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NACOR > Formulas/General Rules > Flashcards

Formulas/General Rules Flashcards

1
Q

Total Frame PD/Box distance measurement

A

A+DBL

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2
Q

Individual Frame PD/Box distance measurement

A

(A+DBL)/2

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3
Q

Horizontal Decentration/ Total inset

A

Frame PD-Patient PD/2

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4
Q

Vertical Decentration/ Seg Drop or Height

A

OC Height - B/2

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5
Q

Minimum Blank Size

A

MBS= ED + (total decentration) + 2
MBS = ED +2(decentration per lens) + 2

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6
Q

Nominal Lens Formula

A

Power = Front Surface Power + Back Surface Power or Dn = D1 + D2

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7
Q

Focal Length
Diopter

A

F.L=1/Diopter
Diopter= 1/F.L (meters)

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8
Q

Prentices Rule

A

Prism=cF
c=distance in cm
F=Dioptre

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9
Q

Effective Power (Vertex distance Adjustment)

A

Peff= P/1-dP

P eff= Effective power
P = Original lens power
d = Change in vertex distance (in meters, positive if moved closer to the eye)

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10
Q

Base Curve

A

BC = 337.5/K

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11
Q

CL RX Over Refraction

A

CLRx=SpectacleRx−VertexAdjustment+Over-refraction

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12
Q

Seg Inset

A

Distance PD-Near PD

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13
Q

Given Prismatic effect and Prescription. Find decentration needed to create prismatic effect

A

C = Prism
F=Dioptre
c=distance in cm
C/F=c

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14
Q

mm to cm?
cm to mm

A

5mm - 0.5cm
?/10 = cm
?x10 = mm

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15
Q

How to find percent of a number

A

PercentageofaNumber=
Percentage/100×Number

example 2/100 x -9.25 = -0.185

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16
Q

FAP = ?
SAM = ?

A

Flatter add plus
Steeper add minus

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17
Q

Steps to RGP solving.

A

1) Identify Corneal astigmatism, Direction and within or outside of nomogram
2) Compensated CL RX?
3)Residual Astig?
4)Use the nomogram to determine BC and DIA.
5)determine cyl power and design of lens using SAM/FAP

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18
Q

What is the relationship between K measurments and BC?

A

The steeper the K(the higher the number) the smaller the BC.

The flatter the K (the lower the number) the bigger the BC.

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19
Q

How do you loosen the fit of a soft lens? 2

A

Steepen the BC (smaller number BC)
Decrease the DIA

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20
Q

How do you steepen the fit of a soft lens? 2

A

Flatten the BC (larger number BC)
Increase the DIA

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21
Q

How do you find the DIA on a soft cl lens? 2

A

HVID + 2mm
based of nomogram given

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22
Q

What is WTR astigmatism?

A

More power in the vertical meridian so it has a steeper curvature.

42.00/45.00@090

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23
Q

What is ATR astigmatism?

A

More power in the horitonzal meridian so it has a steeper curvature

45.00/42.00@090

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24
Q

Where do you see touch in a WTR astig RGP picture?

A

horizontal like a figure of 8 on its side

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25
Q

Where do you see touch in a ATR astig RGP picture?

A

vertical, like a hour glass figure

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26
Q

If the Astigmatism is between 20 degrees of 90 and 180 it is considered WTR and ATR.

If it is out of these parameter what is the astig called?

A

Oblique

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27
Q

If the mires are Clear Clear Clear the fit is ………..

A

Good fit

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28
Q

If the mires are Clear Blurry Clear the fit is …………

A

Flat fit

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29
Q

If the mires are Blurry Clear Blurry the fit is ……………….

A

Steep fit

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30
Q

How do we find Corneal astigmstism ?

A

Difference between the K readings

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31
Q

How do we find Residual Astig?

A

Difference between Corneal Astig and Astigmatism of Prescription after vertexing

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32
Q

What are the steps for Standard Alignment? 1-6

A

1)Horizontal Alignment
2)Vertical Alignment
3)Open temple Alignment
4)Temple Parallelism
5)Alignment of the Bent Down Portion of the Temple
6)Temple Fold Angle

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33
Q

What is the formula to calculate Total Seg Inset using Binocular PD?

A

DBC - Near PD /2

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34
Q

What are the two things you check for in horizontal alignment?

