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CL 2 > GP Astig > Flashcards

GP Astig Flashcards

1
Q

corneal astigmatism is corrected by the ____ surface of a GP lens

A

back; corrected by the lacrimal lens

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2
Q

residual astig is corrected by the t____ lens power on which side(s) of the GP lens?

A

toric; BOTH sides of the GP

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3
Q

T/F: LL will still be plano (thus correcting all the corneal astigmatism) with a back surface toric GP

A

false; toricity will NOT be the same

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4
Q

five GP designs to choose from - IN ORDER you’d choose them: [STBBF]

A

spherical; thin-flex, back surface toric, bitoric, front surface toric

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5
Q

SPHERICAL GPs:

  • T/F: will correct all corneal astig
  • can be used for powers up to ___D
A

true

3D

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6
Q

hybrid CLs provide good vision (GP) with good comfort (SCL) and are available to correct ____ astigmatism up to __D
-ideally you’re looking for what FL pattern under the entire lens?

A

corneal (can ONLY correct corneal)- up to 6D - BUT: it’ll flex too much after 3D
-i.e. Synergeyes, Duette

-alignment!

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7
Q

Hybrid lenses (spherical GPs):

  • remove by pinching where on the lens?
  • use what type of care system?
  • replacement schedule?
A

6 o’clock position

  • SCL system
  • 6 months
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8
Q

THIN FLEX GPs: (flexure)

  • helpful for which patients?
  • MINIMUM ___D for flexure to occur
A

pts w/ WTR corneal astig and ATR residual astig (or the opp; but it’s rare)
-1D minimum for flexure - can flex 1/3 of corneal toricity

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9
Q

what should you do to the following to intentionally DECREASE lens flexure?

  • LD (increase/decrease)
  • thickness
  • centration (increase/decrease)
  • modulus (high/low)
A

decrease LD, decrease thickness, increase centration (steepen BC/peripheral curves), low modulus

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10
Q

Brungardt’s thin-flex design has a (small/large) LD with a (small/large) OZD, uses a (bi/tri/tetracurve) design with a (flat/steep) secondary curve, a (small/large) CT, (flatter/steeper) fit, and good centration

A

small LD; large OZD - makes it a bit thinner

bicurve; STEEP secondary curve (thinner), thin CT, steeper fit

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11
Q

BACK SURFACE TORIC

  • indicated when? how much cyl?
  • is the LL altered?
  • SRcyl is about ____x MORE then Kcyl
  • causes a (greater/lesser) refractive effect than a spherical
A

HIGH corneal toricity; 2.00D or more

  • yes; LL is altered (because it’s the back surface)
  • 1.5x more - rough. could be less
  • greater refractive effect - can correct 25-60% more astig!
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12
Q

what must be accounted for in figuring out how much astigmatism is corrected by a back surface toric CL?
-how do you do the math?

A

INDEX of the lens!
math: 1) find front surface power (F1=n’-n/r), then back surface power (F2=n-n’/r), and add the two values for the amt of dioptric astigmatism corrected

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13
Q

what “rule” applies to back surface toric lenses?

-how does it work?

A

1:2:3 rule - applies to ratio of amounts of cyl in the CLP (in air): BC: OR (that can be correction)
CLP:BC:OR
-also applies to SRcyl:Kcyl:RAcyl

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14
Q

What’s the FIRST thing you should figure out in designing a back surface toric lens?

what are the next 3 things (in order)?

A

BC - select this FIRST! then CLP, PC, CT

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15
Q

(BST design)

-if you’ve chosen the right BC, which type of fit should be mimicked?

A

sph lens on a low WTR cornea (considered “ideal” for lens fitting)

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16
Q

which meridian is determined first in BST design?

-how is each (flat and steep meridian) calculated?

A

FLAT, then steep.

flat: dependent on LD. Start on flat-K or 0.25 flatter; go flatter for larger LD, steeper for smaller LD
steep: find the overall BC toricity (based off Kcyl), add it to the BC of the flat

17
Q

(BST) how is BC selection different for ATR corneas?

A

fit BOTH meridians 0.50D flatter - what BC toricity to equal the full amt of corneal cyl

18
Q

(BST)

T/F: BC system is the same for BST lenses as for spherical GPs

A

true-ish - 1.5mm SCr and 3.0mmPCr, but do it for BOTH meridians

19
Q

when observing rotational assessment of a BST lens; what’s the MOST the dot should rotate on a blink before rapidly returning to nml position?

A

10-15 deg

20
Q

if cyl > 0.75D is found on steep or flat meridian of a BST lens; what lens design might be required as a replacement?

A

bitoric

21
Q

bitorics have a ____ and ____ power effect. Which is equal to the toricity of the CLP? Which is used for eyes w/ significant (>0.75D) internal astigmatism?

A

spherical, cylindrical
sph = toricity of CLP (SPE)
cyl = used for lots of internal astig (CPE)

22
Q

T/F: A bitoric may affect vision like the other 4 types of astigmatic GPs

A

FALSE. it’s the only one that WON’T affect vision, because it won’t blur/distort regardless of rotation

23
Q

SPE bitorics - how do you calculate each surface?

A

back surface: same way as w/ BST design

front surface: resulting lens has the SAME amt of toricity in the BC and CLP

24
Q

T/F: SPE bitorics are indicated when the vision is good w/ a spherical GP, but a poor fit is achieved

  • corneal astig must be >___D
  • refractive astig must be within ___D
A

true

min 2D of corneal cyl
refractive w/i 0.75D of corneal cyl

25
Q

do SPE bitorics have an axis?

A

NO! remember - they’re a type of bitoric - won’t cause changes in VA d/t rotation!…the power rotates w/ the lens

26
Q

which two toricities must equal w/ SPE bitoric lenses?

A

BC toricity = power toricity…or else it’s not a bitoric!

27
Q

CPE (cylindrical) bitorics - used over SPE for lots of internal astig. Which surface corrects corneal astig? How about internal?

A

corneal - back surface

internal - front surface

28
Q

T/F: CPE bitorics may affect vision if not rotated properly

A

TRUE (even though it’s a bitoric - it’s not an SPE)

29
Q

FRONT SURFACE TORICS

  • used for pts w/ significant ____ astig, but only a little ____ toricity
  • does this lens require rotational stabilizers?
A

internal, corneal (b/c BSTs won’t work on eyes w/ <2.00D of corneal cyl)
-yes. big time

30
Q

FST indications

  • less than ___D of corneal astigmatism; requiring a spherical BC
  • greater than ___D of RA - so basically, use FST when pt complains VA isn’t perfect w/ only a sph design
A

2.00; 0.75

31
Q

Four advantages of sph GP over FST GP:

A

1) better POSITIONING - FSTs drop inf d/t prism
2) more STABLE VA - no rotation w/ sph
3) better COMFORT - FSTs are thicker and position inferior
4) better O2 PERMEABILITY - FSTs are thicker for prisms

32
Q

FST design: things to decide (in order)

A

1) BC (Kave-0.50 or 1.00 for 9.2/6)
2) Power (sphero-cyl form) - put a sph GP and add SCOR
3) PC - determined like sph GPs
4) prism - will orient base DOWN; won’t need as much for ATR corrections (already BD shape)
5) CT - find it the same way you normally would (18+/-) AND THEN increase CT by 0.10mm for each diopter of prism!

33
Q

in most cases of rotation/mvmt, FSTs tend to rotate so the bottom of the lens rotates _____

A

nasally - compensate for it using LARS

CL 2 (10 decks)

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