Spherical Soft Contact Lens Fitting

J. Perrigin

OPTO 6374

Spring 2017

Reading Assignment

Bennett & Henry: Chapter 11 pages 270-286

Tables 11.1 &11.2

Some Advantages of SCLs versus

GPs

• Initial comfort, little adaptation

• Variable wearing schedule

• Availability of daily disposables

• Dusty environment not a problem

• High oxygen transmission in most newer

designs

• Ability to fit, dispense, & replace from

inventory

Cons of SCLs versus GPs

Greater risk of microbial contamination &

infection

• Greater risks with non-compliance

• Some parameter limitations but customized

available

• Possible vision fluctuations with high

astigmatic rxes but most do well with

contemporary designs

How to start

• Determine if any special features such as tints, UV block, overnight use, etc are desired or indicated

• Decide on most appropriate replacement schedule

• Decide on spherical versus toric

• For the lenses with the desired replacement schedule find the ones that come in the powers & characteristics you need

– Use Tyler’s Quarterly or other reference

Soft lens replacement schedule

• 1 day

• Biweekly

– Some (AV) may rec weekly if sleep in CLs

• Monthly

• Quarterly: more for custom lenses

• Yearly/conventional: we almost never Rx

for soft now

– replacement schedule determined by Dr.-not regulated

by FDA, but manufacturer usually recommends

specific schedule

– Typically best to use manufacturer recommendation

– More frequent replacement usually less $$ per box

Proven that more frequent

replacement decreases the number of

adverse events

• Today’s soft lens care products are not

designed to make lenses last a year

Lens selection

• Try to stay with state of the art healthiest

designs/materials when possible

• Consider:

– Pt goals: desired wt, activities during wear,

replacement schedule, tints, etc.

– Ocular health, RX, previous CL wear

– Always ask if desire anything special such as

tint, overnight wear, etc

DW/EW/CW/FW

lens type or wear schedule

• DW: remove and clean & disinfect nightly

• CW: continuous wear for up to 30 consecutive nights

• EW: no more than 6 consecutive nights without removal. Clean & disinfect each removal unless discarding

– Counsel pt re increased risk of serious ocular complications with overnight wear espec if std hydrogel

• FW: occasional overnight wear: not assoc with increase in incidence of infection

Wear schedules

• DW Lens: only FDA approved for DW (no overnight) use

– Can be low water and/or thick ct

– Durable, low evaporation rate

– Proclear, etc

• EW or CW Lens: Use for DW, FW, or EW

– Use when require or desire greater O2 transmission (DK values)

– Will either have thin ct or high water content or silicone component. Most effective is silicone.

Why are some high Dks approved

only for DW?

• Some CLs may have O2 permeability (Dk)

high enough for EW use but manufacturer

chose to only seek DW in FDA testing. So

can only market for DW unless do more

testing

• Some do this in order to get lens out into

market sooner & later do EW trials

After selection of the specific lens

product for your patient

• Select BC

• Select power

• Place on eye

• Evaluate movement, centration, corneal

coverage, vision, patient comfort

• Over refract with spheres

• If all OK, ready to teach I/R, dispense

Sag

• The BC/OAD combination produces the

sagittal depth which in turn controls the fit

• 8.6 BC/15.0 OAD would most likely fit

tighter than 8.6/14.0 in same material &

design

• Doesn’t always hold true between brands

and different (thinner) materials

Contact Lens Fitting

by Vishakh Nair

8.4

BC/14.0

OAD

8.7

BC/14.0

OAD

8.3

BC/13.8

OAD

8.4

BC/14.5

OAD

25% 25% 25% 25%

In theory, which will be the

steepest fit?