A

Rotated lens
Skewed bridge

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35
Q

What is checked for in vertical alignment? 3

A

x-ing
face form
Variant/vertical planes

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36
Q

What needs to be adjusted first when addressing glasses out of alignment?

A

The bridge
The x-ing

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37
Q

What is the Open Temple Spread?

A

The angle that each open temples forms in relationship with the front of the frame (90-95 degrees)

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38
Q

How do you check for Temple Parallelism?

A

Do a flat surface touch test - place the glasses upside down on a flat surface

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39
Q

What are the 4 steps if the temple parallelism is not equal?

A

1)check for a bent endpiece
2)check for loose or broken rivets or loose hidden hinge
3)check for bend in the temple shaft
4) if none of the above is wrong, hinge needs to be bent

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40
Q

When looking at the alignment of the bent down portion of the temples what are we checking? 2

A

1) Check for equality in the downward bend.
2) Check for equality of the inward bend.

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41
Q

When checking the temple fold angle what do we do/look at?

A

Fold temples to closed position and observe angle formed at the temples cross.

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42
Q

What 3 angles are part of adjusting nosepads?

A

1-Frontal angle
2-Splay angle
3-Vertical angle

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43
Q

Does the frontal angle change height of the frame?

A

No - it is used for flat or tall noses.

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44
Q

Does the Splay angle change height of the frame?

A

No- The twist on the nosepads adjusts to the specifics of a pxs nose

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45
Q

Does the vertical angle change the height of the frame?

A

It can do slightly but no it mainly moves frames further away or closer.

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46
Q

Do changing the angles of the 3 nosepads angles (splay,frontal,vertical) change the height of the frame?

A

No they dont, increasing + decreasing the distance between them changes the height of the frames

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47
Q

What is the solution to inequality in vertex distance? Left + Right 4

A

If left lens is IN = bring left temple IN
If right lens is OUT = bring right temple OUT
If right lens is IN = bring right temple IN
If left lens is OUT = bring left temple OUT

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48
Q

What is the solution when the lenses are different heights? Right + left 4

A

If left lens is UP = bend left temple UP
If left lens is DOWN = bend left temple DOWN
If right lens is UP = bend right lens UP
If right lens is DOWN = bend right temple DOWN

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49
Q

What is the relationship between the nosepads and the height of the lenses?

A

Widen the nosepads = lowers glasses
Narrow the nosepads = heightens glasses

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50
Q

What kind of tilt is needed in these conditions:
Eyes at OC =
Eyes above OC =
Eyes below OC =

A

= No Pantoscopic tilt
= Pantoscopic tilt required
= Retroscopic tilt needed (not done in practice/new frame choice)

51
Q

If the bifocal segment is too high what should you do to the tilt?

A

Increase the pantoscopic tilt

52
Q

If the oc height is too low how do you adjust the panto tilt to help ?

A

decrease the pantoscopic tilt (not practical)

53
Q

What is the Compounding table for Prism?

A

Right Eye Left Eye
Base out - Base out
Base In - Base in
Base Up - Base Down
Base Down - Base Up

54
Q

What is the Cancelling table for Prism?

A

Right Eye Left Eye
Base out - Base in
Base In - Base Out
Base Up - Base Up
Base Down - Base Down

55
Q

What is the rules for decentering the lens of a Minus Prescription?

A

Up - Base Down
Down - Base Up
In - Base Out
Out - Base In

56
Q

What is the rules for decentering the lens of a Plus Prescription?

A

Up - Base Up
Down - Base Down
In - Base In
Out - Base Out

57
Q

When finding if the cyl is out of ANSI standards what must we do?

A

Find the difference between the two powers (Transpose) use that difference for the tolerance chart. Should be the same as the cyl measurement

58
Q

When looking if the add power is out of ANSI what do we look at?

A

Total add power
sph and add together

59
Q

What are the 1/8th increments from 0.00 to 1.00?

A

0.00, 0.125, 0.25, 0.375, 0.50, 0.625, 0.75, 0.875, 1.00

60
Q

The causes of SPK include viral conjunctivitis, blepharitis, Keratoconjunctivitis sicca and …………..

A

solution sensitivity

61
Q

Corneal Abrasion can be caused by ……………….

A

improper insertion or removal of contact lens

62
Q

Sleeping in contact lenses can lead to a lack of oxygen in the cornea causing …………….

