Flashcards in L4 Transposition Deck (10):

1

## Transposition

###
1) Sphere - add sphere and cyl together

2) Cyl - change the power of the cyl (change the sign)

3) Axis - change the axis of the cyl by 90

2

## Toric Lenses

### Two curved surfaces, but only one is spherical. The one which corrects for astigmatism is known as toridal. Results in lenses with different thickness throughout the lens

3

## Bitoric Lenses

###
Inefficient, not great to look through

4

## Toric Prescriptions can be written in:

###
1) Sphere/cyl form

2) Cross Cyl form

3) Toric Lens form

4) Optical Cross form

5

## Cross Cyl to Sph/Cyl form

###
1) Take one of your cross cyl powers to represent your sphere

2) The difference between the sphere and the second cross cyl is the cylinder power

3) The axis to be used in the sph/cyl form is the one that wasnt chosen as the sphere

6

## Optical Cross to Sph/Cyl form

###
Sphere = take your first value as the sphere - for minus cyl chose the most positive

Cyl = difference between the 2 values

Axis = axis direction of the first number

7

## Toric Transposition (the curves)

###
Sphere curve = curve on the spherical surface (always by itself)

Base curve = lowest curve value (closest to 0) and flattest curve on the toroidal surface. Its opposite the the sphere curve, so if sphere is at the front, base will be on the back

Cross Curve = the highest curve value (furthest from 0) and steepest curve on the toroidal surface - 90 degrees to the base curve

8

## How are toric transpositions written?

###
- Front surface (F1) on the top - this will be convex and so positive

- Back Surface (F2) on the bottom - this will be concave and so negative

Depending on which surface was the toric surface this would be:

- bc/cc divided by sc

or

- sc divided by bc/cc

9

## Toric Transposition from Sph/Cyl form

###
Sphere curve = Sphere - base curve (DS)

Cross Curve = Cylinder = base curve (DC)

cc axis is axis from sph/cyl form

Base Curve = sphere - sphere curve (DC)

bc axis is perpendicular to cross curve axis

10