Parameter changes

Question 1

Increasing LD is essentially going to cause the same effects as steepening the BC, EXCEPT in regard to what fitting characteristic?

Answer 1

lid attachment. - higher LD increases LA, where steeper BC decreases LA
-PURELY based on increased surface area

Question 2

STEEPEN the BC - (better/more/less):

• centration
• movement
• stability
• lid attachment
• apical clearance

Answer 2

better
less
more
LESS
more

Question 3

minimum BC change:
minimum PCr change:
minimum PCw change:

Answer 3

.10
.50 (remember: PCr = BC + 1.5mm)
.20 (remember: start @ .2

Question 4

even though LD is the first thing you decide when CHOOSING a lens, it is (more/less) predictable in its movements compared to BC
-MINIMUM LD change?

Answer 4

LESS predictable - so change BC and other curves before changing LD

0.4mm (remember - 9.2 vs 9.6

Question 5

T/F - changing the OZD affects the ability of the lens to LA

-what DOES it change, then?

Answer 5

FALSE.

Secondary/Peripheral curves (get smaller)

Question 6

Fit characteristics of changing OZD compared to BC and LD? Name the difference.

-minimum OZD change?

Answer 6

Lid attachment - not affected. Everything else is identical to increasing the LD/steepening the BC (assuming you want to increase the OZD)
-0.4mm (same as 0.25 BC)(same as .05mm)

Question 7

The apical FP isn’t what I want, but everything else is good. Should I change the OZD or the LD first? (Assume BC is correct)

Answer 7

OZD - has a greater effect on the apical FP than LD

Question 8

BASE CURVE equivalency: 0.25D = ___mm

Answer 8

0. 25D = 0.05mm

- also = 0.4mm (OZD)

Question 9

T/F: Center thickness affects apical clearance

Answer 9

FALSE.

Question 10

(thinner/thicker) center thickness has essentially the same fit characteristics as STEEPING the BC, increasing the diameter, or inc the OZD

• what’s the MINIMUM you can thin it to?
• MINIMUM CT change?

Answer 10

thinner CT

• 0.1-0.12 (like ET when designing lens)
  0. 03mm at a time - easy does it tiger.

Question 11

when would you ever intentionally increase the CT?

Answer 11

lens sitting up too high - watch for more decentration, mvmt, less stable, less LA

Question 12

Edge lift (ET) PRIMARILY affects interaction with which lid?

• will a (thinner/thicker) ET position more superiorly?
• will a (thinner/thicker) ET cause the watermelon effect?

Answer 12

upper!
(remember, lower lid affected rotation)

• THICKER! will INCREASE LA
• THINNER causes the watermelon!

Question 13

What effect will steeping the peripheral curve have on the edge lift?

Answer 13

STEEPER PC - LOWER EL

Question 14

How does each of the following affect LA:

• higher plus power lens
• higher minus power lens
• ideal edge shape (around what power?)

Answer 14

• less LA; thinner edges
• more LA; thicker edges/flatter APC
• stable LA (-3–> -4D)

Question 15

Lenticular edge designs will affect which two fit characteristics?

• high minus lenses: (plus/minus) carriers - fit?
• high plus lenses: (plus/minus) carriers - fit?

Answer 15

edge thickness; anterior peripheral curvature

• PLUS carrier for high minus - thin the edge, lens will position inferiorly
• MINUS carrier for plus - thin central, inc. LA

Question 16

prism ballasts - what’s the point?

-(sup/inf) position, (slower/faster) mvmt, (more/less upper lid adherence)

Answer 16

rotational stability

-inferior, FASTER, less LA/adherence

Question 17

Center of gravity (think carefully!)

• AWAY from eye - fall inferior, less stable
• caused by (minus/plus) powers, (flatter/steeper BC), (thinner/thicker) center, (smaller/larger) LD?

Answer 17

Lens falls when:

• PLUS powers, FLATTER BC, THICKER center, SMALLER diameter
• lens stays central (toward eye) - exact opp!!

Question 18

lens tends to move (up/down OR lateral) in WR corneas.

-how about AR?

Answer 18

WR - up/down

AR - side/side

Question 19

Why do lenses tend to have temporal position more than nasal?

Answer 19

Nasal cornea flattens faster - Lens goes to steeper temporal side