week 1

Question 1

Most people can tolerate up to ___ D uncorrected astigmatism

Answer 1

Most people can tolerate up to 0.75 D uncorrected astigmatism

Question 2

In Bannon, 1945 study with 2000 patients, how many had astigmatism? % of categories of astig? (WTR ATR oblique)

Answer 2

81% with astigmatism(~80%)
33% WTR
20% ATR
28% oblique (~30%)

Question 3

In Fledelius, 1986 study, what % had >0.50 D of cyl? >1.50 D of cyl?

Answer 3

• 46% of population w/ >0.50 D (~50%)

* 4.7% of population w/ >1.50 D (~5%)

Question 4

For Holden 1975 study, what % of pop had >.75 D of astig?

-what % had bw .75-2.50?

Answer 4

> 55%

~40% had bw .75-2.50

Question 5

GP lenses can correct astigmatism via two

mechanisms:

Answer 5

1) LL of spherical or toric lens corrects all or part of the corneal astigmatism
2) Toric lens power created by cylindrical front and back surfaces that corrects residual
astigmatism

Question 6

Can use a spherical GP lens to correct corneal astigmatism up to __ D and RA of ___ D?

Answer 6

Can be used for RA up to 0.75 D and

Kcyl up to 3.00 D

Question 7

what kind of spherical lens should you select to prevent flexure?

Answer 7

Select aspheric back surface, greater
CT and/or material with high modulus
to prevent flexure

Question 8

what are the 2 options of hybrid lenses Synergeyes offers?

Answer 8

1) Duette
2) Synergeyes A-lots of flexure
* both have GP center and SCL “skirt”

Question 9

T/F: hybrid lenses offer toric powers and styles

Answer 9

FALSE

*theoretically can correct up to 6D of corneal cyl but in reality pry just 3D

Question 10

how often do you replace hybrid lenses? what kind of CL soln do you use?

Answer 10

~6 month replacement

-use SCL soln

Question 11

when is flexure beneficial?

Answer 11

WTR corneal toricity and ATR RA

Question 12

There must be at least ___ D of corneal

astigmatism for flexure to occur

Answer 12

1.00 D

Question 13

Thin design lenses can flex ___ of the amount of corneal toricity or more

Answer 13

1/3

Question 14

List 4 factors you can adjust to increase lens flexure:

Answer 14

1) Decrease lens diameter
2) Decrease thickness profile
(Use lenticular designs if needed)
3) Increase centration
(steepen BC and PCs)
4) Use more flexible (lower modulus) materials

Question 15

Indications for back surface toric lens:

Answer 15

1) Corneal cyl of >/=2.00 D (<2.00 D will cause rotation of lens (even with back toric)
2) SRcyl roughly 1.5 times Kcyl
3) Refractive and corneal cyl axes are the same

Question 16

how much more astigmatism is corrected with back surface toric vs spherical GP? what does this depend on?

Answer 16

25% to 60% more

-depends on index of refraction (n)

Question 17

what is the 1:2:3 rule for back surface toric lenses?

Answer 17

app ratio of ORcyl: BCcyl : CLPcyl
(1:2:3)
*ratio mainly for PMMA which is no longer in GP lenses
also applies to SRcyl = 3 Kcyl = 2 RA (Icyl) = 1

Question 18

what parameter should you determine first for GP back surface torics?

Answer 18

Base curve

Question 19

For 9.2 mm diameter, start with what BC?

what if it is a larger or smaller diameter?

Answer 19

start on flat-K or 0.25 D flatter than flat-K
– Flatter for larger diameters
– Steeper for smaller diameters

Question 20

what is the “Easiest method for Back Surface Toric Base Curve Selection”?

Answer 20

BC toricity selected 0.75 D less than Kcyl

Question 21

what is the “Back Surface Toric Base Curve Selection for ATR corneas”?

Answer 21

BC toricity equal to full amount of corneal cyl (Decreases lateral decentration)
**Generally fit 0.50 D flatter on both meridians for 9.2 mm lens diameter

Question 22

when ordering toric GP, order with dot where? how much rotation of dot with blink is acceptable?

Answer 22

order dot on flat meridian

- dot should not rotate more than 10° to 15° on a blink and return rapidly after blink