A

corneal edema

63
Q

Blunt force trauma or abnormal vessel growth can both cause ………………

A

hyphema

64
Q

Blepharitis can be caused by allergy, poor hygiene and ……………….

A

disruption of the tear film from dry eye

65
Q

Blanching is caused when the ……………..

A

edge of the lens fits too closely to the eye

66
Q

……………… can be caused by over-wearing contact lenses or by sleeping in them which leads to annoxia or hypoxia.

A

corneal vascularization

67
Q

Aging, contact lens wear, ocular surgery, trauma and damage can lead to a variation in the size of corneal endothelial cells known as …………………..

A

Polymegathism

68
Q

Dellen can be caused by corneal dryness and the ………….

A

GP rubbing on the limbus

69
Q

UV damage, dust, and wind can cause ……………

A

Ptergyium

70
Q

………….. can form because of infection, or pathological condition

A

chalazion

71
Q

Dendritic Ulcer is caused by the ……………..

A

Herpes simplex virus

72
Q

The leading cause of a corneal ulcer is ……………… although there are many causes for the open sore on the cornea.

A

infection

73
Q

Age, hypoxia, and genetics can lead to …………..

A

corneal guttata

74
Q

GPC can be caused by………………… 4

A

overwearing or sleeping with contact lenses,
poor hygeine,
tight fitting lenses
allergy to protein buildup on the lens

75
Q

……………. and ……………… can be caused by atrophy of the lid muscles from aging, scarring, or trauma.

A

Ectropian
Entropian

76
Q

When do we refer the patient on the efron grading scale?

A

2.5 or more

77
Q

What are 2 ways to increase DK (oxygen permeability) in a HYDROGEL lens?

A
  1. Decrease lens thickness.
  2. Increase water content.
78
Q

More Water Content = more breathable lenses as more oxygen transmission T/F

A

TRUE

79
Q

Does a low water content lens have a longer lifespan and less breakage?

A

YES

80
Q

What is the disadvantage to a low water content lens?

A

less breathable lens - more chance of vascularization

81
Q

The high water content materials have faster adaption with comfort and wearing time. T/F

A

true

82
Q

What are advantages of Silicone Hydrogel lenses? 2

A

-high Dks with rapid adaptation
-good for patient with vascularization and mild dry eyes.

83
Q

What are disadvantages of Silicone Hydrogel lenses? 2

A

-greater incidence of GPC and arcuate
staining in certain materials
-more likely to have mucin balls

84
Q

The lower the Dk value the less breathability. The more the DK value the more breathability. T/F

A

TRUE

85
Q

How do we now if a lens is well fitting? 3

A
  • Good centration with full corneal coverage in all direction of gaze
  • Sufficient movement to allow tear exchange under the lens during the blink (0.1 to 0.5 mm is generally
    considered optimal)
  • Satisfactory Push-Up Test
86
Q

What are 6 signs and symptoms of a tight/steep fitting lens? (centration/comfort/vision3/physical sign)

A
  • Good centration
  • Good comfort
  • Fluctuating vision between blinks
  • Poor visual acuity
  • Temporary improvement on blinking
  • Blanching/ lens indentation
87
Q

What are 6 signs and symptoms of a loose/flat fitting lens? (comfort/ centration2/ vision2/ physical sign)

A
  • Vision may be blurred after the blink
  • Comfort of fit is poor
  • Poor centration
  • Post blink movement is >0.4mm
  • Peripheral edge standoff
  • Vision is variable
88
Q

What could a loose/flat fitting lens be mistaken for?

A

Inverted lens - check to see if the lens is inverted if signs and symptoms of a loose lens occur.

89
Q

What can happen to the edges of a loose/flat lens?

A

edge stand off

90
Q

What can happen to the edges of a tight/steep lens?

A

conjunctival indentation/blanching

91
Q

When over refracting what prescription do we start with?

A

Plano - +0.25D
then
Plano- -0.25D

92
Q

If the lens rotates clockwise (to the left) what do we do to the axis?
If the lens rotates anti-clockwise (to the right) what do we do the axis?

A

add the axis rotation (100, rotates 30 clockwise, order 130)
subtract the axis rotation (100, rotates 30 anti-clockwise, order 60)

93
Q

What are the 4 checks when checking for CLs movement?

