Soft Contact Lens Fitting

1. healthy eyes

2. willing to take care/wear lenses appropriately

3. can afford the lenses

4. lenses are available

what makes a good candidate for soft lenses?

1. vertex?

2. toric or spherical equivalent?

3. presbyopic/multifocal lens needed?

what are the questions to ask when determining what lens power is needed?

contact lens over-refraction (OR)

• needed at dispensing & any F/U

• tells you if/what changes are needed

• spherical generally is sufficient

1. GP lens that is flexing

2. some toric lenses

3. unanticipated results/poor VA in spherical OR

what are the reasons to do a sphero-cyl O/R?

1. put anticipated spherical OR in phoropter

2. close an eye

3. put up VA chart w/ 20/20 at bottom

4. ask pt what the first letter they can see is

5. add plus & ask them to tell you when they can no longer see that letter

6. add 2 clicks of minus, pt should see the letter again

7. ask if next click of minus makes letters sharper/clearer or just darker/smaller

   1. if sharper/clearer → keep

   2. if smaller/darker → go back to more plus

8. repeat for 1 more click

9. repeat OS

what are the steps for a CL OR?

1. show the pt the difference b/t the SE & full toric correction

2. discuss cost & style difference

3. personality type/attention to detail

4. visual demands at work or significant hobbies

how do you decide whether a toric CL is needed or the SE if okay?

0.75

generally assume that someone w/ a CLRx cyl of ____ or less can be appropriately fit in an SE Rx

sphere

the “standard lens”: assumed to be a lens which only contains sphere power, but inherently it also contains spherical aberration which varies as a function of lens power

aspheric

a lens which has levels of spherical aberration that are controlled in some way (to induce/correct SA), actually the “standard” of today

toric

lens w/ differing power in 2 different meridians; may be on the front &/or back, typically stabilized in some way

multifocal

lens w/ multiple power zones or a gradient power change (spherical aberration) across the lens surface

Alcon/CIBA, J&J

which lens manufacturers are said to have “general levels of SA that vary w/ lens power”?

Bausch & Lomb, CooperVision

which lens manufacturers are said to “aim to counteract for population level of SA when lens is on the eye”?

1 day (DD)

replacement schedule: “dailies” from all the manufacturers

2 week (2WR)

replacement schedule for most J&J lenses, Cooper (only Avaira)

1 month (MFR)

replacement schedule: most Alcon lenses (AirOptix), most Bausch & Lomb lenses (Ultra), most Cooper lenses (Biofinity), J&J Vita

1 day (DD), 2 week (2WR), 1 month (MFR), quarterly (QFR)

what are the different replacement schedule options?

1. lower production cost

2. convenience for pt

3. better health

what are the advantages of daily disposable lenses?

daily wear (DW)

wearing schedule: wearing of contact lenses during waking hours only (no wear during sleep at all)

flexible wear (FW)

wearing schedule: wearing of the contact lenses either as a daily wear &/or extended wear basis, come to mean a contact lens worn mostly on a daily wear basis w/ occasional extended wear (2-3 consecutive nights, like a weekend)

extended wear (EW)

wearing schedule: wearing of contact lenses during waking & sleeping hours for only a few consecutive days (FDA recommends no longer than 6 consecutive nights wear)

continuous wear (CW)

wearing schedule: wearing of contact lenses for up to 30 consecutive nights wear w/o removal from the eye

transparent

completely clear lens w/ no tint at all

visitint/locator

common to many lenses, allows them to be easily seen

enhancing

uniform color embedded throughout entire lens material/matrix optic zone, good for slightly changing the color of light eyes

opaque

often “textured” or dot-matrix, variable color in lens; completely blocks light passing through; good for changing color of dark irises, but noticeable upon lens decentration

ionic

lens surface has a charge, attracts large protein molecules like lysozyme, deposits more

non-ionic

lens surface is not charged, may deposit less

high water content

more transmissible to oxygen, dehydrates more on the eye, deposits more

lower water content

less transmissible to oxygen, dehydrates less on the eye, so may be better for dry eye complaint

hydrogel

• HEMA based

• polymers composed of several monomers joined together in chains which are linked together at intervals by small amounts of cross-linking agents to form a polymer network

• advantages:

  • easily fabricated

  • relatively cheap

  • highly flexible

  • dimensionally stable to changes in pH & temperature

  • proven to be a successful CL material

• disadvantages:

  • relies upon water to combine w/ hydroxyl component to transport oxygen across the material & water has a limited ability to dissolve & transport oxygen

hydrogel

• lens material

• water content changes w/ temperature, dehydration, pH

• side chains are mobile (lens drying causes hydrophobic side chains to rotate to surface, attracting lipids & dewetting lens)

• group 4 materials: increased H2O content

  • ionic

  • unstable

  • now used for disposables

silicone hydrogel

• extremely high oxygen permeability

• facilitates flexibility, wettability, & fluid transport which aids lens movement

• now almost “standard”

• marked lipid deposition

• hydrophobic so wetting agents or surface treatments are often used

HEMA-based hydrogels

• oxygen moves through lens by interaction w/ water molecules

• oxygen transmissibility depends on water content of material & thickness of lens

silicone hydrogels

• oxygen transmission by silicone molecules, very hgih

• less wettable, so needs tx

• not directly related to water content

oxygen permeability

• rate of oxygen flow through CL material

• net volume of O2 passing through sample at a specified temperature, physical property of the material

