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Formulas to know Flashcards

1
Q

When converting Keratometer Readings from mm’s to D…..Each 0.05 mm = approximately______

A

0.25D

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2
Q

When converting Keratometer Readings from mm’s to D…..0.5mm radius=approx______D

A

2.5

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3
Q

When converting Keratometer readings from mm’s to D…..1D change in K=approx______in radius change.

A

0.2mm

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4
Q

Optical Cross: If working in plus cyl: Determine which meridian is most______

A

Minus

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5
Q

Optical Cross: If working in Minus cyl: Determine which meridian is most ______

A

Plus

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6
Q

Optical Cross: Cyl = the difference between_______(not algebraically-like reading a lensmeter!)

A

Meridians

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7
Q

Optical Cross: Axis=________meridian

A

Sphere

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8
Q

Explain Prentices’s Rule

A

Formula gives approx. amount of prism present at any given point on a lens based on the dioptric power of the lens and the distance that point is from the optical center of the lens

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9
Q

What is the formula for Prentice’s Rule?

A

P= dD/10

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10
Q

Prentice’s Rule: P=

A

Amount of prism present at a particular point

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11
Q

Prentice’s Rule: d=

A

d=distance of that point from the optical center, in mm

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12
Q

Prentice’s Rule: D=

A

Dioptric power of lens

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13
Q

Calibrating a projector: RF distance in ft. to screen x ____=height of ______letter in mm on reflecting screen.

A

4.5mm
20/200

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14
Q

*Converting cm to Dioptors: ______________

A

divide cm into 100
**Example: Near point of Accommodation: 25cm 100/25=4

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15
Q

Magnitude of prism effect depends on ___________

A

Size of angle of the apex of the prism

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16
Q

*_______________=prism which appears to displace an object 1 cm at distance of 1M

A

1 prism dioptor

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17
Q

Prism: At 0.5M if the object is displaced 1cm D=____

A

2

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18
Q

*Prism formula…..

A

P=C/D
Prism=Displacement of object in cm divided by Distance from prism in meters

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19
Q

*Hirshberg’s Corneal Reflex test 1mm=______

A

7 degrees of deviation

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20
Q

Measuring Light Intensity:
Light from a single candle falling on a surface at a distance of 1’=

A

1 Candle of light

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21
Q

Measuring Light Intensity:
The illumination of light on a surface is inversely proportional to its____________

A

Distance from the light

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22
Q

What is the formula for Index of refraction?

A

Speed of light/Speed of light in subtance

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23
Q

*What is the formula for Kestenbaum’s Rule for Estimating Magnification for Low Vision Patients?

A

Denominator of VA divided by Numerator of VA=Mag Power
Example: VA 20/100
100 divided by 20=5 x magnifier

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24
Q

What is the formula for Snell’s Law?

A

Angle of Incidence(i) divided by angle of refraction=Index of refraction.

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25
Q

In Snell’s Law:
Mirrors: Angle of incidence=_________

A

Angle of reflection

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26
Q

_____________=reciprocal of its focal distance measured in meters.

A

Dioptric Power of Lens

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27
Q

*What is the formula for converting Focal Length into Dioptors?

A

D=1/F
D=Power of lens
F=Focal length in meters

28
Q

What is the formula for converting Diopters into focal length?

A

F=1/D
D=Power of lens
F=Focal length in meters

29
Q

Astigmatic clock: Multiply lower number by _____to determine approximate _______________

A

30
axis of astigmatism

30
Q

What are the steps to converting minus cyl to plus or vice versa?

A
  1. Algebraically add the sphere and cylinder
  2. Change the sign of the cyl from + to - or vice versa
  3. Add 90 degrees to axis(if adding 90 goes over 180 subtract 90)
31
Q

How do you get vertex distance?

A

Measure distance (in mm) from back surface of lens to the K.

32
Q

*Power compensation for change in Vertex Distance:
When you move a lens, it changes______________

A

the effective power of that lens

(Question was tricky: something like if you move the lens a certain distance what happens)

33
Q

Plus lens:
If lens is moved closer toward the eye this _____________

A

decreases effective power of the lens

34
Q

Plus lens:
You must __________the power of the lens to maintain the same effective power at the VD.

35
Q

Minus lens:
Move lens closer toward the eye will __________________

A

Increase effective power of the lens

36
Q

Minus lens:
You must ___________ the power of the lens to maintain the same effective power at the new VD

37
Q

*What is the standard Axial length of the eye

38
Q

*What is the range of axial length of the eye?

A

22.0-24.5mm

39
Q

What is the standard AC depth of the eye?

A

3.24mm
Range varies (especially with GLC pts)

40
Q

What it the standard dimension of the Lens Thickness?

A

4.63 up to 6.9 mm as it becomes cataractous

41
Q

*What is the average K readings?

A

43.0-44.0
Usually within 1D of the fellow eye

42
Q

What is the average CCT?

A

555 microns

43
Q

When K thickness reading are thicker IOP will read…..

A

higher(real IOP lower)

44
Q

When K thickness readings are thinner the IOP will read…..

A

lower (real IOP higher)

45
Q

Goldmann VF light intensity:
Each step of a-e represents a brighter illumination of _____log unit (1dB).

46
Q

Goldmann VF Light intensity:
Each step 1-4 represents a ____log unit (5dB) change of intensity

47
Q

Goldmann VF light intensity:
Logarithmic (20db is _____times ______than 10dB)

A

10
brighter

48
Q

When calculating Golmann Perimetry Trial Lenses, What is the bowl depth?

49
Q

When calculating trial lens for Goldmann perimetry what ADD would you use for ages 30-40?

50
Q

When calculating trial lens form Goldmann Perimetry what ADD would be used for age 40-45?

51
Q

When calculating trial lens for Goldmann perimetry what ADD would be used for ages 45-50?

52
Q

When calculating trial lenses for Golmann Perimetry what ADD would be used for ages 50-55?

53
Q

When calculating trial lenses for Goldmann perimetry what ADD would be used fro ages 55 and older or cylcopleged?

54
Q

When calculating trials for Goldmann perimetry when do you use cyl?

A

Use cyl if >1D
If <1D use spherical equivalent.

55
Q

Applanation Principle:
Describe Imbert-Flick Principle.

A

The pressure inside a thin-walled sphere=the force necessary to flatten its surface divided by the area of flattening

56
Q

What is the formula for Imber-Flick principle?

A

P=F/A
P=Pressure
F=Force
A=Area

57
Q

*Normal axial length

A

23.5mm
Range 22-24

58
Q

AC Depth

A

3.24mm
Varies esp with glc drops

59
Q

Lens thickness

A

4.63-6.9mm as it become cataractous

60
Q

*K Reading

A

43.0-44.0
Usually within 1D of the fellow eyes

61
Q

Ave CCT

A

555 microns

62
Q

The thicker the CCT the______the IOP

A

Higher(actual IOP lower)

63
Q

The thinner the CCT the ______the IOP

A

Lower (actual IOP higher)

64
Q

*Near point accommodation:
Is 20cm
Is 40cm
What is the dioptic power

A

(I answered +5.00 and +2.00)

65
Q

*Know this :What is IOL power measured in?

A

I answered Diopters(not sure if I was right)

COT (28 decks)

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