A. 8.4 BC/14.0 OAD

B. 8.7 BC/14.0 OAD

C. 8.3 BC/13.8 OAD

D. 8.4 BC/14.5 OAD

20

BC selection

• Corneal curvature measurements required by TX law but not always helpful with SCLs

• SCLs fitted significantly flatter (approx 4D) than patient’s flat K– 43.00K = 7.85 but if fit with 8.6BC (39.25)

• Follow manufacturer’s recommendations

• Typically only 1 to 2 choices within a particular lens series

• Most SCL BCs fall within 8.4mm to 9.2mm range

Reality

• Most current scls offer one BC and one

OAD

– Fits most patients regardless of Ks

• Manufacturer did many trials to find

parameter combination / sag that would fit

the majority of patients

If you have a BC choice

• In general but not always:

• Flat K 41-45D: start with median BC

• Flattest K > 45.00: start with steepest BC

available for that lens

• Flattest K < 41: start with flattest BC

available for that lens

• Follow manufacturer recommendations

SCL BC

• More significant in thicker, less flexible SCLs like

Ciba Night & Day & custom designs

• Almost irrelevant in thin, very flexible SCLs

– Many designs can fit approx 80% of population

with a single BC

• Steepens with on-eye dehydration so PM f/u good

• A particular BC in 1 brand may not fit the same as

in another brand or material

OAD

• Most brands only offer 1 choice

• Need OAD that provides at least 0.5mm extension onto sclera in all directions

• Typical OADs range from 13.8mm - 15.0mm with most around 14.0mm.

• Larger OADs with torics or high RXs to improve centration & stability & for large corneas

• Custom lenses with larger or smaller OAD available for difficult fits

Choosing lens power

• Vertex BOTH meridians of best spectacle

RX to corneal plane

• For low amounts of cyl,

– Rx vertexed spherical equivalent

– Power needed varies slightly between

brands/designs

– CONSIDER toric if -0.75 cyl or > after

vertexing both meridians

For trial fits

• May not have exact power needed in dx set

– DXs usually in only 0.50D steps

• Go with closest and may be good enough to

wear home temporarily

• At f/u recheck OR and order best power for

year supply

Perform OR• Don’t do OR if poor fit: waste of time

• OR = refracting while patient wearing CL

– Only do spherical if good VA obtained

• Can begin OR with “plussing out” or scope over CLs

– Note regularity/quality of retinoscopic reflex & power found

• Question patient re stability & clarity of vision D & N, particularly following blink

Lens power needed

• OR= over refraction. Perform spherical refraction over the trial CLs using either

– Loose lenses outside phoropter

– Phoropter

Add OR results to lens power of lens on the eye

– This is ideally the power needed. If refracting in a very short exam room may need to add -0.25DS to results or reck at > distance. Don’t overplus! If OR LIP or loose lens > 4 need to vertex

Residual astigmatism with a soft

spherical lens

• All of the manifest cyl in the best spectacle

refraction after vertexing

• Front surface aspherics may provide better

acuity but don’t actually “mask” cyl

– Minimize spherical abberation

– Only helps if low illumination or large pupils

Desirable fit

• Good comfort (>8/10)

• Crisp, clear, stable vision D & N

• Full corneal coverage in all gaze positions

• Minimum acceptable overlap onto sclera = 0.5mm 360 degrees. 1mm ideal

– Edge shouldn’t cross limbus with blink

Centration

• Due to large OZWs of

SCLs, if overlap is

adeq, pupil coverage

not usually a prob

except with opaques or

very high Rxs, or

torics

What is not acceptable re

centration

• Corneal exposure or edge continually passing over

limbus

• Limbal blood flow restriction

• Limbal or peri-limbal irritation

• Inflammation

Desirable lens movement

• Post-blink movement approx 0.5mm N & T

– Slightly less ok for some SHs

– Text says .5 to 1.0 but 1mm usually too much

unless in upward gaze

• No resistance & smooth recovery from

push-up

• Lag on change of gaze

Slit lamp eval of movement • Allow lenses to “settle” approx 5 min if sph

– 10-15 min or more for torics & bifocals

– Look again before pt leaves

• Lens movement: Primary function is removal of debris during tear exchange– Traditional meth: observe vertical mvt with NORMAL

blinking in primary & upward gaze. Expect approx 0.5mm N & T in primary & 0.75mm to 1.5mm in upward gaze. Prefer @ least 2 of 3 be in range

