 x 050
163
Light and image displacement
Prisms will displace an object towards the apex
This is different than light! Light reflecting off an object is bent towards the base of the prism while the image displacement is towards the apex. The image is called a virtual image.
164
Difference between real and virtual image
When light shines through a prism, the image produced by the bending of light towards the base is called the real image.
This is different than light! Light reflecting off an object is bent towards the base of the prism while the image displacement is towards the apex. The image is called a virtual image
165
Formula for object displacement
## Footnote
P = C/D
Where P = Prism power (D)
C = displacement of object in centimeters
D = distance from prism in meters
166
Direction of prism
Base In (BI) – the base is in towards the nose
Base Out (BO) – the base is out or away from the nose
Base Up (BU) – the base is up from the nose
Base Down (BD) – the base is down from the nose
167
Compounding and cancelling prisms
Horizontal prisms (BI and BO) are additive (or compounding) if the bases are in the same direction (both BI or both BO).
\* Horizontal prisms have a canceling effect if the bases are in opposite direction (one eye has BO and one eye has BI).
\* Vertical prisms (BU or BD) have a compounding effect if the bases are in opposite directions (one eye has BU and the other BD).
\* Vertical prisms have a cancelling effect if the bases are in the same direction (both BU or both BD).
■
OD: -3.00 +0.75 x115 3.00Δ BU
OS: -1.00 +1.00 x090 2.00Δ BD
It is possible to have prism over both eyes. The total amount of prism power needed is split between the 2 eyes (even though only one eye may be deviating). This is up to the doctor. But we must remember some rules regarding this.
168
Tests for muscle deviations
Tropia
Phoria
EXOTROPIA
HYPERTROPIA
HYPOTROPIA
ESOTROPIA
COMBINATION - EXOTROPIA AND HYPOTROPIA
Tropia – an obvious deviation in the alignment of the eye (strabismus).
Phoria – a latent deviation in which the eyes have a tendency to turn from the normal position (not obvious, elicited by cross cover).
EXOTROPIA – the eye turns out
HYPERTROPIA – the eye turns up
ESOTROPIA – the eye turns in
HYPOTROPIA – the eye turns down
COMBINATION - EXOTROPIA AND HYPOTROPIA – the eye is turning down and out due to an optic nerve tumor
169
Types of prisms
Types of prisms available to use in the clinic are loose prisms, horizontal and vertical prism bars and Risley’s rotary prism.
170
How prisms help strabismus patients
How prisms help strabismus patients
171
Induced prism
Types of prisms available to use in the clinic are loose prisms, horizontal and vertical prism bars and Risley’s rotary prism.
To determine the direction of the induced prism, you need to know if the lens is convex or concave, along with if the optical center is too wide or too narrow
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Prentice’s Rule
We use Prentice’s rule to figure out the amount of induced prism (whether intentional or not).
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Decentration
The optical center must be decentered by 4 mm in each eye. But is decentered inward or outward? Here are the rules…
■Plus lenses decenter in the same direction as the base of prism ordered by Dr.
■Minus lenses decenter in the opposite direction as the base of prism ordered by the Dr.
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Fresnel prism
A Fresnel Prism is a “press on” prism or sticker. It is wafer thin and made out of a flexible, vinyl material. Regular prisms can be very thick so a Fresnel prism is a good way to achieve the effects of a high powered prism without the thickness of a high powered prism. They are available up to 40.00 prism diopters. They have a pattern of thin lines which reduce contrast and will make the vision somewhat blurry
Fresnel prisms can be cut to the shape of a lens and placed over a patient’s existing lens in their glasses. They are easily applied and removable. They are great for double vision situations that are temporary such as nerve palsies.
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whats the formula for refractive index
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whats the focal length and power of a lens formula
see pic
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whats the amplitude of accomodation FORMULA
see pic
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formula of object displacement
see pic
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Formula for prentice rule
see pic
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optical cross
see pic
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all the questions see pic next slide
see pic
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the prism apex should point in the direction of the muscle deviation
true
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A pt needs 4 PD BI OU and their Rx is -4.00, how much should the PD be decentered?
A pt needs 4 PD BI OU and their Rx is -4.00, how much should the PD be decentered?
10mm
P=D x C
4= 4 x c / 10
40=4C/4
10
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what are some things that can causea shift in a patient prescription?
pregnancy, diabetes, cataracts
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what branch of optics deals with the physiology and psychology of seeing
physiologic optics
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if the desired prism is BI on a -4.00 lens which direction woud we decenter
BO
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what type of astigmatism has one focal point in front of the retina and one behind it
mixed
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a hyperopic eye has too much plus power
false
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what test use a light reflexon the eye to determine proper alignment of the eyes
krimsky
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what is the amplitude of accommodation if the pt reports blurred vision at 35 cm
28.5 D
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transpose + 1.75 - 0.75 x 079
+1,00 + 0.75 x 169
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the eye converges light because its overall power is plus
true
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If OD has 3.00 D OB prism and OS has 1.00 D BI prism what is the total primatic effect?
2.00 PD
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what color of light has the longest wavelength
red
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transpose -1.00 + 3.50 x160
+ 2.50 -3.50 x070
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if n1 \> n2 the refracted ray will be bend toward the normal
false
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why should children have cycloplegic refractions
because accomodation is very strong
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extropia is
an obvious deviation where the eye turns out
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what is the spherical equivalent of - 5.25 +1.00 x 075
-4.75 sph
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In the xample of the board, what is the rx for the optical cross in plus cylinder
+4.75 +1.50 x 163
+4.75 +1.50 x 163
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If OD has 5.00 PD BU and OD has 3.00 PD BD, what is the total prismatic effect
8.00 PD
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If the OC was too wide on the +4.00 lens, what direction is the induced prism
BO
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In a 4.00 D where the PD is off by 3 mm, what is the resulting induced prism
1,20 PD
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What Rx is represented by the 2nd optical cross in minus cylinder
-1.25 -2.25 x 180
-1.25 -2.25 x 180
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what is the spherical equivalent of +1.25 - 2.50 x 130
pl sph
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what symptoms can be caused by unintentional induced prism
headaches, double vision, nausea
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image displacement is toward the base of prism
false
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a good temporary solution to double vision is
a fresnel prism
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what happens during accommodation?
the ciliary muscle contracts,
the anterior surface of the lens moves foward
the power of the lens increases
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A series of sprism fused together in increasing strengths are called
prism bars
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what is represented by an optical cross
the power pf the 2 principle meridians
how much astigmatism present'
the axis of the spherical meridians
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what kind of lens corrects myopia and astigmatism
spherocylindrical
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a prism is 2mm from a screen and the image is displaced by 5cm what is the dioptric power?
2.50 PD
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How does a cylinder lens works to correct blurred vision due to astigmatism
increase power in the flatter meridian
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what is presbyopia
decreased accomodation
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