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Cornea and Contact Lenses I > Corneal GP Parameter Prescribing > Flashcards

Corneal GP Parameter Prescribing Flashcards

1
Q

what is the starting point for base curve prescribing?

A

keratometry xKm - 0.75 D

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2
Q

what type of fluorescein pattern do you want and not want?

A
  • want apical alignment (AA)
  • NOT apical touch (AT)- too flat
  • NOT apical vault (AV)- too steep
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3
Q

list 4 possible reasons Km and FP may not agree?

A
  • keratometer not calibrated
  • blew keratometer reading
  • DxCL BC analyzed incorrectly
  • FP interpreted wrong
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4
Q

how close if okay? (ballpark) for KM and FP agreement?

A

let’s say 0.37 D

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5
Q

give an example of SAM FAP: if the base curve is flattened?

A

when the base curve is flattened, the tear lens becomes more minus, thus plus needs to be added to CLP (same amount as BC change)

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6
Q

when deciding on overall diameter (OAD), what are some factors to consider? (list)

A
  • palpebral fissure (PF)- interpalpebral vs. lid-attached
  • diameter of habitual CLs
  • lens position on cornea
  • lids (tight, lose)
  • edge (minus vs. plus)
  • mass (CLP factors in)
  • optic zone size
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7
Q

what change in OAD would you need if there is lid-attached GP?

A

may need larger OAD

so optic zone is over pupil

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8
Q

why is the optic zone size an important consideration for PAD?

A

need to maintain PCw

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9
Q

default OAD at SCCO is

A

9.4mm

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10
Q

advantages of a smaller OAD include:

A
  • covers less corneal surface, better O2 maybe

- less mass (more O2), may center better

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11
Q

advantages of larger OAD include:

A
  • enhances initial comfort b/c interactions with edge

- enhances centration (trapped by limbus)

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12
Q

list of things to consider for optic zone diameter (OZD)

A
  • pupil size
  • lens position (centration) on the cornea
  • OZ of habitual lens
  • adaptation (be patient) to glare
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13
Q

what is the SCCO default for secondary curve radius (SCr)

A

0.7mm flatter than BCr for corneal GP

as compared to non- SCCO dealt of 1.0-1.5 mm

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14
Q

why is Scr of 0.7 mm flatter than BCr good?

A
  • tear exchange, maintain tear meniscus

- capillary attraction

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15
Q

why would a Scr of 0.7mm flatter be not as good/ when would you prefer an even flatter Scr?

A
  • if apical clearance
  • if lid attachment fitting relationship
  • if irregular cornea
  • if scleral GP
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16
Q

what is the SCCO default for third curve radius (TCr)?

A

12.00 mm for corneal GP

range 10.00-13.00

17
Q

TCr is not a fitting curve unless it is:

A

wider than 0.2mm

starts the posterior edge

18
Q

what is the SCCO default for third curve width (TCw)

A

0.2 mm

19
Q

center thickness formula for a corneal GP

A

ct = (0.23) CLP + 0.19 mm

20
Q

what is the SCCO “Arbitrary” minimum ct?

A

0.12 mm

21
Q

edge thickness needs to be ____ to reduce edge chipping

A

0.10 mm or more

22
Q

what will happen to the edge thickness if you increase the center thickness by 0.01mm

A

edge thickness will increase by about 0.01 mm

23
Q

what is the default edge contour for comfort?

A

plus edge

not knife

24
Q

what are a couple examples of when you wouldn’t want a plus edge?

A
  • fitting lid attachment (want minus edge)

- difficulty removing lens (round edge)

25
Q

if plus lens is uncomfortable after adaptation, consider:

A

rounding edge (change something)

26
Q

usual norm for which lens is tinted which color

A

gReen (right)

bLue (left)

27
Q

pros/cons of UV filter on lens

A
  • does not replace sunglasses
  • wont help pingeculae but good for lens/macula
  • more difficult to read FP (need yellow lens)
28
Q

what is unique about the treatment of plasma treated GPs

A

surface treatment (not a coating)

29
Q

what is the process for plasma treated GPs?

A

lens placed in a vacuum chamber, low temperature ionized gases remove organic contaminants

30
Q

what is the resulting changes to the lens surface of the plasma treated GP?

A
  • surface becomes more hydrophilic

- wetting angle decreases (good)

31
Q

when do plasma treated GPs lose effectiveness?

A

about 6 months or sooner if polished or abrasive clearers are routinely used

32
Q

what is the SCCO default for corneal GPs

A

Optimum comfort by Contamac U.S. (Dk= 65)

33
Q

why is the SCCO default with Dk=65 a good lens?

A
  • modifiable
  • warp resistant over time
  • doesn’t scratch easily
  • wets better than higher Dk GP lens materials?
34
Q

when would you need a higher Dk lens?

A
  • extended wear (EW), flexible wear (FW)
  • overnight orthokeratology (OK)
  • compromised cornea (ex PKP)
  • scleral GPs
35
Q

when may you blend the junction of the BC and Scr?

A
  • for keratoconus because smaller optic zone can cause image jump
  • if pt has symptoms of flare, glare

Cornea and Contact Lenses I (5 decks)

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