– Slightly less movement may be acceptable with higher DK/l (high O2 transmission) lenses if good push-up

Inside out CLs

• Edge stand off (fluting) &/or decentration

• Excessive movement, lens awareness, may fall out

• If high modulus such as Night & Day may cause corneal molding especially if inside-out

• Look for inversion markers to help patient

– For thin lenses and for patients with tight lids

not showing adeq movement wi traditional

meth eval by:

• Lens lag on gaze change

– Observe degree of lag & speed of

recentering

– 0.3-0.7mm is desired (just estimate)

• Resistance to push meth (push - up test)

– Observe ease of moving lens from its

static position & speed of recovery

Push-up test

Change of gaze

Tight lids

• May pull lens superiorly

– Traditional movemt may not be seen or

possible. For these pts, if lens moves easily

with the lids, BC to cornea relationship is

usually acceptable.

Precautions in Eval of Movement

• Edge indentation may be > with loose conj

• Flexure of loose conj may give false impression of movement

• Loose conj may decrease movement by enveloping lens edge

• Incomplete blinks: SCL won’t move adequately giving false impression of tight fit

EMR Recording of Fit

Click on yellow box marked observation for choices:

Movement/centration good

Movement good, minimal, or none

Centration good, superior, inferior, nasal, or temporal

For pushup record as no resistance to push or as resistance to push if CL is tight

or could use scale 0-5

For change of gaze can record in mm change with gaze change or just as good lag with change of gaze

Factors Governing Fit

• Sag of lens versus corneal-scleral sag &

asphericity

• Anterior ocular topography

• Lid position & tightness

• Blinking characteristics

• Tear film quantity & quality

• Wear environment

• Physical properties of lens

– Material: stiffer (higher modulus) moves more

– RX

– Thickness: overall, ct & midperipheral t

– Design

More factors influencing fit

Unacceptable fits• Corneal exposure

• Limbal impingement

• Complete lack of movement

• Blink-related visual disturbances

• Conjunctival indentation @ lens edge

In General

• To loosen a SCL fit, while keeping other

parameters constant:

– Decrease OAD

– Flatten BC

– Select CL with greater ct or midperiph

thickness or higher modulus (stiffer)

• To improve centration: tighten fit if movemt still adequate

– Increase OAD or steepen BC

– Try different brand

• To tighten a SCL fit while keeping other parameters constant:

– Increase OAD

– Steepen BC

– Decrease ct or overall thickness

Blinking/Tear Quality• May have more effect on lens positioning &

movement than BC or OAD

• Instead of changing lens fit, try artificial

tears, punctal plugs, lid hygiene etc.

Blinking & quality of vision

• If too steep:

– Vision is clearest immediately after a blink

– Not always seen if very thin CL

• If too flat:

– Vision is blurred immediately after a blink

Effect of lens thickness on fit

• Thicker lenses show > movemt than thin

– Interact more with lids

– >post-lens tear volume

• Except for silicone/hydrogels oxygen

transmission decreases as thickness

increases

Excessively Tight SCLs May:

• Be comfortable initially

• Cause hypoxia, edema, neo, injection,

conjunctival indentation after several hrs

wear

• Trap debris or bubbles behind the CL

• Be difficult to remove- ask patient

• Possibly show “conjunctival drag”

• Increase tendency for “myopic creep”

– Controversial

Excessively Loose SCLs May:

• Cause discomfort/lens awareness

• Cause blurring, fluctuating vision, &

injection

• Cause lens loss, decentration, edge standoff

• Verify not inside out or defective especially

if only 1 eye appears loose

Remember

SCL performance in response to parameter

changes not as predictable as with RGPs

Different brands with same parameters may

not fit the same & F needed may vary

Marginal Fits

• Optimize fit as much as possible by choices

of BC, OAD, material, thickness, O2, etc.

• If best fit still not optimal but you feel the pt

should be wearing SCLs:

– Consider past SCL Hx, presence of neo, edema

– Limit wt to appropriate level

– Rx ATs on regular basis

– Monitor more frequently

– Advise pt & note in record