GPs

custom

are GP lenses mass produced or custom made?

increase width

if you want to flatten a lens by changing the PC width, how should you modify it?

decrease width

if you want to steepen a lens by changing the PC width, how should you modify it?

smaller

a steeper curve radius is a ______ number

no real water content

describe the water content of a GP lens?

less

because GP lenses have no real water content, they are ____ likely to contain bacteria

more

because GP lenses have no real water content, they are _____ resistant to protein deposits

no

do GP lenses absorb liquids & gases?

more

for a GP, lens movement provides ____ oxygen to the cornea typically

GP

• rigid

• mask corneal astigmatism & irregularities

• preferred for better quality optics

soft lenses

• conform to the shape of the cornea

• work better for individuals where the cornea is regular & the Rx is straightforward

1. sharp optics (especially for individuals with astigmatism or irregularities)

2. good corneal health due to tear exchange with blinking

3. wide variety of materials allows for individualization

4. durable

5. deposit resistant

6. good value

7. easy handling & care

what are the benefits of GP lenses?

initial comfort/adaptation

what is the disadvantage of GP lenses?

larger, smaller, bigger

GP lenses started ______ in size, got _______, and now are getting _____ again

cornea

corneal lenses fit to the _______

cornea & sclera

corneoscleral lenses fit to the __________

sclera, valuting the cornea

scleral lenses fit to the ________

spherical/regular GP lenses

• spherical lens in optical area

• use when corneal cyl is not too high (<2.50D)

scleral GP

larger GP lens for unhealthy eyes & irregular corneas, allows for more comfort & moisture chamber on cornea

front surface toric

used to correct cyl that is not corneal (lenticular cyl)

back/bitoric

• used when corneal cyl is high (>2.50) so spherical GP is not stable on eye

• toric back surface provides a more stable lens fit on a very toric cornea, front surface can be toric too to provide better correction

orthokeratology/corneal reshaping lens

corrects vision while sleeping so that no daytime lenses are required

bifocal/multifocal GP

multiple powers in one lens, better function than soft lenses due to lens movement/translation of powers

keeps its shape & delivers the lens power plus the power of the tear layer trapped b/t the lens & the eye

describe how a GP lens corrects vision

1. corneal cyl approximately equals the spectacle cyl

2. GP lens creates a new optical surface for the eye & corrects the cyl via the tear layer &/or lens power

what makes a good GP lens candidate?

WTR

horizontal cornea is flatter than vertical cornea

ATR

horizontal cornea is steeper than vertical cornea

overall diameter

OAD

optic zone diameter

OZD

base curve radius

BCR

peripheral curve widths

PCW

peripheral curve radii

PCR

optic zone diameter

what the patient sees through, must be over the visual axis when fitted or the pt cannot see

optic zone diameter, base curve radius

what makes up the optic zone on a GP?

cornea flattens

why does the lens need to flatten in the periphery?

flatten

secondary, intermediate, & peripheral curves ______ in a standard design to fit the corneal periphery

BC

which curve is the steepest on a standard GP?

flatter, steeper, flattens

the BC of a reverse geometry lens is typically ______, the secondary curve is ______, then the PC _____again

narrower

secondary, intermediate, & peripheral curves also tend to get ______ as they get closer to the edge in a standard GP

no

is the tear layer negligible with GP lenses?

plus, minus

if the lens is steeper than the cornea, we get a _____ powered tear layer, meaning the lens needs extra _____ to compensate

minus, plus

if the lens is flatter than the cornea, we get a ______ powered tear layer, meaning the lens needs extra _______ to compensate

steep

fluorescein pools in the middle but less in the periphery

Bull’s eye pattern

• fluorescein patten that can result from a lens that fits too steep

• fluorescein pools in center, dark in periphery, edge lift

• tear film not exchanged b/t center & outside

• becomes uncomfortable or is immediately uncomfortable

1. lens fits well & holds on over central cornea

2. top lid fails to pull the steep edge of the lens up

3. gravity pulls it down

4. center of gravity of the lens moves farther out in front of the lens the steeper it gets

why does a steep fitting lens usually center or drop?

flat

less or no fluorescein in the center, may be mechanically rubbing, more or excessive fluorescein at the edge of the lens

nasally & temporally

a flat fitting lens often decenters _______

flat

which fit has lots of edge clearance, a flat or steep fit?

high

a flat fitting lens oftne rides ______

lens often gets pulled up by the top lid since it does not fit to the cornea

why does flat fitting lens often ride high?

on K

closely contoured to corneal shape, diffuse fluorescein pattern

flattest

for a toric cornea, a GP rides on the _____ corneal meridian

flattest, steepest

for a toric cornea, fluorescein is less in the _____ meridian & pools in the _____ meridian

lid controlled

hangs off the upper lid, usually larger lens w/ slightly flat base curve

interpalpebral fit

initially centered & drops after blink; usually smaller lens w/ slightly steeper base curve

smaller or tighter lens, pt has higher upper lid position

what things make an interpalpebral fit more likely to occur?

smaller, steeper

if you want to achieve LESS lid control, getting a more interpalpebral fit, you should make the lens _______ or ______

more

the more the lens contours the cornea, the ______ it will stay with the cornea

larger or looser lens, pt has lower upper lid position

what things make a lid controlled fit more likely to occur?

larger or flatter

if you want to achieve MORE lid control, you should make the lens _______ or _____

more

the less the lens contours the cornea, the _____ it will ride with the lid

lid control

which fitting type is more comfortable?

lens movement is minimal & contact w/ lower lid is minimal

why is a lid control fit usually more comfortable?

move very little or not at all after the blink

describe how a lid controlled lens moves with a blink

moves up with the blink then drops to a centered location

describe how an interpalpebral fit lens moves with a blink

allow tear pumping under the lens & control lens position

what do peripheral curves do?

high

lenses with too much edge clearance ride _____

steepen

to make a lens have less lid control, _____ the edges

flatten

to make a lens have more lid control, _____ the edges

greater

the wider the PCW, the ______ the clearance

greater

the longer the PCR, the _____ the clearance

axial edge lift

z value, distance from the extension of the peripheral curve up to the edge of the lens

radial edge lift

distance from the extension of the base curve to the edge of the lens along the radius

flat

steep

on K

flat

steep

steep

steep (bull’s eye pattern)

~0.50D steep

~1.00D steep

~2.50D steep

steep

steep

flat

flat

~0.50D flat

~1.00D flat

~1.50D flat

flat

flat

on K

on K

on K

on K

flat

steep

flat

~0.75D steep