A

the push up test
upward gaze
lateral gaze
blinking

94
Q

Wearing Extended Wear (EW) contact lenses for 7 nights in a row is being compliant with this type of modality. T/F

A

FALSE - 6 nights would be within compliance

95
Q

Name the modality for lenses that are worn only during the daytime, not worn at night and have a strict cleaning regime.

A

Daily Wear (DW)

96
Q

What is the ‘umbrella’ term used to describe a condition that affects the choroid, ciliary body and the iris? You also observe white blood cells in the anterior chamber.

A

Uveitis

97
Q

If there is too much water in the stroma what might happen to the patients vision? 2

A

Haze
Potential blindess

98
Q

What can cause an inferior arcuate staining?

A

Incomplete blink

99
Q

A patient presents to care with Superficial Punctate Staining what could of caused it?5

A

improper use of hydrogen peroxide
cls overwear
viral conjunctivitis
blepharitis
chemical burns/Uv exposure

100
Q

If a patient is suffering from fleicher’s ring what disease is also present?

A

keratoconus

101
Q

A patient presents to care and reports a severe allergy to pollen and a swollen conjunctival tissue. What is the condition and do we need to refer?

A

Chemosis
No need to refer for allergy

102
Q

What is the condition called where structural thinning observed? What are the 4 causes?

A

Dellen

Corneal dryness
GP rubbing on edge of limbus
Injury
Disease

103
Q

A patient comes in complaining of not being able to wear their lens due to comfort and blurred vision while wearing the lenses. What is the probable cause?1 What is it NOT and why?2

A

Scratches and/or dirty lens
(not corneal edema as blurry only with CL on)
(not fit as they ‘come back’ complaining and we would have fit well)

104
Q

If you are making an Bi Toric or Back Toric lens once you have found DIA/BC what do you do? next 3 steps

A

-Find ∆k 2.75D
-Find induced cyl = ∆K X 0.4 1.1D
-Find Calculated over correction (Coc)= induced cyl - Residual cyl

a. If Coc <0.75 use back toric
b. If Coc > 0.75 use bi-toric

105
Q

Stye/Chalazion - What would you do? 3

A

-Hot compression 4 times per day
-No cl wear
- If severe refer to Dr

106
Q

Cataract - What would you do? 1

A

-Refer to Dr

107
Q

Imbedded Foreign Object - What would you do?

A

-Refer to Dr/hospital - emergency

108
Q

Entropian - What would you do? 2

A
  • bandage lens only
  • no to normal cls
109
Q

Pterigium - What would you do? 2

A
  • no to normal cls - depending on the location (near limbal area or not)
    -Refer to Dr
110
Q

Pingecula - What would you do? 1

A
  • yes -depends on the location (not near limbal area)
111
Q

basal cell carcinoma - What would you do? 1

A

-no cls due to touching there lid, risk of infection.

112
Q

Hordeleum - What would you do? 3

A

-Refer to Dr
-no cls depending on severity
-hot compression if small

113
Q

Ectropian - What would you do? 2

A
  • no cls due to exposed eye
    -Refer to Dr
114
Q

GPC - What would you do? 2

A
  • throw lens out - discontinue wear until clear
  • if severe refer to DR
115
Q

Corneal Abrasion - What would you do? 2

A
  • refer to dr/emergency
  • no cls
116
Q

Subconjunctival Hemorrhage - What would you do? 1

A
  • no cls
117
Q

Steep fitting lens - What would you do? and how? 2

A
  • order a flatter lens
    -decrease the diameter
    -increase the BC
118
Q

Flat fitting lens- What would you do? and how? 2

A
  • order a steeper lens
  • increase the diameter
    -decrease the BC
119
Q

What are jelly bumps?

A

jelly like bumps on a contact lens normally due to unhygienic conditions

120
Q

What condition can also be present if a patient has jelly bumps on their cls ?

A

GPC as the jelly bumps can rub the undernath of the eyelid

121
Q

How does GPC affect a soft contact lens? and what should we do?

A

makes a good fitting lens ride high
issue with the pxs hygiene, refit to higher DK or/and daily disposables

122
Q

How do you identify iritis in a picture?

A

redness around the iris mainly but the sclera will be mostly white

123
Q

What is the difference between jelly bumps and mucin balls?

A

jelly bumps are on the outsude of the contact lens
mucin balls found between the back side of the contact lens and the front of the cornea

124
Q

H/V @ axis

A

H/V @ axis

NACOR (2 decks)

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