Formulas to know

Question 1

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

Answer 1

0.25D

Question 2

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

Answer 2

2.5

Question 3

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

Answer 3

0.2mm

Question 4

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

Answer 4

Minus

Question 5

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

Answer 5

Plus

Question 6

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

Answer 6

Meridians

Question 7

Optical Cross: Axis=________meridian

Answer 7

Sphere

Question 8

Explain Prentices’s Rule

Answer 8

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

Question 9

What is the formula for Prentice’s Rule?

Answer 9

P= dD/10

Question 10

Prentice’s Rule: P=

Answer 10

Amount of prism present at a particular point

Question 11

Prentice’s Rule: d=

Answer 11

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

Question 12

Prentice’s Rule: D=

Answer 12

Dioptric power of lens

Question 13

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

Answer 13

4.5mm
20/200

Question 14

*Converting cm to Dioptors: ______________

Answer 14

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

Question 15

Magnitude of prism effect depends on ___________

Answer 15

Size of angle of the apex of the prism

Question 16

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

Answer 16

1 prism dioptor

Question 17

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

Answer 17

2

Question 18

*Prism formula…..

Answer 18

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

Question 19

*Hirshberg’s Corneal Reflex test 1mm=______

Answer 19

7 degrees of deviation

Question 20

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

Answer 20

1 Candle of light

Question 21

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

Answer 21

Distance from the light

Question 22

What is the formula for Index of refraction?

Answer 22

Speed of light/Speed of light in subtance

Question 23

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

Answer 23

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

Question 24

What is the formula for Snell’s Law?

Answer 24

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

Question 25

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

Answer 25

Angle of reflection

Question 26

_____________=reciprocal of its focal distance measured in meters.

Answer 26

Dioptric Power of Lens

Question 27

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

Answer 27

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

Question 28

What is the formula for converting Diopters into focal length?

Answer 28

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

Question 29

Astigmatic clock: Multiply lower number by _____to determine approximate _______________

Answer 29

30 axis of astigmatism

Question 30

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

Answer 30

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)

Question 31

How do you get vertex distance?

Answer 31

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

Question 32

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

Answer 32

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

Question 33

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

Answer 33

decreases effective power of the lens

Question 34

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

Answer 34

increase

Question 35

Minus lens: Move lens closer toward the eye will __________________

Answer 35

Increase effective power of the lens

Question 36

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

Answer 36

decrease

Question 37

*What is the standard Axial length of the eye

Answer 37

23.5mm

Question 38

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

Answer 38

22.0-24.5mm

Question 39

What is the standard AC depth of the eye?

Answer 39

3.24mm Range varies (especially with GLC pts)

Question 40

What it the standard dimension of the Lens Thickness?

Answer 40

4.63 up to 6.9 mm as it becomes cataractous

Question 41

*What is the average K readings?

Answer 41

43.0-44.0 Usually within 1D of the fellow eye

Question 42

What is the average CCT?

Answer 42

555 microns

Question 43

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

Answer 43

higher(real IOP lower)

Question 44

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

Answer 44

lower (real IOP higher)

Question 45

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

Answer 45

0.1

Question 46

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

Answer 46

0.5

Question 47

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

Answer 47

10 brighter

Question 48

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

Answer 48

33cm

Question 49

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

Answer 49

+1.00

Question 50

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

Answer 50

+1.50

Question 51

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

Answer 51

+2.00

Question 52

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

Answer 52

+2.50

Question 53

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

Answer 53

+3.00

Question 54

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

Answer 54

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

Question 55

Applanation Principle: Describe Imbert-Flick Principle.

Answer 55

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

Question 56

What is the formula for Imber-Flick principle?

Answer 56

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

Question 57

*Normal axial length

Answer 57

23.5mm Range 22-24

Question 58

AC Depth

Answer 58

3.24mm Varies esp with glc drops

Question 59

Lens thickness

Answer 59

4.63-6.9mm as it become cataractous

Question 60

*K Reading

Answer 60

43.0-44.0 Usually within 1D of the fellow eyes

Question 61

Ave CCT

Answer 61

555 microns

Question 62

The thicker the CCT the______the IOP

Answer 62

Higher(actual IOP lower)

Question 63

The thinner the CCT the ______the IOP

Answer 63

Lower (actual IOP higher)

Question 64

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

Answer 64

(I answered +5.00 and +2.00)

Question 65

*Know this :What is IOL power measured in?

Answer 65

I answered Diopters(not sure if I was right)