TEST 2

Question 1

How to derive and plot the optical cross

Answer 1

you can derive a prescription directly from an optical cross, you can also create an optical cross based on a prescription. optical is a notation for refractive error and has a meridian and curvature.

Question 2

What does the optical cross represents

Answer 2

is showing the power of a the sphere and the power and axis of the cylinder. its showing what those two powers are

Question 3

How to transpose plus and minus cylinder prescriptions

what changes and what does not change?

Answer 3

Transposition refers to the process of changing the prescription from a plus cylinder form to a minus cylinder form, or from a minus cylinder to a plus, without changing refractive value

Question 4

What does the spherical equivalent represent,

Answer 4

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?

Question 5

Name a situation where spherical equivalent is used?

Answer 5

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?

Question 6

What is the circle of least confusion

Answer 6

Half way in between the 2 focal lines a blurred circle is formed called the “circle of least confusion” and is represented by the spherical equivalent of the spherocylindrical lens

It is the least blurry image possible through a spherical lens.

Question 7

What is the conoid of sturm

Answer 7

Sturm’s interval (or interval of Sturm) is the distance between the 2 focal lines. Ellipses are formed in the space between

Question 8

Wh is Vision not completely sharp with the spherical equivalent?

Answer 8

If we provide correction using the spherical equivalent, the circle of least confusion will be focused on the retina. This provides a slightly blurred image but eliminates the distortion from the ellipses

For minor amounts of astigmatism, a spherical SCL may be considered instead of a toric SCL because spherical lenses may provide acceptably good vision and their fitting does not have the potential for as many complications as toric SCL.

Question 9

How to calculate the sperical equivalent

Answer 9

1) Take ½ of the cylinder power and add it to the sphere
2) Drop the cylinder power
3) Drop the cylinder axis

Question 10

Optical cross example

Answer 10

Question 11

Optical cross example

Answer 11

Question 12

Optical cross example

Answer 12

Question 13

Optical cross example

Answer 13

Question 14

Optical cross example

Answer 14

Question 15

Optical cross example

Answer 15

Question 16

Optical cross example

Answer 16

Question 17

Plotting optical cross

Answer 17

Question 18

Plotting optical cross

Answer 18

Question 19

see pic

Answer 19

see pic

Question 20

Optometrists use

Answer 20

Optometrists use minus cylinder

Question 21

ophthalmologists typically use

Answer 21

ophthalmologists typically use plus cylinder

Question 22

CONTACT LENS PRESCRIPTIONS ARE ALWAYS IN

Answer 22

MINUS CYLINDER

Question 24

More transpose examples

Question 26

sperical Equivalent

Answer 26

Question 27

practice work sheet for test

Answer 27

Question 28

transposition work sheet

Answer 28

Question 29

plus

Answer 29

Hyperopic

plus

shorter eye

astigmatism compund hyperopic

real focal point

magnify

convex

converge

far sighted

too little power

Question 30

Minus

Answer 30

Near sighted

diverge

emmetropic eye

with the rule

Compound myopic

too much power

Question 31

Spherical lenses create a

why?

Answer 31

focal point

because they have the same refractive power in all meridians

Question 32

spherocylindrical lens
creates

Answer 32

2 focal lines perpendicular
to one another.