Optics

Question 1

GP switches

1) what happens to the Fl patterns?
2) will the vision change if the BCs are diff? why?
3) Is VA generally reduced w/ higher PLUS or higher MINUS lens?

Answer 1

1) they swap - one’s steeper, one’s flatter

2) yep - change in LL

Question 2

Is vision reduced when the OR becomes more plus or minus? Which two factors cause this?

Answer 2

minus - means the BLUR is more + - can’t accommodate thru plus
-steeper BC, higher plus lens

Question 3

Name 5 things that contribute to lens flexure:

Answer 3

1) moderate-high corneal toricity
2) thin lens design
3) SOFTER lens material (high Dk)
4) steeper, central fit
5) tight lids

Question 4

T/F: Sph equivalent of the LL changes as flexure occurs due to the bending of the lens

Answer 4

FALSE - SE remains the same - half less in one meridian, half more in the other

Question 5

T/F: Residual astigmatism changes as a result of lens flexure

HOW does flexure affect the RA (w/ regard to WTR vs ATR astig?)

Answer 5

TRUE - less CORNEAL astigmatism is corrected

INCREASED WTR, DECREASED ATR

Question 6

Flexure: INCREASE (WTR/ATR), DECREASE (WTR/ATR)

OR

-steepen the ___, flatten the ____, by (HALF/WHOLE) amt of flexure given?

Answer 6

increase in WTR, decrease in ATR

steepen the steep - so increase x90 for WR
flatten the flat

do this to the existing BC!! call it BCflex, THEN calculate new LL

Question 7

Name the ONLY two conditions where flexure is desirable (relate them to RA)

Answer 7

1) Cornea WTR: RA w/ NON-flexing lens is ATR

2) Cornea ATR: RA w/ NON-flexing lens is WTR

Question 8

Ways to decrease flexure:

Answer 8

• increase CT (remember - by .03 at a time)
• change to alignment OR flat fit
• increase LA
• higher modulus lens material