Dk

oxygen permeability, material specific

Dk/L or Dk/t

oxygen transmissibility, net volume of O2 passing through a specific lens; oxygen permeability divided by lens thickness

decreases

as lens thickness increases, oxygen transmissibility ______ (given the same material)

center

high plus lenses have lower oxygen transmissibility in the ______

periphery

high minus lenses have lower oxygen transmissibility in the ______

Young’s modulus of elasticity

ratio of force to change in length - or - how much force it takes to deform the lens

Force/Change in length

Young’s modulus of elasticity (E) =

increased

______ modulus (E) = material is stiff & harder to bend

decreased

______ modulus (E) = material is more pliable

increased, less, stiff

early silicone hydrogels weighted toward higher O2 transmission, so ____ Si, ____ hydrogel, & the material was more ____

more, comfortable

newer silicone hydrogels sacrifice O2 transmission, have _____ hydrogel & the material is more _____

B+L

what manufacturer is the Ultra brand?

B+L

what manufacturer is the Purevision2 brand?

B+L

what manufacturer is the Infuse brand?

Alcon

what manufacturer is the Air Optix brand?

Alcon

what manufacturer is the Precision brand?

Alcon

what manufacturer is the Total brand?

Alcon

what manufacturer is the Dailies brand?

CooperVision

what manufacturer is the Biofinity brand?

CooperVision

what manufacturer is the MyDay brand?

CooperVision

what manufacturer is the Clariti brand?

CooperVision

what manufacturer is the Proclear brand?

J&J

what manufacturer is the Acuvue brand?

±6.00, 0.50

most often above ______D, power of lenses available becomes limited, usually in ____D steps

least

typically, if in doubt about what power to select if a needed power is unavailable, select the ______ powered & perform an over refraction

loosest

typically want the ______ lens that fits well

0.3

typically, a difference of at least _____ in lens BC is needed for the lens to demonstrate differences in fit

337.5/K

BC (mm) =

steeper, flatter

steeper Ks require ______ CL BC, flatter Ks require ______ CL BC

flattest

you want to fit the ______ lens that is comfortable for the pt & covers the cornea adequately, even during blink & eye movements

13.5-14.5mm

diameters typcially range from _____

8.2-9.0mm

companies typically manufacture 1 or 2 BCs in each lens type, usually ranging from ______

flattest

if there are multiple BCs available, if the pt has flatter than average corneas, try the _____ BC

steepest

if there are multiple BCs available, if the pt has steeper than average corneas, try the _____ BC

flattest BC that fits well

if there are multiple BCs available, if the pt has average corneas, try the _____ BC

centration, movement, corneal coverage

what things are you looking at when you assess the fit of a lens?

good centration w/ equal conjunctival overlap 360deg

describe the centration of a well-fitting SCL

cover the cornea at all times

describe the coverage of a well-fitting SCL

good movement, not moving up onto the cornea or significantly off of the cornea w/ a blink or eye movement; should move at least 0.25-0.5mm w/ a blink in primary gaze & 0.5-1mm in up gaze

describe the movement of a well-fitting SCL

1. rides high

2. decenters superiorly when looking down

3. pt may feel the lens moving

what are some indications of a SCL that is fitting too flat/loose?

1. air bubbles trapped under the lens

2. lens may be very comfortable initially but will become uncomfortable over time

what are some indications of a SCL that is fitting too steep/tight?

smooth reflection w/ minimal bubbles or dry spots

describe a good, wettable CL on surface evaluation

steeper

_______ BC lenses tend to be tighter & not move as much

tighter

some polymer materials are more “sticky” so the lenses tend to fit ______

more

some materials are stiffer (higher elastic modulus) so they move ______

1. base curve

2. material

3. diameter

what 3 things determine the fit of a lens?

discomfort, red eye

what are some reasons to change lenses on a current CL wearer?

1. show the pt the SE & full toric correction

2. discuss cost difference

3. personality/detail orientation differences

4. visual demands at work or hobbies

5. for high minus, cyl decreases w/ vertexing

what are some things to do/consider to determine if the SE or full toric correction is needed?

Alcon, J&J

most _______ & _______ lenses are spheric, the SA varies w/ lens power

B+L, CooperVision

most ______ & _________ are aspheric, they aim to counteract for population level spherical aberration

low, non-ionic

group 1 hydrogel: _____ H2O, _______ (ionicity)

high, non-ionic

group 2 hydrogel: _____ H2O, _______ (ionicity)

low, ionic

group 3 hydrogel: _____ H2O, _______ (ionicity)

high, ionic

group 4 hydrogel: _____ H2O, _______ (ionicity)

group 1

which group of hydrogel are good for dry eye?

oxygen transmissibility

oxygen permeability divided by lens thickness, net oxygen passing through a specific lens

decreased

increased thickness of a lens = _______ oxygen transmissibility

decreased

an increased modulus = _______ pliability of the lens

0.25-0.5, 0.5-1.0

the optimal fit of a SCL is _____ with a blink in primary gaze & ______ in upgaze

smaller, larger

steeper Ks require a steeper CL BC, this is a ______ # in mm, a ______ # in D

larger, smaller

flatter Ks require a flatter CL BC, this is a ________ # in mm, a ______ # in D

flattest

choose the ______ BC that fits comfortably on the pt

steeper, smaller

if the K values are high (47-48), choose a ______ BC, this will be the _______ value in mm

flatter, larger

if the K values are low (41-42), choose a ______ BC, this will be the _______ value in mm